Status of Solar Water Heating Systems: A Review

Solar water heaters are non-polluting systems, which can contribute to tackle the increasing energy demand without affecting the environment. The reduction of greenhouse gases (GHGs) emission, along with a decreased dependency on expensive and polluting fossil fuels, are the main advantages of these systems. This paper describes the status of solar water heating (SWH) systems, technologies, applications and considerations about their feasibility and cost effectiveness. An introduction about the solar thermal systems and their recent market growth is presented. This is followed by a description of the different types of SWH systems based both on different configurations (viz. natural convection and forced mode) and on different collector technologies (including flat-plate and evacuated tube), described in order to show the extent of their applicability. Other main distinctive parameters for optical and thermal analysis of the collectors are presented and a description of the methods used to evaluate their performance is provided. Finally, the financial feasibility of different kinds of SWH technologies and the potential for CO2 emission reduction are discussed, showing that SWH systems can be successfully used for domestic hot water and space heating applications with significant benefits in terms of energy saving, environmental impact and even cost-effectiveness.