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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 hea

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.

Xylakant 9mo ago
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.
- IshKebab 9mo ago
  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).
  - ifwinterco 9mo ago
    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
    - IshKebab 9mo ago
      Right but unless everyone is drawing large amounts of power at the same time it doesn't matter if you use 1kW for 10 hours or 10kW for 1 hour. To the grid they look the same. 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.
      - footydude 9mo ago
        > 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. 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)
      - ifwinterco 9mo ago
        Yep but while that is true at the level of the overall grid, actually the nearest part of "the grid" might be a local transformer that only serves 10-100 houses. 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
  - DrScientist 9mo ago
    You can get things like cheaper overnight tariffs when the demand is lower - if you have some sort of storage system - like a hot water tank - in effect the electricity company is distributing some of that smoothing function to things like hot water tanks, storage heaters or batteries. 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.
a_better_world 9mo ago
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.
- manmal 9mo ago
  Those are great for buffering only a few hours though. That would help avoid the expensive electricity price peaks.
coryrc 9mo ago
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)
- ZeroGravitas 9mo ago
  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 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.
  - coryrc 9mo ago
    > No one is storing 1000C water at home. 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 https://en.wikipedia.org/wiki/Storage_heater Of course heat pumps for DHW should all have a tank for smoothing demand across several hours.
- modo_mario 9mo ago
  Isn't it better to heat the water up to a point (let's say 40 or 50 degrees) and to heat it the rest of the way with resistance heating? >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.
  - leoedin 9mo ago

Xylakant 9mo ago

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.

IshKebab 9mo ago
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).
- ifwinterco 9mo ago
  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
  - IshKebab 9mo ago
    Right but unless everyone is drawing large amounts of power at the same time it doesn't matter if you use 1kW for 10 hours or 10kW for 1 hour. To the grid they look the same. 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.
    - footydude 9mo ago
      > 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. 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)
    - ifwinterco 9mo ago
      Yep but while that is true at the level of the overall grid, actually the nearest part of "the grid" might be a local transformer that only serves 10-100 houses. 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
- DrScientist 9mo ago
  You can get things like cheaper overnight tariffs when the demand is lower - if you have some sort of storage system - like a hot water tank - in effect the electricity company is distributing some of that smoothing function to things like hot water tanks, storage heaters or batteries. 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.

a_better_world 9mo ago

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.

manmal 9mo ago
Those are great for buffering only a few hours though. That would help avoid the expensive electricity price peaks.

coryrc 9mo ago

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)

ZeroGravitas 9mo ago
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 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.
- coryrc 9mo ago
  > No one is storing 1000C water at home. 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 https://en.wikipedia.org/wiki/Storage_heater Of course heat pumps for DHW should all have a tank for smoothing demand across several hours.
modo_mario 9mo ago
Isn't it better to heat the water up to a point (let's say 40 or 50 degrees) and to heat it the rest of the way with resistance heating? >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.
- leoedin 9mo ago