[amluto]

Last year, I had the opportunity to talk to some PG&E-associated contractors [0] who were replacing the distribution transformer serving me. I asked them whether they trusted the anti-islanding protection in everyone’s inverters and whether they would like me to turn off my main breaker. They laughed and said that they couldn’t care less. They were going to intentionally short the secondary circuit if they were doing dangerous work, and if anyone’s inverter was trying to energize it, that was the inverter’s problem.

I’m genuinely unsure what purpose anti-islanding actually serves.

(My inverter is moderately intelligent and formed a one-house microgrid all by itself. That being said, this capability may be at odds with helping the grid survive a major disturbance. When my inverter decides to disconnect from the grid, it cannot support the grid regardless of what its software and the regulators think.)

[0] By which I mean line workers at a company that PG&E contracts with to maintain their distribution network. Apparently PG&E outsources real work. Go figure.

[KennyBlanken]

> I’m genuinely unsure what purpose anti-islanding actually serves.

Scroll up to read about the HNer required to carrying $1M in insurance for having more than 10kW in solar on their roof, which is just...insane. Solar is mired in bullshit to make it seem dangerous, make it look ugly, make it as complex and expensive to install as possible. That's how you end up with regulations requiring what looks like an electrical substation on the side of your home, covered in neon-colored labels. Gotta make sure someone knows the system is "RAPID SHUTDOWN EQUIPPED" from 100 feet away!

Electrical grid operators want you to buy electricity, not make it for them. Their nightmare is becoming "just" a grid.

Their biggest nightmare, however, is you realizing that you no longer need them at all. Lots and lots of people, especially those out in suburban or rural areas, could easily go off-grid these days. Homes are better insulated, heatpumps are quite common, solar costs a fraction of what it used to, lithium ion battery prices are crashing and LiFePo batteries are getting commonplace, etc. So what's a utility to do? Push microinverters that require a grid connection and so on.

[Syonyk]

> I’m genuinely unsure what purpose anti-islanding actually serves.

I think it mostly prevents inverters from trying to destroy themselves feeding into a dead short, or creating weird instabilities - the grid segment is either up or down from the inverter's point of view. Any sane inverter will detect it's trying to feed a dead short and shut down. And if you're grid tied and your grid segment is down, it looks like a dead short.

It's a useful enough filter for people who understand power systems and power system work, because, as your linemen pointed out, if safety is a question, the workers simply create a bolted short across all the phases and neutral, and you're not simply not going to make that ring.

And, yes, migratory line workers are a thing. I don't get it, but relatively few people I've talked to out here (Idaho Power territory) actually work for Idaho Power - it's mostly migratory contract workers doing the power pole inspections and such.

[Veliladon]

> I’m genuinely unsure what purpose anti-islanding actually serves.

Because a typical solar inverter can't handle transient loads. It just spits out whatever power is coming in from the panels. It can't shed if too much is coming in and it can't magically create power to fix a shortfall. The power has gotta go or come from somewhere.

If you have a battery you can soak the transient load and disconnect from the grid and operate as an island but without the grid to act as a buffer for the load the inverter is useless on its own.

[amluto]

Shedding excess power is very, very easy for solar, especially as compared to any other power source. The MPPT can move away from the maximum power point. (Compare to, say, wind or hydro where moving a turbine away from its optimal speed and torque can be quite destructive without extreme care. I visited a small hydro installation with a monstrous space heater to dump power in the interval between when a load disappears and when valves can adjust to reduce the flow of water.)

I am curious how SolarEdge’s inverters reduce output, though. It’s not fundamentally hard, but the inverter does not have appear to have a particularly high speed data connection to the MPPTs, and I haven’t found the underlying mechanics documented anywhere. I’m guessing that the inverter pulls the incoming voltage down such that the MPPTs hit their preprogrammed output current limits and curtail production.

(SolarEdge’s system can’t just dump excess power into a battery — their common configurations have the battery behind a DC-DC converter with considerably lower capacity than that of the inverter’s output. The DC-DC can’t fully absorb the solar string’s output if the sun is shining and an island’s load goes away. The battery itself likely could, at least for a little while, but there isn’t any way for the power to get there.)