a b s t r a c tEnergy efficiency is generally used as one of the most important parameters in order to introduce and compare thermal systems including flat plate solar collectors despite of the fact that the first law of thermodynamics is not solely capable of demonstrating quantitative and qualitative performance of such systems. In this paper, a theoretical and comprehensive model for energy and exergy analysis of flat plate solar collectors is presented through which the effect of the entire design parameters on performance can be examined. Upon the verification and confirmation of the model based on the experimental data, effect of parameters such as fluid flow rate and temperature, type of working fluid and thickness of the back insulation on the energy and exergy efficiency of the collector has been examined and based on the analysis and comparison of results, the optimal working condition of the system has been determined. According to the results, designing the system with inlet water temperature approximately 40 more than the ambient temperature as well as a lower flow rate will enhance the overall performance.

In this paper, a heat pipe evacuated tube solar collector has been investigated both theoretically and experimentally. A detailed theoretical method for energy and exergy analysis of the collector is provided. The method is also evaluated by experiments. The results showed a good agreement between the experiment and theory. Using the theoretical model, the effect of different parameters on the collector's energy and exergy efficiency has been investigated. It is concluded that inlet water temperature, inlet water mass flow rate, the transmittance of tubes, and absorptance of the absorber surface have a direct effect on the energy and exergy efficiency of the heat pipe evacuated tube solar collector. Increasing water inlet temperature in heat pipe evacuated solar collectors leads to a decrease in heat transfer rate between the heat pipe's condenser and water.

An increase in exergy efficiency of flat plate solar collector leads to a considerable improvement in collector’s performance. Different parameters influence the performance of collector. In this paper, Sequential Quadratic Programming (SQP) and Genetic Algorithm (GA) have been employed for optimizing exergy efficiency of the flat plate solar collector. Absorber plate area and mass flow rate of inlet water have been considered as optimization’s variables. The results show the possibility to reach higher exergy efficiency with lower absorber area and consequently lower price. Also it is obvious that SQP method performs optimization process with higher convergence speed but lower accuracy than GA.