Economic and environmental benefits of using batteries and heat pump water heaters to effectively utilize daytime electricity

Addressing climate change is an urgent global concern. One promising avenue is the generation of renewable energy such as solar power. Among major energy consumers, houses have significant potential for the installation of solar power generation systems and self-consumption of the electricity generated. Effective self-consumption of electricity generated in houses is crucial to expanding renewable energy use and reducing carbon dioxide (CO2) emissions. However, in many houses with solar power generation systems, the electricity generated and sold exceeds the household's self-consumption. This study analyzes Home Energy Management System (HEMS) data and simulations to assess how charging storage batteries and operating water heaters during the day can improve self-consumption and to evaluate its impact on CO2 emissions and electricity charges. This study makes a novel contribution to the literature by providing an understanding of the economic and environmental effects of daytime energy storage in real-world settings based on actual measurement surveys. HEMS data from 262 households were analyzed to estimate the effects of implementation and battery charging timing. Within realistic electricity-rate ranges, shifting the timing of energy storage to daytime increased self-consumption by approximately 25% and reduced annual bills, although the savings remain small relative to battery installation costs. Simulations of a modeled house equipped with solar and storage systems examined CO2 emissions under various emission factors, storage battery-linked systems, and storage battery control methods. Assuming wider adoption of solar generation in the future, the emissions were calculated under the condition that the emission factor changes according to the amount of solar radiation. The results revealed that daytime charging generally reduced emissions, although selling electricity was more advantageous, depending on emission settings. These results highlight the need to enhance residential self-consumption rates to accommodate the future growth of solar power generation. Furthermore, they emphasize the importance of communicating the non-economic benefits of installing storage batteries to residents, such as enhanced disaster preparedness, in addition to the economic benefits.