Three grid-connected monocrystalline silicon arrays on the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland have been instrumented and monitored for one year, with minimal gaps in the data sets. These arrays range from 73 kW to 271 kW and all use the same module, but have different tilts, orientations, and configurations. One array is installed facing east and west over a parking lot, one in an open field, and one on a flat roof. Various measured relationships and calculate standard metrics have been plotted to compare the relative performance of these arrays in their different configurations. Comprehensive performance models have also been created in the popular modeling software PVsyst for each array, and its predictions using measured on-site weather data are compared to the arrays measured outputs. The comparisons show that all arrays typically have monthly performance ratios above 0.75, but significantly differ in their relative output, strongly correlating to their operating temperature and to a lesser extent their orientation. The models are within 5 % of the monthly delivered energy values except during the winter months when there was intermittent snow on the arrays and during maintenance and other outages.
Citation: ASME Journal of Solar Energy Engineering: Including Wind Energy and Building Energy Conservation
Pub Type: Journals
photovoltaic (PV) array, data acquisition, performance, PVsyst model, solar, temperature