Best Industry Practice ManualManagement of network constraints on solar PV generationVersion 1.0

2

Since 1978, the Solar Trade Association (STA) has worked to promote the benefits of solar energy and to make its adoption easy and profitable for domestic and commercial users. A not-for-profit association, we are funded entirely by our membership, which includes installers, manufacturers, distributors, large scale developers, investors and law firms. Our mission is to empower the UK solar transformation. We are paving the way for solar to deliver the maximum possible share of UK energy by 2030 by enabling a bigger and better solar industry. We represent solar PV, solar thermal and energy storage. Published June 2018 The Solar Trade Association Ltd. enquiries@solar-trade.org.uk Greencoat House, Francis Street, London, SW1P 1DH 0203 637 2945

Front cover photograph provided by Western Power Distribution

3

Contributors

Adele Ara, Lightsource BP; Tony Byrne, EA Technology Ltd; Antonio Dominguez, Quintas Energy; Chris Hewett, Solar Trade Association; Andy McHarrie, EA Technology Ltd; Paul Morris, EA Technology Ltd; Declan O’Halloran, Quintas Energy; Chris Parkinson, EA Technology Ltd; Victoria Ramsden, Wise Energy (GB) Limited; Federica Rappoli, Lightsource BP; Sean Sullivan, Western Power Distribution; Richard Wilson, UK Power Networks, and all members of the STA Large Scale Asset Managers Working Group.

With thanks to the following companies for their support:

Lead sponsor:

Other sponsors:

4

Foreword

On behalf of the Solar Trade Association (STA), I am pleased to present this first edition of the Best Industry Practice Manual for solar generators and Distribution Network Operators (DNOs). This document is the first of its kind, and marks an important step toward greater transparency, accountability and improved cooperation between distributed generators of low-carbon electricity and the network operators. It is by now well understood that the UK electricity system is in the midst of a period of profound and unprecedented transformation, with important implications for managing the distribution networks in particular. With nearly 13GW of solar capacity on the system and a strong potential for growth in the next decade, solar generators, alongside other decentralised technologies, will be playing an active part in that process. This manual has come about in order to ensure maintenance and development of the networks can happen in the most efficient way possible through greater collaboration. Far from being merely a minor inconvenience, constraints on PV generation due to both planned and unplanned network outages are the most significant cause of lost production, and hence lost revenue, for UK solar generators. Between 2015 and 2017, these losses equated to approximately 1% of total installed capacity, or £10m per year in foregone revenues across the solar industry. Some early research carried out by Quintas Energy on behalf of the STA showed the impact and nature of grid disconnections around the country. Amongst other things, the findings of the research pointed to a need to raise the quality of the dialogue between generators and DNOs as a first essential step towards better communication, cooperation and outcomes. Since then, this initiative has enjoyed the universal support of our members and very constructive engagement with the DNOs themselves. This document is a product of EA Technology’s world-leading expertise in electricity network management, as well as extensive dialogue and engagement between industry and DNO representatives. It has been especially rewarding to see how the experience and knowledge on all sides has contributed to an insightful and constructive vision of the future. We are grateful to everyone who contributed to making this manual a success and especially to Quintas Energy, LightsourceBP, Foresight, Bluefield and Wise Energy for their generous support of this initiative. We are also grateful to Western Power Distribution and UK Power Networks for their commitment to this project and the sector leadership they have demonstrated in endorsing this document. With so many aspects of the future of Britain’s electricity networks yet to be determined, this Best Industry Practice Manual must therefore be as dynamic as the market it serves. This document will be used by our industry to improve the management of the electricity system and we will be developing both its scope and its signatories in the coming months and years.

Chris Hewett Chief Executive, The Solar Trade Association

5

Statement of endorsement

Our organisation supports this first edition of the Solar Trade Association’s Best Industry Practice Manual on distribution network outage management. We will endeavour to mitigate the impacts of planned and unplanned network outages on solar PV generation where reasonably practicable, and we look forward to continued productive dialogue with industry stakeholders as this initiative progresses.

Signed:

Steve White Head of Network Control and Operations, UK Power Networks

Phil Davies Network Services Manager (Wales), Western Power Distribution

6

Table of Contents

1. Introduction

2. Scope

3. Waiver of Confidentiality

4. DNO Perspective

4.1. Statutory and Regulatory Requirements

4.2. DNO Network Design & Investment Planning Process

4.3. DNO Outage Planning Process

4.4. DNO Owner/Operator Forums

5. Effects of Constraints on Solar Generators

5.1. Effects of Outages on Solar Generation

5.2. Issues with DNOs on Communications about Outages

6. DNO and Solar Terminology and Description

6.1. Electricity Network Terminology

6.2. Solar Site Terminology

6.3. Types of Connection

6.3.1 Physical Connection

6.3.2 Capacity Criteria

6.4. Joint Operational Agreements (JOA) and Site Responsibility Schedules (SRS)

7. Standard DNO and Generator Information

7.1. Mechanism for recording / sharing / updating standard information (e.g. web portals)

7.2. Review and Update DNO / Solar contact details for notifications

7.3. Review and Update connection data for solar sites

7.4. Other generation on circuits – Last in/first out sequence for each constraint type

7.5. Recording and transparency of constraint queue (last in-first off; firm vs non-firm) and constraining scenarios

8. Communication on DNO proposed constraints due to Scheduled Outages

8.1. Contacts for communications

8.2. Notification of future constraints

8.3. Effects on Solar sites

9. Liaison on Constraint Mitigation

9.1. Initiation of Discussion on Constraint Mitigation

9.2. Options for mitigating effects

9.2.1. Alternative working hours

9.2.2. Single Circuit Sites - Improvement in Connection Type

7

9.2.3 Opportunity for investment into constraint / duration reducing measures

9.2.4 Intertripping systems

9.2.5 Use of reactive power to avoid voltage constraints

9.3. Active Network Management

9.4. Instructions from National Grid/National Grid driven constraints

10. Communication during Constraint Period

10.1. Before starting constraint

10.2. Updating during constraint

10.3. Updating any constraint instructions

10.4. End of constraint

11. Communications during Unscheduled outages

11.1. General

11.2. Notification

11.3. Updating during outage

11.4. End of outage

12. Review of Constraint due to Scheduled / Unscheduled Outages

12.1. Identification of issues – DNO / Solar

12.2. Communications

12.3. Action plan for improvements

13. Monitoring Constraint Outcomes

13.1. Measurement methodology

13.2. Responsibilities of DNO and Solar

13.3. Collation of data from DNO and Solar

14. Review of Constraints in Connection Agreements following DNO Asset Replacement Work

15. Bibliography

Appendix I DNO Generation Portals

Appendix II Table of Factors for calculating Solar Generation Output

Appendix III Case Studies

8

List of Abbreviations and Terminology

a.c.

Alternating Current - An electric current which periodically reverses its direction, having a magnitude that varies continuously. The rate at which the current’s direction changes is known as the frequency. The frequency for UK power systems is 50Hz.

ANM

Active Network Management

The ENA Active Network Management Good Practice Guide summarises ANM as:

Using flexible network customers autonomously and in real-time to increase the utilisation of network assets without breaching operational limits, thereby reducing the need for reinforcement, speeding up connections and reducing costs.

API Application Programming Interface

CB

Circuit Breaker - a mechanical switching device, capable of making, carrying and breaking currents under normal circuit conditions and making, carrying for a specified duration and breaking currents under specified abnormal circuit conditions such as those of short circuit

CT

A Current Transformer (CT), is to used scale down the measured value of current in order that it can be utilised by instrumentation and protection relays.

A CT provides a secondary Current that is proportional to the primary Current. They are employed for site and remote measurement and indication, metering and system protection applications.

CUSC The Connection and Use of System Code - the contractual framework for connection to, and use of, the National Electricity Transmission System (NETS).

DNO

Distribution Network Operator

A person or legal entity responsible for the distribution of electricity within Great Britain and owns and operates the electricity infrastructure for this to be achieved.

The person or legal entity named in Part 1 of the Distribution Licence and any permitted legal assigns or successors in title of the named party.

There are 14 licensed distribution network areas in Great Britain and each is responsible for a pre-defined area. These 14 DNO licences are owned by six different overall companies.

DSO

Distribution System Operator

A role which may be established in the future whereby the DNO undertakes some of the roles of the GBSO at a regional level to balance supply and demand.

EHV Extra High Voltage – generally Distribution Systems operating at 33kV, 66kV and 132kV

ENA Energy Networks Association www.energynetworks.org/

9

GBSO Great Britain System Operator (See more details in Table 3)

HV High Voltage - a.c. voltages of 6.6kV, 11kV, 20kV and 22kV (nominal)

JOA Joint Operational Agreement

LV Low Voltage - a.c. voltages of 1000 Volts or less

MPAN

Meter Point Administration Number, also known as the Supply Number.

It is a unique 21-digit registration number allocated to each electricity connection. For a generation connection two MPANs are provided for the import and export units.

MW Megawatt

MWh Megawatt-hour

MWp Megawatt-peak

N-1

The design criteria applied to the electricity network that requires it must be capable of maintaining the network to demand customers following the loss of one item of major plant or circuit (ENA Engineering recommendation P2/6)

Ofgem Office of Gas and Electricity Markets www.ofgem.gov.uk Ofgem is responsible for regulating the gas and electricity markets in the United Kingdom to ensure customers’ needs are protected and promotes market competition.

OHL Overhead Line - A line with one or more conductors supported above the ground by appropriate means, for example wood poles or steel towers

PoC Point of Connection - the point at which the output from the solar site is connected to the host DNO electricity distribution network

PV Photovoltaic - A device in which the photovoltaic effect is utilised to generate electricity

SRS Site Responsibility Schedule

STA Solar Trade Association www.solar-trade.org.uk

U/G Underground - directly buried in the ground or cable ducts

UGC Underground Cable

VAr

VAr is the unit for reactive power.

It exists in an a.c. (alternating current) electricity system where Voltage and Current are not in phase.

Due to the capacitive effect of cabling within the generator site at times where a solar park is not operating/generating (for example overnight), there could be a transfer of VArs from the generator site to the DNO system, by a transfer of MW from the DNO system into the generator site.

There can be VAr transfers to the grid during the day depending on what the invertors are instructed to do.

VT A Voltage Transformer provides a secondary Voltage that is proportional to the primary Voltage.

10

WG Working Group

11

Executive Summary

In the last few years the amount of solar generation connected to the distribution high voltage networks has increased rapidly in both volume and capacity, and the major part of the income for the owners of these generation sites comes during the summer months. Traditionally the Distribution Network Operators (DNO) carried out planned maintenance and asset replacement on their networks during the summer months, when the customer load was at a minimum.

This gives rise to a conflict of interest between the DNOs, who have to constraint the network to carry out works, and the solar generators, who do not want their generation capacity constrained in the summer months, the period of highest generation output.

Research carried out by the Solar Trade Association (STA) indicates that in the period 2015 to 2017 the lost production of solar generators as a result of outages on the electricity distribution network equates to approximately 1% of the total installed capacity which represents approximately £10m per year across the industry.

Much good work has been done by both the DNOs and the solar generators to develop forums, web portals and other lines of communication to improve cooperation between the two parties. The STA and its members decided to develop this Best Industry Practice Manual (BIPM) to build on the work done so far to create a framework to formalise what constitutes good practice.

It is important that the DNOs and solar generators understand the perspective of the other, in order to improve the level of dialogue between them. The BIPM describes:

the legal and regulatory requirements that the DNOs must satisfy and the process they undertake to develop the annual programme of planned outages

the impact of constraints for the solar generators

the issues with communications that that have been raised by both parties.

The STA and the DNOs have each provided definitions of the terminology they use which should aid in understanding communications.

The types of connection, both in terms of the physical connection to the networks and the capacity of the network to export generation, are discussed and standard terms have been introduced to gain a better understanding of the reasons for constraints.

The BIPM has identified what is considered best practice for the holding and exchange of information on sites and contact details and allocates responsibilities on both the solar generators for ensuring this data is correct and updated when necessary.

The process and responsibilities for the notification of outages is described. One DNO has developed a web portal to communicate information on outages, which is considered a great step forward. The STA consider that the use of web portals for this process is the optimum way forward for two-way communication, but this is not possible at the present time due to concerns about computer system security. Using the one existing DNO portal as a basis the document details the data fields and facilities that the STA suggest should be included in developments of future portals.

The key part of the BIPM is that covering the liaison on mitigating the effects of constraints on solar generation. When the DNO issues the outage / constraint plan, it is the responsibility of each solar generator affected to determine the impact on their business of the outages and to determine whether they want to discuss whether any mitigation is possible with the DNO, and it is the responsibility of the DNO to respond to such contact.

12

Whilst mitigation measures may or may not always be possible this should be established by effective two-way discussions.

