> This requires chunky copper and clamps.

Yup. But that
engineering issue is the responsibility of the designers of the DC/AC converter "box"!!!

> Then you have the issue of protecting the 120V loads. You can get more than 20A of current out of the alternator, which pushes what you can safely put through standard extension cords.

Naw!!! The car's alternator charges the car's 12 Volt battery, and the DC/AC converter "box" takes the 12 Volts from the battery and makes 120 Volts AC available at the female output sockets. So, if I plug the male end of an extension cord into one of those sockets and connect the female end of the cord to the male end of a power strip with female sockets and have my office lights and electronics, the "loads", connected to the power strip, no more current will flow in the extension cord than is requested, as usual, by the loads. A cord that can carry 16 Amperes, at 120 Volts, would be moving

16 * 120 = 1920 Watts

As I type this, my office is drawing 52 Watts. With my server with its 8 core AMD processor and my laser printer, still looking at a lot less than 1920 Watts. And the printer gets only occasional use and then for only seconds at a time.

The DC/AC converter has more than one female socket supplying 120 Volts, and from that and an ordinary extension cord could drive the refrigerator, toaster, and microwave oven -- again much less than 1920 Watts.

If I start to overload the DC/AC converter, not very likely for my loads and a converter that can supplyk 4000 Watts, I trust that the converter will have a circuit breaker. In that case, this approach to emergency electric power should be not much more of a safety challenge than normal usage.

Note in all of this, the circuit breaker in the house does not get involved, remains ON, and waits for the utility power to come back on. Then the lights in the kitchen, front hall, etc. will come back on, and I will plug my office and kitchen loads into the wall sockets again, disconnect the DC/AC converter, put the car back in the garage, wind up the extension cords, make some notes, and f'get about the outage!

One little issue is: If the Web server computer was running when the power went out, might there be a way to have power to that computer not be interrupted all the way until the power comes back on? Yup: With some shopping, can run the server computer off another box, not very big, that has a little battery inside that can keep the computer running for a few minutes while I switch over to the DC/AC converter and again while I switch back to the utility power.

For the Hacker News audience, this is conversation is drifting into kindergarten level talk:
I'm SURE Hacker News has MANY very well informed engineers on how to have un-interruptible electric power to computers in a server farm and also to the whole farm.

For more, once I wrote a math paper on detecting zero day problems, gave an invited talk at the NASDAQ headquarters, and got a tour and overview of the engineering they did for un-interruptible NASDAQ service, uh, including a remote backup server location. Such magnificent engineering has long been available.

Here I am just trying to contribute to the issue of this thread, using the engine in a car to supply standard 120 Volt A/C electric power. I'm just mentioning that for short term power outages, maybe only a few hours at a time, should be able to do okay with just a normal car and a little box that can supply 4000 Watts of 120 Volt A/C power from a 12 Volt DC battery. That's all I'm trying to do.