Simplified method to estimate grid flexibility: Application to Japanese electrical grids

Abstract Grid flexibility determines the capacity limits of variable renewable energy without any restrictions or wasted energy. In this study, we propose a simple but feasible method to estimate the grid flexibility on a national scale, using available datasets. The method is demonstrated to assess the grid flexibility in Japanese power plants under different operating conditions. In addition, we evaluate the environmental impacts of photovoltaic (PV) and wind power within their capacity limits. The grid flexibility increases from 50 GW to 82 GW, the capacity limit of PV increases from 63 GW to 102 GW, and that of wind power increases from 37 GW to 76 GW, by the suspension of nuclear power plants and the load-following operation of coal-fired power plants. The annual CO2 reductions achieved by PV and wind power generation represent less than 10% of the total CO2 emissions in Japan. Depending on the operating conditions, the capacity limit of PVs may exceed when connecting to a permitted PV power source to the grid.