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Posted: Fri Mar 18, 2016 9:21am

Post Subject: Solar system

I'm looking at a solar system for y boat, and was hoping for advice on whether the controller I am looking at is up to scratch. I intend to run a 400w system, with two pairs of 100w panels connected in series, then the two pairs themselves connected in parallel, sending 24V to my controller, which is in turn to be connected to a 12V battery bank. I am looking at a 20amp MPPT controller - my understanding is that this will handle 400W at 24V, and covert this to 12V for the battery bank to charge from - is this correct, or will I need either 2 x 20A controllers or a controller that takes more amps? many thanks in advance for your help


Posted: Fri Mar 18, 2016 3:28pm

Post Subject: Solar system

As you do not identify the MPPT controller I can not check its specification but I thought most MPPT controllers could handle 100 volts. If yours can then simply connect the panels can be connected in series unless they are modern 30 volt plus "domestic" type panels. Typical around 21 odd volt panels will give 84 volts when connected in series and this is well within the capability of a MPPT 100V controller. By doing it this way you keep the current and thus voltdrop on the panel to controller cables to the minimum so you can use thinner and thus easier to run cables. The thicker high current cables run from the controller to the batteries via a fuse. However this relies upon the 400 watts worth of panels never being able to supply their full output and that is likely to be the case in the UK, especially if you mount the panels horizontally on the roof. 400 Watts @ a charging voltage of 13 volts gives a theoretical current of just over 30 amps. Personally I would be looking for a higher current controller. I you provide details of the controller and panels I will see if I can be more specific.

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