this post was submitted on 12 Mar 2026
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I had a chat about this with a friend who works for the national grid (UK).
Apparently the problem is keeping the grid balanced and stable. Basically, the grid struggles to react fast, so they plan ahead. Things like large scale solar can provide predictions on output. Home solar can't.
When clouds pass over an area it can cause slumps and surges in the local grid. The more home solar, the worse it gets. The current grid is designed to work top down, with predictable changes in demand. It needs upgrading to deal with large scale bidirectional flows.
The plug in units are (potentially) even more ropey. If used properly, they are no worse than normal home solar. Unfortunately, being cheaper, there are worries over the microinverters not shutting down. Either due to the manufacturer cheaping out, or turning on an "off grid" mode.
There are also worries about overloading household circuits. Back feeding bypasses the household circuit breakers and RCDs. They could overload wall wiring and cause fires, or stop an RCD tripping, allowing for a person to be shocked.
I don't know how much this would apply to the American Grid, but I would imagine it would be worse. Your grid is older and larger. You also use 120VAC which makes the current overload issue a lot worse.
Voltage inside of residences is 120v AC, but its 240v thats delivered to each house. I think a bigger difference is that in the USA that 240v AC is single phase where I believe (Germany included) many nations in the EU are 3 phase.
The USA does have 3 phase power for most commercial applications though.
It's worth noting that this is talking about plug in solar, so would be at standard mains voltage.
1kw would be around 4A in Europe, but 8A in the USA. Also, since resistive losses scale with I^2 that's 4x the heat dumped in the walls.
At least in the UK, they tend to run 3 phase to a road, but only a single phase goes into a given house. You need to get a special hook up to get 3 phase to a domestic premise, and they don't like doing it.
Thats fair.
TIL about the UK electrical system. Thanks!
I'm at the edge of my knowledge but that sounds like it matches the USA system (for the number of phases).
The UK uses single phase to the house. This is provided via one 240v hot and a neutral. Their final distribution transformer bonds one side of the output coil to ground and use it as a neutral, which makes the other side of the coil 240v relative to that ground.
The US uses split phase to the house. This is 240v provided via two opposing 120v hots and a common neutral. Their final distribution transformer is almost identical to the UK version: end to end, they have a 240v output. The difference is that instead of bonding one end of the output coil to ground and using it as a neutral for the other end, they instead bond the center of the output coil to ground and use that as a common neutral for both ends.