In situations, where the weight of a renewable energy certificate (REC) for a battery energy storage system (BESS) linked to a photovoltaic (PV) system is applied, it is necessary to evaluate the optimal capacity of the BESS to maximize the profit and prepare for a change in future support policy. The levelized cost of energy (LCOE) was calculated for a range of conditions using the hourly power generation data and charge/discharge guidelines of the nationwide PV plants. As a result, the optimal capacity of BESS under the current REC weight 5.0 was determined to be 2.7 times that of the PV capacity nationwide. In the reference cases of Jeju, Gyeongnam, and Jeonnam, which have the lowest, average, and highest solar radiation of the country, it was confirmed that the economic benefit by BESS linkage was higher in cases of lower solar radiation. If the REC weight is downgraded in the future, the optimal capacity of BESS will also be reduced. If there is no reduction in the BESS facility unit cost, the advantage of the REC weighted value of 3.5 or less will be lower than that of a PV single operation.
