Experimental Performance Analysis of External Compound Parabolic Concentrators With Low Concentration Ratios for Medium Temperature Applications

Due to the mounting concerns about climate changes and depletion of fossil fuels, solar energy, as one type of renewable energy, has attracted a lot of interests from academia, industries, and government in the past few decades. Currently, solar thermal technologies have been applied to the applications at the low operating temperature below 100°C by using flat-plate solar collectors and at the high operating temperature above 250°C by using solar tracking concentrators. For the medium operating temperatures between 100°C and 250°C, flat-plate solar collectors can hardly reach 100°C and solar tracking concentrators are too expensive. In this context, the use of external compound parabolic concentrators (XCPC) for applications operated at medium temperature draws quite attentions because of its higher efficiency than flat plate solar collectors and better cost effectiveness than solar tracking concentrators. However, currently only a few experimental data is available on the actual performance of XCPCs from literatures, especially for the recently new XCPCs with a low concentration ratio. In order to contribute to the knowledge, a series of experiments have been conducted on the new XCPCs recently installed at Bowen Lab, Purdue University, West Lafayette, Indiana. The experiments showed that the XCPCs raised the temperature to 170°C, which is 140°C higher than the ambient temperatures, with a thermal efficiency of 29%. Based on the data collected from the experiments, the optical and thermal efficiencies of XCPCs are determined for different solar irradiations, operating temperatures, and incident angles. A new regression model is proposed and fitted accordingly. The experimental data and analysis demonstrated the feasibility and potentials of using XCPCs for applications in medium temperature range such as solar absorption cooling and heating systems, seawater desalination, solar disinfection, post-combustion carbon capture systems and other industrial process heating.