Earlier quoted context omitted.
It isn't just the cost to collect, it is also the cost to store. Heat is easy and safe to store at just above room temperature in rocks - but you need a lot of rocks. Just to heat my house for a few days would need tons of rock at temperatures I'd allow in my house (I have kids and so I worry they will open the rock container and get burnt). Rocks are not free. You can also use water for storage, but again you have t…
> Just to heat my house for a few days would need tons of rock at temperatures I'd allow in my house (I have kids and so I worry they will open the rock container and get burnt). Rocks are not free Sand/rock heat storage is for industrial and utility scale application, not your house. > You can also use water for storage, but again you have the issue needing a tank (and water is a drowning hazard, plus the worry abou…
I've seen them for a house as well. (when the utility offers a large discount for power used overnight - 40 years ago my local coop was trying to sell my parents on this, but since we had natural gas heat it wasn't worth it) To hold more than a days worth of heat you need a lot of rocks.
Heap pump water heaters work, but you need a large one to hold a days worth of hot water (40 years ago my family had 200 gallons of hot water storage - the utility gave my parents a discount on water heating because we only heated water at night, we ran out of hot water once that I remember). If you want to store more water than a days worth of use then you need more storage. This can become a drowning hazard if we are talking about a couple weeks worth.