The solar companies are prepared to invest in funding mitigation where a positive cost benefit can be shown, both in immediate measures e.g. overtime or night time working, or in measures which may have both an immediate and long-term benefit, e.g. additional points of isolation in circuits. Such funding may be by individual or group of generators, where several are affected by the same constraint.

There is an issue regarding how the benefits of generator investment in the network could be fairly divided between those investing, and whether this would affect the constraint queue. This encompasses a range of legal and regulatory issues and this is highlighted as an area that will require considerable future discussion.

Communications during planned and unplanned constraints are discussed. The review of outages to identify any issues that can then resolved by discussion is an important part of the process.

A set of key performance indicators to measure the impact of scheduled and unscheduled outages. These indicators will provide a means of monitoring how the collaboration between solar companies and the DNOs is affecting the level of constraints and to identify where there has been a marked change in performance.

This is the first edition of the STA Best Industry Practice Manual and it is hoped that all solar generators and the DNOs will adopt the principles it contains. The principles contained in the BIPM may also be relevant to other generator technologies and the STA would welcome discussions with interested parties. There are still unresolved issues, but it is hoped that these will be addressed in future editions as experience is gained in its application.

13

1. Introduction

The Solar Trade Association (STA) in conjunction with its members has carried out work to analyse the impact of grid disconnections due to network constraints on the output of the solar generators. However, the information available to the generators is not always sufficient to determine whether there are mitigating measures that may be implemented to limit, or possibly eliminate, the impact of the constraints on generation.

The STA have developed this Best Industry Practice Manual (BIPM) to cover the interaction between solar generators and Distribution Network Operators (DNO) regarding constraints on generation.

The objectives of the BIPM are to set out measures to:

Improve communications between DNOs and solar generators on outages

Develop a means of triggering discussion between DNOs and solar generators on possible mitigating action for individual outages

Detail possible methods of mitigation

Promote the sharing of information where there are no confidentiality issues.

Whilst this document has been produced by the Solar Trade Association on behalf of the solar generation companies it is anticipated that the principles and methodology will be applicable to other generation technologies.

2. Scope

This document considers best practice for the management of constraints affecting solar generation sites connected to the DNO network at 33kV or higher voltages, and any solar generators that have a dedicated 11kV or 6.6kV circuit back to the primary substation bus bars. This document has been limited to these sites because it can generally be assumed that there are no demand customers on the same circuits

Solar generation sites directly connected to the DNO 11kV distribution network have not been included because of the presence of demand customers on the same circuits, which can have a significant effect on the management of outages.

This document covers the management of scheduled and unscheduled outages as a result of any planned work or faults on the DNO network that requires constraints on generation.

Planned work is assumed to include asset replacement, reinforcement to increase network capacity and/or to connect new load or generation, and maintenance of the DNO substation equipment and circuits.

It should be noted that constraints in the host DNO network may be a result of planned work or faults on the National Grid or neighboring DNO networks.

This document does not cover the process for applying for and establishing new connections, except for an outage required to physically connect new load/generation to the DNO network where it affects another solar generation site.

14

3. Waiver of Confidentiality

In order to allow the sharing of information between DNOs and solar generators it will first be necessary for all parties to agree the actual data that can be shared.

The waiver of confidentiality will be limited to the following information for each generation site:

Site Name – Owner (as assigned by the owner)

Site Name – DNO (as assigned by the DNO)

Location (address)

Site Owner Name

Site Operator Name

Maximum Peak Power in MWp

Type of generation

Constraint Queue Position

15

4. DNO Perspective

4.1. Statutory and Regulatory Requirements

In order to operate as an electricity distribution business in the UK (England, Scotland and Wales) it is necessary to have an Electricity Distribution Licence issued under Electricity Act 1989. When the industry was privatized there were 14 Regional Electricity Companies who each were awarded a licence to operate in their region.

With acquisitions and mergers there are now 6 Distribution Network Operators, but the original 14 licences are still in existence. Ofgem still require the DNOs to produce some reports on a licence basis. Hence the DNOs will still refer to licence areas as sub-divisions of their companies.

DNO’s have a requirement to provide a consistent level of service to all customers which is measured through the Quality of Service Incentives set by Ofgem. DNO’s are incentivised to minimise the number of times demand customer’s supplies are interrupted and the duration of those interruptions; this can create a conflict of interest between the DNO’s and EHV generation customers as the DNO may have to prioritise the connection to significant numbers of demand customers over a single EHV customer who does not have a firm supply.

From a DNO perspective the definition of a firm connection would be a connection that can maintain the full connection capacity required by the customer under a single fault/planned outage (i.e. two points of connection).

The following sections identify some of the statutory and legal requirements

Electricity at Work Regulations (1989)

The purpose of the Regulations is to require precautions to be undertaken against the risk of death or personal injury from electricity in work activities.

Health and Safety at Work Act (1974)

The Act set outs the general principles for the management of health and safety at work enabling the creation of specific requirements through regulations enacted as statutory instruments such as Control of Substances Hazardous to Health Regulation 2002 (COSHH), The Management of Health and Safety at Work Regulations 1999, Personal Protective Equipment (PPE) at Work Regulations 1992 and the Health and Safety (First Aid) Regulations 1981.

Electricity Safety Quality and Continuity Regulations (ESQCR) 2002 (as amended)

These regulations replaced the Electricity Supply Regulations. It places general duties on generators, distributors, suppliers and meter operators to prevent danger, interference with or interruption of supply as far as reasonably practical and to ensure their equipment is sufficient for the purposes in which it is used.

Utilities Act 2000

Under this Act, it shall be the duty of an electricity distributor to:

a) Develop and maintain an efficient, coordinated and economical system of electricity distribution

b) Facilitate competition in the supply and generation of electricity c) Provide a connection to the network (subject to terms and conditions) on request.

16

The Grid Code

The Grid Code sets out the procedures and principles governing National Grid’s relationships with all users of the Transmission System such as Distribution Network Operators (DNOs) and large scale centrally despatched generators.

The Grid Code specifies the technical requirements for the connection to and use of the National Grid Transmission System and must be adhered to at all times.

The Grid Code is divided into a number of sections including:

A Planning Code – that specifies the technical and design criteria and procedures to be applied by National Grid in the planning and development of the National Grid System and to be taken into account by Users in the planning and development of their own systems.

An Operating Code – that covers a wide range of items from demand forecasting to operational planning and the sharing of data amongst other topics.

National Grid is the code administrator and responsible for the maintenance of the Grid Code.

The Distribution Code of Licensed Distribution Network Operators of England and Wales

It covers the technical aspects relating to the connection and use of a DNOs distribution network.

Specifies the day to day procedures that govern how a DNO can operate and develop its distribution network for planning and operational purposes in normal and emergency conditions.

The Distribution Code also exists to ensure that the DNO can meet their Grid Code obligations.

Section DPC7 of the Distribution Code is particularly relevant for the connection of Embedded or Distributed Generation as it covers the following Planning Recommendations:

Engineering Recommendation G59/3-2: Recommendations for The Connection of Embedded Generating Plant to The Regional Electricity Companies’ Distribution Systems

Engineering Recommendation G75/1: Recommendations for The Connection of Embedded Generating Plant to Public Distribution Systems Above 20kV or with Outputs Over 5MW

Engineering Recommendation G83/1: Recommendations for The Connection of Small Scale Embedded Generators (Up To 16A Per Phase) In Parallel with Public Low-Voltage Distribution Networks

The Electricity (Standards of Performance) Regulations 2015

The purpose of these Regulations is to define the standards of performance that must be achieved by DNOs for load customers and prescribe compensation for failure to achieve these standards.

These are measured using the factors of Customer Interruptions (CI) and Customer Minutes Lost (CML) in the Ofgem Quality of Service Incentives scheme to enable an auditable assessment of DNO interruptions to supply which has symmetric annual rewards and

17

penalties depending on each DNO’s performance against their targets for the number of customers interrupted per 100 customers and the number of customer minutes lost.

It should be noted that these regulations do not apply to generation customers.

4.2. DNO Network Design & Investment Planning Process

DNO’s investment decisions are based on ENA Engineering Recommendation P2-6 Security of Supply (July 2006) and are in accordance with the regulatory budget agreed with OFGEM. This document defines the security for demand on a network and does not provide specific requirements for security of generation supplies.

This document forms part of the Licence conditions for the DNO. This document can be downloaded at the following link:

http://www.dcode.org.uk/assets/uploads/ENA_ER_P2_Issue_6__2006_.pdf

A DNO is obliged under its licence to provide the most economic electricity connection meeting the planning and technical requirements laid down within the Grid and Distribution Codes. The calculation carried out during the Connection Charge assessment includes the costs of sole connection assets and a proportion of the costs for any system reinforcement and shared connection assets.

The following is a brief summary of the process that is followed in DNOs when designing and planning work, the execution of which will probably require planned outages which may require constraints on generation.

Work may be required for:

new load or generation connections

cable / overhead line diversions

work to re-locate circuits due to wayleave or easement issues

replacing assets, i.e. the assets have reached the end of their normal life expectancy or have deteriorated to a state where their reliability or performance is suspect

reinforcement of the network components to increase network capacity for load or generation requirements

replacing assets that have failed in service.

Table 1 identifies the main processes that will be carried out in a DNO. It should be noted that this is a generalised overview and should not be taken as a definitive process in use in individual DNOs.

Table 1 DNO Design & Planning Work Process (indicative)

Stage Explanation

18

Stage Explanation

1. Identification of requirement

The need for the work will be identified by

network studies highlighting parts of the network approaching or exceeding full capacity

identification of future load or generation connection requirements

condition monitoring of circuit/substation components that are approaching end-of-life

other technical issues that affect network performance and reliability

The scope and objectives of the work will be developed from this analysis.

2. Outline design options, assessment and outline costs

A series of design options will be developed to identify issues that need to be addressed e.g.

wayleave/easement/lease requirements availability of space in substations for new build geotechnical surveys alternative network configurations timescales technical and economic investment Each option will be assessed and outline costs developed to determine the bets design/cost option to achieve the objectives identified above.

3. Determination of final design

The final design which best meets the objectives will be developed and costed

4. Approval for capital expenditure

The scheme will be submitted for approval by the appropriate authority within the DNO.

5. Planning of work

Development of work programme.

Detailed design of civil works; protection, control and auxiliary power systems; SCADA; etc.

Begin procurement process for long lead time assets (e.g. major transformers can be 12-24 months delivery from placement of order)

Plan sequence of works (e.g. remove old assets before new assets can be installed)

Calculation of connection charge; issue of Connection quotation and relevant contractual agreements and documents, etc.

19

Stage Explanation

6. Operational planning

Development of operational plan

Plan operational requirements for changeover to new assets

Identify requirements for outages or generation constraints and when they will be required

Coordinate with other works scheduled by the DNO and National Grid to identify issues with conflicting outage requirements

Develop final programme of on-site and operational work

Develop contingency plans for possible fault scenarios

7. Commence site works

Remove old assets; carry out work required for the installation of the new assets

Note: Where it is possible to install new assets before removing old assets work on site may have commenced before item 6 above.

8. Install new assets Installation of the new assets

Inspection of new assets installed by ICP

9. Operational work

Commissioning, testing and connection of the new assets to the network.

Inspection and final adoption by DNO of assets installed by an ICP

It can be seen from this sequence that until the operational planning (Stage 6) is completed it will not be possible for a DNO to give any advance communication on possible future generation constraints due to proposed outages or issues with network capacity.

The timescales for asset replacement work will vary considerable depending on the type of work and scale of the project. In general, the higher the voltage level the longer the timescale.

Approximate timescales from identification of requirements to project completion are given in Table 2.

20

Table 2 Approximate timescales for DNO asset replacement work

Type of Work Approximate timescale

132kV substation - new 4 years

132kV substation replacement work 3 years

132kV new circuit 2 / 4 years (cable / overhead line)

132kV circuit replacement work 2 years

33kV new substation 3 years

33kV substation replacement work 2 years

33kV new circuit 2 years

33kV circuit replacement work 1 year

It should be noted that National Grid lead-in timescales could be longer than for DNOs.

4.3. DNO Outage Planning Process

The inter-relationships and responsibilities of outage planning between National Grid and the DNOs are contained within Section OC2 of the Grid Code.

All outages and hence pre-arranged outage plans are generally formulated in voltage level order.

During the Operational Planning Phase (planning for the year ahead), National Grid in accordance to OC2 will issue two versions of their expected outage plan to each licenced area of a DNO. The DNO has the opportunity to comment on the National Grid proposed outage plan.

By the end of Week 49 of the year preceding the outage planning year National Grid will submit their final outage plan for the next year to the DNOs and other Users of the National Grid system.

