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DC water heater element?

Ok, so i said that i would keep you in the loop on my results. Scenario that i am using is replacing lower 240 volt water heater element in my water heater with DC current pulled off of my solar controller from the line feed when the batteries went on float mode not contributing anything to collection of solar energy.
Re-capping: I tried multiple different dc heating elements that did not work very well and will concentrate on the progression of best results.
So I did a comparison test on DC water heater elements. First tried single element 24 volt 400 watt with a dc controlled thermostat. In this first test i attempted to use energy direct from solar panels not going through the solar controller. Panels used were 305 watt , VOC 45.6 volts, ISC 8.921 amps. Tried different panel combinations in parallel and in series, best results were 3 panels wired in parallel. Using 5 gallon bucket of water, the 400 watt element heated water from 75 degrees to 145 degrees. Readings off of the element with 3 panels were 32 volts with 22 amps or 704 watts from a 400 watt element. I installed this unit first in my lower hot water heater bung. Worked great for about 4 hours and then the dc thermostat fried. Not good to push 700 watts through a 400 watt thermostat. Thermostat was still ok and working but I pulled the element thinking that it was going to fry and cause a leak to happen. Next i tried a 24 volt 900 watt single element. It took 1 hour to raise the water temp in a 5 gallon bucket of water from 75 to 125. This was ok but did not do as well as the 400 watt element. Back to the books to see what I could try next. I had someone on here mention a dual probe dc water heater element, next chapter.
 

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I know that my original theory was to power my water heater off of the unused portion of energy but bear with me, I will get there. So i found a dual probe dc water heater element 36 volt and 1200 watts. Element The difference here that it was actually 2 heating elements in one that had two separate connections from two separate sources of energy that was strapped together. I did the same testes with a bucket of water but was not impressed with the results. I then removed the straps and connected it as if was two separate elements. 75 degree water was raised in 30 minutes to 150+. Steam was actually rising out of the container due to the quickly heated water. 3 panels with readings of 30 volts and 20 amps off of the heater element. Ohms per detached element was 2.1 ohms. I installed that element in the lower portion of of my ac water heater. I had previously installed a accumulative ac watt meter between the lines going to the water heater from my main ac power breaker box. My average water watts used weekly was 38 to 39 kilowatts on the water heater. At this time I had previously set the upper element to 140 degrees on the thermostat. Now I replaced the lower heater element in the tank from 240 volts to the 36 volt dc water heater element. I connected the 3 solar panels directly to 1/2 of the water heater element. Full sun 30 volts, 20 amps appx 600 watts being produced. Buttoned up the unit and let it run.
 
Next step, monitored the kilowatt usage of the hot water heater on the ac side to see what the effects were of adding the dc water heater element. On average I was running appx 20 to 23 kilowatts per week or appx 17 kilowatts less than with all ac elements in the water heater. Also due to trying to appease my wife for her hot water needs, I increased the upper ac element thermostat from 140 to 150 degrees just to make sure water would be hot enough for her. So I guess really that the the reduction in ac energy would possibly have been even more if i had not raised the thermostat when adding the dc element to the bottom of the ac hot water heater tank.
 
Next stage of the process, now I started to see how I could take the unused portion of energy that I might be able to use from one of the solar controllers to power the other side of the dc water heater element. There are other ways that this can be accomplished that I will eventually try, but for now this is the direction that I went. With running the Epever 40 amp bn series controller, It has a feature to send a line feed of power to a "light". This could be programmed by the MPT 50 programmer. Options in programming. 1 Feed the load based on voltage limits set upper and lower limits. 2. Load on and off by day and night scenario. 3. Power fed by Load on with timer. 4. Time control by real time clock. I decided to set the load sent to the hot water heater by real clock timer based on peak ours of sunlight during the day. This seamed to work well. It was sending close to 600 watts of energy to the second side of the dc water heater element in the peak hours of the day per my programing instructions. So total energy being fed to the element was 600 watt feed from 3 direct 305 watt panels appx 600 watts on one side of the heating element and 600 watts being fed from the solar controller in peak periods of the day. Next issue.
 

