Doomsday and GT Inverters Reuse?

bart
bart Solar Expert Posts: 30 ✭
in General Solar Power Topics #1
I know the GT inverter is designed to shutdown in the event of utility failure to prevent islanding. And hopefully the utility is restored within a few hours so it's never big deal.

But I started thinking about a prolong power failure lasting weeks or months - some doomsday event for example. Here I have enough panels to generate 324+ volts and about 23 amps and it's completely useless without the inverter. I suppose a solution would be batteries or generator, but it adds expense and maintenance for something that may never happen.

It just seems to me there should be someway to put these idle panels to work during my doomsday event ;). I searched for a DC to DC converter, but didn't really find anything that could convert higher 324 plus volts to some usable voltage outside and isolated from the grid.

So I ask, have any of you thought about what options you might have to convert or reuse your GT system to get usable power?

Thanks, Bart
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: Doomsday and GT Inverters Reuse?

    You can setup some (brand/models of) True Sine Wave Off-Grid Inverters and battery bank and connect your GT inverter to one (behind a transfer switch) and actually run the Off-Grid inverter + GT inverter.

    The Off-Grid inverter sets the voltage and frequency. The GT inverter supplies all the power that it can.

    If the load is greater than the GT inverter output--both inverters will support the load. If the GT inverter is less than the load, the excess power will go backwards through the Off-Grid inverter an actually charge the battery bank. Note that the Off-Grid inverter has to be at least rated for the same or greater power vs the GT inverter output.

    MSW type inverters will probably not work (not sine wave required by GT inverters). And the Off-Grid inverter does not manage the battery bank state of charge--so you have to manual monitor or setup an external charge controller of some type (dump load or turn off the GT inverter).

    Also, the Off-Grid inverters are not rated for this mode of operation--so it is not designed/tested for this type of operation.

    There is SMA's Sunny Island inverters/systems that are designed for exactly this type of operation--but they are not cheap in the US.

    And, it is possible that the latest software update for Schneider (aka Xantrex) Hybrid GT/Off-Grid XW Inverter / Charger may now regulate battery charging (change the output frequency to > 60.5 Hz and the GT inverter will shut down). I have not seen any details--so cannot tell you if this is a supported feature or not yet.

    There have been a few threads here about "AC Coupled" (I call it backdriven) GT/Off-Grid inverters here... But other than Solar Guppy trying this with an XW inverter and Skystream originally selling a Outback inverter system using this topology--I have not seen much other real world use yet).

    With the XW, it does both Grid Tied and Off-Grid operation--so if you rewire your panels to Vmp-array of ~80-100 VDC, you can have a nice GT/Off Grid system without the extra fuss.

    Otherwise, many of us GT inverter folks have asked for a high voltage battery charge controller--even simple, smaller, does not have to be ultra efficient, etc.--that would operate with a 200-600 VDC array so that we can charge a small battery bank in emergencies--but the answer is that the high voltage front end is expensive and inefficient for a battery based charge controller... I guess too there would be the question of how many units would be sold to folks with GT inverters who want a no-fuss small battery backed system.

    So far, ain't happening.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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