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4x36v panels to charge 12v battery … waste of sun?

PhoenixUK

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Apr 5, 2022
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Hello newbie here, can you tell? ???‍♂️

So I’ve managed to purchase quite cheaply, 4x 36v 250w solar panels ?? .

I’ve got a 50a Solar charge controller that works with 12,24 and 36v.

I have a single 12v 110ah deep cycle battery currently. Is it a waste of sun to use this battery? Would I be better off using a matched pair or a triple bank to 24 or 36v, or will the charge controller just charge a 12v battery with 36v panels faster, without wasting the energy?

I need to know if I need to get a 12,24 or 36v inverter!

Thank you in advance for any wisdom you can send my way! ??
 
Do you have a PWM or MPPT solar charge controller?

You have 1000W of solar panels. On a 12V battery that has the potential for about 80A of charge current. On a 24V battery it would be up to 40A of charge current.

If you were to use the 50A SCC on a 12V system then any time your panels could produce more than about 650W the extra power would go to waste.

If you were to use the 50A SCC on a 24 system then you could easily make full use of the 1000W of solar. You could even add another panel or two.

The decision can be narrowed down by the size of the inverter you need and how well your panels will actually perform in your setup. You will rarely get the full 1000W out of the panels. You could actually wire them in 2S2P on a 12V system. Point 2 more easterly and 2 more westerly. Then you will get more power longer through the day. But that may be overkill for a single battery.

Ultimately you should do a power audit and determine your actual power needs. Then determine how much battery and solar you really need.
 
Will it be a "waste"? Well, it won't cost you anything, you've bought the panels, any excess production is free. On the other hand it will have the ability to charge a lot more batteries than you have, so start shopping for a larger battery system if you have a use for one.
 
There are simple formulas we use to scale the various components we install. Looking at your panels you divide the wattage by the charging voltage and get an output amperage value. I always subtract out a fudgefactor for panel derating. So, your 1000W of panels will produce....

(1000W/12.5V charging) X 85% = 80Amps
(1000W/25V charging) X 85% = 40Amps
(1000W/50V charging) X 85% = 20Amps

Batteries like charging at a certain rate, maybe 1/8th of C is optimal for lead-acid, while 1/4th C is optimal for Li. So, the amperages will charge a...

80A X 8 = 640Ah 12V battery
40A X 8 = 320Ah 24V battery
20A X 8 = 160Ah 48V battery

cut those amphour sizes in half for Li

So, use the examples to size your equipment to what you have. Your charging rate is huge for just the 12V battery you have, but if wired four of them in series to get 48V, then it would be somewhat larger than average.

BTW, your 250W panel voltage that produces power is most likely ~30.0V. That's the Vmp. 36V is likely to be the open circuit voltage (Voc) when no power is flowing.
 
will the charge controller just charge a 12v battery with 36v panels faster, without wasting the energy?
There’s unharvested watts, never ‘waste.’

In your case a single battery won’t do much overnight or cloudy days. But in sunshine you can use the watts ‘real time’ with the single battery as a big capacitor.

You need to state your goals to figure out charge controller and inverter. I can’t even speculate what to suggest, although prior posters have suggested logical routes to achieve a likely goal.
 
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