The phase change stuff has positives like taking up less physical space but it's also a much less mature tech than storing hot water.
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.
Earth's oceans and seas act as giant heat sinks.
And that means more trouble as global climate change impacts..
https://www.earth.com/news/ocean-warming-broke-records-for-4...
There's heat storage as discussed here.
Or you can store cold water in a reservoir as a giant battery, pumping it up high when you've got excess power, and letting it back down to generate hydroelectricity from it later.
Or you can boil water to make steam that spins a turbine and use it to convert anything that can heat water (coal, oil, nuclear...) to electricity.
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.
It's gravity that does the generation. Water is convenient because it's weight per unit of volume is very high. Higher than most things we can get our hands on and it's also exceptionally safe.
Since water isn't perfectly clean the main problem you face is corrosion. Which can take a great system and turn it into a nightmare of buried leaks and sudden problems.
As far as our options go it _is_ really convenient.
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)
No one is storing 1000C water at home.
It is true that the temperature deltas 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.
>Versus resistance, which is exactly as efficient at 0°C and 1000°C
It isn't. The difference is smaller than for a heatpump tho obviously.
If you have your own solar ( either direct solar water heating, or solar electricity generation ), the hot water tank is a simple, cheap, reliable energy store.
Sure capacity isn't that great - but pretty much every house in the UK used to have one, so it adds up.
It is true that heat pumps coefficient of performance drops as the output temperature increases. So you need a proportionally larger hot water tank to store the same amount of energy. So it is fair to say there are tradeoffs. But hot water storage is still a necessary part of most heat pump installs - because peak output of heat pumps tends to be below the heat demand of showers.
Where does the energy go then?
One interesting case where "at the same time" actually does happen is overnight car charging. Some chargers are configured to start charging exactly when a cheaper tariff kicks in, which causes big transient issues for the grid. I think modern chargers have a random delay to help with that.
This is partly due to a change in the refrigerant used.
Is this adequately maintained even as temperatures drop? I was recently considering getting a heatpump in addition to my gas installation but I assume I need to go for more than a bit better than resistance heating during winter for that investment to make sense.
Here in the UK some electricity providers offer 'smart' charging (e.g. Octopus Intelligent Go).
In that situation the energy provider controls when to charge the car - e.g. you say "I want the car at 80% by 7am tomorrow" and the energy provider controls the timing of charges.
That's how my EV charges - I plug it in, and Octopus control it.
Benefit for me is that whenever the car is charging my entire home's use gets the overnight rate (even if part of the schedule is charged during the day).
Benefit for Octopus is they can use my car to balance grid demand / schedule the charge when it is most financially effective for them.
I can - at any time - override that logic if I just want it to charge at a specific time for whatever reason.
(I presume this sort of arrangement is becoming more common in other countries too)
At that scale, it's definitely possible that you all plug in your electric cars and turn on your heat pumps more or less at once on a cold evening after work and start cooking your local transformer. Not my day job but I think it is a potential issue when everything is sized assuming ~2kW average demand or something
You're right, of course heat pump water heaters use tanks to smooth out DHW demand, but that same thing isn't feasible for space heating.
2. The electrical to heat conversion efficiency is indeed 100% regardless of the temperature of the resistor. And if you're putting out 1000W, then all input losses are also identical. If you put a 1000W light bulb in the middle of your room, or 2 of them but run both at 500W, you'll get EXACTLY the same heat output in your room, but the single bulb is much hotter.
Right, but UK has/had "storage heaters" which were bricks with nichrome wire. They would heat the bricks really hot during cheap electricity times, and use that heat the rest of the day.
EDIT: I misread "ripping out these energy storage devices" as https://en.wikipedia.org/wiki/Storage_heater
Of course heat pumps for DHW should all have a tank for smoothing demand across several hours.