Is it really this..easy?

[Vigo]

So I went off grid in May with 10kw of PV, 10kw of inverter (2x5kw growatt), and starting with very little battery (but now have more). I live in San Antonio Texas and have ~950feet of water line to the house, about 12-18" down. Suffice to say during the summer i was able to ignore the water heating issue because my 'cold' water was coming out of the ground fairly hot. Enough to put a little steam on the mirror after a long shower.

We finally got a slight break on the summer temps and suddenly i needed to get real and address water heating because now the ground water was only comfortably warm while the sun was actually up (before it was well into the evening!). My existing electric water heater was simply turned off at the breaker all summer, and I had plans to attempt some level of fancy stuff for water heating. I have a spare electric water heater tank, a backhoe, lots of open space, ability to do my own plumbing and wiring, and even have two commercially built ~4x8ft solar water heaters laying around (although one has broken glass). I was planning to do something cool, although i wasn't sure exactly what. Thoughts of pumps, sensors, insulation, valves, thermostats, etc all bouncing around in there.

But for the time being, i rewired my water heater from 240 to 120, unplugged the upper element, and put it on a $12 programmable din-rail timer relay running a grand total of ~5hrs a day at ~1100w. I also adjusted the lower thermostat from 120 to 125 for no real good reason.

My time windows (which i'm sure i'll tinker with a bunch over time), are:
7days/wk 12:30-4:15pm (1100w is very unlikely to bother the system in this time frame as i usually have ~6-7kw solar available and my 'base' load is around 3kw with the ac running, only way i can kill the system in this time period is putting multiple loads through the clothes dryer on high settings)
M-F 6:10a-6:30a (quick reheating before my morning shower)
M-F 6:00p-6:30pm (quick reheating before my 2 small kids' evening bath)

I kind of expected it to be crap. So far, it's...fine?! I haven't run out of hot water yet! And it's hotter than before, so it's definitely hitting the 125 i set the thermostat to. It seems to retain the heat very well, in spite of the fact that this tank is from 1994!

I'm just shocked that this isn't crap. I expected to struggle more. We will see what "winter" (i put that in quotes because of where i live) brings..

 

[sunshine_eggo]

While far less involved, I chose to run my RV water heater on a limited basis over the winter rather than drain it. That way I could winterize everything else, but still have use of the WH when I un-winterized. I found that even in teens and single digits, the water heater only required about 1.5 hours @ ~1400W to reach the set temp. Timed with a remote control wi-fi smart plug that turned on at noon. Never had any issues.

I'm not surprised you're seeing those results. This site:

Water Heating Calculator for Time, Energy, and Power

The calculators on this page compute how long it takes to heat water, how much energy is consumed, and how much heating power is required.

bloglocation.com

Shows that 50 gallons of 68°F water needs 6 hours and 20 minutes to hit 125°F with 1100W of heating.

I suspect it will get worse during winter as we too see pretty wild "cold" water fluctuations seasonally. I swear there are times I get confused which way the kitchen handle goes for cold during summer because cold sometimes feels like it's the hot side that hasn't fully warmed up yet...

 

[Mattb4]

Sounds like it is working for you. I just want to mention that in most electric water heaters the elements (upper and lower) do not operate at the same time. They switch from one to the other.

 

[Vigo]

I had taken that tank out and cleaned out the sediment a few years ago. It always worked fine between then and now, but i noticed when i went back into it this time that i had miswired the elements when i put it back together. So all this time I thought i was operating on 2 4500w elements in the usual manner (lower first, upper maybe sometimes), it turns out i had reconnected it in a way where all i EVER had, was both in series (~2kw vs ~9kw in paralle), and only when the upper thermostat turned on. So i was actually getting by on ~2kw of heating before anyway and just didn't know it.

I felt a little dumb when i figured out what i had done.