Comment by DrScientist
21 hours ago
Indeed.
In the UK there was a unfortunate trend of ripping out these energy storage devices and replacing hot water tanks with on demand electric hot water heating ( only heat the water you need ). And new builds often have no tanks ( as it saves space in the new tiny homes ).
Very short sighted in my view - a very simple way to store energy and everyone uses hot water directly.
They don't work well with heat pumps. Heat pumps lose efficiency as the differential increases, so if you try to store heat in a tank, you quickly drop capacity and efficiency.
Versus resistance, which is exactly as efficient at 0°C and 1000°C, and why those storage heaters used to make sense.
(And storage is directly proportional to temperature differential above interior ambient)
Home hot water heating in the UK with heat pumps is about 250-300% efficient (slightly lower than the efficiency of home heating but still much better than resistive).
No one is storing 1000C water at home.
It is true that the temperature delays affects efficiency. You can use the thermocline to draw from the cooler lower portion of the storage tank to push this further. Or less technically, just a bigger tank, though this has some tradeoffs.
In warmer countries they are set up differently can act as free air conditioning by extracting heat from indoor air at the same time as heating water.
it also reduces peak load - you can heat water up slower with a lower powered heater. I have a 35 liter warm water tank in my garden shed that pulls about 3.5kw - an equivalent on demand heater would need 14kw or more.
I don't see why that matters. You use the same amount of energy and the demand is smoothed out at grid scale (yes I know about tea in ad breaks).
Houses in the UK typically have 100A supply and the whole local grid is sized assuming people use relatively small amounts of electricity. If everyone gets an electric car and a massive heat pump, lots of local transmission will need upgrading
My hot water tank once fell off the wall. On Christmas day. Expensive repair.
Hot water tank was in the basement, which was not insulated. So the mass of hot water contributed very little as a heat reserve for the house.
House was in a northern clime.
Those are great for buffering only a few hours though. That would help avoid the expensive electricity price peaks.