Which didn't justify the ban. Other countries didn't follow suit, main effect was hurting US nuclear industry and increasing pollution.

P.S. These weren't solar panels (i.e. electricity generation), but solar water heaters. A very different tech, a useful tech, but not a global warming solution.

A huge percentage of energy is used for household heating, solar water heaters were definitely a potential contributor to solving global warming (and other concerns of the day like air pollution, acid rain (solved!), peak oil (not a problem as it turns out), or just reducing oil dependency in general).

Solar electricity has become much, much, cheaper and more efficient since then, and heatpumps have made electric heating much more efficient, so solar hot water doesn't look like it's going to be the future (though new installations do still happen today, despite the advances in solar electric). It wasn't a bad bet at the time though.

Solar water heaters reduce the fossil fuel that would be used to heat the water, reducing CO2 emissions very slightly, and therefore can be part of the climate change solution.

This is perfectly true, but as you say a small effect. Even in countries like Cyprus and Israel where nearly every home has a solar water heater and the climate is very conductive it saves something like 1-3% of electricity consumption I recall?

I meant it's not a solution in the class of solar panels, where the electricity can be used for nearly anything. Also heater tech isn't very high tech and didn't need much gov support in developing it. Mandating it in law where climate allows may have been useful though.

Water heating is a sgnifant use of energy so an easy convert to solar there would be significant. Alone not enough of course but still significant

Solar thermal water heaters are a retro technology at this point. It's simpler and easier to install PV panels driving a heat pump water heater.

Yes, at this point. At the time, they were not.

Seriously everyone critiquing 40 year old projects like they just had PVs laying around in the 70s.

And people incorrectly saying Reagan had PV panels pulled down, the troglodyte. /s That solar thermal collectors never really caught on in the US shows the technology was marginal and the decision to remove them (I think when they leaked?) was arguably a good one.

It's not that retro. In some places in the world it's still very common, and heat pumps very uncommon. It's a response that makes sense in the right climate (and I should note Carter did create a tax credit program for it, though it never got popular in the US).

It's still used in some projects. I remember seeing a deep dive into a net zero lodge (for vacationing) someone built just a few years ago that featured all of those: solar water preheating & PV on the roof, as well as heat pump HVAC/water heaters. Perhaps now it would be cheaper to just beef up the PV and active water heating but I'm sure they had their reasons at the time, at least.