Darn, the CTV piece wouldn't play on my laptop. Probably my paranoid security settings.

But I looked up the YouTube versions. There are all sorts of variations on thermal walls, using glass, sunlight, and natural convection to direct heat into an interior space.

I was planning one to ensure ventilation in an outhouse, using scrap wood that had been well-charred on the surface and a glass door I got at the dump.

My single-paned, south-facing sunroom is a good example of how much heat the winter sun still has. It can be -20C outside, but if it gets full sun for a couple of hours I can have lunch out there with only a sweater on. But when I lose direct sun, the temp drops like a stone.

So, the challenge I guess is keeping the heat after you gain it. When the sun goes down, a thermal wall setup will work in reverse unless you stop the air flow.

As for the solar water preheat, it's a great idea as long as it goes through a temperature controlled regular heater before use. Otherwise there's a legionella risk, which can be nasty.