Economic analysis of a photovoltaic battery system for an electrified detached house with a heat-pump water heater: Effect of time-variable electricity pricing

The electrification of residential buildings involves replacing fuel-based equipment with electricity-based equipment using photovoltaic (PV) generators, and is aimed toward reaching a carbon-neutral society. However, the affordability of such devices, including PV and battery (BT) systems, has not previously been evaluated in detail, especially regarding their incorporation with heat pump water heater (HPWH) and air conditioning (AC) units. It is therefore desirable to clarify the economic feasibility of PV-BT systems for electrified houses to promote residential carbon neutrality. This evaluation should be based on time-variable electricity pricing, such as the time-of-use and real-time price systems. This study proposes a three-tiered management approach for electrified houses to improve the self-sufficiency of PV generation using an exhaustive search of daily HPWH, AC, and BT schedules. To minimize the daily net demand of a household, the management approach determined the daily BT charge/discharge based on PV generation, considering the shifted HPWH and AC operations. The affordability and demand profiles of electrified houses equipped with PV-BT systems were investigated based on a 20-year operation period, considering the actual demands in different regions, various loans, time-variable electricity pricing, and feed-in-tariff policies. The results confirmed a trade-off relationship between the net demand and the overall cost of electrified houses based on their PV-BT capacities under time-variable pricing. The increased PV and BT capacities mitigated the net demand of the households; however, the increased BT capacity raised the overall costs, leading to economic losses in households whose repayments for PV-BT system costs have high interest rates.