Solar power is the cheapest source of electricity, far cheaper than from any other new power plant. And it is this which gave India the confidence to announce at COP26 in Glasgow that it would create 500 GW of non-fossil fuel capacity by 2030. It would be the least cost way to meet the country’s increasing electricity needs. But as the attainment of this goal gathers momentum, consequential issues will emerge and these need to be addressed in a timely manner.

When it comes to generation, solar and wind power aren’t flexible; electricity is generated when the sun shines or the wind blows. In the electricity grid, supply needs to be flexible to meet demand at every moment even as demand varies considerably, with sudden surges.

As the share of renewables, solar and wind, in total energy generation rises from the present level of around 10 per cent, solution to the challenge posed by their inflexible generation on the one hand and varying demand on the other would have to be found. At present, flexible thermal power generation along with the inflexible generation of renewables fully meets varying demand and provides grid stability.

Going forward, there would be times when renewable generation and the minimum technically feasible thermal generation will be more than the demand. Renewable energy generation, which has zero cost, would then have to be curtailed. This can be avoided if this surplus electricity could be stored. This need for storage would keep rising as the share of renewables, especially solar power, increases. Then, demand at night can be met if carbon free solar power generated in the day is stored for use at night.

Fortunately, the creation of large-scale grid storage is now technically feasible. Renewable energy along with storage is cheaper than electricity from new thermal plants. This price discovery took place when in response to SECI (Solar Energy Corporation of India) bids for supply of round-the-clock carbon-free electricity, contracts were concluded with the two lowest bidders. Hence if the development of large-scale grid storage is undertaken rapidly, then on commercial considerations alone there would be no need to build new thermal plants.

Pump storage plants

A mature, proven technology for storing electricity is through pump storage plants (PSPs).These provide flexibility in generation that is needed for grid stability and to meet surges in demand. Electricity is used to pump water up in a hydroelectric dam and the pumped water can be discharged down to generate hydropower when needed. If renewable sources of electricity are used to pump water up, then the stored energy becomes carbon free.

Recognising the critical importance of storage in the energy transition, the Ministry of Power recently issued guidelines for the development of PSPs. These are investor-friendly, envisage competitive bidding, and speedier environment clearances. The guidelines also cover off-river PSPs. In off-river projects, where the terrain permits, reservoirs are created at different heights. In a closed loop the water is pumped up using renewable energy.

When electricity is needed, the water is discharged from the upper reservoir and carbon-free power is generated from a hydropower turbine in the lower reservoir. The successful bidder for round-the-clock carbon-free power is already developing an off-river PSP. Exhausted mines, especially of Coal India, could be potential sites for the development of such PSPs. Coal India could re-engineer itself as a renewable energy company and have a bright future as the country moves towards net zero.

Then there is the option of developing concentrated solar thermal plants (CSPs) with storage. These plants use an array of mirrors to reflect and concentrate the sun’s rays at a point to get intense heat. This heat is stored in molten salt. This stored energy is used to generate electricity from a conventional thermal power plant turbine. Over the last decade this technology has seen costs decline by over 60 per cent, making it a cost-effective storage solution.

Costs are expected to decline further when more plants come up, which could lead to economies of scale in the manufacture of the specialised mirrors used in CSPs.

Thermal plants could examine if their sites permit CSPs, as they may it find it easier to develop CSPs. It is time India invites competitive bids for setting up CSPs; China already has a large CSP development programme.

PSPs and CSPs have enormous storage potential and are cost effective. Battery storage at present is more expensive. Going forward, green hydrogen stored either on its own or in ammonia may be the solution for meeting seasonal peaks in demand with carbon-free electricity.

The development of large scale grid storage needs to be taken up immediately as it is essential for the optimal utilisation of the 500 GW non-fossil fuel capacity being created and for having enough flexibility in supply so that the need to build new thermal plants for reliable supply of power is not felt.

The writer is Distinguished Fellow, TERI and former Secretary, DIPP, Govt of India

In the electricity grid, supply needs to be flexible to meet demand at

every moment even as demand varies considerably, with sudden surges