Contradictory relationship between efficiency and renewable energy under breakeven point: Optimal selection of electrical and electronic equipment

The increasing demand for electrical and electronic equipment (EEE), particularly air conditioning (ACs), has caused a significant increase in energy demand. Improvements in energy efficiency increase material and carbon footprints under the production stage owing to the additional use of resources. Higher energy-efficiency models need to compensate for this rise before EEE reaches the end of its lifespan. Thus, the timing of offsetting, named breakeven point (BEP), was analyzed between two models of ACs manufactured in Japan with different energy efficiencies in this study, considering material and carbon footprints based on different lifestyles. Through the analysis, a contradictory relationship between energy efficiency and renewable energy was quantitatively identified; that is, the improvement of energy efficiency leads to a lower BEP, while the increase in renewable energy leads to a higher BEP. When the share of renewable energy in the energy mix reaches more than 40 % in the case of material footprint, the choice of low-efficiency appliances would be even preferable considering the lifespan of EEE and lifestyle. The developed concept contributes to optimal selection among different EEE efficiency from an environmental perspective.