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Plug-In Solar Panels Are Starting to Sprout in U.S. Backyards |Ten U.S. states have legalized systems that can be plugged into standard wall outlets. The technology typically does not require permits (www.nytimes.com)
submitted 1 month ago by to c/nyt_gift_articles@sopuli.xyz
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[–] 4 points 1 month ago (5 children)

I wonder how this works. Maybe it only functions when it detects the wall has 120V power? If it backfed during a power outage it would be like plugging a generator into your house with a cheater cord (never, ever do that) which can step your generators 120V back up into 12-25kV through your local transformer and zap the linesman working to fix your outage on the neutral (a generator backfeeds onto the neutral not the "hot" sides of the circuit. I.e. the "safe" wire suddenly has thousands of volts on it)

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  • [–] 4 points 1 month ago (3 children)

    The European systems definitely have line sensing. They need to, to stay in phase. If the power goes, so does your solar.

    I think some systems can be turned on from an app, but default to off, without mains as a reference.

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  • [–] 2 points 1 month ago (2 children)

    Huh, I wonder how that works. How can it differentiate grid power vs the power it's supplying to the wall? All I can guess is maybe it polls for grid power by cutting its own supply for a few milliseconds to see if the grid is still there? Couldn't find anything getting into the details online...

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  • [–] 3 points 1 month ago (1 child)

    I believe they try and shift the phase slightly. If the mains in present, it will overwhelm the inverter and keep it locked, or at least show up as a distorted waveform. If it can swing the phase freely, then there is no mains power, so it shuts down.

    E.g. (in Europe) an oscillator with a frequency of 49.95 will be dragged to the mains 50.00. By measuring the frequency it will read 50.00, if it drifts low, then it is not phased locked, and so will shut itself down till 50hz reappears.

    Think of it like how metronomes come into harmony. Only 1 is a little desktop unit (your inverter) and the other is building sized (the grid).

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