It is only at this time that the DNO outage planning times can start in earnest assembling the DNOs outage plans. The reason behind this is:

For any National Grid outage that depletes an infeed or places a GSP at single circuit risk, the DNO must ensure that all available interconnection to the GSP is available for system security considerations.

Such considerations will be to ensure that all 132kV and EHV circuits that provide the necessary interconnection are fully intact.

The DNO then commences the formulation of their outage plans of known outages with their 132kV and EHV plans being completed by the end of January and February respectively.

These outage plans can only cover the work that is proposed to be completed during the year and that will require scheduled outages.

The outage planning process should include all types of work i.e. new construction, asset replacement, maintenance, etc. that will require outages. There may be opportunities for the DNO to change the timing of other future work so that it can be completed during the planned outage. The DNO should seek to consolidate all possible work within one outage to eliminate the need for a subsequent outage and any required constraints on generation.

21

Unscheduled outages occur as the result of failures or damage to equipment in the electricity distribution or transmission network.

4.4. DNO Owner/Operator Forums

Some DNOs have already set up Forums to provide a workshop to allow Generator customers to engage directly with DNO’s to discuss and agree on steps that may be taken to decrease the impact of curtailment and disconnection due to planned works on or which will affect DNO networks.

These provide opportunities for the DNOs to

Discuss the impact of outages with Distributed Generation Owners and Operators.

Share outage policy

Enable the improvement in the communication of known forthcoming outages and

potential constraints

It is considered that the DNO portals currently being developed would be the optimum mechanism for holding contact information for each site, provided that the solar companies have controlled access to and can update the information.

22

5. Effects of Constraints on Solar Generators

5.1. Effects of Outages on Solar Generation

Based on research carried out by the STA, the lost production of solar generators as a result of outages on the electricity distribution network equates to approximately 1% of the total installed capacity. This equates to approximately £10m per year across the industry.

Planned and unplanned grid outages are the main cause of loss of production, and hence revenue, for solar generators between 2015 and 2017.

Asset replacement, maintenance and network faults are the reason for the majority of DNO generation constraints between 2015 and 2017.

Long outages usually take place in the months with the highest level of irradiation (spring and summer), multiplying the effect of the outage in the loss of production.

PV systems are designed to be protected against grid disconnections. However, the lifetime of some devices will be reduced if the outages occur frequently. The devices and subsystems most likely to be affected by frequent disconnections are: auto-reclose system, UPS, inverters, pre-magnetisation system and circuit breaker.

5.2. Issues with DNOs on Communications about Outages

Whilst DNOs are giving asset owners advanced notice of planned outages there have been a number of issues and as a result more cooperative engagement between the solar generators and the DNOs has been developed.

Currently only one DNO has developed a web-based platform to detail planned outages and has provided access to the solar site owners. This system is seen as a step change in the quality of communications and has proved to be very useful for asset owners, who can check in the portal both the planned outages and also the historic ones. Whilst it is not possible for solar generators to update details on-line, there is an on-line form to provide updated information on ownership and contact details, and the DNO will manually update the database.

Some DNOs are providing advance notification of outages by weekly emails listing outages up to 8 weeks in advance, and others are simply sending emails when there is planned outage.

The solar generators would like to see all DNOs develop web-based platforms to provide details of planned outages. This is discussed in more detail in Section 7.

Some of the main issues experienced by the solar generators in the notification of outages are:

Identification of solar sites

Some of the notifications give details of the circuit that will be subject to the outage but do not specifically identify the solar site(s) that are affected.

The DNO name for the solar site is not always the same as the name used by the owner/operator.

Registering all the scheduled outages.

Outage notifications are sometimes received by email sent by the DNO field engineers in addition to different outages being automatically sent by the platform.

23

Outages notified by the field engineers are not always registered in the advance notification / platform, and this makes outages management difficult, as the advance notification / platform does not provide the full picture.

Use most up to date contact details through the Company.

DNO Field engineers are not always using most updated contact details to notify outages or communicate with the asset owners. Field engineers should be using the list of contact details in the generation portal to ensure notifications are always received by the right person. The use of a web-based platform by all DNOs would ensure that the correct contact details are available to all DNO staff.

Registering consistently provisional scheduled outages in the notification list / platform.

With the aim of providing full visibility, DNOs are registered provisional scheduled outages in the notification list / platform. However, not all the provisional outages are registered, making the management process difficult. In some occasions, provisional outages are recorded months in advanced, but in other occasions they are recorded even if the outage occurs in a few weeks and we have notified by the field engineer. The notification list / platform does not provide a full picture of what asset managers can expect in the coming months.

Confirm that outages are not duplicated before recording them.

Some outages appear twice. When the outage changes its status from provisional to approved, this process is not always made in the platform, but a new scheduled outage is set up in the generation portal instead, duplicating values.

Late / short notice issued by DNOs

In some cases, the notification of an outage has been made at very short notice or even just before the outage starts.

Overrun of outages

In some cases outages overrun the scheduled time, but no warning is given that this may happen.

One of the main issues for DNOs is that solar generators do not always communicate changes in ownership or O&M contractor. In many cases, it is the lack of communication from generator owners/O&M contractors and changes in contact details that lead to the perceived difficulty in communication from the DNO. In a great number of cases, a DNO will advise a generator owner or an O&M contractor regarding a planned outage or constraint to be advised that they no longer own the site, or they are no longer the O&M contractor for the site.

24

6. DNO and Solar Terminology and Description

6.1. Electricity Network Terminology

In order to aid understanding a list of terms used by the electricity DNOs and in this report are given in Table 3.

Table 3 Electricity Network Terminology

Term Explanation

Apparatus Any item of electrical machinery or equipment in which Conductors are used, or supported, or of which they form a part.

Arc Suppression Coil (ASC) An adjustable reactor of between several tens of ohms and several thousand ohms, which can be used to earth the neutral of a three-phase power system.

Automatic Voltage Control (AVC)

Automatic adjustment of transformer tap position required for transformers on the Primary Distribution and Subtransmission and Transmission networks to maintain system Voltage within limits as the demand changes.

Bilateral Connection Agreement (BCA)

Each party connected to the GB Transmission System shall enter into and comply with a Bilateral Connection Agreement in relation to such connection.

BSP (Bulk Supply Point) A substation owned and operated by a DNO, where the primary intake Voltage is at 132kV with Voltage transformation to 66kV, 33kV or 11kV.

Busbar An electrical conductor (or set of conductors) at a specific location usually used to make a common connection between several circuits at a substation location.

Circuit A medium in which electricity is transferred from one location to another. Such circuits comprise of overhead line or underground cable, or a mixture of both.

Circuit Breaker / Metering Circuit Breaker

An automatically operated electrical switch designed to disconnect a damaged circuit or remove plant from the system for safety and system security and prevent greater damage to the faulted item and additional damage to the rest of the system.

25

Term Explanation

Communications Circuit / Channel / System

Refers to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel in telecommunications and computer networking.

Communicating data from one location to another requires a medium which are called communication channels and use two types of media – cable (wire, cable and fibre optic) and broadcast (microwave, satellite and infra-red).

Conductor An electrical conductor arranged to be electrically connected to a System.

Connection Agreement

The Connection Agreement governs the long-term relationship between the generator owner and the DNO.

Details such as the:

1. Site responsibility ownership schedule.

2. Details of the agreed import and export capacities and connected Voltage.

3. Details of any export constraints.

Constrain / Constraint / Constrained

also known as Curtail / Curtailed / Curtailment

The application of a lower permitted import or export limit to the normal limit as stated on the Connection Agreement.

For a generation site this constraint value may require the generator to operate at:

1. Zero export.

2. An export limit between zero and the maximum value stated in the Connection Agreement.

3. An export limit between zero and the maximum value stated in the Connection Agreement but also at an amended power factor.

Distribution Code

Covers the technical aspects relating to the connection and use of a DNO distribution network.

Specifies day to day procedures that govern how a DNO can operate and develop its distribution network for planning and operational purposes in normal and emergency conditions.

The Distribution Code also exists to ensure that the DNO can meet their Grid Code obligations.

More information on the Distribution Code is available at the DCode website http://www.dcode.org.uk/

26

Term Explanation

Distribution Licence A licence granted under Section 6(1)(c) of the Electricity Act 1989 (as amended. including by the Utilities Act 2000 and the Energy Act 2004).

Distribution System

The System consisting (wholly or mainly) of electric lines owned or operated by the DNO and used for the distribution of electricity between the Grid Supply Points (GSPs) or Generation Sets or other Entry Points to the points of delivery to Customers or Authorised Electricity Operators, or any Transmission Licencee within Great Britain and Offshore in its capacity as operator of the licencee’s Transmission System or the National Electricity Transmission System and includes any Remote Transmission Assets (owned by a Transmission Licencee within Great Britain), operated by the DNO and any electrical plant and meters and metering equipment owned or operated by the DNO in connection with the distribution of electricity, but shall not include any part of the National Electricity Transmission System (NETS).

Exit Point

The transitional point of where the ownership responsibility changes from that of the generator to that of the DNO. Typically, this could be on the outgoing terminals (generator side) of the DNO Metering Circuit Breaker.

Export The total agreed (net) transfer of power from the generator site into the DNO system via the Exit Point.

Firm Connection

A supply that can maintain the full connection capacity required by the customer under a single fault/planned outage (i.e. two points of connection).

It should be noted that even with a Firm Connection it may still be necessary to impose generation constraints under certain network operating conditions.

First Circuit Outage (FCO)

Engineering Recommendation P2/6 (Security of Supply) defines a First Circuit Outage as:

“A fault or an arranged Circuit outage”.

It is also referred to as N-1 in some contexts.

Great Britain System Operator (GBSO)

National Grid is the system operator for the National Electricity Transmission System (NETS) in Great Britain. Responsible for coordinating power station output, system security and managing system frequency.

27

Term Explanation

Grid Code

Establishes the procedures and principles governing National Grid’s relationships with all users of the Transmission System such as DNOs and large scale centrally despatched generators.

The Grid Code specifies the technical requirements for the connection to and use of the National Grid Transmission System and must be adhered to at all times.

It is available to view on the National Grid Electricity Transmission website http://www2.nationalgrid.com/UK/Industry-information/Electricity-codes/Grid-Code/

GSP (Grid Supply Point)

A substation where the delivery point from National Grid’s system to the DNO exists, where the intake Voltage being at 400kV or 275kV.

Transformation takes place at this location to a lower Voltage to be utilised within the DNOs system.

This transformation is generally to 132kV but can also be to 66kV or 33kV.

At a GSP site there are shared assets between National Grid and the DNO and site responsibility schedules etc. exist to define ownership responsibilities.

Import The total agreed (net) transfer of power from the DNO system into the generator site via the Exit Point.

Independent Distribution Network Operator (IDNO)

A company licenced by Ofgem to distribute electricity in the United Kingdom who does not have a defined Distribution Services Area.

Inter-Tripping

The signaling that results in the disconnection of a generator utilising a communication circuit following abnormal system conditions on the DNO system being met. Such abnormal system conditions would have been determined via system studies at the design stage and would be noted in the Connection Agreement.

Isolated

Disconnected from associated Plant, Apparatus and Conductors by an Isolating Device in the isolating position, or by adequate physical separation, or sufficient gap.

28

Term Explanation

Isolator / Isolating Device

Also referred to as a Disconnector

An item of apparatus which is non-automatic and used for rendering Plant and Apparatus Isolated.

Such equipment can be used to establish a point or disconnection (see Point of Isolation) and following the placement of Safety Locks and Caution Notices can be employed as a Point of Isolation on the electricity system to allow for planned works or fault repairs to be undertaken.

Last In First Out (LIFO) The principal of the LIFO stack is that the last generator to apply for connection is the first to be constrained when generation export constraints are necessary.

Live Electrically charged.

Loss of Mains Protection (LoM)

Protection to achieve disconnection of the distribution generator from the Distribution System in the event of loss of one or more phases of their supply.

The technical requirements for such an application are covered in Engineering Recommendation G59/3-2 and Engineering Technical Report 113 – see Section 4.1.

Meter Operator An organisation responsible for installing and operating electricity (and gas) metering.

National Electricity Transmission System Operator (NETSO)

National Grid Electricity Transmission (NGET) in its capacity as operator of the National Transmission System.

National Grid Electricity Transmission (NGET)/

National Grid

The Transmission Network Operator in England and Wales.

Non-Firm Connection

A non-firm connection allows a DNO to constrain the generator in both routine and emergencies or at given times of the day, depending on system conditions. Such constraints will be stated in the Connection Agreement for the generator.

29

Term Explanation

Outage (Planned), also referred to as a Planned Event.

A pre–arranged activity on the electricity system in order that routine maintenance, asset replacement diversion, the connection of new infrastructure can be undertaken and any other works associated with the Distribution or the DNOs Communication System. A pre-arranged outage may affect load and generator Customers on the actual circuit or a part of the circuit where the points of isolation are to be established.

