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Comment by gnicholas | Hacker News Reader

Super useful. Pacific Gas & Electric (which powers much of CA) recently announced that they may pre-emptively shut off power to certain parts of Silicon Valley out of concern for potential fires. In the article I read, they mentioned that even home solar wouldn't work, which seemed crazy. I can now see why this is the case, and what folks should do (get a transfer switch and generator) to be able to power their home with their solar panels.

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Unfortunately, adding a generator and a transfer switch will probably not enable you to get power from the solar panels. You'll also need an inverter that's designed to operate off grid; the anti-islanding feature on a normal grid tie inverter will prevent it from providing power when the grid is gone.

There are a few ways that anti-islanding systems can work, but it's reasonable to imagine that the inverter is measuring the impedance between its output and a nominal AC source: the power grid. If that impedance is too high - and it will be unless you've got a rather large generator - then the inverter will not source power.

Can you please elaborate about the transfer switch and generator - how to use them?

What about just using batteries?

Typical grid-tied solar system would still require a transfer switch, either auto or manual, they're called break-before-make transfer switches because they disconnect the mains supply before switching over to the battery + inverter system or generator. These transfer switches are mechanically interlocked so it's not possible to have both supplies connected simultaneously as this would generally be release-the-magic-smoke catastrophic.

Typical auto transfer switches are fast enough that computer equipment etc won't notice.

Edited to add: if you want truly uninterruptible power then you should do what data centres do: everything runs off the UPS all the time (well, all the computers, maybe not all the cooling system), the only thing that changes is the supply: either mains, batteries, solar, or generator. Or some combination of batteries + the other three.

There's another UPS-source option, which is also my favorite, flywheel!

Back in the 00s I visited a DC that two very large flywheel UPS that were being trialed to replace the battery room.

Flywheels are alive and well in the DC industry. They are used for those crucial seconds while the generator starts up. And as a backup for the UPS-es. (After all, those batteries might not be in top shape all the time.)

Though I imagine eventually battery tech will take over.

If the flywheel can be integrated in to the generator design then generator startup can be almost instantaneous. Synchronisation would still take a few moments.

I don’t know if anyone is building systems like that though?

Yes, they are. Hitek builds those. The 2007 outage of 365 Main in SF, which took down many major web sites, was due to control problems with a set of ten of them.[1] Each unit had a motor/generator, a flywheel, and a Diesel engine on the same shaft. There's a free-wheeling clutch between the Diesel generator and the rest of the system, so the Diesel does not rotate when idle. The Diesel is started by its own starter motor, and when its RPM reaches that of the generator, the clutch engages and it starts powering the generator.

PG&E had a transformer fire which caused large voltage swings. The flywheels kept the generators turning, and the ten Diesel engines started OK. Then outside power came back up, and after a time delay, the Diesels shut down. Then outside power failed again, and because of a timing incompatibility between the power control and engine control, some of the engines would not restart that soon. There was a minimum "off" time on the engine; it had to stop before it could be restarted.

The engines that did start were not enough to handle the load; they overloaded and their controllers shut them down, shutting down the whole data center.

[1] https://www.datacenterknowledge.com/archives/2007/07/24/gene...

Thanks for the info. I used to work in a data centre in Adelaide doing physical infrastructure and security, so this is right up my alley.

> release-the-magic-smoke catastrophic

What's your source for the first part of this phrase?

It's a running joke. https://en.wikipedia.org/wiki/Magic_smoke

Also fun is looking at all the components that have released their magic.

Dave Jones has a good video on it (well series to a degree): https://www.youtube.com/watch?v=SoeVNaz7KGc

The Jargon File.

Magic smoke is injected into electronic components at the factory, in order to make them work. If you let the smoke escape the package, your part has failed permanently. But as long as the smoke remains inside, there is still a chance you can repair any failure by cooling the part off for a while.

> Pacific Gas & Electric (which powers much of CA) recently announced that they may pre-emptively shut off power to certain parts of Silicon Valley out of concern for potential fires

Huh, where can I read about this?

Even just going to pge.com i get an interstitial about it, but no detail.

A couple links:

https://yubanet.com/regional/pge-shutting-off-power-during-h...

https://www.mercurynews.com/2018/06/12/pge-could-shut-off-po...

TLDR: Power lines are a cause of wildfires, and PG&E may shut down power on some transmission lines in times of extreme fire danger.

https://www.sfchronicle.com/business/article/For-PG-E-cuttin...

https://sacramento.cbslocal.com/2018/06/25/pge-cutting-power...

Interesting fact: years ago it was designed to build electric infrastructure above the ground because air friction addsup about 20% of electricty, free. It wouldnt be possible underground. But then, you know, whole State of amedium size country like California, would have no power interruptions in heat spikes.

I read about it in The Almanac [1]. Also, note that the map that shows higher and lower risk zones doesn't actually indicate what locations may be affected by outages. They only show where the affected lines are, but those apparently feed homes/buildings that appear to be in the clear.

1: https://www.almanacnews.com/news/2018/07/25/pge-may-cut-powe...

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