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Because people want their hot water to be consistent. Even just a simple timer that kicks on the hot water in the morning would work, but most people want to h

Because people want their hot water to be consistent. Even just a simple timer that kicks on the hot water in the morning would work, but most people want to have their sink still be hot even when they aren't showering. > it should stay hot for about 24 hours if it is well insulated. It takes 50 kWh to heat a 46 gallon tank up to 140 F. That's a ton of energy. Hotter, larger tanks lose even more energy. Instead, get a tankless heater, backing a small heat pump water tank. You get water as hot as you can possibly want, heated whenever you want, and it never goes cold.

megaman821 3y ago
The whole point of over-sized water tanks isn't to be the most efficient, only to supply a lot of demand when at times of the day when there is surplus energy. Right now, solar and wind are being curtailed more and more. Also, water consistency isn't that big a problem. Today's 120v heat pump water heaters store water at higher temperatures and using a mixing valve to deliver the desired temperature of water. I am just saying, surely electric water tanks, mixing valves, and temperature sensors are orders of magnitude cheaper than the amount of batteries needed to heat an equivilant amount of water.
bluGill 3y ago
Tanks can be insulated and larger tanks have less surface area per volume so keep heat longer. My parents 1988 switched their hot water to a plan where it was all heated at night. 6 people making no effort to conserve water ran out twice in all those years. Yes the.water was hotter in the morning. But the last shower of the day still needed to be mixed with some cold or it was too hot. Tankless is worse than a large tank. Tankless needs a lot more energy now, less over the full day, but when you turn the water on it needs a lot now. A tank easily adjusts to use power when the power company needs it. Sun shining or wind blowing, then heat water to use up whatever is extra. Clouds and no wind, just use the stored energy. Maybe a battery is more efficient, but tanks are cheap
- PaulDavisThe1st 3y ago
  > Tankless is worse than a large tank. I think you missed that the proposal was a tankless heater backed by an air-source electric heat pump heated tank. The idea is that the heat pump may, or may not, get the water to the desired temperature; the on-demand heater just makes up the difference.
  - bluGill 3y ago
    You don't need that backup. Fix the problem, which is either you don't have enough storage or you don't have enough generation. As I tried to make clear people don't need much storage.

megaman821 3y ago

The whole point of over-sized water tanks isn't to be the most efficient, only to supply a lot of demand when at times of the day when there is surplus energy. Right now, solar and wind are being curtailed more and more. Also, water consistency isn't that big a problem. Today's 120v heat pump water heaters store water at higher temperatures and using a mixing valve to deliver the desired temperature of water. I am just saying, surely electric water tanks, mixing valves, and temperature sensors are orders of magnitude cheaper than the amount of batteries needed to heat an equivilant amount of water.

bluGill 3y ago

Tanks can be insulated and larger tanks have less surface area per volume so keep heat longer. My parents 1988 switched their hot water to a plan where it was all heated at night. 6 people making no effort to conserve water ran out twice in all those years. Yes the.water was hotter in the morning. But the last shower of the day still needed to be mixed with some cold or it was too hot. Tankless is worse than a large tank. Tankless needs a lot more energy now, less over the full day, but when you turn the water on it needs a lot now. A tank easily adjusts to use power when the power company needs it. Sun shining or wind blowing, then heat water to use up whatever is extra. Clouds and no wind, just use the stored energy. Maybe a battery is more efficient, but tanks are cheap

PaulDavisThe1st 3y ago
> Tankless is worse than a large tank. I think you missed that the proposal was a tankless heater backed by an air-source electric heat pump heated tank. The idea is that the heat pump may, or may not, get the water to the desired temperature; the on-demand heater just makes up the difference.
- bluGill 3y ago
  You don't need that backup. Fix the problem, which is either you don't have enough storage or you don't have enough generation. As I tried to make clear people don't need much storage.