Although much of the hype has been about solar electric conversion, solar thermal panels have been in fairly common use for supplemental residential heating in the US since at least the early 1950s. The percentage of houses built with them as original equipment has never been high, but most "developments" with 50 or more units would likely have at least one or two, and within a decade after first sale perhaps a half dozen might install add-in units, in areas that get sufficient sun.

Lots of experimenters have used about any material/construction one can imaging for the plumbing, and although I haven't seen Al beverage cans used it's within the general scope of "creative ideas" that have been touted.

Although the usual claim for projects that use them is that the cans are free, scrap dealers in the US at present offer about three cents per can (80 cents/pound), so not selling them for scrap has to be counted as a cost for materials. It appears that the tube assemblies used in the video use about two dozen cans per tube, with 8 or 10 tubes. That's 200 joints to be welded or soldered (or glued). [I didn't get how he puts them together 'cause "she was listening to somethin' else and I couldn't turn the sound up.]

The scene at the beginning showed him taking about 20 seconds to punch a clean hole in one end of one can, so just initial prep of the cans for one exchanger would entail an hour or so of "drill time," with additional for cleaning/polishing the joint and then making a whole lot of joints. Experience has been that welding thin aluminum is a pretty touchy process, so I'd guess 10% scrap rate(?), but he might be really good at it by now.

Probably cost competitive, and maybe lighter weight, than a dozen old truck radiators ... ? maybe ...

Ya gotta know that it's terribly difficult to make a commercially viable product with unconventional methods and materials, especially for a product with "low market penetration." But it's also exceedingly encouraging to see the few people who keep trying. When the applause dies down for this guy, we should have a spokesperson wish him immense good luck with the project.

Along the same lines, a recent article reported a teenager in some remote (desert?) country who built his own "turbine" powered generator to tap the flow (they said water but it looked like sewage) in a local ditch. The town had NO ELECTRICITY and he wanted to be able to get the evening news on an old TV set, and of course charge his - and his neighbors' - iPads or whatever they had. In the process he had to build the turbine, generator, and a battery our of scrap parts and materials, according to the article.

There really is A LOT of this sort of stuff going on, although it's mostly in fairly isolated places. "Somebody" really oughta form up a club to get more people involved.

John