Backup Hot Water Heating


Just sneakin' around....
Preppers have always been inventive at trying to make hot water for off-grid/power outage situations. One of the solar forums I frequent has pages of things people have done. One trick is to use a standard 240v electric hot water heater but run it at 120v, or even less. If you know the power calculations for determining required amps, this lessens the BTUs by half, but lowers the power requirements to 1/4, putting it in the range of some homebuilt solar systems. Takes much longer to heat a tank, but it works. Others have made complex systems and circuitry to only divert power to the hot water heater when the batteries are fully charged first.

Recently, I had a new hot water heater installed, a hybrid. I use very little hot water, so the old tank just sat there keeping water hot all the time for no reason. The hybrid uses a heat pump to heat the water, and only uses electric coils when there is a high demand. Since my demand is very low, I put the heater in Economy Mode, where it's heat pump only, no coils, the goal being too minimize my electric usage. Very low power consumption. After a normal shower, the heater runs for about 2.5-3 hours to come back to 100%.

And then I realized the power needs are so low, it can easily be run with alternate power sources. Instead of 4500 watts of power needed, it drops to under 600 watts using the heat pump mode, less than a drip coffee maker. A small generator will run it. And it's easy to get enough solar panels to cover 600 watts without increasing the battery bank. The panels will easily make enough power to run the hot water heater during the day without draining the batteries, and when night falls, you have a full tank of hot water and still have a full battery bank.

So, without planning for it, I now have as much hot water as I need if the power fails. I remember not having hot water for more than a week after one of the hurricanes. And this is so easy, not sure why I haven't seen or read more about using hybrid heaters for off-grid.