solar panel charge controller location relative to battery and distribution panel

jagmanjoejagmanjoe Registered Users Posts: 2
I wired my home for a lot of low voltage lighting throughout the home when I built it and currently have the 12v batteries in the garage with a distribution panel within about 15 feet of that. For a couple of years now I have been just periodically charging the batteries with a regular charger. I have decided to put a solar panel or two on the roof and set up a charge controller to keep the batteries charged. From the location of the solar panels to the batteries at present is at a distance of about 30 ft. My question and what I am considering is am I better running heavier wire down the 30 ft to the batteries and locate the charge controller there or, would I be better off building a box on the roof near the panels (flat rooftop deck) and set up the batteries and charger there at a short distance from the panels and make the longer run after the batteries to the distribution panel? I live in FL so I am sure I would have to insulate the box and perhaps even set up a small fan to circulate air through the box so it would not get too hot. Oh and added to the mix is that I live on Tampa Bay so salt air is also a consideration.

I do also plan to eventually set up a separate grid tied system for the house but keep this system separate.

Any thoughts and suggestions would be greatly appreciated.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: solar panel charge controller location relative to battery and distribution panel

    Welcome to the forum.

    Normally you are better off having the charge controller near the battery. That way the cables between can be kept short and fat. This is important because it is the circuit that will have the greater need for reduced Voltage drop. Even with a PWM type controller, the charging of the battery is going to be at <15 Volts whereas the panel Vmp should be at least 17.5. Even so 30' of distance is getting into appreciable Voltage-drop without careful wire sizing.

    This brings up the really important question: how much battery capacity do you have? If it is enough to require around 400 Watts or more for charging purposes you are in the area where higher Voltage array & an MPPT controller makes sense.
  • jagmanjoejagmanjoe Registered Users Posts: 2
    Re: solar panel charge controller location relative to battery and distribution panel
    Welcome to the forum.

    Normally you are better off having the charge controller near the battery. That way the cables between can be kept short and fat. This is important because it is the circuit that will have the greater need for reduced Voltage drop. Even with a PWM type controller, the charging of the battery is going to be at <15 Volts whereas the panel Vmp should be at least 17.5. Even so 30' of distance is getting into appreciable Voltage-drop without careful wire sizing.

    This brings up the really important question: how much battery capacity do you have? If it is enough to require around 400 Watts or more for charging purposes you are in the area where higher Voltage array & an MPPT controller makes sense.

    Thanks for your quick response, Cariboocoot.

    Right now I am using a single deep cycle marine battery (not the proper type and I plan to change that) which requires recharging about every 10 days with the current led lighting usage. I do plan to add a few more lights to this 12 volt circuit but not too many more needed. I also plan to add a separate grid tied system of about 2kw with separate panels and battery bank for the main house in the next couple of years.

    I guess my real concern with this is if it would be more efficient to have the long run between the battery bank, charge controller and the solar panel or keep them close to the solar panel, subjected to more overall heat since they will be virtually outside in a box, and have the long cable run from there to my distribution circuit? I recognize that the wiring for both will have to be heavier gauge to limit the loss either way. I hope to get away with one solar panel of about 150 or 200 watts tied to one or 2 proper batteries for this lighting circuit given the limited power consumption and figuring on the overall regular ability to produce solar power here in Florida.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: solar panel charge controller location relative to battery and distribution panel

    The main problem is that in a strictly 12 Volt system (panels at Vmp 17.5) you are dealing with low Voltage everywhere, and the V-drop is going to be an issue on all conductors. It doesn't matter much if it's panels to controller or controller to battery or battery to loads.

    The one advantage to putting the long run between panels and controller is that you can run higher Voltage array and then down-convert to system Voltage with the right controller thus reducing power loss from V-drop. But MPPT equipment is expensive and it usually isn't worth investing in for a small system.

    One panel of 150 to 200 Watts tied to two batteries of any capacity is bound to be a failure. For one thing you're just guessing about capacity. You need to know what the load demand is and size the battery accordingly. Then you need to get enough panel to recharge that battery. Starting with the panel size first and working backwards is a formula for failure.

    Demonstration:
    200 Watt panel will produce about 11 Amps of current for a 12 Volt system (assuming the Voltage matches, which is unlikely these days; usually 12 Volt panels are less than 150 Watts). That would be right for 220 Amp hours @ 12 Volts with no daytime loads as it supplies a bare 5% rate - providing the weather is good. There's zero margin for error here.
    That much battery could give you about 660 Watt hours DC @ 25% DOD, a good functional rate.

    Now, is that how much you use on average or is it greater/lesser? Without knowing you either have a system that doesn't work or one that costs too much for what it does.

    Normally a 12 Volt system using two GC2's (220 Amp hours @ 6 Volts) is the cheapest power base you can get, but requires more like 400 Watts of panel for charging.

    One odd thing you can do to overcome the V-drop issue is to purposefully use "GT panels" with their Vmp around 30 on a PWM controller and let the Volt difference between them and the battery be lost to the line drop. The current will remain the same, but you "accept" the power loss and still have enough Voltage to charge with.
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