[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.)