Generators will be affected in different ways as a consequence of a planned outage:

If within the section where the points of isolation have been established the generator is it will receive no import of electricity or be allowed to export;

If the generator is connected outside the section where the points of isolation have been established, the generator may be required to constrain export fully (to zero) or to a pre-determined export level.

In some instances, constraints are required due to pre-arranged works on the Transmission System.

Outage (Unplanned), also referred to as an Unplanned Event.

It is also referred to as a fault event.

Generators can also be affected via the operation of their Loss of Mains protection which could be attributed to a disturbance on another part of the DNO system or indeed an occurrence on the Transmission System.

Generators can also be affected in different ways as a consequence of an unplanned outage:

If within the section where the points of isolation have been established to undertake repairs in which the generator will receive no import or be allowed to export;

If outside the section where the points of isolation have been established, the generator may be required to constrain export fully (to zero) or to a pre-determined level for the adopted running arrangement.

In some instances constraints are required due to an unplanned event on the Transmission System and may be disconnected remotely via inter-tripping.

Planned Event Refer to Outage (Planned).

30

Term Explanation

Plant Mechanical plant including all machinery and equipment not elsewhere defined as Apparatus.

Point of Isolation The location of where Apparatus and Conductors are disconnected from points of supply where Apparatus and Conductors may become live.

Power Factor The ratio of real power to apparent power flowing in an electrical ac power system.

Primary Substation A substation owned and operated by a DNO, where the primary intake Voltage is at 33kV with Voltage transformation to 11kV or 6.6kV.

Remote Terminal Unit (RTU)

A RTU interfaces with on-site plant to a Supervisory Control and Data Acquisition (SCADA) system by transmitting telemetry data.

Such telemetry data could include switchgear positional status (open / close), Voltage, Current, MW/MVAr, tap position status and any alarms that have been generated remotely. A RTU also enables the remote operation of switchgear, and control of transformer tap position etc. from a central location via SCADA.

SCO (Second Circuit Outage)

Engineering Recommendation P2/6 (Security of Supply) defines a Second Circuit Outage as:

“a fault following an arranged Circuit outage”.

Also referred to as N-1-1 or N-2 in some contexts.

Super Grid Transformer (SGT)

A transformer that steps voltage down from 400kV or 275kV to 132kV, 66kV or 33kV.

System An electrical system in which Conductors and Apparatus are electrically connected to a common source of supply.

System Operator (SO) The System Operator is responsible for ensuring the stable and secure operation of the whole transmission system.

Transmission Licence The licence granted under Section 6(1)(b) of the Electricity Act 1989 (as amended. including by the Utilities Act 2000 and the Energy Act 2004).

Transmission Owner (TO) Transmission Operators (TOs) are licensed to develop, operate and maintain the high voltage system within their own distinct onshore transmission areas.

31

Term Explanation

Transmission System

A system of High Voltage lines and plant owned by the holder of a Transmission Licence and operated by the NETSO, which interconnects Power Stations and substations.

Unplanned Events Term Refer to Outage (Unplanned).

Users

A term that is widely used in both the Grid Code and Distribution Code and is defined as:

Generators, Network Operators and Non-Embedded Customers.

6.2. Solar Generation Terminology

In order to aid understanding a list of terms used by the solar companies and in this report are given in Table 4.

Table 4 Solar Generation Terminology

Term Explanation

Central Inverter

A type of inverter with a high capacity, which means that many

sub-elements (PV Modules gathered in SCB’s) are electrically

connected to it, feeding it with the DC power electricity to be

converted into AC power. The typical order of the Nominal Power

is around 1MW.

Fixed Array

The arrangement where the PV Modules are installed in a

structure with a fixed inclination and orientation calculated to

receive the optimum Irradiation throughout all the year.

The Inclination Angle or Tilt Angle is defined as angle

formed by the normal direction to the surface of the panel with

the horizontal plane.

The Orientation or Azimuth is the angle that the

perpendicular direction to the PV Modules surface projected

on the horizontal plane forms with the Geographical South.

Ground Mount

Installations that have the PV Modules mounted in structures on

the ground. The largest scale plants are installed in this

disposition.

32

Term Explanation

Inverter

The element that converts the variable direct current (DC) output

of a group of PV Modules into a utility frequency alternating

current (AC) that can be fed into a commercial electrical grid or an

off-grid electrical network. The inverters are automatic electronic

devices that can modify their functioning parameters to optimise

the PV Modules production.

PV Module

A photovoltaic module or panel is a packaged, connected

assembly of typical photovoltaic cells. This electronic element

converts the Irradiance received from the sun into DC electricity

power, giving a certain Voltage and Current output. They are

characterized by the Peak Power, which is the electric power that

the module can provide in the Standardised Peak Conditions

Roof Top Installations that have the PV Modules installed on top of the roof

of a certain building

Row

The physical arrangement of the PV Modules in the Solar Plant. It

is a description usually used in Fixed Arrays, though some of the

tracker technology grouping can be referred this way too. A row

usually contains several strings.

String

A group of PV Modules electrically connected in series. The

Voltage of each panel in the string is added, while the current is

limited to the minimum value of the panels of the group.

String Combiner Box

Also known as Combiner Box, Junction Box, String Box, etc. The

String Combiner Box (SCB) is an electric box that gathers a

certain number of strings connecting them in parallel to two

different busbars, one for the positive and one for the negative

pole. The electrical energy from all the string is conducted to a

single DC output where the voltage is limited to the minimum

value provided for one of the strings grouped, and where the

current is the sum of all the current of the connected strings. It

also contains protection devices and may contain monitoring

devices as well

String Inverter

A type of inverter that is connected to a single string. With a lower

capacity than the Central Inverter, around 10-40kW, these

devices can optimise the Solar Plant by enhancing the

performance of each string individually, which usually have a

different optimum operation point due to different levels of

irradiance that they receive.

Structure

The physical element on which the PV Modules are installed.

Depending of the technology used, it can be Fixed Arrays or

Tracker.

33

Term Explanation

Switchgear

In an electric power system, switchgear is the combination of

electrical disconnect switches, fuses or circuit breakers used to

control, protect and isolate electrical equipment.

Substations

Also known as cabinets, it is the building that houses electrical

devices such as the inverter and/or transformers and its

protections. In the recently built Solar Plants, the substations are

typically concrete prefab buildings that houses the whole package

inverter-transformer.

Tracker

An installation where the system comprised a structure, a drive

system and an automaton device that interact to modify the

angles of the PV array to increase the amount of solar energy

(Irradiation) captured. The automaton is programmed to activate

the drive system to modify the angles in the structure relative to

the sun’s position so that it is perpendicular to the sun’s axis. The

system can be Single Axis if it only modifies the inclination, or

Dual Axis if it modifies both inclination and orientation. The gain

in using these systems is estimated in a 30% in compare to the

Fixed Array. The maintenance and operation costs increase as

well.

Transformer

An electrical device that changes the voltage level of an electric

input from a circuit connected to it. It is used in the PV Plant to

increase the voltage from the AC output of the inverter to the

voltage level of the distribution net, typically 11kV or 33kV in the

UK.

Output Calculation Factors

Standardised Peak Conditions: or Peak Conditions, are the conditions under which the PV Modules are tested in the laboratories to classify them by the power they can produce. The Peak Conditions are:

Irradiance: 1000 W/m2. This can be referred as well as Wp/m2.

Temperature: 25°C

AM (Air Mass): 1.5. the Air mass is a measure of the distance that the sun energy travels to reach the PV Module surface.

Since the power is completely dependent on the weather conditions, these standardised thresholds provide a common reference to compare the power of the different PV Modules. The Power under these conditions is measure in “Watt Peak” (Wp) and its multiples. The Peak conditions do not set a theoretical limit to the Panel Power.

Performance Ratio: or PR, it is referred to the non-dimensional figure that defines in percentage the performance of a PV group in comparison to its performance in the Peak Standardised Conditions. This number sets a relationship between the energy production and the solar raw energy received in a PV System for a certain period considering the capacity of the elements under study. A PV System can be from a panel to a whole plant. The general formula for the energy output calculation in a certain period is shown below:

34

𝑃𝑅𝑝𝑒𝑟𝑖𝑜𝑑 [%] =𝑃𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 [𝑘𝑊ℎ]𝑝𝑒𝑟𝑖𝑜𝑑

𝐼𝑟𝑟𝑎𝑑𝑖𝑎𝑡𝑖𝑜𝑛𝑝𝑒𝑟𝑖𝑜𝑑 [𝑊ℎ𝑚2 ] ∗

𝑃𝑒𝑎𝑘 𝑃𝑜𝑤𝑒𝑟[𝑘𝑊𝑝]

𝑃𝑒𝑎𝑘 𝐼𝑟𝑟𝑎𝑑𝑖𝑎𝑛𝑐𝑒 [𝑊𝑝𝑚2 ]

The Peak Irradiance, as described in the previous paragraph, is a constant value of 1000 W/m2. The period for electrical energy and irradiation must be the same. The Peak Power is the installed capacity of the elements under study, for which the Peak Power considered is the sum of the Peal Power of every PV Module in that PV System.

A healthy PV System can typically reach a PR around 80 to 95%, where numbers above 100% are hardly ever produced in the average installations.

Irradiance: in radiometry, irradiance is the radiant flux (power) received by a surface per unit area. The SI unit of irradiance is the watt per square metre (W/m2). In the PV industry, this power is emitted by the sun and received by the PV Modules.

Irradiation: it is the energy measured per area unit by a surface receiving a certain Irradiance in over time. It is measured in (Wh/m2).

Production: is referred to the energy measured during the period considered by the elements under study, and it is measured typically in kWh.

The Energy output is normally measured by Energy Meters. When a disruption takes place and a PV Plant is not producing, the losses are calculated by using a reference PR and the actual irradiance measured by the Irradiance Sensors during the Disruption Period (DP) for the Affected (Aff) Peak Power.

𝑃𝑟𝑜𝑑. [𝑘𝑊ℎ]𝐷𝑃 = 𝐼𝑟𝑟𝑎𝑑𝐷𝑃 [𝑊ℎ

𝑚2 ] ∗𝑃𝑒𝑎𝑘 𝑃𝑜𝑤𝑒𝑟𝐴𝑓𝑓[𝑘𝑊𝑝]

𝑃𝑒𝑎𝑘 𝐼𝑟𝑟𝑎𝑑 [𝑊𝑝𝑚2 ]

∗ 𝑃𝑅[%]𝐷𝑃

For this estimation, a modelled Constant PR is used.

However, where the disruption is produced only in part of the plant, a Partial PR is usually more precise. This PR is calculated with the energy produced by the available part of the plant during the disruption period and the actual irradiation during the same period, but in this case reducing the Peak Power to the available one. Then, this PR is used to calculate the energy that the affected part of the system, using its peak power, would produce. This estimation is based on the assumption that this part of the plant would operate under the same conditions.

35

6.3. Types of Connection

6.3.1 Physical Connection

The Voltage level and connection arrangement is determined by the required export capacity of the generator. A general indication of the connected voltage of a generator connection is shown below in Table 5.

It is purely an indicative guide and as based on the availability of the Voltage level near to the point of connection.

In some cases, for example, a generator connection at 132kV (that could generally be accommodated at 33kV) or a generator connection at 33kV (that could be accommodated at 11kV) may be necessary due to the lack of local 33kV or 11kV circuits respectively.

Following design and cost analysis techniques a conclusion would be drawn to determine if it would be economic to extend the generator connection to the lower voltage circuit from the area where the generator site is located or provide the connection at a higher Voltage level.

Table 5 Generation Export Capacity and Associated Typical Connection Voltage

Generator Export Capacity (MW)

Location:

Urban or Rural

Typical Connection Voltage (kV)*

(3-phase)

0 – 0.25 Rural 0.415

0 – 0.5 Urban 0.415

0.25 – 2.0 Rural 11.0

0.5 – 5.0 Urban 11.0

4.0 – 20.0 Rural 33.0

7.0 – 20.0 Urban 33.0

+ 20.0 Urban and Rural 66.0/132.0

A typical connection for a solar farm established in a lightly loaded rural location would generally be made from an overhead line circuit.

Connections to the generator site would usually be provided via a single circuit teed into the existing overhead line should all technical design requirements be fulfilled. A connection of this type is generally of the Non-Firm type and this is the type most often requested.

Should a Customer require a more robust connection to reduce generation export constraints for planned outages and credible fault scenarios, a level of redundancy of electricity distribution assets would be required.

This request could be accommodated albeit the Connection Charge to the Customer would be greater. Examples of such an arrangement are:

A circuit direct back to a 33kV busbar at a BSP in lieu of a teed connection to an overhead line; or

A second circuit provided to the site from a separate source busbar from which the first circuit is connected.

