Only I would expect the design would not be 3 dimensions as you asked but mostly all forces in one plane 😁

A cool. That is a known wide spread design. This is a very high force, I'm impressed. But it will come at a cost of displacement correct? We aim to make brickets for cooking fuels and we have a lot of groundnut shells. These groundnut or peanut shells have a a lot lignin so it is possible with wetted mass (softening)and perhaps heating with fire (lignine becomes like a glue at 200degC). After that the brickets are sundried. The bricket shape could be like icehocky pucks or at least the shape to cook with.

I think the wooden design is not that interesting to generate, but with a pellet release and refilling in one lever go (or two steps). That would be an interesting puzzle, yes?

You are right, of course. Also repetitive thermal expansion comes into play here. We can compare it with repairing a broken heating element or other single part, instead of replacing it. My patience to properly glue it was also part of failure, hehe.

You have drawn me almost in this equally sized Rabbit Hole. ..must resist... Echo?!...noo

Unfortunately that would negate the high storage temperature of sand (up to 800 degree c) as water will turn into steam after 100deg. So it is either low temperature sand or water with lower energy density.

I like aluminium powder idea. And use the metal bar as heatpipe is a good idea. I would not see temperature as problem as most materials you mention can handle 800 deg. The idea is that you can draw energy from it thus cooling it. I think a molten salt chamber uses this combination of fast transfer and high temperature

Also if these are not load bearing beams ( they have been almost cut throughto allow the pipe going through), make the gap wider and put some isolation around the pipe. But only if the pipe is the case of the water problem

Ah I see now there is double thread 😶‍🌫️

Good question on the low power of motors. Most of the low cost pumps have often DC brushed motors which do not need a controller to steer but uses a brush. Once there is not enough power (in the morning and evening) I think there will be a point where the power will be too low to overcome the torque and the motor stops. The centrifugal pump can still rotate easily compared to other types so I would expect the startup current will be low as well. Panels will deliver a constant voltage while the current will drop when light conditions are dropping. I think the simplest is to search for these aQuarium pumps (24/7 performance) on 12v but I doubt many cars/trucks have built in fishtanks ^^)