Medium-term flexibility options in a power plant portfolio — Energy storage units vs. thermal units

Increasing the share of fluctuating renewables will require additional flexibility in the electricity system. In this paper, we present a model-based approach on how to measure the effect of additional flexibility. The agent-based market simulation model PowerACE has been enhanced to make use of optimization methods (MILP) for the unit commitment of the agents enabling us to quantify the economic benefit of flexibility at agent level. In this analysis, we compare the flexibility offered by thermal power plants to that offered by storage units for the case of existing power plant portfolios of the major German electricity generating companies. We find that for the medium-term (2020), additional storage units up to a total output of 2,000 megawatts and up to a total storage capacity of some 16,000 megawatt hours are economically more viable than gas or other fossil fuel fired power plants as they allow power plants to be dispatched in a more efficient way, i.e. less operation in part load and less start-up and shut-down events occur.