Matching intermittency and electricity storage characteristics through time scale analysis: an energy return on investment comparison
A high penetration of variable renewable energy sources in an electricity generation mix leads to strong constraints on the whole system to ensure a continuous balance between electricity production and consumption. We have developed a new numerical methodology to quantify the relevance of several electricity storage devices that would provide the required flexibility. First of all, through a signal analysis (wavelet decomposition) of photovoltaic power (PV), wind power and load time series, we study and characterize the intermittency at different time scales. Then, each storage technology is evaluated for each time scale from an energy return on investment (EROI) standpoint. They are also compared with the possibility of curtailing excess electricity instead of storing it. The relevance of a given technology especially depends on its efficiency and embodied energy. For instance, we show that batteries are not appropriate for long term storage because of their high embodied energy. However, they are a good choice for short term applications with high cycle requirements because of their efficiency. We characterize the relevance of storage devices, their sensitivity to the production mix and to technological characteristics. We point out that satisfying the energy demand of exceptional events only with storage devices requires an over-sizing of the whole system. It underlines the complementarity of energy storage with dispatchable electricity sources. We eventually show that seasonal electricity storage is particularly difficult to ensure with a good energy return on investment.