The implications of producing and integrating renewable energy into the grid in real time are manyfold. The variability of renewable-based power, frequent ramp-up and back-down of conventional generation and the associated cost, merit order violation and load restriction are some of the inherent challenges associated with renewable energy. At the same time, low flexibility of coal plants, high cost of gas-based generation and inadequate hydropower generation are some load balancing constraints. The existing transmission network was designed for a stable power output. The growing renewable energy generation therefore creates significant grid issues, including lack of transmission availability, backing down of cheaper power, and high reactive power. Multiple technologies are being adopted by the power sector to address these issues. According to B.B. Mehta, chief engineer, state load despatch centre, Gujarat Energy Transmission Company (GETCO), these issues include accurate forecasting of renewable power, ancillary services at the intra-state level, operative hydro stations and energy banking between states. The future of grid integration lies in energy storage in the form of battery-based storage and operative pumped mode of hydropower stations. As per Debi Prasad Dash, executive director, India Energy Storage Alliance, the country’s storage potential between 2018 and 2025 stands at about 300 GWh.
While energy storage is a relatively recent phenomenon, consequent to the high penetration of renewable-based power, storage technology has evolved rapidly. Besides the dominant lead-acid and lithium-ion (Li-ion) batteries, other technologies such as nickel-chromium, redox-flow, sodium-sulphur, nickel-manganese spinal cathode-based, zinc bromine and vanadium flow batteries are also gaining popularity. Battery storage has a much faster ramp rate, low installation time, and unlimited start-stops and can work in both positive and negative directions, thereby effectively providing twice the capacity. However, expensive and bulky battery-based storage systems have proven to be prohibitive.
As per Mehta, pumped hydro storage power plants are also an important part of India’s energy storage dynamics. At present, the country has nine pumped storage plants aggregating about 4,785 MW, of which only five plants totalling 2,600 MW are in operative mode. Two plants are currently under construction, with a cumulative capacity of 1,080 MW, while four more (2,600 MW) are at the planning stage. It is important that all inoperative pumped mode hydro plants are made operative on highest priority. Meanwhile, a regulatory framework for pumped mode operation will be required from the Central Electricity Regulatory Commission.
A detailed cost-benefit analysis explained by Mehta considers pumped mode hydro storage power plants against the backing down of wind power over a period of one year. The analysis has been carried out in Gujarat and the available energy for pumped mode in the state is at 75 per cent efficiency. As per Mehta, using pumped hydro storage can potentially lead to savings of up to Rs 940 million per year. According to Dash, Li-ion battery systems have experienced a 75 per cent decline in prices over the past few years. Global prices fell from $790 per kWh in 2011 to $180 per kWh in 2017. The price drop can be attributed to the economies of scale achieved by manufacturers as they crossed over 5 GWh of production capacity by 2015. Further, there has been significant advancement in the optimisation of cell chemistry and an increase in utilisation from 20 per cent to over 40 per cent (2015).
The way forward
According to Customized Energy Solutions research, there will be at least three global companies with an annual production capacity of over 50 GWh and another five with capacities of over 20 GWh for Li-ion batteries. The total global projected capacity for 2020 now stands at over 400 GWh. With 175 GW of renewable energy capacity to be installed by 2022, the corresponding renewable power will have to be integrated smoothly into the grid. Energy storage technologies, both battery based and in pumped hydro mode, are expected to play a key role in providing grid stability.
However, the operational challenges associated with pumped hydro plants and the prohibitive cost profile of battery-based storage will need to be resolved. To this end, India should target at least 5-10 GWh of battery manufacturing capacity by 2020 and 50 GWh by 2025. Meanwhile, including energy storage in state and central renewable energy policies will help provide a robust policy framework for its adoption. Making energy storage a part of renewable energy tenders, such as that for solar plus storage in the Andaman & Nicobar Islands will also help create the demand for storage technologies. Moreover, with electric vehicles and charging stations, the role of battery-based storage in grid integration becomes even more pronounced.
Based on presentations by B.B. Mehta, Chief Engineer, State Load Despatch Centre, GETCO; and Debi Prasad Dash, Executive Director, India Energy Storage Alliance, at a recent Renewable Watch conference