Thermal modelling and experimental evaluation of a linear Fresnel lens solar collector for water heating.

This paper presents an energy performance analysis of a solar collector with Linear Fresnel lens as solar concentrator. A solar collector prototype was proposed, constructed and evaluated from a theoretical and experimental perspectives. The solar collector uses a 0.3 m × 0.3 m Linear Fresnel lens as solar concentrator, a copper pipe located at the lens focus as radiation receiver, and water as heat transfer fluid. A thermal reduced model based on semi-empirical heat transfer correlations and first law of thermodynamics was developed in order to estimate output temperatures and heat transfer between the main components of the collector, using operating conditions as input variables. The proposed model was able to estimate heat received by the absorber pipe, convection and radiation losses to surroundings, water outlet temperature, and the thermal efficiency of the collector. The model was validated by experimental tests carried out under real outdoor conditions. Solar radiation, ambient temperature, wind speed, and temperatures of water inlet, water outlet were measured by an experimental set-up. The prototype reached a maximum input-output temperature difference of 3.96 °C, and an average thermal efficiency of 10% during the tests. Results showed that the proposed model can estimate the efficiency and the temperature of the water outlet with a maximum difference of 0.6 % and 0.96 °C respectively.