Posted by: @heacol

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@derek-m The cheapest and best heat energy storage is a thick concrete slab with a well designed low temperature under floor heating system

I don't dispute that may be true, if you are happy to have your floor ripped up and one installed. 🙄 Also I don't think that it would supply hot water, which I do believe was what the reply concerned.

A 2000 litre thermal store would cost around £2k, and store a similar amount of heat - you’d get 100kWh from 90C down to 40C. The warmstone operates at much higher temperatures, which is great for some applications though.  I’d want to place either of them inside the thermal envelope - there’s bound to be loads of losses from pipework, even if the object itself is well insulated.
All of these heat store things are crucially reliant on TOU tariffs to make them viable, without which they are pointless.

Posted by: @robl

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A 2000 litre thermal store would cost around £2k, and store a similar amount of heat - you’d get 100kWh from 90C down to 40C. The warmstone operates at much higher temperatures, which is great for some applications though.  I’d want to place either of them inside the thermal envelope - there’s bound to be loads of losses from pipework, even if the object itself is well insulated.
All of these heat store things are crucially reliant on TOU tariffs to make them viable, without which they are pointless.

Thank you Robl, for quite some time I have been trying to convince people of the cost effectiveness of storing heat energy using water. The major problem I can see at the moment is that the TOU tariffs are not competitive, and though the overnight cheap tariffs may be marginally costs effective, your local DNO may take exception to you drawing 100kWh of electricity over a 4 or 5 hour period on a single phase supply.

I suppose one way to improve the overall efficiency would be to use a HT ASHP (at maybe a COP of 2) to raise the temperature to 60C or more in the heat store during the cheap overnight period. This energy could then be used to supply the home heating throughout the day, though on the colder days it may require some assistance from the heat pump. Adding solar thermal and/or solar PV, with or without battery storage, could possibly improve the overall efficiency even more on many days, even in the Winter months.

There are many solutions that can be considered, though much depends on how much you are willing to spend, and possibly how much disruption your beloved is willing to suffer. 😡