Yes, there are serious safety concerns. Both islanding, which is where a circuit is hot when it shouldn't be, and from a circuit overload.
Your circuit breaker protects your circuits by putting all the load (eg your microwave) on one side, and your supply (mains power) on the other. If too much load is present, the circuit breaker trips.
However, plugin solar puts invisible supply on the load side, which your circuit breaker cannot see. Let's make an absurd example so you can see what the problem is, then scale it back.
Imagine someone buys 5 panels that can each supply 5amps. They plug them into outlets on a 40 amp circuit. They then proceed to run their toaster, microwave, vacuum, and hair dryer. They can draw 65 amps through the wires before the circuit breaker trips. (40 from mains, 25 from the panels)
Let's say they had a good electrician who installed 6AWG wiring on that circuit, which is rated for 50 amps. The circuit breaker used to trip at 40, so no problem. But now up to 65 can go across the wires and suddenly you are exceeding rating for wires.
Now you might say, "most of these are 3.5 watts, and they clearly say don't use more than one". But I say that's a "good intentions solution". We should make it mechanically impossible to do the wrong thing. Maybe these panels could try to communicate over the electrical wires, and if they detect a signal from another panel they should self limit. Maybe we need to rethink circuit panel design. But as it stands people will absolutely buy one of these, decide they love it, and then buy 4 more.
> Imagine someone buys 5 panels that can each supply 5amps. They plug them into outlets on a 40 amp circuit. They then proceed to run their toaster, microwave, vacuum, and hair dryer. They can draw 65 amps through the wires before the circuit breaker trips. (40 from mains, 25 from the panels)
Circuit breakers trip bidirectionally, so the circuit breaker itself would protect if too much current is drawn through to the mains panel.
How, precisely, would you get 65A through the wiring on this 40A circuit, if I drew 40A of consumption and had 25A of supply?
The 25A cancels out the 40A, so the upstream feed would only see 15A total. You do get 65A of total current drawn through the breaker panel, which is a concern, but the supply wiring would not see 65A. Subpanels (which, this would be a subpanel if it only had 40A capacity) are typically going to be just fine.
Plug in solar inverters turn off when they detect a loss of grid power. Anti-islanding is a requirement for them to be certified.
This moves the problem though.
In the original example, RCD/circuit protection is regulated on the _property_ side, e.g UK has EICR for electrical install. Once its done for a property, its good until next inspection (in theory)
This moves the protection to the _appliance_ , which while it needs to meet certification, is much harder to police a consumer electronic device, than a physical unmovable premise.
I think these are great, but there will inevitably be devices that don't implement the spec correctly that still get sold to willful or unwillful consumers that result in danger to everyone.
Ok, for those models, strike concern number one.
anti-islanding is required for all models of plug-in solar
https://news.ycombinator.com/item?id=50070844 : UKGOV has gone for the warning notice solution.
I think this is probably fine, since UK circuits are typically 20A. Apart from fault current (which would have to be line to line, since line to ground would trip the RCD), it's quite hard to end up with more than 20A of stuff plugged into regular sockets unless you're overinvested in portable heaters. All the big stuff - cookers, heat pumps, showers - is on separate breakers from the sockets.