Solar Insolation

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.

PV Array Tilt and Azimuth Angle

The maximum amount of solar insolation falls on PV module when it is facing exactly perpendicular to the incoming irradiance. This is achieved through the adjustment of the array tilt angle (relative to the horizontal ground surface) and the array azimuth (east to west facing)

Dual axis tracking arrays continuously change the array tilt and azimuth to keep the PV module constantly perpendicular to the incoming irradiance.

Single axis tracking arrays have a fixed tilt angle but continuously change the array azimuth to keep the PV module facing as close as possible to the incoming irradiance.

For fixed flat plate PV modules the tilt and azimuth is generally selected to optimize the array output (net energy kWh generate) over the whole year. The fixed PV arrays at the DKASC are all set at a tilt of 20 degrees and azimuth of 0 degrees (Solar North). The exception to this is the solar compass that also has east facing (Az = 90 degrees), west facing (Az = -90 degrees) and flat (tilt = 2 degrees).

Temperature

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/Dirt

Dust and dirt block light to solar panels reducing their output. Horizontal installations are generally avoided, to prevent dust build up.

At the DKASC all PV arrays are given an annual full cleaning to remove dust. The time and dates of this cleaning are posted in the notes on the data section.

Shading

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.

At the DKASC we aim to ensure that know arrays are subject to shading from trees, buildings or other arrays within the hours of 08:30 and 16:30 each day.