Impact of utilizing PV surplus electricity on CO₂ emissions from the residential energy systems

In order to reduce CO₂ emissions in the residential sector, the installation of photovoltaics (PV) has been increasing extensively. However, such large-scale PV installations cause problems in the low-voltage distribution grid of the residential sector, such as PV related voltage surges. In this study, the utilization of suppressed PV output through energy storage devices was proposed. Using demand side energy storage devices reduces voltage surge, transmission loss, and CO₂ emissions from the residential buildings. The objective of this study was to add voltage constraints of the low-voltage distribution grid to an operational planning problem that we developed for the residential energy systems, and to quantitatively evaluate the potential of heat pump water heater (HP) to utilize the PV surplus electricity, while considering the electrical grid constraints based on the minimization of CO₂ emissions. We found that when a 4.5 kW HP with 370 L storage, which utilizes PV output, was added to the system, the reduction in CO₂ emissions was more than twice compared with that in the case of adding 4 kWh battery (BT) to a PV and gas fired water heater configuration. Further, the effect of utilizing the suppressed PV electricity by HP was almost equivalent to that by the BT. Therefore, the potential of HP in utilizing PV surplus electricity is higher than that of the BT in terms of CO₂ emissions reduction in the residential sector.