Thermodynamic efficiency comparison between thermal and electric storage for photovoltaic-driven chilling system

Abstract

Abstract Faced with the ever-increasing pressures from climate change and environmental pollution, stand-alone photovoltaic (PV) power generation is promising in providing electricity to the air conditioners. However, the solar energy is usually susceptible to the weather changes, making the power supply unreliable. To mitigate the effects caused by the solar intermittency, additional energy storage buffer is necessary. In this paper, stand-alone PV chilling systems with water tank thermal energy storage (TES) and battery electric energy storage (EES) strategies are quantitatively compared by evaluating the thermodynamic efficiency, respectively. A chiller model is firstly built, based on which the initial steady states are derived. Secondly, the EES and TES system models are built based on the compressor speed control strategy and refrigeration cycle model. The resulting chilled water temperature fluctuation curves in TES and EES PV chillers are subsequently obtained. Quantitative comparative results in this paper are threefold. i) The average chilled water temperature of the TES strategy is 11.08% lower than that in the EES strategy; ii) The average cooling energy amount stored in the TES strategy is 43.6% larger than that in the EES strategy, indicating that the chilled water tank has a better energy storage potential in the given PV chiller system; iii) The water volume of TES is optimized to derive the maximum cooling energy storage rate which is 76.92% larger than that in the EES system.