36

The method of physically connecting solar generation sites to the host DNO network varies dependent on:

the location of the site

the DNO network topology in that area

the type of connection that was requested by the site developer.

The DNO circuit to which the solar site is connected is often a mixture of overhead lines and underground cables throughout its length. From the perspective of the solar site exporting generation the actual make-up of the circuit is irrelevant. However, it will affect the reliability of the connection, as overhead lines are more susceptible to weather related damage than underground cables.

The solar site may be connected to a Ring or a Radial circuit:

Ring circuit: The circuit is connected at either end to a substation through which power can be imported / exported to the wider electricity network. It allows the transfer of electrical energy between substations.

Radial circuit: A non-interconnecting circuit connected at one end to a substation through which power can be imported from or exported to the wider electricity network. The other end may be connected to a substation which only supplies power at lower voltages to load customers, or it may be solely connected to the generator

The terminology in Table 6 can be used to describe types of connection for the solar site

Table 6 Types of Network Connection

Main Circuit type Explanation

DNO Substation Radial The solar site is connected directly to a DNO substation which is on a radial circuit.

DNO Substation Ring The solar site is connected directly to a DNO substation which is on a ring circuit

Dual Circuit Radial The solar site is looped into a radial circuit.

Dual Circuit Ring The solar site is looped into a ring circuit.

Single Circuit Radial The solar site is teed into a radial circuit

Single Circuit Ring The solar site is teed into the ring circuit

This results in a number of different types of connection to the DNO network as shown diagrammatically in Figure 1.

A solar site with a single circuit connection has only one route for exporting generation, irrespective of whether it is connected to a ring or radial circuit, assuming that there is no capability for disconnecting the circuit either side of the teed connection (see under mitigation Section 9.2).

37

A solar site with a dual circuit connection into a ring circuit has two possible routes for exporting its installed capacity. A dual circuit connection on a radial circuit has only one possible route for exporting generation.

It should be noted that no connection configuration will guarantee that a site will never be subject to constraint.

Figure 1 Types of Connection

In general the following will apply for the different types of connection:

Solar sites with single circuit connections will be constrained for any outage on the circuit to which they are connected, irrespective as to whether they are on a ring or radial circuit.

Solar sites with dual circuit ring connections will probably not be constrained for an outage on one of the ring circuits.

38

Solar sites on radial circuits, irrespective of the type of connection, will be constrained for any outage between the site and the circuit out of the source ring substation.

Solar sites with dual circuit radial connections should not be constrained for outages on the ongoing circuit.

Solar sites with DNO Substation ring connections will probably only be constrained when the outage involves the switchboard to which they are connected.

Whilst the above are general statements, it should be noted that the likelihood of the DNO imposing a constraint during an outage, for all types of connection, will be also be dependent on:

the physical location of switching equipment on the circuit to isolate the section of the network to be worked on,

other internal / external system constraints (e.g. National Grid outages),

the capacity criteria as discussed in Section 6.3.2.

6.3.2 Capacity Criteria

The connection availability is also subject to capacity and demand criteria on the electricity network. This is sometimes, but not always, included in the Connection Agreement for the site. The different types of connection are given in Table 7 with the following terminology:

Connection Circuit The DNO owned circuit which connects the metering point/point of supply for the solar site to the rest of the system/upstream system.

Upstream circuit Any NG or DNO owned circuit other than the connection circuit. Upstream circuits can be switched in or out without directly disconnecting the solar site.

Constrain / Constraint Reduction in real power export from a generator following an instruction from the DNO.

Emergency Action Requirement to disconnect / constrain the solar site under extreme network conditions. Emergency actions would be unlikely before occurrence of one planned or unplanned outage and a second unplanned outage on a DNO’s network or a network the DNO is dependent on

Extreme network conditions Occurrence of simultaneous and numerous unplanned outages. Emergency actions would be unlikely before occurrence of one planned outage and a second unplanned outage.

Network intact conditions All DNO circuits available to be put on load.

39

Table 7 Types of Connection – Capacity / Demand Criteria

Type of Connection Description

non-firm connection with no upstream constraints

Circuit only has one metering point.

With the exception of the circuit connecting the Solar site to the DNO network, the DNO has stated no requirement to constrain the Solar site under planned N-1 outage or system intact conditions.

DNO always expects to be instruct emergency actions

firm connection with no constraints

Connection has two fully independent metered connections where each metered connection is capable of fully accepting the maximum export from the site providing all upstream circuits are available

DNO has no requirement to constrain the Solar site under planned N-1 outage conditions.

DNO always expects to be instruct emergency actions

non-firm connection with constraints

Circuit only has one metering point.

DNO has stated at least one scenario that would require to constraint of the Solar site under planned N-1 outage or system intact conditions. All constraint instructions are via written or verbal instruction ahead of real time.

DNO always expects to be instruct emergency actions

firm connection with constraints

Connection has two fully independent metered connections where each metered connection is capable of fully accepting the maximum export from the site providing all upstream circuits are available

DNO has stated at least one scenario that would require to constraint of the Solar site under planned N-1 outage or system intact conditions. All constraint instructions are via written or verbal instruction ahead of real time.

DNO always expects to be instruct emergency actions

non-firm connection that is under ANM

Circuit only has one metering point.

DNO has stated at least one scenario that would require to constraint of the Solar site under planned N-1 outage or system intact conditions. Management of active power output from the Solar site is moderated by a continually updated electronic set point from the DNO

DNO always expects to be instruct emergency actions

40

Type of Connection Description

firm connection that is under ANM

Connection has two fully independent metered connections each capable of fully accepting the maximum export from the site providing all upstream circuits are available

DNO has stated at least one scenario that would require to constraint of the Solar site under planned N-1 outage or system intact conditions. Management of active power output from the Solar site is moderated by a continually updated electronic set point from the DNO

DNO always expects to be instruct emergency actions

6.4 Joint Operational Agreements (JOA) and Site Responsibility Schedules (SRS)

To establish safety management systems that comply with governing statutes such as the Electricity at Work Regulations, the Electricity Safety, Quality and Continuity Regulations, the Distribution Code, etc., a JOA may be included as part of the original Connection Agreement. A Site Responsibility Schedule (SRS) will normally form part of the Connection Agreement irrespective of whether a JOA is included.

A JOA will normally consist of the following parts:

An Agreement with details of the installation and safety management procedures to be adopted and signed by all parties.

An Operational Diagram of the solar site network showing the ownership, operation and control boundary.

Where an Operational Diagram is not sufficient, then it will be supported by a Site Responsibility Schedule (SRS) of all the equipment adjacent to the interface and defining the owner, maintainer, operator, control party etc.

An Attachment containing supporting information e.g. contact telephone numbers, Authorised / Competent Persons etc.

The ownership of any System and its components will generally determine the responsibility for its control. Where individual Systems are directly connected, and so as to comply with the requirements of the Distribution Code, the relevant System owner shall define in its SRS, the plant and apparatus it owns and controls and the extent of any authority granted to carry out work or operations on that System. At all times, the provision of sufficient records for the safe operation of plant and apparatus, must be made.

A SRS will consist of the following:

A schedule of all HV equipment adjacent to the PoC with the host DNO

Clear instruction on the HV equipment ownership

Clear instruction on the HV equipment maintenance service provider

Clear instruction on the HV equipment authorised operator

Clear instruction on the HV equipment system control authority

41

Where there is a need to update the necessary information for either an existing JOA or SRS, this will be formally recorded and communicated between all parties involved. In the first instance, a ‘request for change’ form will be used to record and communicate change. It is the responsibility of any web portal owner to subsequently update its data in-line with the submitted ‘request for change’ form. Upon completion, the web portal owner will issue an electronic change notification to its designated users

A ‘request for change’ form will consist of the following:

Details of the affected site

Contact details of the requesting organisation

Confirmation of the organisation’s relationship with the site (owner/occupier)

Contact details for the previously designated person at that site

(Allowing the passing of ownership from that designated person to another to be confirmed)

Contact details of the new designated person

Whilst the majority of the information in the JOA will not change over the life of the site the site owner, operator and contact details of people could change. Any such change should be notified to the DNA as soon as possible.

42

7. Standard DNO and Generator Information

7.1. Mechanism for recording / sharing / updating standard information (e.g. web portals)

It is only the DNOs who have information on all their connected customers and generators, so they are in the process of developing web portals to improve the two-way flow of information. The level of development and interaction by third parties varies across the DNOs. This provides an opportunity to generators to influence the design and data in these portals to enable maximum benefit for all parties.

The DNOs and solar generators have identified some of the issues they have experienced regarding communications as follows:

The site name used by the owner/operator is not always the same as the name that used by the DNO

The solar owner and operator company may change over time

Staff changes in solar owner and operators change over time

Staff changes may occur in the DNO if person specific contact details are used

Notifications of outages may be sent to the owner or the operator

Some notifications are issued via the postal system and addresses may not be correct or mail can be delayed.

The notification of scheduled and unscheduled outages requires that accurate information is available to the DNOs on who should be contacted for each site that may be affected.

It is considered that the DNO portals currently being developed would be the optimum mechanism for holding contact information for each site, provided that the solar companies have access to and can update the information.

The following is suggested as the basic requirements of the data in the DNO web portal:

Site (Owner): Name, location, owner, type of generation, generator capacity, etc.

Site (DNO) Name, substation reference number, location

Owner: Name, address, contact details, etc.

Operator: Name, address, contact details, etc.

DNO Contact Name, address, contact details, etc. Note: DNOs prefer to use standard company contact numbers or group email to practically eliminate the issue of staff changes.

Notification Contacts The people who the Owner has specified the DNO should inform of scheduled and unscheduled outages for this site - name, company, email address, telephone numbers.

This would normally be up to a maximum of 5 contacts.

Scheduled Outages Details of proposed scheduled outages for the site / owner / operator; selectable 1, 3, 6 and 12 months in advance.

Historic Data Data on scheduled and unscheduled outages that have been completed. This historic data should be maintained on the portal and be suitable for download in a standard file format.

43

Details of the suggested data fields for each of the above sections are given in Appendix I.

In order to ensure that all communications solutions with the DNO portals are standard and easy to adapt to it would be preferable that a form of Application Programming Interface (API) could be used which would allow users to extract the information they want.

At present, this is not possible as DNO company security policies do not permit third parties to directly connect to the DNO systems. This is an area that the solar generators will wish to discuss with the DNOs in the web forums.

At present there is only one DNO with a web-based portal that provides advance information on outages. The remaining DNOs provide information varying from an 8-week advance programme to emails warning of imminent outages and this means that outage notifications are sometimes missed.

The development of web-based portals by all DNOs is seen as the best option to improve communication of outages.

Until these systems are available it would be preferable if the all the DNOs provided a list of all outages scheduled in the next 8 weeks / forecast for the next 12 months, possibly in spreadsheet format, on a weekly basis.

7.2. Review and Update DNO / Solar contact details for notifications

It is the responsibility of both the Owner and the DNO to develop and implement procedures to identify and change the contact details when staff or companies change.

The DNO will make provision for the generator to provide updated contact details and to implement the revised contact details within 2 working days of the receipt of the revised details.

The contact details should be reviewed by the generator on a routine basis to ensure that the required information is being sent to the relevant staff. Any contacts specified who no longer require the information should be removed from the list.

If the DNO proposes to change their contact details or the change notification procedure then the generators should be informed in advance of the proposed change.

If the structure or software platform of the portal changes it is the responsibility of the owner of the portal to inform the registered users of the changes and to highlight any checking, amendments or additional information requirements that may be required. It is the responsibility of the DNO or the registered user to ensure their particular information is correct.

7.3. Review and Update connection data for solar sites

The types of connection of the solar site to the DNO network was discussed in Section 0.

The concepts will also assist developers in planning new generation connections to minimise the effects of future outage constraints and will also enable a more rigorous assessment of future income streams.

This data is not easily available to the solar companies and it is considered that it would be useful to enable them to review those sites that are more likely to suffer constraints. It may have been made available to the original site developer as part of the Connection Offer, but frequently has not been passed to subsequent site owners.

44

The information on connection type is known by the DNOs but is rarely written down in any documentation which is why it has been identified as a datum on the site details for the web portal. It is practically impossible for the generators to determine this information from the network data that is made publicly available by the DNOs.

When network alterations take place, it is the responsibility of the DNO to ensure that the connection type and connected Primary/BSP substations is reviewed and updated where necessary.

The DNOs should include in the Connection Agreement documentation a schedule that shows the type of connection and details the information that would be required for the web-based platform.

