The Impact of Shade on Your Solar Panel

Many of our motorhomes have a lot of gear on the roof that can cause shading on some of our panels, which can reduce efficiency.

I’ve been having a few discussions recently regarding increasing solar to be able to be off grid for extended periods. So I thought this might be an interesting distraction from Covid 19.

Here is some data I have been collecting from my own system since installing 3 x 400W panels in January.

shad on solar panel2
The front panel incurs shading from the satellite dome every day.
Photograph by
Wayne Hunt

To fit all three on the rear of our rig, the front panel is hard up against our satellite dome so it does incur shading every day.

The two rear panels are wired in series and are through a 60amp Victron MPPT controller, the front panel is through its own 30amp Victron MPPT controller.

Since installation, the rear two panels have generated 59 Kw/h of energy and the front panel 28Kw/h.

So the single shaded panel has delivered 47.5% of the energy generated by the two unshaded panels.

Now the two in series are obviously running at twice the voltage of the single panel, they are all wired with 4.0mm2 tinned cable, so the series pair will also have a slight efficiency gain over the single panel due to reduced volt drop, in reality maybe 1%, so 2.5% to 3.5% differential that can be attributed to shading.

“In this real life example I was expecting the impact to be much greater as the front of the panel is within 2cm of the dish dome.”