Integrated and separate collector storage type low-temperature solar water heating systems with latent heat storage: A review

The fluctuating and discontinuous availability problem of solar energy can be significantly reduced by utilizing thermal storage, especially latent heat storage (LHS). The most practically feasible designs of integrating the solar water heating systems (SWHS) with LHS are integrated collector storage (ICS) and separate collector storage (SCS). In the present article, the ICS-SWHS-LHS and SCS-SWHS-LHS designs have been extensively reviewed. The effect of operating parameters viz. HTF inlet temperature and mass flow rate have also been reviewed. For the ICS-SWHS-LHS, the flat plate collector (FPC) designs have been extensively studied in the literature. However, the thermal efficiency of the evacuated tube collector (ETC) has been found significantly better than the FPC-ICS-SWHS-LHS. For the SCS-SWHS-LHS, the thermal performance of all the designs of latent heat storage units (LHSU) has been found approximately the same. The thermal storage capacity of shell and tube type LHSU has found a maximum of all studied designs. A comparison between the ICS-SWHS-LHS and SCS-SWHS-LHS designs has also been presented. Both the designs have some merits and demerits in their design, operation, and performance. This study would be helpful for researchers and designers in selecting a particular design for specific applications.

Automated summary

The use of thermal storage, particularly latent heat storage, can effectively address the fluctuating availability of solar energy. The integrated collector storage and separate collector storage designs are the most practical in combination with solar water heating systems. This article extensively reviews these designs and examines the impact of operating parameters. The study finds that evacuated tube collectors have significantly better thermal efficiency than flat plate collectors in the integrated collector storage design, while different designs of latent heat storage units have similar thermal performance in the separate collector storage design.