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Keep the Shade OFF Your Solar Panels

Did you know that a tiny bit of shade on your solar panel can reduce its power output considerably?

Consider this: Bright sunshine mid-day in Portimao, Algarve, Portugal. Should be making heaps of power. Yet the instruments tell me that I am barely breaking even with the fridge.

Why is that? The sun, and the wind are to the south. That means that the boat is pointing into the wind and sun. The boom is not tied off to one side, which means that it is along the centerline of the boat. That means that there is a shadow from the boom (and mast), that extends aft onto the solar panels. The shadow is not large – just the width of the cradle cover, so it covers maybe an eight of the area of the solar panel.

I then go and pull the boom across to one side and tie it off. Now there is no longer the boom shadow on the panels, though there is still some shadow from the mast, which is a lot smaller.

Suddenly our power output went up to +7 amps.

My understanding is that the reason for this is that solar cells that are in the shade have a high resistance and so actually detract from the energy produced by the unshaded cells. In other words, it is not just that they don’t produce, they actually cut down the output that is being produced in the rest of the panel.

The moral: Always tie the boom off to one side so the panels aren’t shaded, and do whatever else you can to avoid any shadows on the panels.

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