Effects of Operating Temperature on the Heat Transfer Characteristics of Photovoltaic Systems in the Upper Midwest

Abstract

This paper presents the heat transfer characteristics of a stationary PV system and a dualaxis tracking PV system installed in the Upper Midwest, U.S. Because past solar research has focused on the warmer, sunnier Southwest, a need exists for solar research that focuses on this morepopulated and colder Upper Midwest region. Meteorological and PV experimental data were collected and analyzed for the two systems over a oneyear period. At solar irradiance levels larger than 120 W/m2, the array temperatures of the dualaxis tracking PV system were found to be lower than those of the stationary system by 1.8 آ°C, which is a strong evidence of the different heat transfer trends for both systems. The hourly averaged heat transfer coefficients for the experiment year were found to be 20.8 and 29.4 W/m2 آ°C for the stationary and tracking systems, respectively. The larger heat transfer coefficient of the dualaxis tracking system can be explained by the larger area per unit PV module exposed to the ambient compared to the stationary system. The experimental temperature coefficients for power at a solar irradiance level of 1000 W/m2 were −0.30% and −0.38%/ آ°C for the stationary and dualaxis tracking systems, respectively. These values are lower than the manufacturer's specified value −0.5/ آ°C. Simulations suggest that annual conversion efficiencies could potentially be increased by approximately 4.3% and 4.6%, respectively, if they were operated at lower temperatures.