Insolation measures the amount of solar energy available in a given area in a given time. For industrial, commercial and residential solar power systems, insolation is commonly measured as kwh/(kwp*y), or kilowatt hours per year per kilowatt peak rating. These are general measurements, as the solar constant varies with the Earth-Sun distance and solar cycles.
Factors that affect insolation include the time of day (length of light's path through the atmosphere based on solar elevation angle), cloud cover, relative humidity and the presence of airborne impurities, such as ash and smog. The map below provides estimates of insolation for the United States. For insolation estimates outside of this area, please use the following Solar Insolation Map (pdf). For additional information on determining the estimated solar hours in a given area, please contact us.