Insolation

Example of irradiance for a location under different weather conditions.

A Peak Sun Hour (PSH) is a standardized unit that is used to quantify the amount of solar energy that a location receives during an day, month or year. A Peak Sun Hour is defined as 1m² receiving sunlight with a irradiance (sunlight intensity) of 1000 W/m² for 1 hour. The average PSH value for a given location will largely determine the amount of energy that a PV system produces, therefore it is a very important value for PV system design.PSH for a location is based upon real world testing and observation and can be calculated for a particular day as follows:

Peak Sun Hours (PSH) = sum of average irradiance measurement for each hour ÷ 1000 W/m²

Example 1: An irradiance testing station gives you the following data for a particular day. What is the PSH value for this day?

Time	8:00	9:00	10:00	11:00	12:00	13:00	14:00	15:00	16:00	17:00
Average irradiance	200 W/m²	300 W/m²	500 W/m²	800 W/m²	1000 W/m²	1000 W/m²	800 W/m²	500 W/m²	300 W/m²	200 W/m²

Peak Sun Hours (PSH) = (200 + 300 + 500 + 800 + 1000 + 1000 + 800 + 500 + 300 + 200) W/m² ÷ 1000 W/m²

Peak Sun Hours (PSH) = 5600 W/m² ÷ 1000 W/m² = 5.6

Estimating PV production with PSH

The power rating of PV modules is determined by testing under standard test conditions, one of which specifies that the test be performed with light of an irradiance (sunlight intensity) of 1000 W/m². Note: additional loss factors - due to high temperatures, shading, soiling (dirt on module) etc. - must be taken into account to arrive at a realistic estimate of production under real world conditions.

PV source production estimate = PV source power rating × Peak Sun Hours

Example 1: You have a 100 W PV module. It will be installed in a location without shade that has an average daily Peak Sun Hour value of 4. Without accounting for loss factors, how much energy will this module generate on average per day?

PV source production estimate = 100 W x 4 PSH

PV source production estimate = 400 Wh