Measuring Irradiance, Temperature and Angle of Incidence Effects on Photovoltaic Modules in Auburn Hills, Michigan
United Solar Ovonic (USO) installed a photovoltaic (PV) module testing system in Auburn Hills, Michigan (Latitude 42.6978, Longitude -83.2419) in March of 2010 for the purpose of evaluating the impacts of irradiance, temperature and angle of incidence (AOI) effects on PV module performance. We considered various test-bed designs and ultimately, constructed a source-meter-based current and voltage measurement system coupled with a data acquisition system recording readings from weather-station instruments that track solar irradiance, temperature and wind speed. Current, voltage and power observations, correlated to our weather-station device readings, were collected from commercially available PV modules manufactured from mono-crystalline silicon (c-Si), amorphous silicon (a-Si) and copper indium gallium selenide (CIGS). We observed thermal annealing in a-Si and the effects of temperature on c-Si and CIGS. c-Si module temperatures above 25°C appear to diminish power by approximately 0.5%/°C. The results were consistent with our expectations based on existing literature. From this, we infer that the test-bed is effective at measuring module performance.
Our results support, but do not confirm the hypothesis that a-Si modules deliver more energy (kWhrs) per peak-watt (Wp) than other PV materials. Confirming the hypothesis would require both testing a statistically significant number of PV modules and performing a quantitative analysis of the accuracy of the test-bed. This is important because PV is typically sold on a $/Wp basis. The Wp rating is based on a module’s performance under standard test conditions (STC) of 1000W/m2, 1.5 air mass (AM) and 25°C module temperature. A new PV rating system proposed by the International Electrotechnical Commission (IEC) creates a series of testing conditions based on a variety of weather conditions. USO’s PV measurement system is capable of collecting observations fitting most, but not all of these test conditions. Due to the array’s northern location, none of our observations fit the IEC’s high temperature conditions.