Item — HN Reader

Great idea! Want to learn more on the safety though...

> Once in place, people simply plug a micro-inverter into an available wall outlet.

later

>Gründinger and experts at the German Solar Industry Association noted that the devices don’t generate enough power to strain the grid, and their standardized design and safety features allow them to integrate into balconies smoothly and easily.

This seem to talk to the safety of the grid and the balcony. What is done when electricians power down the apartment or worse, the building to work on something? The wires remain energized despite proper distribution panel shut down. Do these setups have auto shut off if they see no other power on the plug they are on? what if it is the building, wouldn't other panels still energize the wires, so they would not shut down? Just asking, as my personal experience is quite hair raising and crispy when it comes to inappropriately de-energized circuits. ;)

7 comments

Anti‑islanding detects the power frequency and constantly tries to shift it. If the grid is on, its frequency won't budge, so the anti‑islanding doesn't trip. If the grid is off, the frequency shifts and it shuts off. A second one would just make it shut off faster.

Curious: is anti-islanding an actual feature, or a necessary behavior of any power source that adds power to the grid? I can't imagine how a second power source would work at all if it weren't syncing to the main source's AC phase. So it seems that if you implement the syncing, you get anti-islanding for free (assuming you handle the case of a missing main source phase by not providing power at all).

This is a newbie question, and I look forward to learning how it's more complex than this.

If the question is "is it an 'actual feature' or is it 'necessary behavior'" then the answer is: Yes.

Simple grid-tied microinverters are completely incapable of doing anything without a grid to work with, and this is necessary: A non-synchronized AC generation source can't survive long before becoming an expensive puff of smoke instead.

Anti-islanding is an actual feature that is also inherent in the design of grid-tied inverters: When there is nothing for them to sync to, they output nothing.

It’s not necessary in that the inverters need to support it (they could just do randomly staged power ons, and the first one could pick the phase).

However, there’s a problem in addition to electrocuting utility workers (the ones around here assume islanding during outages, so that’s less of an issue now).

Say you plug the microinverter into a 16A 120V outlet in the US, and the power goes out while you’re running a 240V 40A clothes dryer. The island is definitely going to collapse at that point, and might do bad stuff on the way down.

Even in that weird non-existent corner case instance, it is a necessary function because a hypothetical microinverter is completely and utterly incapable of kickstarting a grid.

You could totally have half a dozen microinverters scattered around your household, connected to each other but temporarily not to the neighborhood distribution network.

I could have that; many homes in the world do have that. And when the grid dies, the microinverters all die with it.

Thanks, I think that answers my question. It seems like there is a lot of regulation to enforce a behavior that was already necessary for microinverters to work at all. But given the risk (utility worker electrocution during outages), I also understand why utilities are extra-conservative about it.

> Do these setups have auto shut off if they see no other power on the plug they are on?

Yes. This is Germany we are talking here. I doubt any other country has higher (and more annoying) safety standards.

Well of course but the manufacturers of the micro inverters sure try to cheat:

https://www.heise.de/news/RelayGate-Deye-Solar-Microinverter...

From what I remember, it turned out that the electronics were sufficient. Though the chance of issues (e.g. in case of a software but) were/are increased.

Well, it turned out that the micro inverter in question did not contain the necessary physical relay to show conformity with the claimed norms on electric safety (related to disconnect from the grid in case of grid failure).

They only had a software implementation and were forced to send all customers in Germany a free relay dongle to ensure safety.

Micro inverters pretty much all have automatic shutdowns in these situations. They can ‘boost’ the phase/voltage, but won’t replace it if it is missing.

It's called "NA Schutz"[1] and is required for all german micro-inverters by VDE-AR-N-4105:2018. Which in turn is national law following EU directive.

[1] https://de.wikipedia.org/wiki/Netz-_und_Anlagenschutz

That they shut off is important for a more obvious reason: The microinverters plug into a normal outlet. So the flow of power is invented to the normal situation, here the prongs of the plug are energized. The body that writes the electrical regulations of course wanted a mandatory special plug and socket that had to be installed by a licensed electrician, which mostly makes balcony solar financially a non starter. Finally they relented after much discussion.

These microinverters do not output anything if they do not detect the grid.

> What is done when electricians power down the apartment or worse, the building to work on something?

Well, I hope that any competent electrician will measure if there's still any voltage on the circuits after pulling the breakers.