Accumulated Performance Comparison of Solar PV and Solar Thermal Water Heating in New Zealand

Abstract

The rising global energy demand and environmental harm caused by reliance on fossil fuels highlight the urgent need for sustainable solutions in residential water heating. This study conducts a comparative numerical analysis of solar photovoltaic (PV) and solar thermal water heaters under New Zealand's typical weather conditions. By integrating the National Institute of Water and Atmospheric Research (NIWA) meteorological data, hourly simulation results were performed to analyze energy output, water temperature profiles inside storage tank, and levelized cost of electricity (LCOE) under varying seasonal conditions, including summer, normal, and winter. The highlight of this study is the evaluation of accumulated water performance within the storage tank under real‐life operating conditions. This includes the impact of actual weather fluctuations (including ambient temperature and solar radiation), target hot water temperature, heat losses from the tank, and typical household water usage patterns along with the replenishment of cold water. Under identical weather conditions, the simulations results indicate that the solar thermal system outperforms solar PV system across key performance metrics. For solar water heating applications, the thermal system generated 5847.59 kWh of energy annually per 10 m of collector area, compared to 2780.41 kWh from the PV system. Although the thermal system required 33.7% more auxiliary energy annually (964.59 kWh) compared to the PV system (721.38 kWh), it delivered better energy utilization efficiency. This is highlighted by its produced‐to‐used energy ratio of 6.06, which is 58% higher than the PV system's ratio of 3.85. The efficiency translated to better economic advantages, with thermal achieving a 61.9% lower LCOE for produced energy at 0.0766 NZD/kWh compared to PV's 0.2013 NZD/kWh, and a 40.2% lower LCOE for used energy at 0.4641 NZD/kWh versus PV's 0.7757 NZD/kWh.