Understanding Peak Sun-Hours
The solar PV sector often uses the term “peak sun-hours” for system design calculations. However, what does it really mean? Is it the same as the hours of sunlight received?
The answer is No.
Imagine a place that receives 5.5 hours of sunlight daily during the summer. Of course, due to the rising and setting of the sun and the variations in solar energy received during the day (due to variable cloud cover, rain, dust in the atmosphere etc.), the amount of energy received is not constant over the full 5.5 hours (refer fig.). It will be highest at solar noon (the point where the sun is at its highest in the sky), and lowest during sunrise and sunset.
However, PV system designers are interested in the average solar insolation for a location, which when multiplied by the number of sun hours gives them the total solar energy received at the location (in kWh/m2/day).
This value is exactly equivalent to assuming that the sun shines at its maximum intensity (assumed to be at 1,000 W/m2) for a fixed number of hours, and by doing so delivers the same amount of energy as received during the total number of sun hours. This hypothetical equivalent number of hours is called “peak sun-hours”.
For instance, a place that 7 kWh/m2/day as average solar insolation can be said to have 7 “peak-sun hours” (7 X 1000 W/m2/day).