Existing water heater for excess PV

[Henrysangret]

I uses a two element system but it is 60 gallon and I use both elements at 110vac. The top element has the cutoff. When the tank reaches the max temp it shuts the heater off, which doesn’t happen often.

 

[nate_syd]

I think the point that TRW was making is if you series them you half the power. It sounds like you are overpowering the small tank system and need to rebalance things.

yeah I understand what TRW was saying (2 resistive elements in series = 1/2 current & 1/2 power). I've already rigged it up & have it working.
But you need to understand what is happening inside a hot water tank, there's stratification layers of heat inside of it - just doing this trips the safety cutoff.

When you connect both elements, both are heating.

The bottom thermostat is still below 70deg so its "on", but the area around the top element & themostat goes above 80deg, which triggers the 80deg OTC safety cutoff killing all power.
You can run both elements, but need to turn off the top one when you're getting close to the limit.

I cant use the top elements thermostat to switch that element in/out of series - as its a peak/off-peak setup, and switches the neutral (BIG issues if you join off-peak to peak circuits)

 

[GLC]

I replaced my lower 220 water element with dual element 36 volt/600 watt element each. I have 3 solar panels on the east side of the house and 3 solar panels on the west side of the house. I believe the panels are 305 watt each. They are connected directly to the water heater element. With sun shining every day, my upper element does not even turn on so basically the hot water setup is all on solar. I also have a set of feed wires coming from one of my solar controllers to feed one side of the hot water heater elements in the 1 to 4 o'clock time of the day. I send this energy to the side of the element that is fed off of the east facing panels since during this time of the day no amps are coming from the east facing panels. My two sets of batteries normally go on float at around 3 pm each day. So by heating water when the batteries go on float, I am using energy that would normally go to waste.

 

[efficientPV]

This chart is the garage water tank temperature. It is worth noting that the tank typically
starts heating by 8am indicating that excess power is being diverted. Long dips are the overnight
heat loss and deep narrow dips are from laundry water use, sometimes twice in the morning. Highest
temps are around 130F where the upper element shuts off. In five days of use the temperature never
drops below 90F. The garage water heater has the lowest priority of energy use after the house tanks.
Tank water is fed into the cold water inlet of the washing machine so all cycles use more hot water
than a normal home machine. Super +++ The soap dispenser at camp stays spotless. At my home machine
the dispenser has to be cleaned periodically. I've even done internal cleaning because of mold buildup.
If you have one of these machines, consider a blend valve to make the the cold water inlet hotter.
And this is what you do with excess power. I love getting free hot water! Typical diversion to this
tank is only about 100W to 460W. When it is all day, 2KW is overkill and a misuse of equipment resources.
No special heating elements were used. Just the two 5,500W 240V elements that came with the tank in parallel.

How I read the chart is the first day there were two laundry loads. Second day was one load that was
interrupted. Forgot to put soap in and it was restarted. Or a cloud came over and the washer stopped and
I didn't notice. The washer strictly runs off array power, no battery backup. When a big cloud comes it stops.
The next day no laundry. The t two wags at the top are the upper element thermostat turning off. The next
day was another load of laundry. With no washing the prior day the tank was evenly up to temperature with
no temperature stratification. Good data in needed to understand what is happening. These temperature data
recorders are awesome.