The Central Electricity Regulatory Commission (CERC) has taken a number of initiatives to ensure secure grid operations, in light of the government’s ambitious target of increasing the renewable energy capacity to 175 GW by 2022. The commission recently issued the draft procedure for the implementation of the framework on forecasting, scheduling and imbalance handling for renewable energy generating stations at the interstate level.
The procedure has been proposed for renewable energy generators that are regional entities, given that most of the upcoming projects are likely to be connected to the interstate transmission system (ISTS). These will be applicable to all renewable energy projects aggregating a capacity of 50 MW and above, wind and solar-based ultra mega power projects aggregating 500 MW and above, renewable energy projects with a capacity of 5 MW to 50 MW developed by a generation company within its existing station, lead generators, principal generators, qualified coordinating agencies (QCAs), as well as solar power park developers (SPPDs).
Role of entities
As per the draft procedures, the renewable energy generation company/QCA/ SPPD will be responsible for providing information related to available capacity, day-ahead forecasting and scheduling through a web-based application maintained by the regional load despatch centres (RLDCs). It will also provide real-time data of generation and 15-minute block-wise meter reading of the previous day to the concerned RLDC. Further, the generation company will be responsible for metering, data collection, transmission, as well as coordination with the RLDC, state load despatch centre (SLDC), regional power committee (RPC), Power Grid Corporation of India Limited (Powergrid) and other agencies. It will also undertake commercial settlement of charges, using automatic meter reading technologies for transfer, analysis and processing of interface meter data, and furnish power purchase agreement rates for the purpose of deviation charge account preparation to the respective RPCs.
The concerned RLDC, on the other hand, will be responsible for scheduling, communication and coordination with the renewable energy company, for forecasting generation and making it available on their websites. It will also process interface meter data and compute the net injections by each renewable energy generation company.
As per the CERC’s draft procedures, RLDCs will forecast generation at the regional level to facilitate secure grid operations, for which a forecasting agency may be hired. Renewable energy generation companies will have the option to utilise their own forecast or accept the forecast given by the concerned RLDC by paying the required fees. However, any commercial impact due to scheduling based on that forecast would be borne by the generation company. The framework also suggests that RLDCs and renewable energy generation companies should have multiple forecast providers for lower forecast errors.
Scheduling and despatch
The renewable energy generation companies/QCAs will schedule the generated power like any other generator and would be paid as per the scheduled generation and not according to the actual generation. The RLDCs will upload the day-ahead schedules of energy generation on their website every 15 minutes for a 24-hour period commencing at 00:00 hours.
The renewable energy generation companies will be given more opportunities to revise the schedule by giving advance notice to the RLDC. There may be one revision for each time slot of one and a half hours starting from 00:00 hours of a particular day, subject to a maximum of 16 revisions during the day (as against eight revisions allowed currently as per the Indian Electricity Grid Code, 2010). The revisions will be effective from the fourth time block, the first time block being the time block in which the notice was given. However, any revision in schedule made by the renewable energy company/QCA selling power through collective transactions will not be allowed.
As far as connectivity is concerned, an SPPD will be responsible for applying for connectivity on behalf of all solar power generators within the solar park and for registering the solar park with the respective RLDC/SLDC. It will also act as the nodal agency at the connection point. For other generating stations, the lead generator will undertake all operational and commercial responsibilities. The renewable energy generation companies, QCAs and SPDDs will also be obligated to indemnify the concerned RLDC at all times.
Powergrid will install all interface meters at the ISTS level, whereas at the intra-state level, the state transmission utility or SPDD will be responsible for the installation of these meters. These interface meters will be capable of time-differentiated measurements for 15-minute block-wise active energy and voltage-differentiated measurement of reactive energy. The data telemetry at the turbine/inverter level will be provided by the renewable energy generation company to the RLDC. The frequency of real-time data update to be shared will be for 10 seconds or less as per the existing practice followed by the RLDCs.
Treatment of RECs
The deviations of all renewable energy generation companies will first be netted off by the concerned RPC on a monthly basis. In case the actual generation is more than the scheduled generation, notional renewable energy certificates (RECs) will be credited to the respective deviation settlement mechanism (DSM) pool. After netting off, the deficit will be balanced by purchasing an equal number of solar and non-solar RECs through the power exchanges within three months of the finalisation of annual accounts by the RPC.
So far, four states – Tamil Nadu, Rajasthan, Karnataka and Madhya Pradesh – have come out with intra-state forecasting regulations. The forecasting and scheduling code remains similar across these states with all of them providing for day-ahead scheduling at an interval of 15 minutes for renewable energy generation companies and re-scheduling them every one and a half hours. Further, these regulations identify the roles of various entities involved as well as provide guidelines for metering, telemetry and data communication.
The proposed deviation charges in the case of under or over-injection of power differ from state to state. These charges vary from Re 0.50 to Rs 1.50 per unit for different error slabs. For instance, for an absolute error of over 35 per cent in Karnataka, the charges payable for 15-25 per cent of absolute error will be Re 0.50 per unit and for 25-35 per cent, the charges will be Re 1 per unit, while the balance deviations will be charged at the rate of Rs 1.50 per unit.
As the size of the renewable energy market expands and load uncertainties increase, the security of the national grid has emerged as a key focus area for the CERC. The notification of the draft procedures for forecasting, scheduling and imbalance handling for renewable energy generation stations ensures stable grid operations and will act as a catalyst for the growth of green power in the country.
Going forward, the regulatory framework could be up for more changes in order to maintain a continuous load generation balance, counter generation outages and unexpected load surges or crashes, as well as allow large-scale integration of variable renewable energy.