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India is committed to increasing the share of renewable energy in its electricity generation mix. With the rapidly declining cost of power from large-scale wind and solar projects, the renewables’ share has risen from around 5 per cent in 2014–15 to over 9 per cent in 2018–19.1 By 2021–22, over 21 per cent of the power produced in India would come from renewables. However, the renewable energy sources (barring geothermal) are inherently intermittent and variable, changing over a wide range of timescales. Reliable and cost-efective integration of Variable Renewable Energy (VRE) with the electricity grid will be essential to achieve the ambitious goals of deployment.

However, the share of VRE in the electricity mix is not uniform across India and shows drastic geographical and seasonal variability. For example, in renewable resource rich States such as Karnataka and Tamil Nadu, renewables accounted for over 50 per cent of electricity supplied during the months of July and August 2018.2 On particular days, the share exceeded 70 per cent. Studies indicate that while moderate levels of VRE penetration can be managed through the traditional fexible power system operation, higher share of VRE would necessitate additional fexibility measures such as energy storage.

Strategically deployed energy storage systems (ESS) would be able to absorb the fluctuations in supply and demand by storing surplus energy generated in the system and providing the stored energy for use whenever demanded. In addition to balancing the variable output of renewables, energy storage can provide multiple additional grid management services, such as frequency regulation, provision of spinning reserves, peak shaving, deferring transmission capacities, enhancing forecasting accuracy, avoiding curtailments, etc.

Energy storage includes a diverse range of technologies which may broadly be classified as mechanical (such as pumped hydro, flywheel), thermal (such as molten salts), electrochemical (batteries, including lead acid, lithium ion and others), electrical (super capacitors) and chemical (hydrogen). These technologies are at various stages of development and differ vastly in terms of their performance capabilities, longevity, and cost. Presently, for grid applications, pumped hydro storage is most widely used and the share of batteries has been rapidly increasing. In perspective, about 166 GW of utility-scale energy storage capacity was operational globally in 2018. While 160 GW of this capacity was through conventional pumped hydro storage, electro-chemical storage (batteries) capacity had reached 3.3 GW and is the fastest growing segment.

In recent years, R&D investments, economies of scale, and manufacturing experience have led signifcant cost reductions for many storage technologies. In particular, lithium-ion (li-ion) batteries have beneftted from the production scale-up experience from consumer electronics applications, with prices falling from $1140/kWh in 2010 to $176/kWh in 2017, the trend is projected to take the prices to as low as $70/kWh by 2030.4 At current costs, energy storage for durations beyond few minutes impacts the cost of delivered electricity signifcantly. But if the projections are correct, storage for longer durations could be fnancially viable very soon.

Large MWh sized battery storage projects have emerged very recently. The Hornsdale Power Reserve is a notable example where a Li-ion battery with 129 MWh storage capacity capable of delivering a power output of 100 MW has been installed adjacent to a 315 MW wind power plant in Hornsdale Australia.5 The battery can be used fexibly for stabilizing the grid, lowering wind power curtailment and also shifing the load to the cover for periods of low wind output. Several more battery storage projects of capacities 50 MWh and above are under installation in the United States, Germany, UAE, and so on.The positive outlook towards future of batteries is propelled by the rapid growth in the electric mobility sector. The battery technologies developed for modern electric vehicles (EVs) can be directly adapted for large-scale grid connected energy storage projects. Also, the batteries that have completed their life in an electric vehicle (having degraded in terms of charge holding capacity) are still capable of serving grid applications, and can be reutilized. Growth in EV sales would thus directly impact the viability of batteries of VRE integration.

As the number of EVs increases, an interesting possibility arises. EVs connected to the grid could be utilized as distributed storage systems. The vast numbers and geographical distribution of EVs could provide multiple grid management services without the need for large-scale centralized investments. If combined with time-of-use tariffs and smart grid technologies, such Vehicle-to-Grid(V2G)systems would be able to lend much needed flexibility to the grid for optimally balancing VRE. Suitable regulatory and market mechanisms could unlock the potential of this available storage capacity in EVs. For widespread deployment of batteries and other storage technologies in the country, it would be of prime importance to strengthen the indigenous manufacturing capabilities. This would require a planned and coordinated approach to promote investments through conducive policy measures and incentives. The “National Mission on Transformative Mobility and Battery Storage” being implemented by NITI Aayog is an initiative in this direction. The Mission includes a Phased Manufacturing Programme to support setting up of large-scale, export-competitive integrated batteries and cell-manufacturing
Giga-scale6 plants in India. The programme would go a long way for ensuring indigenous availability of battery storage systems that are affordable, efficient, and reliable. As we continue to move towards an energy mix dominated by renewables, energy storage is likely to play an increasingly important role. Technologies are evolving rapidly and storage assets are capable of adding economic value through multiple services. We could soon see large-scale energy storage systems being deployed ubiquitously in conjunction with renewable energy installations, and if the cost and technology trends continue, storage could potentially enable delivery of round-the-clock power from renewables that is both affordable and reliable.

Article contributed by Mr Dipesh Pherwani, Scientist B, MNRE.

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