An Analysis of Solar Radiation in the Northwestern United States for Photovoltaic (PV) Installations

Global horizontal irradiance (GHI) is the total amount of solar radiation that reaches a point at the earth's surface. (GHI= direct horizontal+ diffuse horizontal irradiance). In this research we analyzed solar irradiance in the Northwestern United States. We did statistical analysis with the data that we received. We first compared forecast model output with measured ground data. Our comparative analysis showed that the forecast model consistently predicts larger GHI values than are measured. Then we compared consecutive five-minute global horizontal irradiance (GHI) averages. Results from this part of the analysis showed that the solar radiation received in each five-minute interval had a large difference from the next interval. We can infer that high standard deviations and absolute deviations we computed were due to cloud effects. The forecast model outputs were collected from the WRF model as run at the University of Washington and global horizontal irradiance (GHI) data was available through the University of Oregon Solar Radiation Monitoring Laboratory.