Curtailment of renewable electricity as a flexibility option

Curtailment of renewable electricity as a flexibility option
October 17, 2019 Policy Paper

Executive summary

With increasing shares of electricity generation from renewable energy source (RES), the fluctuations of RES electricity generation are increasing too. This presents a challenge to electricity system operators across the world, among them Ukraine’s Ukrenergo. The need to balance these fluctuations can be addressed by adding flexible generation or storage capacity as well as demand response and transmission capacity.
We argue that temporary curtailment should be considered as another regular flexibility option in the system operator’s toolbox, both in the short and long run. We show that in the short run, curtailment helps to mitigate the green-coal paradox – a situation where increasing RES shares have to be balanced by old coal plants with high minimal loads, leading to higher system emissions. Precautionary curtailment in very windy and sunny hours significantly reduces system emissions because it allows to keep nuclear units running instead of old coal plants. If 100% of renewable electricity were fed into the grid, these nuclear units would have to be shut down.
We find that using curtailment as a dispatch flexibility option allows for a nuclear electricity generation share of 57% and a RES share of 14% while reducing the thermal generation share from 56% to 24%. This altered generation mix implies a reduction of total GHG emissions from 94 to 40 Mt CO2.
We also find that 17% of potential RES electricity is unused if curtailment is implemented in the day-ahead dispatch process.

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