The development of Fresnel lens concentrators for solar water heaters: a case study in tropical climates

Abstract

This paper discusses the application of Fresnel Lens Concentrator for Solar Water Heater which is a case study in Indonesia. The purpose of this study was to find an empirical equation of the relationship between Direct Normal Irradiance (Ib) and focal point temperature (Tf). The research location is Latitude: 7.9553 °S and Longitude: 112.6145°E. The SM-206 solar power meteris used.The Fresnel lenses are made of PMMA material. Its specifications are: diameter=1000 mm; weight=2 kg; thickness=2 mm; groove pitch=0.5 mm and focal length=880 mm.The main experimental setup consists of a PMMA Fresnel lens and a receiver. The conical cavity receiver has specifications; geometric concentration ratio,CRg=8, and V=2 Liters. Temperature measurement is done using a temperature data acquisition system. The K-type thermocouple is used to measure: 1) ambienttemperature (Ta); 2) the focal point temperature (Tf); 3) receiverwall temperature (Tr); 4) watertemperature (Tw). The experiment obtained the results of the empirical equation for the relationship between Direct Normal Irradiance (Ib) and focal point temperature (Tf). The increase in solar radiation produces a focus temperature, exponentially. At DNI 858 W/m2 it can produce a focal temperature of up to 1064 °C. The efficiency of the receiving cavity of the thermal cone which contains 2 litres of water and CRg=8 under conditions of relatively Direct Normal Irradiance ( =675 W/m²) is about 10.61 %. Furthermore, the energy that can be generated in heating water is 0.17–0.32 MJ, in 100 minutes. Heat convection and radiation loss can be reduced by adding an insulating layer to the walls and coating the surface with black