Companies seeking new generation connections should ensure that this connection information is made available by the DNO and should also commit to providing up-to-date contact information to the DNO. In addition, should a generation site be sold the seller should ensure the connection information is passed to the new owner, inform the new owner of their responsibility to provide current contact details to the DNO and inform the DNO that they have sold the site.

45

7.4. Other generation on circuits – Last in/first out sequence for each constraint type

Where there is more than one generator on a circuit it may not be necessary to constrain all the sites for certain outages.

Normal practice is to constrain generation sites based on reverse date order in which they accepted a connection to DNO network. This can be referred to as the constraint queue, or a Last In First Out (LIFO) stack. The sites in this queue can vary for different network constraints.

Where there are two or more Connection Offers for connection into the same circuit, and there would be limitations to the capability of the system with two or more connections, then the connection and Connection Offer is termed to be interactive. The Connection and the level of any export constraints would again be on the basis of which Connection Offer was accepted and returned to the DNO first.

It would assist all generators if it was possible for the DNOs to detail on the web-based platform the constraint queue that will operate for an outage on any specific site.

When an outage requires a reduction in the connected generation capacity then generators in the constraint queue are sequentially constrained until the unconstrained generation matches the available capacity in the network.

7.5. Recording and transparency of constraint queue (last in-first off; firm vs non-firm) and constraining scenarios

The individual generators do not always know if there are other generators connected to the same circuit or their position in the constraint queue. This information is held by the DNOs and is subject to commercial confidentiality.

Whilst the requirement for confidentiality is understood it should be possible for some information to be made available provided that the owners of the generating sites agree to such disclosure.

The database should have a facility against each site that allows the site owner to waive confidentiality in the DNO database (for the data identified in Section 3) which will allow the site name to be visible on outage schedules to other owners whose sites are subject to the same outage and who have also waived confidentiality.

Where a site owner does not set this marker for a specific site then it will not be visible to any other owner, and they will not see other generators. However, in order to obtain the maximum benefits to all parties, including themselves, all generation owners should set the marker to waive confidentiality.

The objective of this waiver is to allow sites affected by the same outage to be visible to each other to allow joint discussions with the DNO to identify if there are any options that would mitigate the overall impact of the proposed constraints.

46

8. Communication on DNO proposed constraints due to Scheduled Outages

8.1. Contacts for communications

Good communication is impossible if the contact details are inaccurate or not updated as companies and staff changes take place.

It is the responsibility of the Owner of a solar site to decide who is to be the points of contact for the DNO for:

the advance notification of planned constraints

the liaison / negotiation on possible mitigation of planned constraints

the notification giving confirmation of the constraint date, time and duration

The notification of the removal of the constraint.

The main point of contact for each solar site may be the O&M contractor, with the Owner receiving a copy of the notifications.

In Section 7.1 the data requirements for the people who the DNO should notify were proposed. It would be the responsibility of the owner of the site to ensure that this list of contacts on the portal is kept up to date to take account of changes in companies and staff.

In the event that there is a failure to respond from the specified contacts then it is the responsibility of both the DNO and the solar companies to raise the issue with the other.

The main factors that need to be addressed to ensure good communications are as follows:

A single point of contact for all generation issues within a DNO’s total area of operation – this may not be a specific person. DNOs will respond within 2 working days.

A single email address / phone number for enquiries per licence area (if multiple licences are held by a DNO).

Establish via the DNO website a Generation Web Portal for all generators (of all technology types) to access. The Generator Portal will allow the generator owner, or their appointed representative to:

o Access for reviewing generators connected at EHV and 132kV to;

Review historical export constraints as a consequence of outages at EHV, 132kV and Transmission System level.

Review future outages that are currently in the DNO’s Outage Plans that would require a constraint of the generators output.

Update the operational site contacts, e-mail addresses and contact names/numbers to ensure that the DNO has full and current details. This is not to replace the existing process of updating the Connection Agreement for the site.

It is recommended that generators of all technology types also have an approach that mirrors that of the DNO (excluding the web portal).

This would greatly simplify the way in which the two parties communicate effectively.

47

8.2. Notification of future constraints

The DNO process for developing the forward outage plan is described in Section 4.3.

The DNOs will inform the generator owners and operators on a weekly basis of those outages requiring generation export constraints at e-mailed for outages and constraints commencing and continuing within a 4 week and week ahead duration.

The date of the outage where a generation export constraint is required will be subject to variance and the more advance notice that is provided increases the probability that the outage date will change as the outage plan develops and becomes reality.

However, in order to avoid confusion, the DNOs require that all outages involving the constraint of generation are either approved or provisionally approved in order for the outages to be made visible to generator owners or operators via the Generation Web Portal.

Generators require as much visibility as early as possible of planned outages involving generation export constraints.

It must be noted that any outage provided via a Generation Web Portal or via e-mail must be treated as purely an indication that the outage is to proceed with dates subject to variance.

The DNO should issue an email to the relevant site notification contacts of outages due to take place in the following 4 weeks that will require generation on that site to be constrained.

The final confirmed date of any planned outage and any consequential generation export constraint will ultimately be confirmed via the formal written notification from the DNO.

The generators would prefer that when the 12-month plan is available the outages should be posted on the web portal so that the solar generators can evaluate the future impact on their operations.

It should be noted that the 12-month forward plan:

a) is based on a snapshot of planned outages at the point the plan was created and the plan is likely to change based on the operational needs of the network or if the DNO receives requirements for the connection of new load or generation.

b) all scheduled outages over 4 weeks in the future are provisional and subject to modification and possible cancellation unless the DNO specifically has stated otherwise.

It is the responsibility of the owner / operator to review the scheduled outages outside the 4-week schedule and evaluate the impact on their generation.

There is an onus the solar companies to identify constraints that are particularly onerous and initiate discussions on possible mitigation action that may reduce the effects of the proposed constraints (see Section 9).

The solar generators want to understand the reasons for scheduled and unscheduled outages that require constraints, but only in broad categories as detailed in Table 8.

48

Table 8 Reason for DNO Outage

Reason Comment

Replacement Replacement work on substation or circuit assets

Equipment Failure Failure of substation equipment including protection and control systems

Maintenance Will include substation, protection and circuit maintenance at all voltage levels

Network Fault Faults on overhead line or underground cable circuits

New Connection Load or generation

Repair Planned repairs to substation equipment or circuits

Weather Faults caused by adverse weather conditions

Other Includes commissioning works, network voltage issues, nuisance, tripping, protection and control, third party damage, transient, and vegetation issues

8.3. Effects on Solar sites

The DNOs can have no discretion between solar and non-solar technologies as they are required to treat all Customers equally. This principle is laid down in the Quality of Service Incentives by Ofgem, which covers the treatment of load customers. DNOs treat all generation as individual sites and do not distinguish between different technology types. Hence, although this document sets out the best practice for solar it will effectively dictate the best practice for all generation types. Depending on the timing in which individual generators accepted a Connection Offer from a DNO the scenario could exist where for example generators connected to the same circuit could have different levels of constraint. This scenario is not due to the technology type of the generator but the time in which the generator applied for and accepted a Connection Offer and subsequently where they resided in the “Connection Queue”. It could well be that there are different generation sites connected to the same circuit or BSP that have different levels of constraint. The ordering of constraints is a Last In-First Out (LIFO) basis. DNOs could potentially facilitate different technology types “trading” non-constrained export levels during an outage. This could be subject to regulatory considerations. An example would be a wind farm trading a non-constrained export to a constrained solar park during the summer months, but this would be ultimately down to the generator owners willing to share information and be willing to fully participate in such a regime. The DNO will work with generators to facilitate communication to address areas of confidentiality that are leading to avoidable inefficiencies like the failure to ‘trade’ non-constrained export levels.

49

9. Liaison on Constraint Mitigation

9.1. Initiation of Discussion on Constraint Mitigation

When a solar site is constrained there is an obvious loss of production and financial detriment of the site owner. There have already been instances where several owners of generation sites subject to the same outage have collaborated to minimise the overall impact.

The effect of a proposed constraint on a solar site can be calculated using factors as multipliers of the installed capacity of a solar site to estimate the output generation in any specific month. A table of these factors has been produced by the STA and is given in Appendix II.

The calculation for a solar generation site is as follows:

Prospective Lost production in MWh = P x Fd x N

Where P is the Peak Power Output in MWp of the site

Fd is the Daily Yield Expected Factor for the relevant month (from Appendix II)

N is the number of days the constraint will be in force

It is essential that the generators receive as much advance notice of constraints as possible so that they can assess the impact on site and determine whether to initiate discussions on possible mitigation. There must be sufficient time for options to be discussed, financial assessments to be carried out and to allow possible work on the network to be undertaken.

It is the responsibility of each solar generation company to assess the business impact of a planned constraint(s) on a site and to decide whether to initiate discussions with the host DNO regarding possible options for mitigating the effect of the constraint(s).

When a generator contacts the DNO to initiate discussions on a planned constraint, the DNO should typically respond within 2 working days. The intention is for this to be an initial response that acknowledges the request for dialogue with the generator, perhaps including

an indication of how long any detailed response might take and

indicating whether there may be any possibility for mitigating the constraint.

As part of the response it would assist the generators if the DNO could inform them of any mitigation that the DNO has already considered to reduce the duration of the constraint, and if there are further measures that could be applied but which require additional investment.

Where a solar company or companies initiates discussion with the DNO to mitigate a specific constraint the DNO should, within the limits of confidentiality already discussed, inform other generators affected by the same constraint that such discussions are taking place.

Where sites owned by different companies are subject to the same constraint they should coordinate their discussions with the DNO.

9.2. Options for mitigating effects

The following sections discuss possible options that could be considered to reduce the impact of constraints on solar sites.

50

In all cases the DNO would incur additional costs and would require compensation or active investment from the solar companies.

Where options for mitigating constraints are available that would require investment in the network, and the generator(s) indicate their interest in funding such investment, the DNO should facilitate the development of such options to enable the best option for all parties to be implemented.

Whilst the solar generators would ideally prefer the DNO to have assessed the costs of possible mitigation when planning the outage, it is accepted that this cannot be done in all cases.

However, when a generator requests discussion with a DNO regarding possible mitigation it would be expected that the DNO would be able suggest possible options with indicative costs for discussion.

9.2.1. Alternative working hours

It may be possible for the work scheduled to be carried out to be done during the night, although this will probably only be possible for work in substations.

It is more likely to be feasible for maintenance work than for any other type of work.

It would be the responsibility of the DNO to determine whether the work for which the outage is required could be carried out during the hours of darkness. If so, then the DNO should provide the affected generators with an indication of the additional costs that would be incurred.

It would be the responsibility of the generators to liaise with other generators affected, to assess the costs and inform the DNO whether they want to take advantage of the proposal.

9.2.2. Single Circuit Sites - Improvement in Connection Type

The effects of outages on sites with single circuit connection could be improved in a number of ways;

9.2.2a Addition of Line Switching

The problem with the single circuit connected site is that there is no alternative circuit to export the generation when there is an outage on the main circuit.

Where the main circuit is an overhead line it is relatively easy to add additional switches to the circuit to provide an alternative as shown in Figure 2.

For the site connected to a ring circuit it is possible to add one or two switches to the OHL either side of the connection. This would mean that any outage would only affect one side of the circuit and that some or all of the generation could be exported down the other side.

When the site is on a radial OHL there is only a gain if one switch is installed on the ongoing leg of the circuit. This will enable the site to continue to export generation for any outages beyond the switch.

It is possible to add switchgear to underground cable circuits, but this would be an order of magnitude more expensive.

51

Figure 2 Addition of Switchgear

9.2.2b Upgrade to Dual Circuit

It is possible to upgrade the connection type from a single circuit to a dual circuit as shown in Figure 3. This will require the establishment of a new ground mounted DNO substation at the solar site and providing a second circuit from the connection to the main circuit.

Whilst this is a costly exercise, if the solar site is constrained on a frequent basis there may be a cost benefit in pursuing this option.

Figure 3 Single to Dual Circuit

9.2.3 Opportunity for investment into constraint / duration reducing measures

The solar generators would be interested in discussing investment opportunities with the DNOs if there is scope for doing this, either for a scheduled outage or for work that could prevent future constraints from being necessary.

The DNOs have to review the network on a regular basis for the publication of Distributed Generation EHV Constraint Maps. It should be possible for the DNOs to identify circuits with

52

multiple generators where investment would reduce the future need for constraints in outage conditions, whether planned or unplanned.

The DNOs should proactively develop outline proposals and indicative costs that would reduce or remove the constraints and invite the generators involved to an initial feasibility discussion. It would be the responsibility of the generators to determine whether there was a viable business case for the proposal before any further discussions.

One of the main issues is that not all the generators who could benefit from such a scheme would agree to invest in it. The allocation of extra capacity or reduction in constraint requirement would need to be determined. The concept of the Constraint Queue, or Last In First Out, would need to be reviewed and an agreement established as to how it could be revised to take account of investment contributions.

