greening the grid -solar & wind integration, issues ... bbsr - re...distribution system is 10 mw...
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NPTI CONFERENCEChallenges & Issues in Grid Integration & Stability
11-01-2019
Greening the Grid -Solar & Wind Integration, Issues, Challenges and
Case Studies
ERLDC, POSOCO
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Wind Potential ~ 100 GW(at 80 m hub- height)
Solar Potential ~ 750 GW(4-7 kWh per sq. m per day)
National Offshore Wind Energy Policy
Solar Cities~ 60 Nos.Green Energy Corridors
Renewables CAGR~ 18 %
Installed RE Capacity – 72013 MWas on 31st Oct’18
34 Solar Parks – 20 GW
Solar RPO ~ 8 % of total generation by 2022 (Excluding Hydro)
Solar PV Reverse Bidding ~ Rs. 2.44/kWhr
Wind Atlas, 2015
Renewables on the Rise…MW to GW
Wind Reverse Auction ~ Rs 2.43 / kWhr
(21%)
(7%)
(13%)
(57%)
(2%)
Renewable in Indian Power System
Region Installed Capacity (MW)Northern Region 13634Southern Region 35971Western Region 21024Eastern Region 1084
North Eastern region 287Islands 13
All India 72013Source : CEA Oct’18
Eastern Region Renewable Target 2022: 12646 MW (12237 MW Solar; 135 Small Hydro & 244 MW Biomass )
Source : Niti Ayog report
Challenges in integrating 175 GW RE by 2022
Technical Standards for
Grid Connectivity
Forecasting Scheduling Metering
Accounting Settlement
Frequency & Voltage Control,
Congestion
Flexibility
Market Design
Visibility at control centres
Intermittency & Variability
Uncertainty
Location Specificity
Characteristics
Renewable : Dependency on Various Factors
Variability of Renewable PowerNon variable renewable energy generation refers to sources ofelectricity that can be generated at the request of power gridoperators or of the plant owner. Since wind power and solarpower cannot be controlled by operators, so these are termed asVariable Renewable Energy (VRE) sources.
Lesser Variability
High Variability
Renewable : Variability
RES injection coinciding with
Morning Demand ramp
RES injectionopposite of
Morning Demand ramp
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Renewable : Ramp Variability
RE Impact on Net Load
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Peak load = 7 MWSolar generation = 10 MW
(A)Solar increasing
Import decreasing
A
(B)Solar decreasing
Import increasing
B
Diu Island
Effect of aggregation on variability
One Wind Turbine
100 Wind Turbines
One PV plant
18 PV plants
Forecasting RE generation
• A prime necessity to minimize deviations betweenschedule and actual dispatch
• Different approaches are preferable for differingtime frames to produce the best forecast
• Most accurate forecasts can be obtained by usingmany local and global scale models and combiningthem to form a single multi model ensemble.
• Indian Meteorological Department (IMD) hassignificant resources and experience in traditionalweather forecasting
Two main approaches• Statistical approaches working on single Numerical
Weather Prediction (NWP) forecasts• Uncertainties derived from ensembles of predictions
Physical wind power forecasting• derive wind speeds at turbine hub height from the NWP
model and use explicit descriptions of relevant physicalprocesses to calculate the electric power output of theturbine
Statistical wind power forecasting• describe the relationship between various model
parameter of the weather model and the measuredpower output
• Based on past data analysis, following clustersare formed for integrated scheduling andforecasting of wind generation for high windpenetration states
State Area/zone wise Wind generation passes
Tamil Nadu Muppandal, Udumalpete, Theni, Thirunelveli
Karnataka Chitradurga, Chikkodi, Gadag
Rajasthan Udaipur, Jaisalmer, Jodhpur
Gujarat Kutch, Saurashtra
Maharashtra Sangli, Ahmednagar, Satara
• Time series models using on-site measurementsare adequate for the very short term time scalefrom minutes up to a few hours
• Forecasts based on cloud motion vectors fromsatellite images show a good performance for atemporal range of 30 minutes to 6 hours
• Grid connected bulk solar power generationrequires forecasts up to two days ahead or evenbeyond
• Numerical weather prediction (NWP) modelsare considered to be most appropriate
Challenges in RE Forecast
• Dependency on Accuracy of Weather Forecast.• Continuous Improvement in Forecast and Confidence level.• Number of Forecasting Revision is fixed : Sufficient Time for
taking action in Short Term Forecast.• Ramp Forecast for meeting the Ramping requirement :
Reducing Deviation, Absorbing RE and Optimizing OtherEnergy Sources.
