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post #16 of Old 02-22-2012
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Originally Posted by jkzdad View Post
so if I employ 4 kyocera panels above my bimini each 135KW how do you back into what that would supply to the batteries for power on a daily basis. I would guess you would apply the amount of KW in the panels against your most demanding 24 hour period of need. I am trying to measure what the boat can handle conservatively with panels vs. worst and then average amp hour needs.
That would give you 135W x 4 = 540W. Figure about 5 hours/day x 540W for fixed panels (probably less when you're actually sailing, since the boat is swinging around), and you get 2700 Wh(watthours). If you divide that by 15 (remember, charging voltages are higher than 12V; and you have to account for inefficiencies in the charge controller -- even an MPPT controller ain't perfect), you get 180Ah/day. I would round that down to 150 Ah/day, since there are all sorts of other inefficiencies involved in such a system, and that gives you a pretty good estimate of the maximum charging capability of your panels. If you are going to go with that sized PV system, I would try to keep your daily usage somewhat below that (maybe 25%, or 112.5 Ah) to give you enough charging capacity to bring you batteries back up after a few cloudy days in a row. Your battery bank should be large enough to last at least 4 or 5 days w/o any charging (unless you want to run the engine, or have a wind turbine), so you'll have to have four or five pairs of golfcart batteries (or the equivalent capacity). If you want to go with your original 500 Ah estimate (which I still think is way too high) you need to scale everything (panels, batteries, controller, et cetera) up by a factor of four or five.

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