The members of the STA would like to see all DNOs actively identifying opportunities for improvements to the network that would reduce the impact of, or eliminate entirely, future constraints on generation due to planned outages. When new generators are being connected the DNO should determine whether it is possible to improve the network to minimise the impact of future outage constraints for existing generators.

In order to provide an incentive for the generators to invest in network improvements there needs to be a tangible benefit for those who contribute over generators who may also benefit but do not contribute.

Any such works should release additional network capacity but at present there is no mechanism for the allocation of such additional capacity. The generators would welcome discussions as to how such a mechanism could be developed. It is suggested such capacity could be allocated to contributing generators, based on the proportion of contribution, before applying the original system capacity to the constraint queue. This should mean that the contributing generators should not be fully constrained during future outages.

It is accepted that the ordering / re-ordering of a constraint queue and the re-allocation of network capacity are issues that are subject to a number of legal and regulatory requirements, and as such may require discussions with regulatory bodies as well as DNOS.

9.2.4 Intertripping systems

In some cases, the DNO may impose constraints during an outage in order that it can comply with the operational requirements under ER P2/6 in the event of a second circuit outage.

It may be possible in some instances to develop and implement intertripping systems that could allow the DNO to remove the constraint during the outage on the basis that if a second circuit outage occurs the solar site will be automatically disconnected, without warning, by the DNO control system. There is a risk that the sudden shutdown could cause damage to the generators equipment, but this is no different from the effect of shutdown under fault conditions.

Where there is a DNO circuit breaker controlling the site, there may be opportunities to utilise existing communications links as part of an intertripping system. However, due to the high reliability required of intertripping systems a more reliable communications link may be required.

Where there is no local DNO circuit breaker then it would require the DNO having access to communicate with the private “G59” circuit breaker. This would have to be investigated on

53

an individual basis to determine whether the communication and operational facilities were compatible with such a scheme.

An intertripping system simply monitors the status of the network, which is different to active network management, which is discussed below.

9.2.5 Use of reactive power to avoid voltage constraints

There may be options for solar sites to provide reactive power to assist the DNO in supporting the network and maintaining voltages within regulatory limits, which may assist the DNO in reducing constraints on generation.

Inverters have reactive power control capability, which means they can create / consume reactive power to support the network voltage at the Connection Point. This has the potential to become an additional income stream for the solar generators.

This would require the appropriate control systems for the invertors, communications to the DNO control room and appropriate software.

It is technically feasible and warrants further investigation but may not prove to be economically practical.

This will have more relevance in the change from DNOs to DSOs.

9.3. Active Network Management

Historically the DNO networks have been designed and operated on the basis that the flow of electricity is from central generation down to demand customers. Distribution networks have a finite capacity to accept export from embedded generation before unacceptable voltages or circuit loading will occur on the distribution network.

Network operators must avoid unacceptable network conditions by ensuring that the current flows and voltage profile remain within acceptable limits.

In situations where there is insufficient network capacity to avoid such conditions, the DNO must intervene to stop generation exporting too much power into the network, or in other words generation management strategies must be employed.

The most prevalent strategy employed so far is referred to as passive network management where generation is constrained to reduced or zero export upon commencement of a period where the network is at risk. This is known as a passive constraint and is clearly inefficient at avoiding lost generation production. Passive network management suited the DNO model of network management as it reduced DNO operational costs. Costs, staffing levels and fixed tangible assets were kept at an efficient and minimum level.

Active network management refers to a condition where instead of turning generation off as a precaution to avoid potential network issues, the ability of the network to accept generation is constantly recalculated in real time and generation is continually turned up or turned down to utilise the available network capacity.

Active Network Management (ANM) is the term used to describe real time management of the flow of electricity between generators and demand customers within the electricity distribution network.

At present there is no industry agreed definition of what is ANM.

54

ANM has been around for many years but has been a manually intensive process as it required additional shift staff. The advent of low cost computing has allowed ANM to become an automated process where generation output is varied following network capacity calculations made by a computer programme.

When considering constraints on solar generation the application of ANM could enable the DNO not to constrain generation for an outage, with the proviso that if a second outage occurred the generation would be automatically disconnected by the DNO without notice.

In practice there are many factors that must be taken into account, not least of which is monitoring and communications systems that would need to be introduced.

The ENA have produced a comprehensive Good Practice Guide on ANM which is available for download from the following link:

http://www.energynetworks.org/assets/files/news/publications/1500205_ENA_ANM_report_AW_online.pdf

9.4. Instructions from National Grid or DNO for National Grid driven constraints

Where National Grid have defined planned outages, this will have been considered by the DNO when developing the scheduled outage plan.

It is unlikely, therefore, that solar generators will be involved in communications with National Grid, unless a specific solar site is directly connected to the National Grid transmission network.

55

10. Communication during Constraint Period

In order to provide a good connection service that aligns with customer needs the DNO will respond to any requests from the affected generator(s) for discussions regarding planned network constraints, as discussed in Section 9.1. A comprehensive and robust strategy of engagement should be followed at all times, thereby facilitating joint discussions.

This section is concerned with good practice in terms of communication during the period of the outage.

10.1. Before starting constraint

The DNO will issue a report of known planned constraints to the affected generator(s) site owner and operator a minimum of 4 weeks in advance of the planned interruption start date. The notice of supply interruption will include the following:

The date/time of the interruption period

The reason for interruption

The requirement including date(s) / time(s) for constraint on generation

Where known, the DNO and the generator owner(s) are encouraged to update any web portal with appropriate contact details for the planned outage period(s). It is acknowledged that contact details are subject to change, never the less every effort should be made to ensure accuracy.

In the event web portal access is not available then contact details will be exchanged using an agreed method.

Upon request, the DNO will provide access to a comprehensive work plan of activities so that a common understanding can be achieved.

10.2. Updating during constraint

During the constraint period and where more information becomes available to the DNO, an update should be issued to the generator(s) via email and/or posted on the web portal (which could then automatically send an email). This information should include:

General progress (ahead of schedule/ on-schedule / behind-schedule)

Any relaxation / cancellation of the constraint on generation

Any change in project contact details

For protracted constraint periods (> 24hrs) the DNO is encouraged to update the generator(s) on a daily basis, especially where the constraint is likely to be completed early or to overrun. Ideally this communication should take place between the DNO designated field coordinator and the equivalent generator site operator. The update should be brief and of a high-level nature.

56

10.3. Updating any constraint instructions

Where a previously agreed constraint on generation period changes or has the potential for change the following information should be updated and formally communicated:

The new date(s) / time(s) when there is a requirement for constraint on generation

The anticipated date(s) / time(s) for a relaxation / cancellation of the constraint on generation

10.4. End of constraint

Upon completion of the planned outage and following the return of the HV System to normal running, the DNO should notify all the affected generators that work is complete and all constraints on generation have been removed.

The DNO should issue a summary of the completed outage to the generator(s). Ideally this information should include measurable data such as:

The exact date(s) / time(s) for completed outage(s)

The exact date(s) / time of any incomplete outage(s)

The exact date(s) / times(s) where the constraint on generation was applied

The exact date(s) / time(s) where the constraint on generation was relaxed and / or removed

57

11. Communications during Unscheduled outages

11.1. General

Unscheduled outrages can occur as a result of the failure of equipment, adverse weather conditions or third-party damage, collectively referred to as ‘faults, in the remainder of this section. It is outside the control of the DNO.

The section of electricity network containing the fault will be automatically disconnected and alarms are likely to be sent to the DNO Control Centre. The DNO will then take action to isolate the faulty section, restore the remaining network where possible and commence remedial work.

It should be noted that whilst it may be possible for the DNO to restore supplies to load customers there may not be sufficient capacity in the re-arranged network to allow unconstrained generation from all connected generators.

The generator should identify one of the contacts as the person to contact for real time operational matters. A second contact should be identified in the event that the issues require escalation to a higher level.

11.2. Notification

The DNO should identify the generator(s) affected by the fault and notify both those who have lost connection to the network and those where a constraint will be required. This information should include:

The date/time the fault occurred

The requirement for constraint on generation

11.3. Updating during outage

As more information on the fault and required repairs becomes available to the DNO then an update should be issued to the affected generator(s) and/or posted on the DG portal. This information should include:

The date/time the fault occurred

The date(s) / time(s) when there is a requirement for constraint on generation

The anticipated date(s) / time(s) for a relaxation / cancellation of the constraint

It should be noted that due to the nature of faults the information may be subject to change as further details become available, which could require an increase or decrease in the duration of the constraint.

58

11.4. End of outage

When the network is returned to normal the DNO should notify all the affected generators that all constraints have been removed.

The DNO should also issue a summary of the details of the fault and the constraint to the affected generator(s) and/or posted on the historic outages section of the DG portal. This information should include:

The date/time the fault occurred

The actual date(s)/times(s) where the constraint was applied to the generator

The actual date(s)/time(s) when the constraint was relaxed and/or removed

The date/time that the fault repair was completed, and all generation constraints removed.

The reason for the constraint

59

12. Review of Constraint due to Scheduled / Unscheduled Outages

12.1. Identification of issues – DNO / Solar

It is vital that learning is taken from each of the individual constraint management cases carried out by individual STA Member companies, in order to promote continual learning and improvement in the constraint management process that will benefit all STA Member companies. In order to determine trends and to ensure that like for like comparisons can be carried out, it is important that the information gathered for each constraint management case is consistent; therefore, the following information has been identified as being relevant to increasing the knowledge of constraint management, and forming the basis of information collection for each case study:

Generator Owner

O&M - the assigned O&M Contractor and/or their subcontractor

Asset Management Business (If Applicable)

DNO/TNO

Site affected by the constraint

Installed capacity

Start date of the constraint

Finish date of the constraint

Duration of the constraint

Potential loss

Constraint type (Full, Partial)

Reason for the constraint

Constraint notified (date)

Constraint Management Result (Full, Partial, None)

Mitigation Measure(s) (purchased generation capacity, network reconfiguration, Active Network Management…)

Saved export (kW)

Innovative method (Y / N)

The constraint management case records will be held in a central database that will be managed by the STA (or one of its representatives). The database will be made available for any participating member companies (including DNOs/TNOs) and will be used to review and make improvements in constraint management.

60

12.2. Communications

Improvements in the constraint management process will be communicated through STA committee meetings, and liaisons between the STA and DNO/TNO representatives. Any innovative constraint management methods will be communicated across all STA member companies and DNOs/TNOs through official representatives, whose contact details will be held by the STA.

Whilst the constraint management database will be held and managed by the STA (or one of its representatives), communicating the results of the constraint management case will be the responsibility of the organisation operating the site effected by the constraint (O&M, EPC or Asset Manager).

12.3. Action plan for improvements

The constraint management database will be reviewed on a regular basis to determine whether:

Improvements in the constraint management process can be identified;

Whether any innovative methods have been employed;

Improvements to this best industry practice manual can be implemented;

In addition to the regular constraint management database reviews, this best industry practice manual will also be reviewed, in-line with the document’s review date (section ##). This review will be carried out by the STA (or one of its representatives) and will include participation from participating DNOs/TNOs.

Any proposal for improvement to the constraint management process or this best industry practice manual will need to be sanctioned through the STA and the participating DNOs/TNOs.

61

13. Monitoring Constraint Outcomes

There is a desire from both the solar companies and the DNOs to develop a methodology to measure the impact of scheduled and unscheduled outages. These indicators will provide a means of monitoring how the collaboration between solar companies and the DNOs is affecting the level of constraints and to identify where there has been a marked change in performance.

13.1. Measurement methodology

The basic information available for the development of the methodology is that which it is suggested should be available on the web portal database detailed in Appendix I.

Assuming the DNOs host web portals with the data specified then the data that would be available to both DNOs and generators on a site basis is as follows:

DNO

DNO Licence Area

Number of Outages

Scheduled / Unscheduled Outage

Outage Duration

Constraint Duration

Constraint Type

Outage Type

Reason for Outage

Owner

Sites

Generation Capacity (MW)

Lost Production (MWh)

The availability of this data will enable Performance Indicators to be calculated by a variety of measures on a DNO / DNO Licence Area basis.

The performance indicators that can be calculated are given in Table 9.

Table 9 Measurement Factors

Performance Indicator Description

Number of outages Count

Number of scheduled outages Count

Number of scheduled outages by Outage Reason

Based on Table 8

Number of unscheduled outages Count

Number of unscheduled outages by Outage Reason

Based on Table 8

Incident Ratio Number of incidents / number of sites

Production Loss (MWh) For scheduled and unscheduled outages

Production Loss Ratio Production losses (MWh) / installed capacity (MW)

For scheduled and unscheduled outages

62

Performance Indicator Description

Production Loss by Outage Reason

Based on Table 8

Production Loss Ratio by Outage Reason

Based on Table 8

Number of Outages by Outage Reason

Based on Table 8

13.2. Responsibilities of DNO and Solar

It is the responsibility of both the DNO and the solar generator owner to ensure that the data on the web portal is updated both before and after the outage is completed.

