Create own grid?

System
System Posts: 2,511 admin
in Advanced Solar Electric Technical Forum #1
I have a grid tied 3.1KW system with a Fronius inverter that I installed myself. Of course when the power goes off I have no backup power.

I was wondering if one could create their own grid with an off grid inverter with batteries? When the grid power goes off, sync the grid tied inverter to the off grid inverter and have a manual switch to the house loads instead of the grid. One question is if there are no loads, where will the excess power go? Would it fry the off grid inverter? Any thoughts?

Otherwise, I would have to get a hybrid inverter, rewire the panels for lower voltage (250v DC now) and not use the grid tied inverter.

Thanks, Greg
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: Create own grid?

    There have been discussions here and elsewhere... (see this thread for one).

    And, yes, it is possible to connect a 3kW off-grid inverter + battery and use a three kW Grid Tied solar (or wind) inverter to create your "own grid"... And the extra energy from the Grid Tied inverter that is not used by your loads will actually back-drive your off-grid inverter and charge the battery bank.

    However, there is really no good controller/inverter interface at this time to properly control the charging of the battery bank (could over charge your batteries)--so it is very easy to overcharge using this technique.

    So, in the end, it is known to work with several brands/models of inverters, and at least one company is selling based on this principle (Skystream Wind Turbines), and it is unknown all of the issues/reliability/safety concerns that give some "experts" pause.

    If you have the money, can afford to make a few "smoky" mistakes, and have the background to safely make the system work (don't kill utility lines men, or burn down your home)--it can be done.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • System2
    System2 Posts: 6,290 admin
    #3
    Re: Create own grid?

    Thanks, I'm not sure if I want to fry my inverter experimenting. :D
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  • fatheadl
    fatheadl Solar Expert Posts: 31 ✭✭
    #4
    Re: Create own grid?

    you could try this

    http://www.outbackpower.com/pdfs_general/AC%20Coupling%20in%20Renewable%20Energy%20Systems%20White%20Paper.pdf
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  • System2
    System2 Posts: 6,290 admin
    #5
    Re: Create own grid?

    The problem with the Outback inverter it is 120v and my grid tied is 220v. I guess I could use a transformer?
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #6
    Re: Create own grid?

    Or use a Xantrex XW inverter which is 240V output
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #7
    Re: Create own grid?

    The Xantrex XW is a fine solution... Just to round out some more options, Outback offers a couple auto-wound transformers that support the 120:240 requirements. Not cheap.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #8
    Re: Create own grid?

    I don't know that I could build a good wind gennie for < $200. A set of magnets, I think runs about $400:

    http://tech.groups.yahoo.com/group/axialflux/message/1625
    > $17 per magnet. Takes 24 magnets to make Hugh Piggott Axial Flux
    > Permanent Magnet Alternator
    > Steve Spence http://www.green-trust.org
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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