A review of solar water heating systems

A review of solar water heating systems for domestic and industrial applications is presented. They are grouped into two broad categories as passive and active solar water heating systems. Each of them operates in either direct or indirect mode. Their performances, uses and applications, and factors considered for their selection are reported. The active systems generally have higher efficiencies, their values being 35%-80% higher than those of the passive systems. They are more complex and expensive. Accordingly, they are most suited for industrial applications where the load demand is quite high or in applications where the collector and service water storage tank need not be close to each other or for the applications in which the load requires more than one solar collector. On the other hand, the passive systems are less expensive and easier to construct and install. They are most suitable for domestic applications and in applications where load demand is low or medium. Generally more research and development work are needed to further improve the existing level of efficiency for it to serve effectively as a viable alternative to the conventional means of hot water generation. The actual field testing experiences, together with the prospects and economic problems that affect popularization of the systems, are also presented. Their possible solutions are suggested. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3167285]