Unlike other renewable energy rich countries where grid management is for the purpose of energy management, the grid management in India actually targets to solve the capacity management problem. The power market structure of India is comparatively complex unlike other countries and with the penetration of massive variable renewable energy like wind and solar, the grid management becomes the crucial issue. Though the policies in RE target a massive inclusion of wind and solar for a sustainable future and to achieve 40% of total installed power generation capacity from renewable energy by 2030, the back down issue in wind and solar in different RE rich states becomes a common problem and the IPPs/generators become reluctant about the wind and solar production even in the RE rich states due to heavy financial loss created through back-down.
It is interesting that Wind and Solar got the status of ‘Must Run’, but due to the variability and intermittency inherited in these varied sources, system operators like SLDCs require curtailing the generation of Wind and Solar to manage the grid. Without going in the deep analysis of frequency, reactive power and voltage regulation, let us stick to the problem of capacity management as it is the basic problem required to be solved first to mitigate the issues back-down. Other parameters like frequency, reactive power or voltage control can be interrelated using some extra constraints in the capacity problem.
Back-down problem can be viewed as the balancing of demand and supply, it is quite natural that if the demand of energy is high and generators are not able to supply that required amount, there is a possibility of shortage and the same time if the supply is so high that the demand is not able to consume the total supply, the curtailment must be there. One can go for the wheeling in and out analysis in this respect with complex analysis considering different utilities and control areas, but considering the market structure and complex grid network of India, the extra supply cannot be managed so smoothly, hence back-down becomes the easiest approach for system operators to maintain the balance in the network by reducing the overflow.
To mitigate the power shortage and back-down, the forecasting and scheduling of the Wind and Solar power generation is an effective tool. As per the F&S regulations, each wind and solar generators have to submit the day-ahead schedule of their power generation as it gives a rough idea to the system operators about the availability of the variable energy and the capacity requirements of other conventional sources. The day-ahead schedule is the most crucial for any grid management as it decides the capacity allocation of different energy sources. Hence the day-ahead schedule of solar and wind generation must be as much accurate as possible to reduce the possibility of back-down. Since SLDCs will have the schedule one-day ahead for each wind and solar generators, there should not be any capacity allocation problem if they implement the balancing properly.
But wind and solar are variable in nature and it is obvious that due to some natural phenomena the day-ahead schedule is not as much accurate as predicted all time. Hence, as per regulations, wind and solar generators can update their schedule maximum 16 times and 8 times, respectively, but the unnecessary revisions create problems in capacity management. It is easy to see that the variability of wind and solar and the variation in conventional energy sources are different, moreover the generation of conventional energy sources cannot alter instantaneously due to the technical infeasibility. Hence forecast with minimum revision is an effective tool to mitigate the back-down issue.
It is quite natural that the aggregation of forecast or aggregated forecast as the case may be, cannot be an effective tool for balancing the demand supply. For example, let us consider two plants A and B are at East and West Rajasthan respectively, such that the geographically Plant A and Plant B are geographically separated. Plant A and Plant B have the schedule generation of 200MW and 400 MW respectively, but their actual generation is 350 MW and 250 MW respectively. Hence the Plant A has (350-200) MW = 150 MW over-production at East Rajasthan and Plant B has (400 – 250) MW = 150 MW under production at West Rajasthan. If aggregation is allowed, the aggregated schedule of plant A and plant B is (200+400)MW = 600 MW and the aggregated generation is (350 + 250) MW = 600 MW. In aggregation there is no deviation. But in reality, there is 150 MW over-production in East Rajasthan and 150 MW under production at West Rajasthan. Since the transmission capacity is not infinite, that 150 MW over production cannot be transferred to West Rajasthan instantly and freely. Hence there can be a back-down at East Rajasthan and power shortage in West Rajasthan in reality. Hence, the plant specific level forecast creates an effective solution for planning and balancing the grid without proposing erroneous deviation like aggregation.
As SLDC is a statutory functionary under section 32 of the Electricity Act and in the discharge of its functions, SLDC is entitled to act in the larger public interest while dealing with the scheduling and dispatch. But, unfortunately, probably SLDC is not doing its load forecasting properly so that it can achieve to solve its capacity management problem perfectly. In case any IPP/Generator is providing accurate day ahead forecasting, then SLDC should also plan accordingly, so that it can instruct the conventional power accordingly to generator as per SLDC’s requirement, so that back-down on the renewable energy can be minimized and IPP/ Generator should not suffer financially. In case SLDC would have down proper load forecasting arrangement, then all the IPP/Generators who have submitted accurate day ahead forecasting, should not be back-down. So, in the regulation, even if the day-ahead accurate forecasting is provided, then there is no responsibility on the SLDC to plan properly. It is still vague that even if any generator has already given a day ahead forecasting then SLDC has sufficient time so that it can plan its energy management as well as requirement. Such, enabling provisions have not been incorporated, which is the need of the day.
IPP/Generators are providing their forecasting, but SLDC has not planned properly, so IPP/Generators are suffering enormously. So, in that case SLDC is failing to perform its statutory duty. Back-down provision was incorporated in the Act, believing that such back-down will be properly planned and scheduled. Till date, as conventional energy was used as the main source of supply for energy, so SLDC had no other option than to back-down. When there is green energy available, SLDC should understand its load forecasting and plan accordingly, so that green energy should be accommodated. It should not be a case that SLDC is doing charity by accommodating green energy, it is highly required and need of the hour. So, the Commission should also direct SLDC, that SLDC should also start utilizing the forecasting data so that back-down can be reduced significantly. When, there is a day ahead forecasted data available with SLDC, they should also guarantee that if the same is accurate, then SLDC should also plan accordingly and such plant generation shall not be backed down at all. Effective utilization of the forecasted data is not evident from the act of SLDC. Regulation is silent on these issues and has put only conditions to the IPPs/Generators, but no responsibility is imposed on SLDCs to utilize the same and reduce the back-down issues.
IPP/generators must access the data of load variations, conventional energy generation and wind/solar actual and schedule generation to analyse the back-down issue to check the back-down was inevitable or not. If by analysis it is found that the backdown was not inevitable then who will take care of that high financial loss of the IPPs due to forced back-down?