Rather than buy a battery several years ago, we bought a 400L HWS with a single element changed out to a 2.4kW from a 3.6 (from memory) as well as a 4.5kW solar system (not much roof space).
It runs on a simple timer from 1000-1400 which we switch off if it’s cloudy. It can keep hot water for about 4-5 days for a family of 4 with me having daily showers (dirty job). We are on-grid though but try not to use grid to heat water. A smarter inverter would probably be better.
If I did it again, a dual element HWS set to a lower temp at bottom so the element doesn’t try to get the cooler lower water up to 65 degrees. You can set the top element at 65 and the lower at 50 I think.
Basically a giant kettle, no moving parts.
Seems most useful for those with time of use billing for their electricity. And heat pump water heaters can be even more efficient.
There’s a company taking this further in making a fully integrated hot water and home heating heat pump system: https://www.canarymedia.com/articles/heat-pumps/these-new-double-duty-heat-pumps-can-warm-both-air-and-water
Until batteries get cheaper, it could be a better return per $ to look at a system like this.
I don’t understand the mechanism they expect to use to draw the energy back out of the water heaters and the article doesn’t seem to mention it. TEGs arent very efficient. Water heaters don’t get hot enough for steam generators. I guess you could use the hot water to supplement house hold heating via radiators. But that becomes a complex system. Anybody got any ideas about what they might be talking about?
They seem to just be looking at hot water production alone for typical home uses. By heating (or even overheating) that water when renewable supplies are abundant using smart controls for time of use plans, it offsets more energy production for far less money than batteries would cost.
