[TheSpiceIsLife]

When the grid goes back up the system would check the grid frequency and phase, and slowly match that waveform over a few minutes by making light changes.

When the two are aligned within a good-enough tolerance the system will switch back to it's regular state of mains + solar ( + batteries + wind + generator + etc / whatever).

These are all solved problems with commercial off the shelf components.

[zaarn]

Are these commercial off the shelf components as cheap as a microinverter?

[TheSpiceIsLife]

I just typed microinverter in to Google and clicked on shopping.

It looks to me like microinverters are a commercial off the shelf product?

Will a microinverter do all of the things a multi-component phase-syncing system with automatic transfer switches do? I don't see why a microinverter can't be built with these components integrated. I can't tell you if such a unit exists as I'm not well versed in the product range.

As far as a price comparison goes, I guess it only makes sense to compare a like-for-like system?

[zaarn]

From what I know, you will need a sync check relay, ie a relay that only closes when you're synced up. Those are generally available for 1MW and upwards (one manual notes a minimum constant load on the internal grid of 500 kW or it won't work), look like about the size of half of a car battery, at a price of "contact our sales team".

Could it be made cheaper? Probably. If you get it wrong, the grid probably doesn't care but you'll briefly pump about 500W into the device that is supposed to have 500W going out of it. The reason these are big and expensive is that it requires significant safety gear so nothing explodes even in the worst case. And that safety gear is expensive. So you sell it to people who not only can afford it but also really really need it (ie, 1MW and upwards where you enter the domain of "can fry small section of grid")

[stephen_g]

Any old IGBT or even just a highly spec’d MOSFET paired with an optoisolator (a couple of dollars of parts) could do that for a small system, based on input from the inverter’s existing controller.

The specialist devices for large installations you’re talking about are only expensive because you need more expensive parts for the far larger amounts of current you’re handling (and probably because they’re made in lower volumes than commodity inverters), not because they’re doing anything particularly difficult.

[TheSpiceIsLife]

I used to work with a few (16 odd) Siemens 200kVA UPS that did the syncing.

There’s no technical reason the requisite electronics can’t be built on a much smaller scale.

Home grid-tie solar inverters are clearly capable of syncing, so the electronics are already present.

[zaarn]

grid-tie inverters are capable of syncing to a present signal, what they can't do is provide their own waveform and sync that to the grid when it comes back online.

[Dylan16807]

Providing a 60Hz waveform and syncing it to the grid the easy part. You could make a standalone device that does it out of a twenty cent microcontroller.

[londons_explore]

Yes. It's all pretty much the same hardware with different firmware.

Manufacturers of solar hardware love to charge you an extra $1000 for that extra firmware though...

[zaarn]

You need more hardware when you want to sync to grid after being off grid. You need one on the inverter and a seperated output, most grid-tie inverters simply have one port for everything. If you use one port for everything you can hardly sync the house grid to the external grid since you can't both provide power and try to sync the phase.

[namibj]

Err, you can provide the power, you do need another voltage sensing connection to the grid though, and might want an automated breaker to not have to attend the device and re-connect inverter and grid once sync is complete. If the inverter is properly fused, you should even get away with a LED or a small display that shows you whether it's safe to reconnect or even how long until sync is complete.