Performance Evaluation of a Novel Solar Thermal Water Heating System Integrated with Thermal Energy Storage: A New Zealand Case Study

Abstract

This study evaluates a solar thermal water heating system integrated with thermal energy storage (TES) for domestic hot water supply in New Zealand. A conventional system without TES was first assessed as the baseline case and then compared with a TES-integrated system using Paraffin RT60 as the phase change material and Therminol 55 as the heat transfer fluid. The analysis was based on three selected seven-day periods in 2025, representing summer, winter, and intermediate weather conditions. The simulation results show that TES improves the stability of the water temperature inside the tank, the effective energy usage, and overall system performance when excess solar energy is available for storage. The performance enhancement is most obvious in summer, moderate under intermediate weather conditions, and relatively limited in winter due to less availability of solar radiation. Based on the simulation, annual energy production increased to 6746.93 kWh with TES compared to 5342.88 kWh without using TES, which shows a 26.28% increase. Notably, useful energy consumption increased from 1274.55 kWh to 2327.59 kWh, an 82.62% increase. The produced-to-used energy ratio decreased from 4.19 to 2.90, which shows a 30.85% improvement in energy utilization. The consumption-based LCOE decreased from 0.4825 NZD/kWh to 0.4016 NZD/kWh, while the production-based LCOE increased from 0.1151 NZD/kWh to 0.1386 NZD/kWh. Overall, the solar thermal system with TES improves useful heat delivery and economic performance when evaluated based on actual energy consumption.