You turn on the gas plants. That's fine. If you run the gas plants 36 days a year, you've cut emissions by 90%. If overhead means you have to double the amount of emissions (say, to have hot spares), you've still cut emissions 80%.

We don't absolutely have to hit zero to do enormous good to the environment. Cut power plant emissions 80% and it won't be the long pole in the tent any more. The biggest efforts will be in concrete and transportation and agriculture.

We already have the power plants built. We've got plenty of time for things to evolve as solar and other renewables ramp up, and fossil fuels go offline. It's not some kind of knock against renewables if they can't solve 100% of the problem. 90%, or even 80%, is just fine.

If you need to build a gas power plant to compensate for the production solar and wind can't give when you need it, the price per watt of electricity explodes.

Picture this: It's 9PM on a cold winter day, sun has been down for hours and there was not been a lot of wind today. People are home, watching TV and heating their home. Batteries are now empty (they started depleting at around 5Pm when the sun went out). You now need to produce 100% of the peak electricity consumption of the year, using gas, oil, coal, nuclear or hydro.

This scenario shows that whatever you do with wind and solar, you need to be able to produce 100% of the peak electricity consumption with controllable power plants. The cost of wind and solar is not the cost of the power plants vs the cost of the gas power plant it replaces, but on top of it. For every GW of wind you add to the grid, you need to add an equivalent GW from a controllable source just in case. This backup GW won't be used most of the time, but the cost of it should be taken into account when you compute price per GW.

It is unfair to compare the price per GW between solar/wind and gas/nuclear/coal/hydro, when the feature of both are so different. Solar and wind provide amazing ROI, when they want to, not when you need it to. So the cost needs to include the price of the backup system that's going to stay dormant 80% of the time. Ans that significantly change the math of it all.

The only way to get out of this is to either reduce our total energy consumption, so that the current controllable plants can provide enough, and then build solar and wind, to reduce how often we need to rely on them. Or to find a green and controllable energy source, like hydro (which has other issues).

Build more PV. PV is now so cheap that in most places it genuinely makes more sense to build PV based on winter output, with batteries for overnight use, rather than to build coal or nuclear. It’s close either way for gas, but the price trend suggests that even gas will stop being economical this decade.

And by “most places” I include the UK, which is north of the entire contiguous USA.