Abstract: With the output of energy storage systems as the research objective, this paper studies the volatility of photovoltaic power generation from the perspective of time and frequency. The frequency of photovoltaic power generation is decomposed by the EMD algorithm. Through studying the residual value of the IMF obtained by decomposition, the following conclusion is found: in cloudy weather,the energy storage output within the photovoltaic power generation system is frequent with strong capability of stabilizing the photovoltaic power fluctuations;in sunny weather,the output of the energy storage system is regular and time fixed.