Through a 9-minute video message broadcast across the country on April 3, the Prime Ministerasked the citizens of India to switch off their lights at 9 p.m. on Sunday, April 5, for 9 minutes and light oil lamps (diyas), candles, mobile flashlights instead.
This 9-minute community ritual has been ostensibly proposed to boost morale in the times of lock down and social distancing. However, since the announcement was made, power grid operators have suddenly become frontline workers along with doctors in the fight against COVID-19. Here is why
The lighting related electric load is not separately measured, but can be estimated. Based on assumptions about the number of households that will participate in this event and the quantum of lighting they usually use that will be turned off and on again in 9 minutes, it is estimated that the grid will see a dip of anywhere between 10,000 to 20,000 MW. The assumptions used to arrive at these estimates are shown in Table 1.
Power System Operation Corporation Limited (POSOCO) provides daily reports for the load on the grid (which is now a national grid). I have constructed a typical all-India load curve based on the Daily Report from POSOCOfor April 4, 2020. If we assume a 20,000 MW drop in the load at 9 p.m. (because it is better to be prepared for a bigger dip than a lower one) there is a significant fluctuation that occurs almost instantaneously. This can be seen in the figure below.
While the grid is accustomed to fluctuations and changes in both the supply and demand, these fluctuations are usually spaced over a larger time period, typically of more than at least half an hour. Managing this 9-minute event is therefore going to be a challenge.
It is possible that such fluctuation, especially if it is spatially concentrated (in large cities, for example), may cause a cascading impact. For example, if a significant quantum of load disappears from the grid suddenly in a particular location, there will be a power surge in other regions causing line trips, in turn causing voltage instability.
If this is spirals out of control, and occurs in a sufficiently large number of locations, it may even lead to a blackout. In a situation when at the very least hospitals need to function non-stop, not to mention other essential services, such as water supply, sanitation etc. a blackout is a terrible scenario to even contemplate.
We are hopeful that power system engineers at POSOCO as well as in state utilities will come up with strategies to manage this. For example, it has already been suggested that spinning reserves, hydro power, and staged load-shedding may be used to manage this event.
The figure above also shows a simple linear load-shedding rate, starting after the morning peak load at 9 a.m. going up to 9 p.m. in the evening and a similar ramping up thereafter. This would involve about 1.8 GW of load-shed every hour. (The figure shows is a linear trend, and the actual load-shedding required would be much less at the nation-wide level).
However, managing the rate of ramping as well as load-shedding will be a headache for power utilities. In many regions, residential and commercialfeeders are not separate, so regional load-shedding may also lead to power cut-off to essential facilities (even hospitals) in some areas.
To manage high rates of ramping in the power supply (when the lights shut down and when they start up again), cheaper thermal generators will have to be temporarily run at technical minimum loads and hydro and natural gas generators (wherever available) will have to be used. This is likely to result in a significant increase in costs as well.
The question remains --- why does a system have to go through so many hoops and somersaults to avoid a collapse, for an event that will have absolutely no impact on the fight against COVID-19?
Surely, people’s morale can be boosted by providing information about lives being saved and workers being fed. Lighting oil lamps and candles and sending the power grid into crisis mode for no reason, at a time when we have many challenges facing us, defies logic.
The writer is associated with the Energy Environment Program, School of Natural Sciences and Engineering, National Institute of Advances Studies, Bengaluru. The views are personal