No Grid on a Grid

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scoot scoot
scoot scoot Registered Users Posts: 3
in Grid Tie and Grid Interactive Systems #1
I have 78 solar panels on grid with enphase micro converters . I want to play with wind generation. What I would like to do is tie a new battery inverter into household system. This would supplement my solar production. BUT I also want the wind system to continue to feed the house if the grid goes down. I need to know if there is an automatic switch that would not let the wind energy back charge the grid for safety reasons but give my house emergency power.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #2
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    Re: No Grid on a Grid

    You can get Grid Tied Inverters rated for use with wind turbines (SMA Windy Boy series for example). But, as you say, no emergency backup power.

    Another method is a Hybrid AC Inverter... Uses a battery bank and a Hybrid inverter that can run GT mode when the grid is up, and switch over to run Off Grid mode when the utility is down. And you can run solar/wind/water etc. to dump power to your battery bank, and the Hybrid inverter takes care of the Grid UP and Grid DOWN situation (as with any wind turbine project, you probably will need a dump load or similar to manage the battery bank state of charge--and it interactions with GT/OG modes).

    The last method is to get the Windy Boy type GT Inverter and setup a standard off grid inverter + battery bank system. When the utility is down, the Off Grid inverter setups a "local or micro" grid which can supply power from the battery bank or receive power from GT (solar and wind) inverters to share the loads and even recharge the battery bank.

    This AC coupled (or back driven) AC inverter is becoming a bit more common--But it is still something that requires a lot of thought and the right hardware. There are more off grid inverters that have the AC Coupled logic built into them now (SMA has a whole product line, XW from Xantrex/Schneider, the next model from Magnum Inverters???, and such).

    The short answer is for random/short outages (days to a week or so) is usually a backup generator. For longer outages or places with unreliable power (weeks/months/daily outages), then a battery based system is probably the answer.

    But then you are looking at the question of simply using a Solar+Wind solution that charges a battery bank behind a standard off grid inverter (which may not be any less expensive than a standard hybrid grid inverter) or go with the GT inverter and Hybrid inverter solution...

    Usually, you have to do a couple paper designs and see what works best out for you.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
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    Re: No Grid on a Grid

    If I understand correctly the answer would be "yes".

    The wind turbine can be used to keep the batteries charged (you will need a dump load to divert the energy to once they are charged: turbines should not be allowed to "spin free").

    The batteries can power an off-grid inverter with built-in transfer switch. While there is utility power available it will power the loads connected to the inverter's AC OUT. If the utility goes down the inverter will supply power to those loads (using the batteries which are kept charged by the turbine).

    There are variations on this general theme, including having the system separate from the grid and manually (or automatically if you can build the circuit) switch them to utility if the batteries are too low. None of these options are particularly efficient as they involve energy transfer in to and out of batteries. It is quite a common practice in those parts of the world where the utility grid is unreliable.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #4
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    Re: No Grid on a Grid
    scoot scoot wrote: »
    I have 78 solar panels on grid with enphase micro converters . I want to play with wind generation. What I would like to do is tie a new battery inverter into household system. This would supplement my solar production. BUT I also want the wind system to continue to feed the house if the grid goes down. I need to know if there is an automatic switch that would not let the wind energy back charge the grid for safety reasons but give my house emergency power.
    Understand that whether you are talking about wind or about solar, emergency backup power comes from batteries. Wind and/or solar recharges the batteries when you are running off grid, but the power you use is buffered by the batteries.
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