Sunpower Modules in Off Grid systems

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I have 2 Sunpower 225 modules and I would like to use them in a mobile off grid system. By mobile in mean in a trailer that can be moved to provide power for small events. I think the best controller will be the Morning Star TriStar MPPT - 45A. I plan to charge a 12V battery bank and connect a Suprex 2500W inverter. ( I have the modules and inverter already, but not the charge controler)

The problem is that the SPR 225 mods need a positive ground to operate properly. (I have a lot of grid tied experience) Morning star says I can add 1 ground point in the system on the positive side. It can be on the module side, the battery side or load side. The The problem comes in the inverter - it has a ground terminal on the back. So if I ground the positive side of the modules, what do I do with the ground terminal on the inverter?

My other question is how do I ground a mobile system? Do I need to pound an 8' ground rod in the earth every time I set it up? There will be a lot of people (possibly inspectors) around this system and I want to make sure the AC side of the system is safe. Can I ground to the frame of the trailer?

Thanks, Solarob

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,501 admin
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    Re: Sunpower Modules in Off Grid systems

    I believe the SunPower need a positive ground referenced to a real ground rod. Positive or Negative grounding to an RV chassis is probably not going to do too much one way or the other (drag chain/rubber discharge strap dragging on the earth/road may help).

    Positive ground of your RV DC power system may cause grief with any DC appliances (DC car radio, LED fixtures, possibly DC fans, DC power bricks for computers/TV's/etc.). So--unless your DC power is purely for an inverter (TSW may be a better choice), it may not be a good idea to positive ground.

    Note: you could get into some weird configuration problems--such as remote displays for an Inverter, communications ground polarity problems with computer interface (such as RS-232 to laptop), etc. Not saying you will--but positive grounding is "different enough" that you cannot assume everything will play nicely together.

    I believe Tony/Icarus has some older 90 watt SunPower panels connected to his negative ground cabin power system--And, as far as I know, he is very happy with them.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Sunpower Modules in Off Grid systems

    Welcome to the forum.

    In a mobile application there is no Earth ground. Quite often the ground consists of the chassis (-) and nothing else. Some equipment (charge controllers/inverters) will have their DC (-) tied to their cases. Ordinarily this does not present a problem, but the (+) ground Sunpower panels want the grounding mass tied to plus. Here's a thread that describes the situation with a fair amount of detail and some reference links: http://forum.solar-electric.com/showthread.php?t=4718