Jan, the main advantages to hooking your panels up in series is to reduce the wire size from the panels to the controller and gain efficiency during less than perfect weather. If you were to hook up your 3 panels in series you would get roughly 50 to 60 volts in full sun at roughly 5-6 amps. Versus needing a wire that can carry 15-18 amps in parallel.... Then on cloudy days when your panels do not generate anything now you will produce roughly 20-30 percent of their rated capacity using an mppt controller. It is the way to go... Maybe not now but eventually.
Jan White wrote:Thank you! That's helpful.
So there's nothing actually harmful with having 3 panels for 4 batteries; the harm happens when we try to use the system as if we had 5 panels.
So now that I'm looking at charge controllers (mppt), I see that an appropriate size for the number of panels we currently have is 40A. I'm thinking about the future though. So I'm thinking I should get a 60A to allow for panel purchases. Using a 60A charge controller for three 100W panels is probably another example of imbalance, but there isn't any harm done by it, unless we try to use the system more intensively than its limitations (in our case the power going into the batteries). Do I understand?
Side question. Is there a benefit to wiring panels in series, only to drop the voltage down again for our 12V battery bank? You mention getting higher amperage, but does that really matter for our size bank?
Jan White wrote:Hmmm...
I think our batteries are 90Ah. The only thing it says on them is 220 minutes runtime 25A @ x temp, etc. So 220/60*25=91.6 repeating.
Which, going by your rule of thumb, means 9A charging @ 13V x 4 batteries equals 468. With fudge factor for poor conditions, that would bring us up to 6 panels. A 60A controller won't cover that many on a 12V system. Can I ignore the poor condition fudge factor somewhat if I'm using an mppt controller?
Jan White wrote:
The Epever brand is what I was looking to get anyway, so I'll go ahead with that. I think I'm going to go with a 60A one. It'll take 150V, so I should be good if we decide to add two or three panels at some point and wire in series.
Michael, the way you calculated the necessary amperage of the charge controller was unfamiliar to me. I'm going by combined wattage of panels 300/lowest voltage in system 12*safety factor 1.25. Do you think that's overkill?
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