I had a typo in my earlier response - it should have been 13+ kWh per day (18
hours) in my example. This is not out of line - 40% of a household kWh use can easily be heating water (if resistance electric). The usage that you're describing is a better fit, but pretty modest use by conventional home norms. Again it is a wide, wide range based on occupancy, patterns of use. Throw a teenager in the mix with 30-minute showers, or hot water clothes washing and it can be notably different.
We've been diverting excess PV, or 'opportunity' diversion as it's sometimes called for a number of years. It works really, really well and like this, the appeal is you effectively are getting Btus packed away without plumbing, penetrations, antifreeze or any of the normal details of solar dhw systems.
You are also ignoring how much cumulative power there is in the morning and on cloudy days when operated at power point.
I understand that the energy is useful, even in small amounts over an extended period. On the other hand we haven't talked about "recovery" much either. If the use is conservative and accumulated over the course of a summer day it is definitely measurable. In a more consumptive home, the 3rd or 4rth shower would be pretty miserable.
I like the approach and the concept. As I said earlier, I just have trouble with this:
Their claim is for supplemental heating during the day to eliminate a majority of grid power heating. The water would start at 120F
Leave out majority, or increase the array size, and I'm on-board with the message. Otherwise, I liken it to the days when they tried to convince us that a 7 watt CFL could replace all our 75 & 100 watt incandescent bulbs.
Still very clever. Regards, ~ks