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dnix71:
Still risky. If anything fails and you backfeed the grid, the power company will know, and you may cause damage or personal injury to others. That is part of the high price for an inverter capable of doing that. Two completely unconnected systems is fool-proof and much less expensive to operate.

The hard part of that arrangement is deciding which appliance is connected to which system. That one is your best call.

joestue:

--- Quote from: dnix71 on February 04, 2024, 12:05:20 PM ---Still risky. If anything fails and you backfeed the grid, the power company will know, and you may cause damage or personal injury to others. That is part of the high price for an inverter capable of doing that. Two completely unconnected systems is fool-proof and much less expensive to operate.

The hard part of that arrangement is deciding which appliance is connected to which system. That one is your best call.

--- End quote ---

The issue isnt backfeeding the grid when it goes down, unless its just your local, single pole transformer fuse that blows. Your system will not be able to power the neighbors house and their 4500 watt water heater when it turns on.

I've only found one account online of a backfeed situation, a whole neighborhood and a dozen generators, and im not sure i believe it. Likely the power company lineman thought the circuit was off when it wasn't.

I trust the ul1741 standard that just about everything complies with will work in a grid down environment, as you will need a minimum of 20kw system to supply even a couple houses.

My concern is the power company finding out the meter is turning backwards. Some say it will record it as if power is being consumed. I called my utility and they wouldn't tell me. A friend is on the same utility and his milling machine spindle sends 25kw back up the power grid for 100 to 200 milliseconds during spindle stop. They dont care about that. But, that 2000 joules is not enough for the meter to spin 1/4 turn backwards, each turn of the meter is 7.2 watt hours or 25,920 joules.

Also the utility has no incentive for you to use their grid as a battery due to the duck curve. They may let you if you sign up for 8 cents off peak and 30 cents on peak kwh.

So either use a non grid tie system that can't backfeed, or trust that a dual redundant non backfeeding grid tie system was installed without the utility permission and take the chances that if it does backfeed, they will disconnect your service.

As long as you dont backfeed more than 6000 joules, the meter wont flag the regen power on many smart meters because they use a mechanical 2 flag quadrature encoder to count the turns.

The problem would be more like 50 watts backfeed for an hour, 6000 watts for a tenth of a second wont matter

dnix71:
I have been told the new meters here will set a flag if you backfeed. They are also network capable and if you disable or try to disable remote disconnect features like time of day or loading shedding arrangements they pay you to accept (disconnect a/c or hot water during peak loads) they will know and fine you big time. You can get an free app for your phone that will show realtime use. It makes no sense to risk your account just to save a few dollars backfeeding sometimes without permission. If you just don't plug it in to their system, they cannot and will not know.

MattM:
Tyrants.  Especially if the danger from backfeeds are minimized with controllers.

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