• Turbulent & chaotic processes : Localized Wind/Rainfalls• Including the impact of local topography : Not captured in
standard weather model• Change in Method with Change in Time of Forecast• Continuous Assessment : Which one is Best Forecast
Forecast Error Impact on Reliability and Economy
Handling Renewable Generation
- Provisions in IEGC & CEA Connectivity Standards
Special provisions for renewable sources
MUST RUN STATIONS– Run-of-river power stations - Controlling may lead to
spillage– All renewable energy power plants, whose tariff is
determined by the CERC– Shall not be subjected to ‘merit order despatch’
principles.EXCLUSION
– Biomass power plants, , and non-fossil fuel basedcogeneration plants (dispatchable)
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Scheduling of solar generation• Scheduling compulsory with effect from 1.7.2011, for
new solar generating plants with capacity of 5 MW andabove connected at connection point of 33 KV level andabove and , where pooling stations commissionedafter 03.05.2010
• Schedule to be given by the generator based onavailability of the generator, weather forecasting, solarinsolation, season and normal solar generation curve
• To be vetted by the RLDC in which the generator islocated and incorporated in the inter-state schedule.
• If RLDC is of the opinion that the schedule is notrealistic , it may ask the solar generator to modify theschedule.
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Wind generation Scheduling
With effect from 15.07.2013 Scheduling of Wind Gen.necessary:
i) where the sum of generation capacity of such plantsconnected at the connection point to the transmission ordistribution system is 10 MW and aboveii) and connection point is 33 KV and above,iii) and where pooling stations commissioned after03.05.2010
For capacity and voltage level below this, as well as for oldwind farms ( A wind farm is collection of wind turbinegenerators that are connected to a common connectionpoint) it could be mutually decided between the WindGenerator and the transmission or distribution utility, as thecase may be, if there is no existing contractual agreement tothe contrary .
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There may be one revision for each time slot of one and halfhours starting from 00:00 hours of a particular day subject tomaximum of 16 revisions during the day.
Such revisions shall be effective from 4th time-block, the firstbeing the time-block in which notice was given.
Deviations from schedule by solar and wind generators to bedelinked from frequency and shall be accounted for and settled inaccordance with the provisions of CERC DSM Regulations
Schedule Revision, treatment of deviation
General connectivity standards• B1. Requirements with respect to Harmonics, Direct
Current (DC) Injection and Flicker• (1) Harmonic current injections from a generating station
shall not exceed the limits specified in IEEE Standard 519.• (2) The Generating station shall not inject DC current
greater than 0.5 % of the full rated output at theinterconnection point.
• (3) The generating station shall not introduce flickerbeyond the limits specified in IEC 61000. Provided that thestandards for flicker will come into effect from 1st April2014.
• (4) Measurement of harmonic content, DC injection andflicker shall be done at least once in a year in presence ofthe parties concerned and the indicative date for the sameshall be mentioned in the connection agreement
General connectivity standards• (1) The generating station shall be capable of
supplying dynamically varying reactive powersupport so as to maintain power factor within thelimits of 0.95 lagging to 0.95 leading.
• (2) The generating units shall be capable ofoperating in the frequency range of 47.5 Hz to 52 Hzand shall be able to deliver rated output in thefrequency range of 49.5 Hz to 50.5 Hz. Provided thatabove performance shall be achieved with voltagevariation of up to ± 5% subject to availability ofcommensurate wind speed in case of windgenerating stations and solar insolation in case ofsolar generating stations.
Fault Ride Through (FRT) capability
• VT/Vn is the ratio of the actual voltage to the nominal system voltage atthe interconnection point during the voltage dip
• the individual wind generating units in the generating station shallgenerate active power in proportion to the retained voltage;
• during the voltage dip, the generating station shall maximize supply ofreactive current till the time voltage starts recovering or for 300 ms, whichever time is lower.
(3) All wind farms connected at 66 kV and above shall remain connected to the grid when voltage at the interconnection point on any or all phases dips upto 15% of the rated (nominal) voltage:
Instances of > 800 MW wind generationloss due to absence of LVRT capabiltiy
General connectivity standards(4) Wind generating station connected at voltage levelof 66 kV and above shall have facility to control activepower injection in accordance with a set point, whichshall be capable of being revised based on thedirections of the appropriate Load Despatch Centre.As far as possible, reduction in active power shall bedone without shutting down an operational generatingunit and with reduction being shared by all theoperational generating units pro-rata to their capacity.(5) The standards in respect of the switchyardassociated with the generating stations shall be inaccordance with the provisions specified in respect of'Sub-stations' under Part III of connectivity regulations.
