Forum Discussion

freetheheal's avatar
freetheheal
Explorer
Jun 08, 2020

Basic Questions on Solar Install

I'm finally getting rid of the generator and looking to install solar. Right now I have a 2000W inverter and 450AH of lead acid batteries. I'm looking at installing (3) 175W panels and an MPPT charge controller. I'd like to run my idea by the forum and make sure I'm not missing something.

My run from the panels to the charge controller is about 25'. From what I've found I should wire the panels in series and run a 10 gauge wire. I'm looking at the Renogy Rover 60 mppt controller and that can handle up to 140V which is well within the parameter of the open circuit voltage of the 175W panels which is 24.3V per panel and allows room for additional panels down the road if the need arises. Does anyone see an issue with this or something that I'm missing?

From the charge controller to the batteries I am going to run 8 guage wire (5') with a 60amp fuse.

And between the solar panels and charge controller I was going to mount a 10amp fuse (the solar panels optimum operating current is 8.62amps).

Does this seem like a good plan so far? Am I missing anything? Thank you for your input and help.
  • Boon_Docker's avatar
    Boon_Docker
    Explorer III
    Jun 08, 2020
    Yes, sounds like a good plan. You will have only a 0.2 volt voltage drop from the panels to the controller by running in series.

    I would install an inline circuit breaker instead of a fuse between the panels and controller. That way the circuit is protected plus you can also take the panels out of circuit if need be.

  • time2roll's avatar
    time2roll
    Nomad
    Jun 08, 2020
    24.3 Voc seems low for a 24v panel and high for a 12v panel. Double check the spec.

    Take additional precautions with 75+ volts. This can bite pretty hard.

    #10 down to the controller is fine. #8 is fine but seems a bit light... If buying wire I would go #6.

    Fuse from the panels is not needed but can serve as a disconnect. Verify it is rated for the voltage.

    Probably only need 40 amp controller unless you expect to expand.

    Looks like a great system.
  • BFL13's avatar
    BFL13
    Explorer II
    Jun 08, 2020
    freetheheal wrote:
    I'm finally getting rid of the generator and looking to install solar. Right now I have a 2000W inverter and 450AH of lead acid batteries. I'm looking at installing (3) 175W panels and an MPPT charge controller. I'd like to run my idea by the forum and make sure I'm not missing something.

    My run from the panels to the charge controller is about 25'. From what I've found I should wire the panels in series and run a 10 gauge wire. I'm looking at the Renogy Rover 60 mppt controller and that can handle up to 140V which is well within the parameter of the open circuit voltage of the 175W panels which is 24.3V per panel and allows room for additional panels down the road if the need arises. Does anyone see an issue with this or something that I'm missing?

    From the charge controller to the batteries I am going to run 8 guage wire (5') with a 60amp fuse.

    And between the solar panels and charge controller I was going to mount a 10amp fuse (the solar panels optimum operating current is 8.62amps).

    Does this seem like a good plan so far? Am I missing anything? Thank you for your input and help.


    Three 175w with "optimum current" (Imp I guess) 8.62 means Vmp is 20.3v. Isc will be higher than Imp 9a? and Voc 24.3

    So expected max amps to battery to decide wire gauge controller to battery: (panels aimed at high sun--flat on roof you get less but do worst (best?) case here)

    3 x 175 = 525w with 10% heat loss = 472.5w lose 3% line loss (WAG on 25 ft #10 copper one way at 8.62a) = 458w input to controller. Say controller is 4% inefficient, so output is 440w

    amps to battery no line loss:
    440/12v = 36.7a
    440/14.5= 30.3a

    So yes, #8 is a good wire gauge for that run from controller to battery.

    On a perfect clear day in May at 49N Lat, you could expect an AH haul of about 190AH with that set-up. So you should be good with the 450AH bank not to need the generator much in the sunny half of the year in the Lower 48 states.

    A few cloudy days in a row though, and out comes the generator! In the darker and cloudier half of the year, you will need the generator more often.

    You will do well with that set-up, but you can't change the weather, so hang on to the gen.
  • 2oldman's avatar
    2oldman
    Explorer II
    Jun 08, 2020
    You don't need to fuse panels. I have 6 12v panels in series and have rarely seen anything over 110 volts.

