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[Dan123]

It has occurred to me that there is another energy storage device that many people have in their house. Water Heater with a tank. It holds about 50 to 80 gallons of water. It takes 8.33BTU to raise a gallon of water by 1 degree F. So 50 gallons by 80 degrees would require about 33,300 BTU. If it is a hybrid water heater, then it can use about 4-5 kWh of energy to do so. So for about $1000, you can have 4-5 kWh of energy storage. Similarly to a Powerwall, there can be modes for backup (heating during the day only), for self-consumption (heating only when there is enough solar), and time-of-use. Hybrid water heaters also produce cool air, which can be used to cool the garage (and the Powerwall in it). Why isn't there such a product in the market? I would think that there would be enough demand for this, especially in states that require solar self consumption and limit net metering.


Also, I don't understand why they don't have an AC system that, instead of heating outside air, uses water as a heatsink.

 

[NuShrike]

It has occurred to me that there is another energy storage device that many people have in their house. Water Heater with a tank. It holds about 50 to 80 gallons of water. It takes 8.33BTU to raise a gallon of water by 1 degree F. So 50 gallons by 80 degrees would require about 33,300 BTU. If it is a hybrid water heater, then it can use about 4-5 kWh of energy to do so. So for about $1000, you can have 4-5 kWh of energy storage. Similarly to a Powerwall, there can be modes for backup (heating during the day only), for self-consumption (heating only when there is enough solar), and time-of-use. Hybrid water heaters also produce cool air, which can be used to cool the garage (and the Powerwall in it). Why isn't there such a product in the market? I would think that there would be enough demand for this, especially in states that require solar self consumption and limit net metering.


Also, I don't understand why they don't have an AC system that, instead of heating outside air, uses water as a heatsink.

Maybe there's an API or some controller we can customize to get that behavior out of the hybrid water-heater.

I want one which is also dual-fuel: gas-backup, heat-pump otherwise. Even better, hook it into the HVAC system, so it can also backup heat via solar-thermal panels.

Take it even further, water-cool your solar-panels by sinking their ambient heat into the water-tank. Somebody recently had the idea of using the ambient heat to purify water.

Apparently, we're on the bleeding edge of these ideas at this point. Somebody should make a smart-home company to make these happen.

 

[Ampster]

Also, I don't understand why they don't have an AC system that, instead of heating outside air, uses water as a heatsink.

I would guess because after the AC has heated the water what would it do with the heat after that? My heat pump water heater doesn't run that much because we don't use that much water. So I am not using 33k BTU per day. I also run the heat pump at off peak hours at 12PM at $0.13 per kWhr so more of my solar generation gets credited at $0.50 per kWhr during the day. It is only a couple of kWhrs per day. I suppose what might work would be to coil some copper tubing above my AC compressor to preheat the water in the summertime. Problem with that is that the water would be cooled below ground temperature in the winter unless I had a three way valve to bypass the coils in the winter.
On another note, a friend in Southern California uses a separate HPWH to run a hydronic heating system in the winter.

 

[ewoodrick]

What would you expect the solution to do? If you use the energy for heating, then you have to turn around and heat the water back up. If you want to store the energy, then a hot water heater isn't the most efficient way to do so, you have to continuously add power to keep it warm. But then if you are in a power outage, you lose hot water.

Don't expect to take that energy and convert it back electricity, that conversion is really bad.

The reason you don't see the solution is that water is a lousy storage solution for heat.

 

[Dan123]

What would you expect the solution to do? If you use the energy for heating, then you have to turn around and heat the water back up. If you want to store the energy, then a hot water heater isn't the most efficient way to do so, you have to continuously add power to keep it warm. But then if you are in a power outage, you lose hot water.

Don't expect to take that energy and convert it back electricity, that conversion is really bad.

The reason you don't see the solution is that water is a lousy storage solution for heat.

Water is a great solution for storing heat. Most households need hot water daily. And heat loss of an insulated water tank is only a few percent per day. That's better than 10% loss that Powerwall suffers from charging and discharging.

Using smart water heater can improve self-consumption, by heating the water when there is an overproduction of energy. It can also help with shifting the time-of-use for people with TOU plans. And it can help with the "duck curve"