At present, installed electricity generation capacity in India is about 330GW. About 17.5 % (57.5GW) is through renewable generation (wind: 32.3GW, small hydro:4.3GW, solar:12.5GW and balance biomass generation: 8.1GW). Renewable energy capacity is likely to reach 30% by FY19. The country has set an ambitious target of adding 175GW of renewable generation capacity comprising 100GW solar, 60GW wind and 15GW bio mass, small hydro and others by 2022. The solar capacity target includes setting up of 34 solar parks with around 20GW capacity. Recently, the government has decided to establish another 20GW under solar parks. But wind and solar generation are susceptible to variability, which affects power system operations. In order to integrate high penetration of renewables several actions must be taken such as flexibility in the conventional generation, Renewable Energy Management Centres (REMCs) and augmentation of transmission systems.
But to begin with there is no policy framework for electrical energy storage in India. The government should come out with one indicating the target & incentive package to encourage developers. This would facilitate appropriate regulatory framework in the country. Recently, CERC had come out with a discussion paper on storage, but it does not include pump storage, which is the most cost-effective and largest bulk storage source in the world. The national electricity policy mandates that a spinning reserve of at least 5% at the national level should be created to ensure grid security, quality and reliability of power supply. This amounts to almost 16.5GW considering present installed capacity. It is yet to be implemented. At least, 5GW reserve should be implemented on national basis to start with. More important, the country needs a time-based reserve system.
Primary reserves (to be available in few seconds) are realised through automatic control of turbine speed governors. All generators must operate with free governor mode of operation (FGMO). As per IEGC/CEA technical standards, in thermal units all governors shall have a droop setting of between 3% and 6%, whereas 0-10% in case of hydro units. Primary reserves could also be provided by hydro pump storage. Secondary reserves (few seconds to 15 or more minutes) involve automatic generation control, which delivers reserve power to bring back the frequency and area interchange to target values. Tertiary reserves (to be available from 15 mins to few hours) for manual change in dispatching and unit commitment to restore secondary control reserve.
Forecasting (both load & RE generation) is also essential to ensure resource adequacy. Suitable regulatory framework for forecasting, scheduling and imbalance settlement for RE generators at both inter-state and intra-state level needs to be implemented strictly. Green Energy Corridor project had envisaged REMC at regional/state-level and it’s implementation should be expedited.
There is need for augmenting the transmission corridors in renewable rich states with coordinated transmission planning ahead of installation of renewable generation. Technical standards for RE generation incorporating features such as low voltage ride through, high voltage ride through, frequency thresholds for disconnection from the grid, active and reactive power regulation by RE generators need to be notified and implemented at the earliest.
Further, ancillary services need to be put in place as support services for reliable operation of grids. Ancillary Services provide a framework for operationalising the spinning reserves and the modalities of scheduling, metering and settlement of the reserves. It would address congestion management and facilitate optimisation at the regional & national level. CERC has recently ordered technical minimum schedule for operation of central generating stations and inter-state generating stations to be 55% of maximum continuous rating loading or installed capacity of the unit of generating station. This should be brought down to about 40%.
Flexibility in existing fleet of conventional generation as well as pumped storage plants, demand side management/demand response may be utilised for meeting changing load profile and maintaining system stability. Time-of-the-day tariff implementation would quickly bring implementation of demand response. Flexibility requirements should encompass the minimum and maximum generation level as well as the ramp up/down rates. Thus, market design of the power sector needs to be dynamic in nature. Renewable energy can now produce power that is even cheaper than coal. Their integration into the power system, therefore, depends on the presence of other technologies.