Solar power capacity in India is now over 150 GW. This extraordinary success seems to be facing problems now. The system is unable to absorb all the solar power that can be generated. 23GWh of curtailment per day has been reported. Solar power is generated without any further cost and hence curtailment means loss of free electricity.
Have we been creating solar capacity faster than we needed to? Maybe we should slow down and give up the goal of creating 500 GW of fossil fuel free capacity by 2030. These doubts are occurring just when we seem well set to achieve the ambitious target announced by the Prime Minister. Many Discoms are reported to be reluctant to sign fresh PPAs for solar power after completion of the SECI bid process.
Solar power is generated only when the sun shines on a solar panel. For the remaining part of the day, the Discom needs to supply electricity from alternative sources. Traditionally, the Discoms have been entering into long term Power Purchase Agreements (PPAs) usually with thermal power plants. These plants have enough flexibility in generation to supply electricity to meet demand which on any day varies, more on some days and less on others.
Solar power has complete inflexibility in generation and therefore as its share grew, thermal power generation needed to become more flexible. But there are technical limits. Regulations require thermal plants to be able to bring down generation to 55% of full capacity. But if the share of solar power generation rises to levels during the day when thermal power plants reducing generation to 55% still results in supply exceeding demand, then grid stability is in danger and curtailment of solar generation becomes unavoidable.
Creating an integrated all India grid has been a major achievement; state grids becoming integrated into regional grids and then into the national grid. Investments to increase transmission capacity follow the demand signal coming from new investment in generation and the destinations where the power generated would be consumed. The problem that is being seen flows from the fact that solar projects take less time, about a year and a half, to put up whereas transmission lines take longer, three to four years. So, some of the problems being experienced result from transmission capacity lagging behind. This is a solvable coordination issue.
From the Discom perspective there are two problems. As the transmission capacity created for solar projects is used only when the sun shines, real transmission costs have been rising. Then for supply of electricity outside solar hours, they have long term contracts for thermal power where they pay fixed charges irrespective of how much power they take. This makes the per unit cost of electricity rise as the capacity utilisation of a thermal plant goes down to accommodate the inflexible solar power generation in the day.
Create as much storage as possible; Battery Energy Storage Systems (BESS), PSPs (Pump Storage Projects), and Concentrated Solar Thermal Projects (CSPs) with storage. And all three together and as rapidly as possible. The good news is that the market discovered price of solar power with storage is now lower than new thermal power. On purely commercial considerations, new thermal plants need not be built to meet additional demand. But the quantity of storage capacity needs to rise manifold. As storage increases where there are large solar projects in states such as Rajasthan, Gujarat and Karnataka, curtailment of solar power generation would end as it would be stored for supply in the evening. Further increase in storage would then enable thermal plants to generate at full capacity with generation in solar hours being stored to provide electricity at night and during peak demand hours. Storage thereafter would give confidence that reliable supply would be possible without contracting for new thermal capacity and giving the consumer cheaper electricity.
The Discoms need to contract for storage capacity. Battery prices are low. They get installed easily without needing much land in about a year. Discoms need to choose the optimal mix of sizes and locations and begin inviting a series of large bids individually as well as collectively through SECI. Depending on market response, the feasible pace of scaling up would emerge. Awarding contracts for 10, 000 MWhr initially would be a good beginning.
In PSPs electricity is used to pump water to a higher reservoir which is then allowed to fall and generate hydroelectric power when needed. River sites have been identified, and development of over 75 GW has been initiated. The Ministry of Power needs to work with the state governments to steer progress. Forest and other clearances could be given quickly using satellite and/or drone imagery to determine the number of trees, their species and on this basis, the money that the project developer has to pay. Off river PSPs require the creation of two reservoirs at different heights. These can be developed faster. The first off river PSP unit has been commissioned recently. The government should use satellite and drone imagery to identify sites and recover this cost from developers when sites are given.
CSPs use mirrors to reflect solar radiation to heat molten salt, the stored heat is used to generate steam and run a turbine to generate thermal power when needed. The areas adjacent to the large solar projects are ideal locations for CSPs. The transmission lines are already there, and their capacity utilisation would rise. The intention of developing, say, 10,000 MW of CSPs in phases may be announced and bidding initiated. The size of the market would get private investment to produce these special mirrors, reducing the cost of these projects substantially.
Rapid growth of solar power capacity now requires equally rapid growth of storage. Curtailment of solar power would end if we award large contracts for battery storage immediately. And begin development of PSPs and CSPs at full speed so that the need for new thermal power plants begins to end.
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