It will be necessary for the DNOs and solar generator owners to collectively review the data on a regular basis and assess the effectiveness of the measures.

Consideration should also be given to how the measures can be made available to regulator(s) and shareholders and the degree of confidentiality.

13.3. Collation of data from DNO and Solar

Historic outages that have resulted in an export constraint whether partial or full will be available via the Generation Web Portal. The data available should be that given in Appendix I.

However, generator owners and operators should also maintain their own records as generator sites may be affected via operation of the generator site Loss of Mains protection for system disturbances that may even not be associated with the DNO system. Access to historic records will enable generators to check if loss of generation is associated with a constraint or is a site equipment issue.

The STA could develop and maintain a database on behalf of its members to produce summaries and trends for information.

63

14. Review of Constraints in Connection Agreements following DNO Asset Replacement Work

Some Generator Connection Agreements detail the constraints that will be applied for specific network operating conditions where circuits or plant have to be taken out of service, for whatever reason.

When a DNO has completed asset replacement or reinforcement work on the network it may release capacity or alter the network operating conditions which previously required constraints.

Where

a) a site Connection Agreement specifies conditions for the application of constraints, and

b) the constraint has been applied to a generation site for the purposes of asset replacement or network reinforcement

then the generator should request that the DNO review the constraint conditions in the Connection Agreement.

If so requested the DNO should review the constraint in the Connection Agreement and amend the specified constraint where possible.

Additional constraints should not be applied under this review as that implies that the network capacity has been reduced.

64

15. Bibliography

The following documents have been referred to in this Manual

Connection and Use of System Code

Control of Substances Hazardous to Health Regulation 2002 (COSHH)

Distribution Code of Licensed Distribution Network Operators of England and Wales

Electricity (Standards of Performance) Regulations 2015

Electricity Act 1989 (as amended)

Electricity at Work Regulations (1989)

Electricity Safety Quality and Continuity Regulations (ESQCR) 2002 (as amended)

ENA Active Network Management Good Practice Guide

ENA Engineering Recommendation G59/3-2: Recommendations for The Connection of Embedded Generating Plant to The Regional Electricity Companies’ Distribution Systems

ENA Engineering Recommendation G75/1: Recommendations for The Connection of Embedded Generating Plant to Public Distribution Systems Above 20kV or with Outputs Over 5MW

ENA Engineering Recommendation G83/1: Recommendations for The Connection of Small Scale Embedded Generators (Up To 16A Per Phase) In Parallel with Public Low-Voltage Distribution Networks

ENA Engineering Recommendation P2-6: Security of Supply

Energy Act 2004

Grid Code

Health and Safety (First Aid) Regulations 1981

Health and Safety at Work Act (1974)

Management of Health and Safety at Work Regulations 1999

Personal Protective Equipment (PPE) at Work Regulations 1992

Utilities Act 2000

65

Appendices

Appendix I DNO Generation Portals – Suggested Data and Facilities

Appendix II Table of Factors for calculating Solar Generation Output– UK DNO Licence Regions

Appendix III Case Studies

66

Appendix I Distributed Generation Portals – Suggested Data and Facilities

The following information is suggested to form the basis of the DNO web-based DG Portals

A1.1 Site Details

Updated by DNO SC

Site Owner Name √

Site Name – Owner √

Site Name – DNO The name the DNO knows the site as

√

Site Address √

DNO Substation Name The DNO substation name √

DNO Substation Number The DNO substation number √

DNO Licence Area OFGEM still requires DNOs to report against the original

√

Import MPAN √

Export MPAN √

Type of Generation Solar; Wind; etc.

Maximum Peak Power (MWp) √

Site Operator Name √

Type of Connection From Table 6 √

DNO Primary Substation 1 Name of the √

DNO Primary Substation 2 √

BSP 1 √

BSP 2 √

Owner Agreement to visibility The owner has waived the confidentiality so that the site will appear on the outage schedule for any site on the same circuit where the owner has also waived confidentiality

√

67

A1.2 Site Owner (for each Site, updated by Owner)

Company

Company Address

Company Contact 1 - Name

Company Contact 1 - email

Company Contact 1 - Landline

Company Contact 1 - Mobile

Company Contact 2 - Name

Company Contact 2 - email

Company Contact 2 - Landline

Company Contact 2 - Mobile

Emergency Contact Number

A1.3 Site Operator (for each Site, updated by Owner)

Company

Company Address

Company Contact 1 - Name

Company Contact 1 - email

Company Contact 1 - Landline

Company Contact 1 - Mobile

Company Contact 2 - Name

Company Contact 2 - email

Company Contact 2 - Landline

Company Contact 2 - Mobile

Emergency Contact Number

If the contact details need to be entered individually for each site this will make the process very time consuming. The portal should allow the user to select the list of sites to which the contacts are applicable.

Generators should consider the use of email group In-boxes for the notification of constraints.

68

A1.4 DNO Contact (for each Site, updated by DNO)

Company

Company Address

Company Contact 1 - Name

Company Contact 1 - email

Company Contact 1 - Landline

Company Contact 1 - Mobile

Company Contact 2 - Name

Company Contact 2 - email

Company Contact 2 - Landline

Company Contact 2 - Mobile

Emergency Contact Number

A1.5 Solar Contacts for Notifications of Scheduled and Unscheduled Outages (for each Site, updated by Owner)

Contact 1 Contact 2 Contact 3 Contact n

Company

Name

Function Owner

Operator

Authorised Person

Email

Landline

Mobile

Nominated Emergency Contact

Y / N Y / N Y / N Y / N

If the contact details need be entered individually for each site this will make the process very time consuming. The portal should allow the user to select the list of sites to which the contacts are applicable.

Generators should consider the use of email group In-boxes for the notification of constraints.

69

A1.6 Scheduled Outages (updated by DNO)

Site Name - Owner

Site Name - DNO

Start Date / Time

Duration (days)

Constraint Type

Reason for Outage From Table 8

DNO Outage Reference

Outage Status Planned, Confirmed

It should be possible to view scheduled outages at the site, owner or operator level and for up to 12 months in advance of the current date.

A1.7 Historic Outage Data (Scheduled and Unscheduled)

Updated by DNO SC

Site Name – Owner √

Site Name - DNO √

DNO Outage Reference √

Outage Actual Start Date / Time √

Outage Actual End Date / Time √

Constraint Actual Start Date / Time √

Constraint Actual End Date / Time √

Constraint Type √

Outage Type Scheduled / Unscheduled √

Reason for Outage From Table 8 √

Lost Production (MWh) √

70

Appendix II Table of Factors for calculating Solar Generation Output – UK DNO Licence Regions

The following table gives factors which can be used as a multiplier of the installed capacity of a solar site to calculate the approximate output generation in any specific month.

The factor is calculated using output expected in MWh / Peak Output in MWp. The Factor has been calculated for each month then divided by the number of days in the month.

DNO Licence Region

Daily Yield Expected Factor by Month

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

East Midlands 0.9 1.3 2.6 4.0 4.1 4.4 4.0 3.3 3.0 1.8 1.1 0.7

Eastern 0.7 1.3 2.4 3.8 4.3 4.4 4.2 3.6 2.9 1.8 1.0 0.6

North West 0.6 1.2 2.3 4.0 4.5 4.4 4.0 3.3 2.7 1.6 0.7 0.4

South Eastern 0.8 1.3 2.5 4.1 4.2 4.6 4.3 3.6 3.0 2.0 1.1 0.7

South Wales 0.9 1.7 3.1 4.5 4.8 5.0 4.6 3.9 3.4 2.0 1.2 0.8

South West 1.0 1.7 2.9 4.4 4.4 4.9 4.1 3.6 3.3 2.0 1.3 0.9

Southern 0.9 1.3 2.6 4.0 4.1 4.5 4.2 3.5 3.0 2.0 1.1 0.7

Manweb 0.8 1.1 2.3 3.7 4.1 4.1 3.7 3.0 2.7 1.5 0.8 0.5

West Midlands 0.8 1.3 2.6 3.9 4.0 4.4 3.9 3.2 2.9 1.8 1.1 0.7

Yorkshire 0.8 1.3 2.7 4.0 4.4 4.2 4.1 3.1 2.9 1.7 0.9 0.6

The calculation of the factors in the table is based on the following:

Monthly PR Expected: based on reasonable assumptions developed by Quintas Energy for each region.

Monthly Irradiation Expected: based on the historical irradiation values from Meteonorm

Monthly Yield Expected: Monthly PR Expected multiplied by Monthly Irradiation Expected to obtain MWh expected by installed MWp.

Daily Yield Expected: Monthly Yield Expected divided by the number of days in the relevant month to get the daily value. This is the value included in the above table.

71

The following table gives factors which can be used as a multiplier of the installed capacity of a solar site to calculate the approximate annual output generation. These factors are based on based on reasonable assumptions developed by Quintas Energy for each region.

DNO License Region Annual Yield Expected (MWh/MWp)

East Midlands 951.58

Eastern 945.30

North West England 901.61

South Eastern 978.16

South Wales 1,094.81

South West 1,048.46

Southern Electric 974.53

SP Manweb 863.48

West Midlands 937.76

Yorkshire 933.59

72

Appendix III Case Studies

The case studies in this Appendix have been provided by member companies of the Solar Trade Association.

73

CASE STUDY 1

Site Name Site 1

Site Capacity 4,992 kWp

Site Location Bedfordshire

Grid Connection Voltage 33kV

DNO UKPN

Notification Date 09/02/2018

Outage Planned Start Date 12/04/2018

Outage Planned End Date 05/05/2018

Outage Planned Duration 24 Days

Constraint Type Full

Reason for Outage Improvement work on the network

Actions taken to reduce/lift the outage

On the notification UKPN included an option to reduce the outage affecting the site

UKPN proposed to fit 33kV isolators on the line to reduce the outage from ~3 weeks to ~2 days required for its installation. The cost of the isolator installation was included in the proposal

Following completion of the cost benefit analysis, UKPN was notified that the Owner was happy to proceed with the installation of the isolator at the cost proposed by the DNO

The process took ~2 weeks (including communication with the DNO, cost benefit analysis and internal approval of the cost)

Proposed Remedial Plan Isolator installation

Proposed Remedial Plan Cost [£10k - £30k]

Estimated/Actual MWh Loss [350MWh - 450MWh]

Case Study courtesy of Lightsource BP

74

CASE STUDY 2

Site Name Site 2

Site Capacity 43,664 kWp

Site Location Pembrokeshire

Grid Connection Voltage 33kV

DNO WPD

Notification Date 07/07/2017

Outage Planned Start Date 14/08/2017

Outage Planned End Date 03/11/2017

Outage Planned Duration 82

Constraint Type Partial (25%)

Reason for Outage Transformer replacement in 2 substations in the network

Actions taken to reduce/lift the outage

WPD did not propose any option which would have allowed the site to be fully exporting to the grid

Following an internal review of the network configuration, a proposal for the installation of a hard wire inter trip at one of the two substations affected by the works was submitted to the DNO

The DNO confirmed that the installation of the inter trip was a viable solution and they scheduled the work for the first week of August at no cost for the site Owner

The works took ~1 week and at the beginning of August, the DNO confirmed that the constraint was no longer required

The process took ~1 month (including internal analysis and conversation with the DNO)

Proposed Remedial Plan Isolator installation

Proposed Remedial Plan Cost Hard wire inter trip Installation

Estimated/Actual MWh Loss [5,000MWh - 7,000MWh]

Case Study courtesy of Lightsource BP

75

CASE STUDY 3

Site Name Site 3

Site Capacity 4,244 kWp

Site Location Devon

Grid Connection Voltage 33kV

DNO WPD

Notification Date 06/06/2017

Outage Planned Start Date 09/07/2017

Outage Planned End Date 09/07/2017

Outage Planned Duration 1

Constraint Type Full

Reason for Outage Overhead Network Refurbishment

Actions taken to reduce/lift the outage

WPD did not propose any option which would have allowed the site to be fully exporting to the grid

Following a review of the weather forecast, the DNO was requested to investigate if it was possible to move the outage during the night. They confirmed that works could have been carried out during the night at a cost for the site Owner

Two days before the Outage Planned Start Date, the DNO was notified to move the works during the night

The process took ~1 month (including internal analysis and conversation with the DNO)

Proposed Remedial Plan Work moved during the night

Proposed Remedial Plan Cost [£1k - £5k]

Estimated/Actual MWh Loss [12MWh - 20MWh]

Case Study courtesy of Lightsource BP