To achieve the goal of reducing greenhouse gas in buildings, the Korean government formulated mandatory regulations that mandate the installation of renewable energy systems in buildings. Because the evaluation of these regulations is conducted at the building design stage, it cannot be guaranteed that the target building will show the expected energy performance after its completion. In this study, the regulation level of renewable energy supply obligation ratio (RER) by the Korean renewable energy installation obligation was compared according to cases through hourly-basis simulations. The target renewable energy system consisted of a photovoltaic, proton-exchange membrane fuel cell, and battery energy storage system. Three different renewable energy system design scenarios were investigated to compare the annual energy production and RER calculated according to the current RER calculation methods with those obtained through simulation. The simulation results showed that the larger the capacity of the battery energy storage system, the more significant was the difference in the RER between the current calculation and simulation results.