Flexibility
Flexibility for the 21st century power system
Symptoms of power system inflexibility– Balancing generation and load difficult leading to
frequency excursions or dropped load– Significant renewable energy curtailments; mostly
due to excess supply and/or transmissionconstraints
– Area balance violations– High price volatility
Need for Flexibility
• Large 660 MW, 800 MW and 1000 MW sets being introduced• Changing load profile, Flexible conventional generation needed to facilitate
integration of renewables• CEA Standard Technical Features for 660MW/800 MW Sets
• Technical minimum recommended – 40%• Two shifting of machines envisaged
Need of More Ramping (Flexibility) from Hydro, Thermal and Gas to Absorb 170 GW Renewable.
Renewable : Ramping Support Requirement
Net load curves for Low, Intermediate and High RE penetration scenarios
G-t-G Study : 2021-22 conditions
Ramp up and Ramp down requirements in each of the three RE penetration scenarios
Scenario Ramp-down requirement (GW) (8AM-1PM)
Ramp Up Requirement (GW) (2PM-9PM)
Low RE Scenario 63 101
Intermediate RE Scenario
77 115
High RE Scenario 96 134
G-t-G Study : 2021-22 conditions
More Spinning Reserve to Meet Variability of Demand and Renewable Energy
Renewable : Spinning Reserve Requirement
Impact on System Inertia
Reduction of power system inertia• The increasing penetration of wind energy in the power
grid will effectively reduce the overall system inertia andincrease the equivalent system droop
• The change in these two vital system parameters willadversely affect the frequency regulation capability of thenetwork, leading to increased peaks and dips in frequencyafter every load events
• If the WTGs provide no inertial and droop capabilities intimes of low system frequency, the robustness of thesystem will be in danger
• If variable speed WTGs are to be used for integrating windenergy into the power grid, the hidden inertia and droopcapabilities from these machines can be extracted
Synthetic Inertia• Synthetic inertia is achieved by reprogramming power
inverters attached to wind turbines so that they emulate thebehavior of synchronized spinning masses
• intelligent, distributed response of an entire wind plant to afrequency disturbance could potentially minimize overall gridfrequency deviation and improve recovery speed.
• The rotating mass of variable-speed wind turbines is decoupledfrom the grid frequency and does not inherently exhibit aninertial response unless controlled for that specific purpose.
• the kinetical energy of the rotating blades could be used for asynthetic inertia control
• The controlling methods could be implemented as anadditional feedback loop for the converter
• If the frequency is lower than the nominal, the controllingextracts additional energy with torque increase, which slowsthe rotation of the blades
Control Concept• Use controls to extract stored inertial energy• Provide incremental arresting energy (meaning kW-s)
(5%-10% of rated power) during the first 10 seconds ofgrid events.
• Allow time for governors and other controls to act• Target incremental energy similar to that provided by a
synchronous turbine-generator with inertia (Hconstant) of 3.5 pu-sec.
• Focus on functional behavior and grid response: doNOT try to exactly replicate synchronous machinebehavior
• The technical constraints and limits like the rotationspeed and the converters scale must not be exceeded.
• Demand for additional torque should reduce as theWTG approaches its minimum allowable speed
Balancing Capability Enhancement
• Primary objective is to avoid frequency deviations and unscheduled power flows arising out of RE integration
• Avenues• Short Term - improvement in load forecasting• Improving accuracy of RE generation forecasting• Enhancing system operation and plant flexibility• Medium Term - intraday balancing with storage
type hydro plants
Balancing Capability Enhancement
• Enhancing geographical size of control areas thatare to be balanced
• Development of large scale pumped storage typehydro-electric plants
• Introduction of demand side management• Long Term – Increasing geographical dispersion
of wind generators• Power storage options, technology improvement
Suggestions
Primary•All India - 4000 MW
•Outage of Ultra Mega Power Plant (UMPP) or any similar event
• Automatic, Decentralized, mandated as per Grid Code
Secondary• All India - 3623 MW
•NR – 800 MW•WR – 800 MW•SR – 1000 MW•ER – 660 MW•NER – 363 MW
• Automatic, regional level with suitable compensation
Tertiary
• All India - 5218 MW•NR – 1658 MW•WR – 1353 MW•SR – 1343 MW•ER – 857 MW•NER – 65 MW
• Manual, state level• UnRequisitioned Surplus
Adequate Reserves and Ancillary Services Market
Higher number of units should on Bar….for handling large and fast ramps
Need of Adequate PrimaryResponse from generators(Presently under RGMOand inadequate responseobserved)
Need of Pan IndiaOperation of AGC toprovide Secondary Controlfor balancing (Pilot Projectin Northern RegionCompleted)
Requirement of adoptionof RRAS at State level tohave adequate TertiaryControl.
