Why, exactly? It's not electrical power storage, sure. But a water heater is by definition energy storage. You want hot water, it takes time to heat, so keep it in a buffer.
And in fact a well-insulated modern tank is a very efficient store for energy that you're going to use at some point anyway. It makes perfect sense to use it as a flexible load to buffer grid management.
> On another note, I wonder how resisitve heaters compare to heat-pumps.
Heat pumps are sort of an orthogonal trick. Ultimately they work by using a lower temperature state to "steal" energy from the cooler outside temperatures. They don't make "heating" any more "efficient" per se. But if you have such an outside environment (i.e. colder than whatever the operating temperature of the heater is, but still warm enough to provide energy to the coolant) they are worthwhile.
Heat pumps are no trick any more than solar panels or solar water heaters are. Resistive heat is 100% efficient while heat pumps are over unity usually 300-400% efficient although usually denoted as coefficient of performance (COP) as number ex 3 or 4. For every 1 watt put in 3-4 watts of heat come out. Real efficiency in terms of energy paid for vs energy provided to heat is what matters.
The reason they are over unity is they are taking heat from one place and moving it somewhere else. If they are pulling heat from outside air they are basically solar assisted. Technically anything above absolute zero has heat energy, even very cold outside air has plenty of heat to pump into your living space. Temperature is not heat, you can raise temperature by putting the same amount of heat in a smaller space, its like using a transmission to increase torque by lowering rpm.
Not sure you're disagreeing with me. That's indeed how they work, and it's... a pretty neat trick! So are phototransistors, for that matter. Not sure I'd put radiative solar water heaters in the same boat, but semiconductors and thermodynamics make for great tricks.
I am disagreeing with "They don't make "heating" any more "efficient" per se."
They definitely do make it more efficient at least in the ways that matter to people, less energy paid for the same heat.
I guess all technology is a trick, but normally that denotes its not really doing what is said, which you reinforced by saying it is not more efficient.
Air source heat pump water heaters and direct solar water heaters are similar in they both utilize solar energy to heat water. Then again if you really get down to it you could argue everything is indirectly solar powered, just some forms you must pay for the energy, while heat pumps and solar collectors get it directly from outside your home heat pumps just require some energy to collect it.
I think you just mean different things by "heating" - if you're talking about heating in a closed system, they're the same - 5 joules of energy are needed to increase the total heat energy by 5 joules, with either approach.
The advantage of the heat pump is that we are, for, say, 3 joules of energy, heating part of the system by 5 joules and heating the other part of the system by -2 joules.
This is great for home heating and the like because we don't care about making the outside slightly colder.
There's a limit to the 'energy' the system can store: the amount of heating that can be pre-buffered and used effectively later.
This comes with the downside of leaking energy a lot faster than batteries. Moreover, the more energy stored, the faster the leakage.
All that is not to say this is useless. Just to say the role played by heaters is different from batteries. Notably, neither are a good solo solution to the volatility of renewables.
I know that in the Netherlands, stuf like this would require infrastructure upgrades. There is simply not enough copper running to consumer houses to handle the amperages.
And in fact a well-insulated modern tank is a very efficient store for energy that you're going to use at some point anyway. It makes perfect sense to use it as a flexible load to buffer grid management.
> On another note, I wonder how resisitve heaters compare to heat-pumps.
Heat pumps are sort of an orthogonal trick. Ultimately they work by using a lower temperature state to "steal" energy from the cooler outside temperatures. They don't make "heating" any more "efficient" per se. But if you have such an outside environment (i.e. colder than whatever the operating temperature of the heater is, but still warm enough to provide energy to the coolant) they are worthwhile.