CO₂ Reduction Potential of Solar Water Heating Systems on a Municipal Basis

Abstract

The present study assesses the CO₂ reduction potential of solar water heating systems (natural circulation) for single-family houses considering the natural and social conditions of local areas in Japan. The life cycle CO₂ reduction is estimated by municipality when installing solar water heaters instead of conventional water heaters (i.e. oil, LPG, natural gas and electricity) used at present. The estimation results reveal that the CO₂ reduction potential greatly varies from 156 to 589 [kg-CO₂/household/yr] depending on the local areas. The CO₂ reduction rate is also in the wide range of 11.1% to 28.7%. The total CO₂ reduction potential in Japan is estimated to be 6.73 million [t-CO₂/yr]. Local CO₂ reduction potential is mainly affected by the three local factors: fuel-types of conventional water heaters, feed water temperature and air temperature. The local areas where electric water heaters are widely used (e.g. Chugoku region) have high CO₂ reduction potential. Similarly, the local areas with low water temperature have high CO₂ reduction potential (e.g. Hokuriku region). However, when air temperature is extremely low, the CO₂ reduction potential is small because solar water heaters do not operate due to freezing (e.g. Hokkaido region).