This study aims to quantitatively clarify the effects of storage battery introduced to districts where large variable renewable energy (VRE) is implemented. Such districts will have difficulties in balancing between power demand and supply, and to keep the load frequency control (LFC) ability, and will be forced to curtail much VRE without storage battery. Authors developed a simulation model to optimize generation mix and hourly operation of thermal power, pumped hydro generation, and storage battery considering partial load efficiency, LFC supply and demand, and power transmission between districts. With this model, the authors obtained the following results on Japan's power system in 2030. (1) Some capacity of battery can decrease VRE curtailment rates as well as total power generation costs. However unit generation costs increase by the drop in thermal power capacity factors. (2) The curtailment rates can decrease to zero by having extremely large capacity of battery though this is a very expensive way. (3) The required battery capacity decreases when VRE ratios to power system size are averaged among districts.
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