Controlled Constant Heat Transfer.

Sand seems to be one popular choice

Yes, sand is the thermal energy store material. It's how to extract usable heat without going anywhere near steam temperatures and pressure systems regs.

I don't think you prevent every scenario where the pipe could get hot so, design for that possibility.

If steam is generated, design so the steam displaces water from the pipe and prevents further steam generation. Have an expansion tank to absorb the displaced water. You may want to have a one loop through the heat storage, separate from the flow you want to heat.

That higher temp is the issue.

Mineral oils would struggle I think, but molten salt might span that but maybe not 200 to 600.

Why do you want to get so low a temp? There's are many waste heat sources which can that. Most energy stores want to produce electricity using steam.

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That higher temp is the issue.

Mineral oils would struggle I think, but molten salt might span that but maybe not 200 to 600.

Why do you want to get so low a temp? There's are many waste heat sources which can that. Most energy stores want to produce electricity using steam.

So, excess energy would be produced from solar and stored in batteries in a domestic property setting.This takes care of electrical energy required to run the house day to day. The excess energy would go into the insulated thermal store rather than back into the grid. This would stay as thermal energy to be tapped into on demand for domestic hot water and heating requirements via conventional central heating system.

So, the challenge is, to tap into the thermal store and only take out the energy required, without heat losses. I E, I don't want to cool down from a higher temp in order to achieve 60 deg C, but only take out 60 deg C from the heat store. It's a big challenge I know. Thanks for taking the time to reply everyone.

Extracting 60degC hot water direct in one step from this hot sand box with a wide turndown is to me impossible. First of all, copper pipe isnt the right choice material for a design temp of 600degC, it may have to be 1-1/4 Cr superheater piping.
I gave this some thought yesterday after I replied you, and all I see at the moment is a high pressure steam system with desuperheaters and a great deal of wasted heat. Otherwise see what you can do with something like Dowtherm A

This company seems to be leading the way in the UK. Interesting website and a few videos explaining progress so far.

These guys have one working.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.