Solar energy is free, environmentally clean, and therefore it is accepted as one of the most promising
alternative energy sources. The effective use of solar energy is hindered by the intermittent nature of its
availability, limiting its use and effectiveness in domestic and industrial applications especially in water
heating. Conversion of solar energy into thermal energy is the easiest and most used method. The
efficiency of solar thermal conversion is around 70% but solar electrical direct conversion system has an
efficiency of only 17%. Solar water heating systems are mostly suited for its ease of operation and simple
maintenance. Many research papers revealed that the improvement on thermal efficiency of solar water
heating systems resulted in techniques to improve the convection heat transfer. Solar water heating
systems are classified into two broad categories as passive and active systems. Passive techniques have
been used to improve the convective heat transfer. The techniques like insertion of twisted tapes and its
geometry, etc., play a vital role to improve the performance of solar water heating systems. This review
paper summarizes the previous works on solar water heating systems with various heat transfer
enhancement techniques include collector design, collector tilt angle, coating of pipes, fluid flow rate,
thermal insulation, integrated collector storage, thermal energy storage, use of phase change materials,
and insertion of twisted tapes. This paper also discussed the methods to optimize and simulate the solar
water heating systems to understand flow and thermal behavior in solar collectors that would lead to the
improvement of the thermal performance of solar collectors.
Solar energy is free, environmentally clean, and therefore it is accepted as one of the most promisingalternative energy sources. The effective use of solar energy is hindered by the intermittent nature of itsavailability, limiting its use and effectiveness in domestic and industrial applications especially in waterheating. Conversion of solar energy into thermal energy is the easiest and most used method. Theefficiency of solar thermal conversion is around 70% but solar electrical direct conversion system has anefficiency of only 17%. Solar water heating systems are mostly suited for its ease of operation and simplemaintenance. Many research papers revealed that the improvement on thermal efficiency of solar waterheating systems resulted in techniques to improve the convection heat transfer. Solar water heatingsystems are classified into two broad categories as passive and active systems. Passive techniques havebeen used to improve the convective heat transfer. The techniques like insertion of twisted tapes and itsgeometry, etc., play a vital role to improve the performance of solar water heating systems. This reviewpaper summarizes the previous works on solar water heating systems with various heat transferenhancement techniques include collector design, collector tilt angle, coating of pipes, fluid flow rate,thermal insulation, integrated collector storage, thermal energy storage, use of phase change materials,and insertion of twisted tapes. This paper also discussed the methods to optimize and simulate the solarwater heating systems to understand flow and thermal behavior in solar collectors that would lead to theimprovement of the thermal performance of solar collectors.
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