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Tuesday, September 28, 2021

The balancing act: A tough task cut out for grid managers

With a massive deployment of renewable capacity, the thermal plants will need to undergo a paradigm shift, which could be testing for grid managers

Written by Anil Sasi | New Delhi |
September 11, 2016 2:00:35 am
hydro-759 The total hydro capacity in the country, which is 42 GW now, would be 52GW in 2021, according to CEA estimates.

Earlier this year, the Chinese National Bureau of Statistics announced that coal consumption in the country fell for the second year running. With a national target to add 141 GW of solar and wind energy by 2022, India is on the verge of overshadowing China in pursuing a low-carbon energy strategy. There could, however, be three major fallouts of this.

One, a sharp reduction in emissions could be on the cards, from an average carbon dioxide emission rate of 0.732 kgCO2/kwh to 0.600 kgCO2/kwh by 2021-22, even by the most conservative estimate, primarily due to the government’s thrust on renewables. Two, in view of the 50,000 MW thermal capacity under construction, there is practically no new thermal capacity required to be taken up beyond 2022, according to a new draft National Electricity Plan for 2017-22. And lastly, with such a massive deployment of renewable capacity, the country’s thermal plants will need to undergo a paradigm shift from operating as base load plants to variable output plants, which could be a testing experience for grid managers who would have to forecast accurately to balance the grid supply with demand and require project operators to fine tune power plant controls on an unprecedented scale. Since the impact of forecasting errors of solar and wind power availability on grid frequency is instantaneous, the grid operators would have to devise and implement an automated response from the fleet of thermal power stations and reservoir-based hydro stations.

The Central Electricity Authority (CEA), the apex planning body in the power sector that has worked on the Plan, has estimated a typical availability of 70GW -80GW from their estimated addition of 141GW of wind and solar power by 2020-21. According to experts, on a bright sunny day in summer, the peak availability of wind and solar combined could go up to 90 GW. During the June- September period, rivers start swelling and the run-of-river hydro power plants generate electricity round the clock.

The total hydro capacity in the country, which is 42 GW now, would be 52GW in 2021, according to CEA estimates. Out of this, around 40 GW would be generated round-the-clock in summer and monsoon, in order to not waste available renewable energy. Power regulator CERC’s regulations categorise hydro plants as “must-run”, so that energy of the water is not wasted. Since conventional hydro is also renewable energy, considering wind, solar and hydro, the max renewable energy power during summer-monsoon season could be of the order of 120 GW against a projected all-India intra-day demand of about 160-170 GW in 2021 (projection based on the historical growth trend in demand). Also, the 5 GW nuclear plant capacity always run at base load.

What this means is that the massive fleet of over 266 GW thermal plants in the country will have to ramp down to technical minimum and some of them may have to back down also when solar power peaks, and start ramping up in the afternoon from 3pm onwards to as the sun goes down and the net demand rises to its daily evening peak which may be of the order of 200 GW in 2021. Present coal capacity is about 182 GW and overall thermal capacity (coal plus gas) is 211GW.

With such a massive deployment of renewable capacity, and since India does not have much fuel for gas-based power plants and hydro is mostly run of the river, ramping up and down to adjust to the vagaries of solar and wind generation every day would be required to be done by coal-fired plants. For this, the thermal plant operation will undergo a paradigm shift from base load plants to variable output plants and it will be a testing experience for grid managers and would warrant fine tuning of plant operation and controls. Added to the factors that could suppress demand, the government’s move to push LED bulbs, solar pumps is projected to lead to savings of 200 billion units by 2022.

In order to operate the county’s large thermal capacity daily on flexible mode, CERC has issued regulations ordering that the coal-based plants will have to operate up to a lower limit of 55 per cent of rated capacity as compensation will be provided for partial load operation as well as for backing down the coal-based plant. Ancillary service regulations have been put in place by CERC, empowering the national load dispatch centre to back down a power plant if required and vice versa. CERC has also issued regulation making it mandatory for interstate wind and solar plants to forecast their output. Renewable energy management centres are also being set up which will be equipped with sophisticated forecasting tools and help the state and regional load despatch centres (SLDCs and RLDCs) in wind and solar forecasting. With a wind-cum-solar portfolio of the order of 140-175 GW, forecast accuracy would be a key factor in enabling stable grid operation. CEA regulations levy a mild penalty for deviations up to 30 per cent on RE power. The forecast of the planned 40 GW roof -top solar capacity and intra-state wind generation would have to be done by the SLDCs. On all-India basis, a forecast error of the order 10-15 per cent would translate into power supply imbalance in the range of 10,000MW requiring a faster response from the state and regional grid operators, keeping them on their toes from sunrise to sunset.

So, while on the policy front, the CERC has already issued regulations for compensation for varying the output, backing down of conventional plants and deviation settlement mechanism for solar and wind plants, the efficacy of the new regulations for RE integration will have to be tested in practice, and may have to be fine-tuned with experience. The RE forecasting centres are under development and they will be expected to provide reliable forecast. The state load dispatch centre of each control area within India will have to learn the forecasting of their own RE sources.

According to the Electricity Plan, which was presented before the power ministry, by 2017-22, the total capacity addition is going to be 115 GW and 22 GW, a total of 137 GW (including hydro addition of 15 GW, nuclear 2.8 GW and coal 0 GW- excluding 50GW that is under commissioning). What is interesting, though, is that these factors in zero additional coal-based capacity requirement during 2017-22, excluding 50 gw are already under construction.

Also, the assumption of 7.44 per cent rise in peak demand (CAGR) between 2016-17 and 2021-22, as factored in the plan document, underlines a likely GDP growth assumption of 9-10 per cent considering the past trend of relation between GDP growth and electricity demand. This is likely to be optimistic, considering that GDP growth is lower.

The peak demand of 199GW for 2016-17, as provided in the 18th EPS (as per projections made in 2010), has been reduced to 170 MW. However, the actual simultaneous all India peak likely in 2016-17, according to officials involved in the exercise, may be about 150GW. The actual peak in June 2016 was 147.5 GW as per NLDC report and could be about 150 GW later in October, the likely peak demand month of this year.

On the positive side, the state grid operators of RE rich states are by now familiar with operating the grid with up to 20 per cent RE contribution on certain days. However, scaling up further would require greater skill and ensuring that the thermal plants give the desired response.

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