How to get 240V split phase for off-grid

Peter_V
Peter_V Solar Expert Posts: 226 ✭✭✭
in Off Grid Solar & Battery Systems #1
Can you wire any of the smaller, say 300 watt, inverters together to get 240V split phase or is a 120v/240v transformer the cheapest way to do this?

I'm trying to come up with a way to bootstrap my grid tied array during an extended power outage. I don't really expect one, but it's better to be prepared and not need it than the other way around.

I'm already wiring in a generator inlet with lockout so I can bring my house up off grid during power outages, but I'm trying to figure a way to do it with an inverter instead.

I have a Prosine 1800 that I use in my workshop and I can dig up a 1-2,000 watt transformer. That's probably the way I'll go, but I'm trying to make sure I consider all of the available options.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: How to get 240V split phase for off-grid

    In general inverters not designed to be "stacked" won't; there's no way to synchronize the frequency. Using an autotransformer is best.

    But back-driving a grid tie inverter from an off grid one has more than its fair share of problems too. There's more than one thread about it on the forum. Synchronization troubles, over-powering problems, et cetera. Some have done it with generators too. It's also likely to void any warranty as it is clearly not "intended use".

    Maybe you want to look into the new Xantrex 600 Volt charge controller and a small, stand-alone emergency off-grid set-up. Still cheaper to use a gen for emergency power.
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  • Peter_V
    Peter_V Solar Expert Posts: 226 ✭✭✭
    #3
    Re: How to get 240V split phase for off-grid

    One of the advantages of micro-inverters is they will drop out one at a time as you approach the voltage cut off. This is due to slight manufacturing differences in cutoff voltage plus differences in the lengths of wiring.

    I know several people who have successfully tested bringing up Enphase inverters using backup generators. In fact I've yet to hear about anyone that was unsuccessful at trying this.

    From what I understand, the only remaining concern is the voltage limit. I believe the voltage drop in the wiring as well as the transformer will be sufficient to protect the Prosine/etc.
    I can always modify the transformer windings if needed.

    As I said, this idea is for extended power outages. I won't bother with it for typical outages that only last a few minutes to a couple hours.
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  • System2
    System2 Posts: 6,290 admin
    #4
    Re: How to get 240V split phase for off-grid

    I have enphase as well and are looking for the same thing. I have seen some 240v inverters at The Inverter Store but I am not sure how picky Enphase is about the voltage.

    I was considering a generator as well but if I was going to use that I might as well just have a large generator and be done with it. A solar "primer" for the Enphases would be ideal.
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