PCM-Based Energy Storage Systems for Solar Water Heating

Abstract

Use of solar energy has seen significant growth in recent years. One of the key areas of direct use of solar energy is domestic water heating. A properly designed solar water heater can provide most of the hot water required for residential applications in a cost-effective and environmental-friendly manner. A major requirement of solar water heaters is the control of the water delivery temperature from the solar heater. Consistent water temperature should be maintained at the outlet of the system as required for specific applications. Also, heating of water is dependent on the availability of solar energy which naturally varies during the daytime and can be affected significantly by local weather conditions. One of the ways to overcome this difficulty is to use an intermediate phase change material (PCM)-based energy storage system which stores part of the solar energy during peak supply and releases it during lean periods. This chapter presents a study on the use of PCM-based energy storage systems for solar water heating. At first, a brief description of solar water heating process is given. This is followed by a discussion on the use of energy storage systems for solar water heating. Subsequently, a CFD model is presented to simulate the charging and discharging of a PCM-based energy storage system. The model is based on the enthalpy method and can capture the evolution of melting and solidification of PCM due to the flow of heat transfer fluid in the energy storage unit. The effect of important parameters such as flow inlet temperature and velocity, storage unit dimensions, and charging time on melting and temperature evolution is analyzed in detail.