Learning Center

Power Production

Inspired Designs

Expert Installations

Decades of Experience

Professional Service

NREL Solar Irradiance Map U.S.
Image Courtesy of NREL
Peak sun hours MD DC region commercial solar installations

Peak Sun Hours

       The average daily sun hours  in units of kWh/m2 per day is referred to as “peak sun hours.”  A peak sun-hour is roughly the amount of solar energy striking a 1-square-meter area perpendicular to the sun’s location over a 1-hour period straddling solar noon in the summertime.

       So we can compare apples to apples, the amount of power is standardized at 1,000 watts (1 kilowatt) hitting that 1-square meter surface. By adding up the various amounts of solar irradiation over the course of a day, and counting them as units equivalent to 1 solar-noon midsummer hour (1,000 watts per square meter for 1 hour), we get a useful comparison number—the peak sun-hour.

      Being able to calculate the peak sun hours is useful for solar installations because PV modules are often rated at an input rating of 1kW/m2.

Solar Insolation

      The number of average daily sun hours is referred to as “solar insolation.”   Peak sun hours refers to the solar insolation which a particular location would receive if the sun were shining at its maximum value for a certain number of hours. Since the peak solar radiation is 1 kW/m2, the number of peak sun hours is numerically identical to the average daily solar insolation. For example, Baltimore receives 4.7 kWh/m2 per day, which then means that Baltimore  receives 4.7 hours of sun per day at 1 kW/m2.

       The daily amount of solar radiation striking any location  varies from sunrise to sunset due to clouds, the sun’s position in the sky, and the atmosphere. Maximum solar radiation occurs at solar noon—the time when the sun is highest in the sky, compared to the rest of the day. Sunlight in the morning and evening does not deliver as much energy as it does during midday because at low angles, there are more atmospheric filters to sunlight. Besides day-to-day differences, there are also seasonal effects.

       In midsummer, due to the sun’s higher position in the sky, an hour of sunshine packs more energy than the same hour of sunshine in the winter.  Power production for commercial solar installations will be greater during the summer because of the sun’s more direct position over an installed PV array.

Solar Insolation from monitoring

Ready to take the first step?

Get a complimentary contact-free quote by this time tomorrow