Faster markets and shorter settlement period
Airlines Banking
May 08, 2017National Electronic Funds Transfer
(NEFT) system – Settlement at half-hourly intervals
Railways
Data Time-Interval Annual Cost*
1 Minute Rs. 13,20,000
2 Minutes Rs. 7,50,000
5 minutes Rs. 2,75,000
15 Minutes Rs. 60,000
Stock Exchanges
*NSE Annual Data Charges, Capital Market Segment
Petroleum
5-minute Scheduling vs. 15-minute Scheduling
Strong Interconnections, SAMAST and enabling framework would enhance RES absorption by
taking advantage of diversity
Need of More Number of PSP for Flexibility Support
A Few Significant Steps
Renewable Energy Management Centres
NLDC, Delhi
NRLDC, Delhi
WRLDC, Mumbai
SRLDC, Bengaluru
Andhra Pradesh
Tamil Nadu
Karnataka
GujaratMadhya Pradesh
Maharashtra
Rajasthan
• Co-located with Load Despatch Centres (LDCs) –State/Regional/National (11 Nos.)
• Forecasting , Real time tracking of generation from renewable sources
• Advanced decision-making and control systems
• Single source information repository and coordination point
• Different skill sets for personnel manning REMCs and LDCs
• Implementation under progress
Dedicated IMD Portal for Power Sector
Intra-State Settlement System and Imbalance
Handling
Forecasting (Load/ RE generation/ Net Load) Spinning Reserves
Frequency Control (Primary/Secondary/
Tertiary)
Technical Standards for RE Generation Ancillary Services
Balanced Portfolio Flexibility - Harnessing and Incentivizing
Market Design Enhancements
Communication in Power Sector
Capacity Building of all stakeholders
Web-Link: http://powermin.nic.in/sites/default/files/uploads/Final_Consolidated_Report_RE_Technical_Committee.pdf
Technical Committee on Integration of RE
Greening the Grid National Study – Key Points
https://posoco.in/reports/india-renewable-integration-study-report/
Collaboration of Ministry of Power, USAID, CEA, CTU,
POSOCO and state utilities
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https://posoco.in/download/fold-posoco-report-on-operational-analysis-for-optimization-of-hydro-resources/?wpdmdl=14168
Operational Analysis for Optimization of Hydro Resources
Key Recommendations• Optimization & Incentives for Flexibility• Ancillary Services from hydropower
(Regulated tariff ISGSs already within the ambit of FRAS)
• Coordinated Scheduling & Despatch Transmission Planning impacting Hydro Flexibility
• Multi Part Tariff• Silt Forecasting & Coordinated Flushing • Inflow Forecasting• Review of Standards• Revisiting Hydrological Constraints• Renovation & Modernization
Summarizing…..• Integration of wind and solar plants in large scale is the only
way to achieve sustainability and energy security• Accuracy of forecasting VRE sources and state load forecasting
has to improve• Proper scheduling, accounting and settlement practices at
intra-state level need urgent implementation• Country-wide operationalization of primary and secondary
control as early as possible. (Tertiary control in the form ofRRAS is already in place)
• Rejuvenation of existing pump-storage capabilities andjudicious utilization of hydro flexibility
• Incentivizing flexible operation of existing coal fired powerstations. (CERC regulated generators are already compensatedfor backing down generation, as per the provisions of IEGC)
• Improvement of real-time data availability from RE stations
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“Engineers like to operate sophisticated power systems,economists like to think about optimal incentives, andlawyers like to write rules and agreements. Power sectorreform brings all of them into close contact. But none ofthem can succeed at their chosen tasks unless they worktogether in designing sustainable institutions.”
- World Bank Report: Transmission System Operators – Lessons From The Frontlines- Beatriz Arizu, William H. Dunn Jr. and Bernard Tenenbaum
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