I have it thought out. Notice I did not say figured out. I think I have a solution to my hot water needs. I was my first idea, but with a very large heating element. 4500 Watts to be exact. This element will heat only 20 gallons of water. In the winter I will have the large tank set at 110 degrees. And in the summer I will have it set at 100. This mainly has to do with the mixing of hot water with cold at the shower.

As I have thought out. The heating element will heat the pre-heated water from the large tank. The deferential is always going to be 20 degrees. Maybe less if I can tweak it over time. So currently I am using 6kW hours with my tank set at 125 degrees. I take long showers. It helps me to relax. so after 20 or so minutes in the shower I have used about 30 gallons of hot water. Now the wife wants to shower. She likes her showers hot. (Think 2 GPM of just hot water.) SO hot she has to get out or she will get burned after 20 minutes. She uses 40 gallons. So If you have just used 70 gallons of hot water from an 80 gallon tank the last 10 gallons is not going to be as hot as the first 10 gallons because of the mixing in the tank. (These hot water gallonages go down in the summer because of mixing with warmer water.) Enter the mini-tank.

For right now I will have the tank set at 110 degrees. The mini-tank is set at 130 degrees. The mini-tank will use about 3kW hours to heat 60 gallons of water 20 degrees above initial temperature. (notice the 10 less gallons because of the slight hot water temperature increase.) The large tank will use almost half as much energy as before. This would be about 3.5kW hours. It does not make sense but I know that before the incoming water temperature started to decrease I had the tank set at 115 degrees. The incoming water temperature was 68 degrees. Now the incoming water temperature is about 60 degrees and I have to set the tank up to 125 degrees. (double-edged sword, mixing at shower and in the tank.)

Worst case, I have to set both tanks at 120 degrees. Then the mini-tank is just boost the water from the big tank when it gets cooled by the incoming cold water. In the end this may be the route to take for best electricity savings. Time will tell.