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Re: Solar Panels on Bimini with Split Backstay

 

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Don,

There are so many variables that contribute to real life panel performance, it is important to not get too caught up in ¡°precise numbers.¡± I think Calder uses the nominal voltage for his estimate, 12v. Anything from bird poop, to salt and dust buildup, to clouds, and shading can degrade panel performance. And in practice my Solar panels rarely hit the 150w output they are rated for. Even direction of travel. Today heading north under absolutely clear skies, my starboard panel produced 890 Wh. The port panel, next to the radar pole only produced 300 Wh due to shading a really small portion of the panel, this all because the sun was behind us. Had we been heading south, both panels would have produced in the same neighborhood. Nonetheless, I was still happy with the 1200 Wh (100ah) they produced, more than I ?consumed today.

My understanding of flexible panels is they are designed to flex over a firm surface, like a curved cabin top or hard dodger or bimini and not designed to be flexed. There are very fine wires and connectors in the panels, repeated flexing can cause these to break. The advice to mount them on something that won¡¯t flex as much is good advice.?

Separating the panels into port and starboard makes more sense to me over orienting them athwartship. A shadow from the mast or sails will affect both panels if mounted athwartship but only one panel if the panels are oriented fore and aft.

Here¡¯s the Calder article I referenced. It is getting a bit dated, however the basic information is still valid.





Dave
Second Star
S362 #113
Fair Haven, NY/Lake Ontario

On Apr 13, 2025, at 8:11?PM, Oceans via groups.io <oceans100t@...> wrote:

Dave,?
Thanks for the valuable info from Nigel Calder. ?So much for the advice of the marketing departments! ?
FYI, The panels under consideration are Semi-flexible - SunPower Monocrystalline - Shade Tolerant as sold by Custom Marine Products. ? The Ocv for the 120W is 23.1, for the 140W is 25, and for the 155W is 28.9. ?Cell Efficiency for all panels is 24.4%, and all are Grade A+ SunPower cells. ?I'd like to believe these are reasonably high quality panels. ?Please confirm or deny my assumption. ?Each of the 3 panels will be connected to separate Victron Smart Solar MPPT 75-15 Solar Controllers. ?Is a rough estimate of improved efficiency with these cells and controllers possible?
Using Calder's formula, for the 465W array I am dividing the 1400Wh by 12.8v to get 109Ah/day, and for the 395W array x 3 = 1185Wh/12.8 = 93Ah/day. ?Does the formula call for division by 12.8 for AGM's or some other value like 12.0 or 13.0?
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Brian,
I too have been working through the challenge of how to best place the panels on the Bimini. ?Custom Marine suggests using a sheet of 4mm Policarb-Double Walled under the solar panel to smooth out sharp the curve of the center bow to allow the panels to be placed lengthwise rather than athwart ship. ?I was concerned concerned about UV degradation when I researched this product. ?One of the flat sides is UV protected but the sides, which would be also exposed to sunlight, are not. ?
I cut some 1/4" masonite to match the size of the panels as an experiment and realized they do a nice job of smoothing out the sharp ridge caused by the center bow. ?I then tried placing the masonite on the bottom of the Bimini and it worked even better. ?As a result I plan to use 1/4" Starboard under the Bimini by modifying the center zipper to hold the pipe in place. ?I will send photos in a separate email.
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Don Fleming
Duet
S-38-1 #77
Hudson River
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