The strategy of power managers to use hydro and gas-fired plants to absorb the sharp load changes during the lights-out seems to have paid off on Sunday, April 5.
Hydro and gas-powered plants can support fast changes in load. Gas turbines are machines that can ramp up or ramp down rather quickly and, world over, they are often used to support the grid supplied with fluctuating wind power. Similarly, water can be stored in dams and reservoirs and can be released in a planned manner to achieve a sharp increase or decrease in hydro power.
It appears that the total sharp change in load was of the order of some 20 GW in 20 minutes. Power consumption on a Sunday typically hovers between 100 to 120 GW. On April 5, the changes in load, though swift, happened over a more prolonged period of time than the 2 to 4 minutes expected by power managers, probably indicating that people eased out of the lights-out more gradually than expected. They took slightly longer to switch on their house lights, likely spending more time on rooftops and such.
Data from the Brookings India Electricity & Carbon tracker shows that the demand climbed down from the usual peak of 118 GW at around 7.30 p.m. and was gradually decreasing until about 8.55 p.m. This was as per the norm.
Dramatic fall
Then it dramatically fell from around 110 GW at 8.55 p.m. to 87 GW at 9.10 p.m. This indicates people were switching off their lights through 9.10 p.m. The demand had fallen to 100 GW at 9 p.m. at the scheduled time of lights-out. It was back up to 104 GW by 9. 25 p.m., from 87 GW at 9.10 p.m. The climb tapered off to 110 GW by 9.50 p.m. After that the demand followed its usual pattern.
Just as the power managers had planned, the generation from hydro power plants toed the dip and surge pattern of lighting loads. From around 25 GW at 8.50 p.m., hydro generation fell dramatically to less than 9 GW at 9.10 p.m.. Hydro power climbed to 19 GW at 9.30 p.m. The sharp change was therefore of the order of nearly 60%. This meant hydro plants across the country were quickly able to ramp up the storage and release the water to the turbines.
Gas generation, too, fell from 7.4 GW at 8.55 p.m. to 5.5 GW at 9.15 p.m. before picking up to 7 GW at 9.30 p.m.
Nuclear generation remained flat at around 4.7 GW throughout. Nuclear plants cannot handle sharp changes in load.
Coal-fired generation
Coal-fired generation did not exactly follow the pattern of the load changes caused by the lights-out. The dip was more calibrated and gradual. The climb up was also gradual. From a peak of 85 GW at 7.15 p.m., coal-fired power was gradually reduced to 72 GW close to the lights-out. Then the fall was sharper, touching 68 GW at 9.15 p.m. After a slightly sharp rise, coal-fired plant generation was slowly raised to 83 GW by 10.30 p.m. Coal-fired power supplies the bulk of the demand in India. It is the base on which sharp changes in load can be accommodated through other sources of power generation.
The exercise showed that the Indian grid could handle large load changes if done in a planned way. Blackouts are a different matter and typically happen unplanned. Blackouts at one place can spread to other places when power plants that are not designed to take sharp load changes are forced to take those changes.