8 export limiting in practice, james hoare

Part of the BRE Trust

James Hoare CEng MIET MEI

BRE National Solar Centre -Associate Consultant LHW Partnership LLP - Partner

24th September 2014

Export Limiting in Practice

• Grid Background

• Evolution Renewable & PV Development

• A Fictitious Application Example

• A Real Life Example

• Q&A

The UK Grid - Background

– Pre 1926 – Decentralised System with local generating supply companies

– 1926 CEGB established with a Nationwide synchronised 132kV network

– 1965 400kV Network established based around centralised power stations and decentralised demand customers

Statistics at Privatisation in 1990

11,500 kM 400 kV circuit, 9,800 kM 275kV Circuit, 5250 kM 132kV circuit. Essentially 1 GenCo (nearly no IPPs) 12 Regional Electricity companies

Purpose – with a centralised energy policy to get energy from

Generators Consumers

The UK Grid

1989 – The Electricity Act paved way for Privatisation in 1990

1990 CEGB (Central Electricity Generating Board) broken up into

National Grid (Transmission) & Powergen, National Power, Nuclear Electric with NGC controlling the Pumped Storage (principally Dinorwig / Ffestiniog) asset for emergency demand balancing.

12 Regional electricity Companies (now 6 DNOs) distributing from 132kV to 33/11 & LV customers.

To that point both the transmission & distribution networks had ben designed and evolved for centralised and not local power generation

The UK Grid

As part of 1989 Electricity Act introduced the NFFO (Non Fossil Fuel Obligation) a precursor to the RO (Renewables Obligation).

The first tranche was October 1990 with a number of projects mainly Wind, Landfill Gas, Straw/Poultry litter & Hydro. (No PV)

Local Cornwall projects were mainly wind

Connecting these to the distribution network was

uncomplicated, as though the network was designed for

consumers, (not prosumers) , the relative impact was

minor, and plenty of generation capacity.

Delabole Goonhilly Carland Cross St Breock

What is a Prosumer? A Prosumer is a term evolving in Europe to define an entity (domestic, commercial, public sector) that

Produces energy & consumes Energy

The UK PV Industry

– First Grid tied PV System(s) were connected in 1994

The UK PV Industry year 2000

– Total PV Connected Capacity c1MWp

– No FIT’s or ROC’s (nor in Germany)

– A large project was typically 12kWp

– G83 not in existence

Largest UK PV programme at the time

BP Solar Project Sunflower a 1098 kWp programme covering canopies on 76 UK petrol stations from 1996 to 2002

– Total PV Connected Capacity April 2015 c8GWp (8000 MWp)

– Circa 700,000 DNO grid connected Installations

– A large project is now 50-60 MWp

– At peak PV output in July 2015 a sunny weekend day will meet c15% of UK early PM national demand (UK demand data - source gridwatch.templar.co.uk)

The move from Centralised to Decentralised (prosumer) power generation, and the rapid growth of the Renewable market, has started to put pressure on the Distribution network that is evolving from consumer based demand

system to a prosumer system.

Consequently there are now network constraints on connecting DG

What is Network & Export Constraint? When the potential amount of locally generated electricity has reached a level when the DNO cannot accept any more without breaching its Licence conditions & ESQCR – a constraint may be needed

The solutions are

– impose an export constraint to limit the export of energy

– Upgrade the network to accommodate the requirement

Currently The Electricity Regulator Ofgem’s regulations means that the cost of network reinforcement for Distributed Generation Projects should be paid for by generator and not bill paying customers (DUOS). The DNO’s have to enforce this.

Electricity Safety Quality & Continuity Regulations

Principal Stakeholders

Reportable by Members of public, Meter operators, distribution and transmission companies , generators and suppliers

Key aspect in context

The DNO is licenced and legally bound to provide phase voltage to customers at 230V +/- 10% (ie between 207 & 253V)

Demand Customers reduce voltage with increased demands ,

Prosumers can raise grid voltage with increased generation

(G83/2 is 262V to allow 3% volts rise between DNO connection and inverter)

White Goods are built to work within ESQCR limits

For European Harmonisation all electrical appliance are designed to work between 207 & 253V

A DNO can be prosecuted if for example was found to be caused by providing to a voltage outside ESQCR regulations

White Goods are built to work within ESQCR limits

When is Export Limiting Network Reinforcement Required?

