Influence of operating conditions on solar energy utilization efficiency of flat plate solar collector

Abstract

For the last 20 years, solar collectors have been developing rapidly in the use of energy in buildings. Under experimental conditions, the solar energy utilization efficiency (SEUE) of flat plate solar collectors (FPSC) can reach more than 80%, but the engineering application of SEUE is low, and even the collector heating cannot meet the design requirements. In this paper, based on the existing thermal performance of FPSC, the influence of ambient meteorological parameters and hot water system operation parameters on SEUE is studied using experimental tests and analytical calculations. The results reflected that the collectors connected to the auxiliary heaters will affect SEUE, with series-connected systems having greater SEUE than parallel-connected systems. When the solar radiation intensity was low, the SEUE of parallel-connected systems was more likely to be negative. Under calculated conditions, when the water inlet temperature was 20, 30, 40, and 50 °C, the SEUE of the collector was 0%, and the corresponding solar radiation intensity was 113, 184, 225, and 328 W/m2, respectively. Reducing the average water temperature of the collector can reduce the heat loss in the energy conversion process between the collector and the air and increase the SEUE. When the solar radiation intensity was 500 W/m2, the collector inlet temperature decreases from 50 °C to 30 °C, and the SEUE increased from 20.9% to 38.5%. The research results can provide a parameter basis for the design of the FPSC system, especially the connection mode of collector and auxiliary heat device, and the design of system water temperature.