A PSH is that time of the day when the intensity of the solar radiation reaches 1kW/m2 over a period of 1 hour. It is an ideal measure which would require the angle of inclination of the panel to the sun to be perpendicular and that the panels have zero shading. It therefore varies greatly during the day depending on the location of the sun and the cloud cover. Areas closer to the equator receive more sunlight with the maximum irradiance coming in at about noon.

See the below table for regional Peak Sun Hour (kW/m2/day) figures in the U.S.A. from the N.R.E.L.

NREL Sun Hour Data for the USA


1PSH = 1000W/m2 (or 1kW/m2) of sunlight per hour

PSH does not give the hours that the area receives sunlight i.e. from sunrise to sunset. Instead it is the total insolation received for the whole day over a 1m2 area divided by the PSH figure of 1kW/m2. Certain areas in Arizona receive total solar irradiance of 7000W/m2 over a period of 1 day. We divide this figure by 1000W/m2 to get 7 peak sun hours.


The curve below indicates a correlation between the total solar insolation received for a day and the sun hours.
Daily Solar Insolation Curve



The importance of this figure is that it enables you to gauge the amount of power your solar system will generate. When the irradiance on the panel is at its peak (1kW/m2) a 250W panel will ideally output 250W ignoring the resistance and temperature losses. Therefore an area like Chandler, AZ with 7 sun hours a 250W panel will ideally output 1750Wh.

For more information on Solar and assistance in designing a solution contact our specialists here or through +1 480 218 1877 or +1 410 877 6887.
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