The DNO may propose an export constraint or network

reinforcement for 2 principal Reasons when you apply to

connect a PV (or other DG system)

1. The voltage rise may put the network out of ESQRC

compliance

2. The thermal capacity of the network has been reached

If the network fault level has been reached, export constraint

will not resolve the issue.

A Fictitious Worked Example to demonstrate the impact of export constraint, and options of how to manage the impact

Fictitious Case Study – 50 kWp Rooftop The Eden Project Offices , St Austell

Assumed Annual Electricity Consumption c50,000 kWh

Initial idea

Install a 50kWp array to match annual consumption with

a combination of onside consumption with some export

System Size 50 kWp System

Annual generation 47,000 kWh

Estimated On Site use 50%

Export 50%

Revenue from

FITs, Export, Import offset

Decent ROI & IRR

To Proceed with project - No Planning needed, just DNO approval…..

ENA Connection Application sent to DNO

for 50kVA PV connection

A few days later the DNO responds outlining

You can connect a system to export 50kW

– Due to the level of existing DG connections in the

area, network network upgrade costs in the order of

£500,000 will be required , or you can connect a

system that can export 20kW (KVA) with no additional

reinforcement needed.

NB Figures Entirely fictitious and fabricated

What do you do?

But what do you do?

The 2 key things you need to assimilate are

1. Relationship between kWp and real time kW system

yield quantum.

1. On Site Energy Demand profile (if any)

In context of

Exported Energy = Generated energy – onsite demand

Do annual / monthly yield and other such models help

when there is an export constraint?

Yes a bit , but in reality not very much

Generation

PV Syst can output

modeled Hourly generation

data sets in CSV/Excel

Key Graph – derived from PVSyst Hourly Generation

Max output 50kW

Area under line

Hours x % of max 50 kW

= total kWh

Mean operating output 11kW

Key Graph – derived from PVSyst

Findings

• PV System will be generating for 47% of year

• Max output is 50kW

• Average operating generation output is 11 kW (22%)

(This is not generic and is project / location specific)

Annual Hours of Unconstrained Outputs as a Percentage of Max 50kW Output

Unconstrained Output

5 Periode gleit. Mittelw.(Unconstrained Output)

Point for the example 50 kWp

System where a 20kW export

constraint will need to limit

the outputs to keep within

20kW export

20 kW Export limit total export

Max PV Gen Export Constraint

On Site Demand (5d/weekend)

