After years in the sun, even the best quality plastic begins to take on some surface roughness and hazing. The diligent boat owner immediately reaches for his buffer and compound, certain that a shiny panel is a happy panel. In fact, panels are often ruined by attempts to restore the plastic.
To determine the benefits, if any, of polishing, we took sheets of 1/8-inch acrylic and lightly abraded them with 400 grit sandpaper, approximating a severely weathered panel. We compared the light transmission with a non-abraded sheet at a variety of light angles, using a camera light meter as our guide.
With the sun at 90 degrees to the panel, the glossy panel transmitted 10-15 percent more light; however, when the angle declined to 60 degrees, there was no measurable difference. Based on our observations, it appears that light surface scratches on the solar panel surface have no significan’t effect on output.
The plastic also yellows beneath the surface of the panel. But polishing isn’t going to do much about that; it is too deep in the plastic to compound out without serious risk of damaging the panel.
Although a semi-flexible panels can be bent to a 1-meter radius, that doesn’t mean they like it. Ask any honest manufacturer, and they will tell you that a semi-flexible panel mounted in such a way that it experiences even minor repeated flexing-for example, on a loose bimini, or even worse, across a bow or ridge-is destined for an early death. The same thing happens when you polish them. Even if you place them on a flat, firm surface, both machine and manual polishing subject the panel to thousands and thousands pressure and minor flexation cycles, which causes growth of micro cracks within the solar cells.
In the cases we’ve heard of, panels typically lost 50 to 80 percent of their output capacity. The semi-rigid panel manufacturer Solbian, on the other hand, allows hand or low-speed machine polishing, but their panels are more substantial than most; we can only advise extreme caution.
To keep your panel happy just clean it. An occasional wipe with vinegar will remove lime spots. Any of the cleaners recommended for soft vinyl are a safe bet (Protecting Clear Vinyl Windows.Practical Sailor, January 2014). In our view, the risk of doing further damage outweigh any noticeable gains in performance. For more on selecting and installing solar panels, see the March 2018 issue of Practical Sailor online.