Estimation of Hourly CO₂ Emission Factors during the Expansion of Variable Renewable Energy and Evaluation of Non-Residential Buildings Using These Factors

Abstract

The Sixth Strategic Energy Plan anticipates a rapid expansion of renewable energy toward 2030. CO₂ emissions from building power consumption are typically calculated using a consistent CO₂ emission factor throughout the year. However, with the increasing use of renewable energy, the CO₂ emission factor varies over time, and the energy consumption of buildings also fluctuates. This variation can hinder accurate assessment using conventional calculation methods. In this study, we calculated future hourly CO₂ emission factors and assessed CO₂ emissions of non-residential buildings by region and building use. The key findings are as follows: 1) In regions with a high ratio of wind power generation, such as Hokkaido and Tohoku, the CO₂ emission factor decreases in winter. Conversely, in regions like Kyushu and Kansai, where the ratio of solar and hydraulic power generation is high, the CO₂ emission factor decreases around May. 2) An estimation of annual CO₂ emissions from electricity consumption in office buildings in Kyushu showed an 8.6% error between calculations based on a fixed annual CO₂ emission factor and an hourly CO₂ emission factor. 3) In regions where hourly CO₂ emission factors significantly decrease during the day, a substantial peak in CO₂ emissions occurs in the evening when electricity demand and hourly CO₂ emission factors are high.