[ghubbard]

Great article, lots of technical details. A simple answer to the 'Why' can be found in the middle under the 'Off Grid Without Batteries' headline.

> If you have a typical grid tied system (microinverters or normal string inverters, so easily 95+% of installed rooftop solar), the system is technically incapable of running off grid (without additional hardware). There's no waveform to sync with,

[jccalhoun]

I agree that there are a lot of good technical details. However, I wish the article had started off by saying, "It's Not Power Companies Being Evilly Evil - It's Homeowners Being Cheap" instead of waiting more than half way through it.

[raverbashing]

"there's no waveform to sync with" is technically correct and a very poor excuse

A residential no-break has no waveform to sync with as well.

Something capable of syncing to the grid and then more or less keeping pace even if the main grid goes down should cost very little today. (And when the grid goes back it shouldn't have drifted too much unless something ridiculously big happened)

[avianlyric]

It might be worth reading the rest of the article. Which points at that the big reason why you can run off grid is because solar panels without a battery store are effectively incapable of usefully powering variable loads without:

Only running at a fraction of their max available output allow enough headroom for high peak startup draw from loads, and headroom for clouds and planes passing overhead.

Frequently cutting in and out as the load regularly exceeds available supply.

Keeping the frequency sync is the easiest problem to solve, the article even covers what would happen if you tried to use a little generator to produce a sync signal.

[zaarn]

The grid isn't a fixed frequency. While on average the grid doesn't change phase, the reality is that the grid may be out of phase by several seconds most of the time.

When the grid comes back from a blackout, chances are that it browned out beforehand so your sync is to a low frequency and coming back it'll be high frequency because the grid wants to compensate for loads jumping back on.

Additionally the components to generate your own waveform are cheap, yes, but not that cheap, adding them to the microinverter would increase cost quite a bit.

And you'd still need a transfer switch because if you happen to be 180 degrees out of phase, which CAN HAPPEN then your panel will behave like a dead short at double grid voltage. The current flow will definitely exceed the maximum tolerances and the magic smoke goes out.

You will absolutely need a transfer switch just so you don't fry all your devices the moment the grid comes back. Even then, syncing to the grid is a rather delicate maneuver since the grid will be constantly changing phase and it'll be simpler to shut down all inverters, connect back and have it all run back up on the grid itself.

[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.