Polishing Solar Panels

Our sunny optimism soon loses its shine.

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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 significant 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.

Practical Sailor has been independently testing and reporting on sailboats and sailing gear for more than 45 years. Supported entirely by subscribers, Practical Sailor accepts no advertising. Its independent tests are carried out by experienced sailors and marine industry professionals dedicated to providing objective evaluation and reporting about boats, gear, and the skills techniques required to cross oceans. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser who has been director of Belvoir Media Group's marine division since 2005. He holds a U.S. Coast Guard 100-ton Master license, has logged tens of thousands of miles in three oceans, and has skippered everything from pilot boats to day charter cats. His weekly blog Inside Practical Sailor offers an inside look at current research and gear tests at Practical Sailor, while his award-winning column,"Rhumb Lines," tracks boating trends and reflects upon the sailing life. He sails a Sparkman & Stephens-designed Yankee 30 out of St. Petersburg, Florida.

3 COMMENTS

  1. How come apparently the only allowed solar panels on a boat have to be flexible? Even though those are 1) wildly overpriced 2) hugely underpowered 3) grossly prone to self destruct
    The only advantage I see is they weigh a lot less than the full blown glass-panel-aluminum-cadred counterparts. But I’ve seen people mount them on beefy (BEEFY!) stainless steel frames – where’s the logic in that?

  2. As a licensed electrical engineer who has specialized in solar for the last 15 years and who just finished the install of 450W of SunPower flexible modules on my 36′ cutter, I can tell you this article is spot on. DO NOT polish or flex flexible modules any more than you have to. DO NOT drill holes in them or stich them with zippers, as is becoming common – you have invalidated the warranty and doomed your panels to a premature death. The best of the flex modules will most likely last 5 to 10 years and the best of the rigid framed modules 20 to 30 years. Rigid frame with glass facing are the best option IF you can come up with a good way to mount them – a solar Bimini being one of the best. So why flex modules then? Because on my boat they were the only thing that would reasonably fit without making the boat look ugly.

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