Overview of Derating Factor Calculation Methods for Renewable Energy Capacity Mechanisms

Ensuring sufficient power generation adequacy is a requirement for the electricity system security and reliability. Many foreign power markets have introduced different types of capacity mechanisms such as centralized capacity markets and decentralized capacity obligations. The derating factor is one of the major design elements of the capacity mechanism, representing the percentage of the installed capacity of the unit to characterize its effective capacity. Conventional power systems have a large number of thermal power plants and small system fluctuations, so the derating factor can be calculated easily based on historical data. With high penetration of renewable energy, renewable power generation contributes can significantly affect system adequacy and thus, should participate in the capacity mechanism. However, due to its stochastic characteristics, the calculation method of its derating factor needs to be studied again. This paper summarizes the relevant practical experience and academic research from the US and Europe in terms of renewable energy derating calculation, consisting of two major categories, i.e. historical data method and probability analysis method for comparative analysis. In addition, it analyzes the influence of the synergy effect caused by renewable energy on the derating factor, including the synergy effect between different power generation technologies, renewable energy and load. Finally, based on the status quo of the power market and carbon emission planning in China, feasible recommendations are put forward for the calculation of derating factors in China's adaptation to high-proportion renewable energy systems.