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Old 28-11-2013, 05:39   #31
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Re: Fixed Solar Installation

Pardon my ignorance, but when you say your "pontoon", what do you mean? Is that the pontoon of a catamaran trimaran? Or is it some sort of float that's part of your mooring?

Re charging from solar, two things come to mind. I just skimmed this thread, so sorry if I'm repeating....

1) All batteries have a self-discharge rate, and different batteries are better or worse in this respect. But something in the C/50 to C/100 range can be expected. This might be the primary source of your discharge. Also, CO detectors are typically always on and will draw a little too, along with any fire suppression system you might have. They are all small loads, but a small load running 24x7x365 becomes a big load when charging sources are limited.

2) The self-discharge rate also creates a minimum charge current. Your bank is about 500ah, so at C/100 you can expect a self-discharge rate of 5A, and 5A is essentially a break-even charge current. Anything less than that and you aren't really charging the batteries - just slowing the discharge. Additionally, for effective charging you need enough current to raise the battery voltage to at least it's constant-voltage charge voltage. That's about 13.6V for 12V, or 27.2 for your 24V bank. I think something between C/50 and C/20 is a good minimum charge current, with C/20 being clearly better. The difference comes down to whether you want something that will maintain a full charge (C/50), or actually be able to bring the batteries up to full charge from some state of discharge (C/20).

From this you can estimate a range of solar power needed to accomplish what you want. C/50 on your 500ah bank is 10A charge current @27.2V. Allow for 80% efficiency compared to the peak, ideal output represented in the panel ratings, and you need.... crunching numbers .... about 340W of panels.

Oh, on the self-discharge issue, I think I read that AGM batteries have a lower self-discharge rate than flooded batteries. The C/50 to C/100 that I used in this example is for flooded batteries, so it's worth checking the specifics of your batteries - it might improve the situation.

twistedtree is offline   Reply With Quote

installation, solar

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