Carbon emissions impacts of operational network constraints: The case of Spain during the Covid-19 crisis

Operating a highly decarbonized power system is technically complex and introduces novel challenges for system operators. To this effect, the hourly day-ahead market schedule must be compliant with all the network security criteria. If required, specific generators should be curtailed or started up after the market clearing via so-called redispatching actions. In this paper, we analyze the bias in emissions intensity of electricity generation that result from not internalizing grid operational limitations in the day-ahead market clearing. In other words, we investigate the incremental emissions resulting from actions by system operators to make the day-ahead market schedule physically feasible. We use hourly data from the Spanish power system between 2019 and 2021. We estimate that while redispatching actions accounts for 2–4% of total annual electricity demand, they represent 6–11% of the annual power sector's CO2 emissions. We find that volumes of fossil generators started up for network security reasons by system operators increase in hours during which the share of renewables in the supply mix is relatively high but, additionally, show that volumes also significantly increase during hours with low energy demand, as during the Covid-19 crisis. These latter actions are not triggered to alleviate grid bottlenecks, but to solve location-specific operational constraints requiring a minimum volume of synchronous generators always running. Because of these actions, we estimate that the emissions from the day-ahead market schedule are downward biased between +0.00391 and + 0.0145 tn of CO2 for each additional MWh of scheduled wind or photovoltaics. We offer several recommendations to better align the day-ahead schedule with the grid operation needs leading to a reduced need for redispatching actions.