    New member after 9 years. Don't see that every day.
  • Lwiddis's avatar
    Lwiddis
    Explorer II
    Jun 08, 2020
    Ten gauge will work, eight is better from panels to the controller. Six from the controller to the batteries. Do it once. Do it more than minimum. “Dumping” the generator isn’t the best plan IMO. If you have a generator available, you won’t need it. If you don’t...
  • freetheheal's avatar
    freetheheal
    Explorer
    Jun 08, 2020
    Thanks for the added clarity. Sounds like I should run #8 wire and I can get MC4 connectors for it which is nice. I also may need to think about adding a 4th panel. The circuit breaker is also nice to take the panels off line if I need to.
  • freetheheal's avatar
    freetheheal
    Explorer
    Jun 08, 2020
    BFL13 wrote:
    freetheheal wrote:
    I'm finally getting rid of the generator and looking to install solar. Right now I have a 2000W inverter and 450AH of lead acid batteries. I'm looking at installing (3) 175W panels and an MPPT charge controller. I'd like to run my idea by the forum and make sure I'm not missing something.

    My run from the panels to the charge controller is about 25'. From what I've found I should wire the panels in series and run a 10 gauge wire. I'm looking at the Renogy Rover 60 mppt controller and that can handle up to 140V which is well within the parameter of the open circuit voltage of the 175W panels which is 24.3V per panel and allows room for additional panels down the road if the need arises. Does anyone see an issue with this or something that I'm missing?

    From the charge controller to the batteries I am going to run 8 guage wire (5') with a 60amp fuse.

    And between the solar panels and charge controller I was going to mount a 10amp fuse (the solar panels optimum operating current is 8.62amps).

    Does this seem like a good plan so far? Am I missing anything? Thank you for your input and help.


    Three 175w with "optimum current" (Imp I guess) 8.62 means Vmp is 20.3v. Isc will be higher than Imp 9a? and Voc 24.3

    So expected max amps to battery to decide wire gauge controller to battery: (panels aimed at high sun--flat on roof you get less but do worst (best?) case here)

    3 x 175 = 525w with 10% heat loss = 472.5w lose 3% line loss (WAG on 25 ft #10 copper one way at 8.62a) = 458w input to controller. Say controller is 4% inefficient, so output is 440w

    amps to battery no line loss:
    440/12v = 36.7a
    440/14.5= 30.3a

    So yes, #8 is a good wire gauge for that run from controller to battery.

    On a perfect clear day in May at 49N Lat, you could expect an AH haul of about 190AH with that set-up. So you should be good with the 450AH bank not to need the generator much in the sunny half of the year in the Lower 48 states.

    A few cloudy days in a row though, and out comes the generator! In the darker and cloudier half of the year, you will need the generator more often.

    You will do well with that set-up, but you can't change the weather, so hang on to the gen.


    Do you mind explaining some of your numbers further? What are the numbers 12V and 14.5 represent from your equation 440/12V=36.7a and 440/14.5=30.3a? And what is the amperage telling me from those equations. Sorry if it seems like a dumb question I'm just not following all of it.

    Currently if we're conserving battery power we can stay 3 days without using the generator and bringing the batteries down to 70% (so using about 45amps per day). But more then likely once we have solar we'll be using around 70amps a day running things we would wait to run until we were on generator power.
  • Boon_Docker's avatar
    Boon_Docker
    Explorer III
    Jun 09, 2020
    freetheheal wrote:
    Thanks for the added clarity. Sounds like I should run #8 wire and I can get MC4 connectors for it which is nice. I also may need to think about adding a 4th panel. The circuit breaker is also nice to take the panels off line if I need to.


    Running your panels in series (75 volts @ 8 amps) for 25 feet.

    10AWG wire gives a voltage drop of 0.20 volts.
    8AWG gives a voltage drop of 0.13 volts.
  • BFL13's avatar
    BFL13
    Explorer II
    Jun 09, 2020
    Watts is volts times amps. More battery voltage for the same controller output watts means fewer amps. The trick is to get the batteries up in voltage and keep them there long enough to get them nearly full before dark. (not likely to get to true full while still camping)

    Your peak state of charge will be just before supper. Then you use the microwave and then watch a movie and furnace at night then make breakfast maybe use a toaster and the MW for that. Now you can recharge the batts as best you can before supper as long as it doesn't rain.

    So keep the generator. You don't need more panels and watts on the roof. If there is no sun, more panels won't help. If there is sun, you have enough. Rving off grid you need some of everything to get by for whatever happens.

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