[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.

[zaarn]

And then you'd still have to switch over and you'd need a sync check relay for safety (if you don't and the microcontroller is off because you forgot a comma somewhere, your inverter explodes).

Additionally producing the clean sinewave that you'd need for this is not that easy, atleast not at the quality levels you want for this (if your DAC that produces the wave is off by 1% then at a 2kW load you're going to burn up 20W somewhere that doesn't like 20W being burned up)

[Dylan16807]

Redundancy and fail-safes are important but can also be inexpensive. Most of the expense comes from being a niche product right now.

How is being off by 1% going to hurt anything? I'm quite sure my mains voltage is already more than 1% off.

If I get solar it had better not explode every time my air conditioner kicks on.

[TheSpiceIsLife]

I'm no electronics engineer, but don't regular home UPS units already do all of this? I'm talking about the type of units sold by computer and office supply shops to provide backup power for home / SOHO IT devices.