Spanish secondary reserve requirements, clearing and usage

The technical and economic importance of electricity ancillary services, responsible for guaranteeing the reliability and security of the power systems, is growing due to the continuous penetration of intermittent technologies. Indeed, changes in the net demand are forcing more expensive thermal generation to provide reserves while reducing their energy production. Therefore generation companies' are more and more concerned with reserve markets and their impact on the electricity market forecasting models. This paper analyses historical data from the Spanish electricity market to better understand and forecast secondary reserve requirements and real-time secondary reserve usage. It focuses on the relationship between secondary reserve requirements by the System Operator and the secondary reserve finally cleared, the long term evolution of secondary reserve requirements with respect to the intermittent generation growing, their annual and daily seasonalities, the real-time secondary reserve usage and its annual and daily seasonalities, and some additional hints for the requirements forecasting. Several interesting and not always intuitive conclusions are drawn from the analyzed data.