I wanted to report back on using the Waste Not Hi Mode in the Classic for water heating, mainly for Watt.
I've had this set up for a few weeks now, and it works totally awesome. This is not a voltage-based "dump". The Classic is smart enough so that it will only turn on the water heater if there is excess power available from the RE system for the particular charge state it's in.
In Bulk MPPT I never see the water heater come on. But once it gets to Absorb voltage the Classic looks at what the batteries are taking for current vs what it determines is available from the panels. If there's more power available than what is being used by the bank it activates the Aux port and we start heating water. In the initial stages of Absorb when the bank is still pulling up to 80 amps it will cycle the water heater on and off to maintain the Absorb voltage. As the bank gets charged up it leaves the water heater on more. At the end of the Absorb stage the water heater is on all the time.
I have the ending amps for Absorb set at 30 amps. So when the batteries are pulling 30 amps it drops into float and finishes the last 5% of the battery charging. Once in float the water heater is always on until the stat kicks it out at 190 degrees.
The solar Classic interacts beautifully with the wind Classics. Even if there is little or no solar power, if the wind system gets the bank up to the Absorb level and holds it there for the max Absorb time set in the solar Classic, it activates the Aux1 port and starts heating water with wind power.
Both of our 55 gallon water heaters are up to 190 degrees by mid-afternoon for the whole last two weeks. We have so much hot water heated with free electricity (well, not "free", when you figure in equipment costs, but still.....) that my wife has been using her dish washer just to use it up and cool the water heaters down a bit so we don't get burned when we take a shower or something.
I have used various relay type voltage based controllers to do this, from Coleman Air ones to Morningstar RD-1's. This is the first time I have had a smart enough controller to properly charge the bank, and use the excess power to operate a water heater without using PWM schemes for "dump". The PWM schemes are fine, but it requires an SSR and driving water heater elements at part of their rated power with PWM does not provide efficient water heating. Using a simple contactor and powering the element at it's full rated 2,000 watts @ 240 volts is about 95% electrically efficient, and it works to actually get LOTS of hot water.
If we get some poor power days, our two water heaters can store enough hot water for about five days if we cut back on the excess use (like the dish washer) before the water gets too cold to take a comfortable shower. And on a good we can heat them both from well temp to 190 with this system in one day. I have figured out that it takes about 36 kWh of power to heat both of our heaters from well temp to 190.
I have to giggle with this system. When all the energy saving folks are promoting turning the thermostat down in your electric water heaters to save on power, we got ours cranked to the Max. And when we turn on the faucet we get hot water with a good head of steam on it
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Chris