Many factors influence the output of a photovoltaic array:
Solar insolation is the energy in sunlight.
The solar insolation that a location receives over a day is expressed in peak sun hours. This is the number of hours of sunlight at 1000W that would be equivalent to the total energy received at a location during the day.
The sunlight received at a site will be affected by the position of the sun, the length of the day, and the amount of clouds and other interference in the sky.
Insolation can be either “direct” or “diffuse”. Direct insolation reaches the earth’s surface in an uninterrupted path from the sun. Diffuse insolation is scattered light reflected from particles in the atmosphere.
Solar panels generally convert direct insolation into electricity more effectively than diffuse. Some photovoltaic materials use diffuse insolation more effectively than others.
The output of a solar panel decreases as temperatures increase.
High ambient temperatures limit the amount of electricity a panel can produce. Solar panels also generate their own heat as they produce electricity.
Dust and dirt block light to solar panels reducing their output. Horizontal installations are generally avoided, to prevent dust buildup.
Shade blocks direct insolation from the panels.
A small amount of shade has a large impact on the output of a solar panel, as it changes the flow of electricity through the panel.