% of Max

47 MWh none 0 100%

% of Max

47 MWh none 0 100%

% of Max

47 MWh none 0 100%

% of Max

47 MWh 49kW 0 99.99%

% of Max

47 MWh 48kW 0 99.9%

% of Max

47 MWh 47kW 0 99.9%

% of Max

47 MWh 46kW 0 99.90%

% of Max

47 MWh 45kW 0 99.9

% of Max

47 MWh 44kW 0 99.9%

% of Max

47 MWh 43kW 0 99.9%

% of Max

47 MWh 42kW 0 99.9%

% of Max

47 MWh 41kW 0 99.9%

% of Max

47 MWh 40kW 0 99.9%

% of Max

47 MWh 39kW 0 99.8%

% of Max

47 MWh 38kW 0 99.5%

% of Max

47 MWh 37kW 0 99.4%

% of Max

47 MWh 36kW 0 99.3%

% of Max

47 MWh 35kW 0 99.0%

% of Max

47 MWh 34kW 0 98.6%

% of Max

47 MWh 33kW 0 98.2%

% of Max

47 MWh 32kW 0 97.6%

% of Max

47 MWh 31kW 0 97.0%

% of Max

47 MWh 30kW 0 96.3%

% of Max

47 MWh 29kW 0 95.5%

% of Max

47 MWh 28kW 0 94.6%

% of Max

47 MWh 27kW 0 93.7%

% of Max

47 MWh 26kW 0 92.6%

% of Max

47 MWh 25kW 0 91.4%

% of Max

47 MWh 24kW 0 90.2%

% of Max

47 MWh 23kW 0 88.8%

% of Max

47 MWh 22kW 0 87.3%

% of Max

47 MWh 21kW 0 85.8%

% of Max

47 MWh 20kW 0 84.0%

% of Max

47 MWh 20kW 0 84.0%

Conclusions from Model

• 84% of max yield in Cornwall with a 20kW export

constraint on a 50kWp system is still probably higher

than yields in North of England with no constraint

• There are lots of variables, so allowing sensitivity and

contingency are important.

Model With on site Energy Demand • 50kWp Array

• 20kW export Constraint

• On site Consumption

If Site Demand is added to the 50kwp system

with an export constraint of 20kW max

Assumption for model

5kW – continuous at weekends (Sat & Sunday)

Weekday model graded in incremental steps of 5kW

(Historic HH consumption data is desirable if available)

January sample HH Consumption Data

% of Max

47 MWh 20kW 0kW 0kW 84.0%

% of Max

47 MWh 20kW 0kW 0kW 84.0%

% of Max

47 MWh 20kW 5kW – 5kW 88.1%

% of Max

47 MWh 20kW 10kW – 5kW 90.5%

% of Max

47 MWh 20kW 15kW – 5kW 92.5%

% of Max

47 MWh 20kW 20kW – 5kW 94%

% of Max

47 MWh 20kW 25kW – 5kW 95.1%

% of Max

47 MWh 20kW 30kW – 5kW 95.9%

Key Factors

• A Degree of sensitivity / contingency is required as

both solar radiation and on site demands are

intermittent and will vary year on year

• PVSyst estimates hourly outputs in kWh, so need to

be careful when matching to on site demand as 1

kW for one hour = 1kWh (as does 0.5 kW for half

an hour and 1.5KW for half an hour) – Sensitivity

needed

• The more consumption information the better – Half

hourly data, and a thorough energy consumption

profile is helpful. (The more demand info the better)

Conclusions from Modeling

• The impact of network constraints is probably less than

anticipated, and a larger array than anticipated may be

possible.

• Choose a conservative and least optimistic solar

dataset. Maybe use P90 irradiance data

• If you are modeling with historic Half Hourly

consumption data remember this is historic and not

assured year on year

• Allow contingency, and be cautious with energy yield

projections – the level of yield risk is higher than total

export.

• If in doubt Ask BRE NSC for modeling assistance !

Export Limiting Case Study – a 1.2 MWp Zero Export Rooftop – Vegetable Storage Cambridgeshire 2013

• Large provider of parsnips to supermarkets

• Large onsite energy use for refrigeration

• DNO could not allow any export due to large wind

farm on same circuit

Export Limiting Case Study – a 1.2 MWp Zero Export Rooftop – Vegetable Storage Cambridgeshire

• Undertook Modeling of 2 years historic consumption data

• Modeling showed 1.2MWp would provide 95% of

maximum projected generation output with zero export

constraint.

• System installed

• DNO Witness test on G59 & export limiting system

• Learning experience solar gain reduction on roof reduced

energy consumption by a few %

Commissioned March 2013

• 1.2MWp 4,400 PV Modules

• 9 x 100 kW Inverters

• G59/2 Switchgear

• PLC based Export sensing Actuator & Controls

• Subsequent application to DNO for variable export

allowance successful

• Site can export 97% of time, so nearly 100% of

projected yield is attainable

• Ultimately Active Networks will prevail

Thank You

Any Questions?

8 export limiting in practice, james hoare

uk pv industry year

total pv

kv network

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uk petrol stations

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