[usrusr]

Thermal for heating/hot shower or thermal for some adventure in driving a generator?

For heating, photovoltaics supplying a heat pump is starting to give direct thermal a run for the money (well, not actually for the money yet, direct thermal is still cheaper, but at least in terms of how much you could harvest from a given roof area)

If money isn't an objection at all, e.g. if you strive for that sense of achievement of a good setup, there are hybrid modules that pick up the 20% or so photovoltaics achieves and still funnel the remaining energy into heating a liquid medium.

[taneq]

This idea was a flat "panel" of parabolic reflectors focused on heat exchanger tubes, driving a heat engine. The new bit was that the heat engine was going to be open loop (basically Brayton cycle with the compression stroke pushing air into the heat exchanger and expansion stroke driven by heated air from the exchanger) so its power density would have been much higher and cost lower than the usual Stirling cycle engines which cost a ridiculous amount for what they are.

I had all the thermodynamics worked out and it would have been something like 5x as cost effective as photovoltaic. Then the cost of photovoltaic panels dropped 10x in a year. C'est la vie, at least my roof is covered in PV now. I've thought of running some tubing under the panels to pre-heat water for our solar hot water system but these days it's scarcely worth the bother (at least where I live which is pretty much perfect for solar power.)

[snickmy]

There are hybrid solution of panels that are basically layering a PV over a Thermal Panel (pipes with fluid inside). I never saw them getting massive traction. I wondered why.

Some example: https://www.convertenergy.co.uk https://dualsun.com/