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Next step, so things seemed to work well but then there was a day that we had a lot of cloud cover. This drained my batteries because even though the controller was programmed to feed energy during the peak sun hours in the day there was next to no sun. (Like I said, there are other ways that this can be done probably but I am going in this direction first.) I then programmed my controller, Discharging Limit Voltage, Low Volt. Disconnect Voltage, and Low Voltage Reconnect Voltage. I programmed the controller to stop sending energy to the load feed if the batteries dropped below reading 26.0 volts. This seems to put programming in place so that on cloudy days, the water heater load feed would not deplete my batteries but would feed the water heater with as much possible energy during the day. That is where i am at as of now. Updates to follow.
 
Great work. You are making progress. Have you tried N Ac element off an inverter? Since you are now using batteries?
Not as of yet, the ac elements that I have checked are 8 to 12 ohms where the dc elements are 1.4 to 2.1 The greater the ohm, I have found, the less proficient as far as generating heat with a dc energy source. Although you could go through your inverter and use with ac, which would work, you would kill your batteries very quickly. Resistance heating is just too wasteful using batteries when trying to use it on the ac side through an inverter.
 
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Not as of yet, the ac elements that I have checked are 8 to 12 ohms where the dc elements are 1.4 to 2.1 The greater the ohm, I have found, the less proficient as far as generating heat with a dc energy source. Although you could go through your inverter and use with ac, which would work, you would kill your batteries very quickly. Resistance heating is just too wasteful using batteries when trying to use it on the ac side through an inverter.
Yes I meant going through an inverter. I will admit I do not know the science and there obviously would be inverter losses but after all watts are watts
 
Next step, so things seemed to work well but then there was a day that we had a lot of cloud cover. This drained my batteries because even though the controller was programmed to feed energy during the peak sun hours in the day there was next to no sun. (Like I said, there are other ways that this can be done probably but I am going in this direction first.) I then programmed my controller, Discharging Limit Voltage, Low Volt. Disconnect Voltage, and Low Voltage Reconnect Voltage. I programmed the controller to stop sending energy to the load feed if the batteries dropped below reading 26.0 volts. This seems to put programming in place so that on cloudy days, the water heater load feed would not deplete my batteries but would feed the water heater with as much possible energy during the day. That is where i am at as of now. Updates to follow.
I for one have been following your progress closely. I am ready to pull the trigger on this system to feed my under floor heating. Cant wait for the next update!
 
Sorry for the lack of updates. Just a quick one now. I will send some pics this weekend. So previously I stated, "So total energy being fed to the element was 600 watt feed from 3 direct 305 watt panels appx 600 watts on one side of the heating element and 600 watts being fed from the solar controller in peak periods of the day. " Since the dc element actually has 2 separate heating elements. I decided to install 3 more panels on the south east side of my house to catch morning sun to heat water. So now I have 3 panels on the south east and 3 panels on the south west. We are now catching solar in the morning/noon and noon/afternoon. Just FYI, I am purchasing my 305 watt panels used at $80 per panel so there is not a lot of cost for them. I also tied one solar controller line feed on the same dc element that is fed with morning sun to energize that element in the afternoon. Yes, the voltage is increased on one element because now there are two separate feeds feeding one element but there are no amps being fed in the afternoon off of the east facing panels. So basically one side of the element is being fed in the afternoon off of three panels and the other side of the element is being fed off of 3 panels facing east and off of the solar controller in the afternoon with the west facing panels. The feed from the solar controller in the afternoon is sent by programming the controller to send energy only when batteries are at levels on float and will disconnect if the battery voltage drops to a pre programmed low non acceptable level. Pics will follow this weekend. All In all my whole solar set up is working great. I have a 2200 sq foot home, all electric. last months bill had dropped to $59. I am feeding almost all 110 feeds to the house off of solar. Still need to pretty up some wiring and add some outside disconnects but for now until I get a wild hair idea I am done for now.
 
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So total energy being fed to the element was 600 watt feed from 3 direct 305 watt panels appx 600 watts on one side of the heating element
Now that I've added another 600w 12v element and another set of 6 180w panels to the east we seem to be running in unison except at 12v rather than 24v.

What may be of interest is I've run a cable from the PV to another set of 12v led lights on my fishtank. These come on at sunrise and go off dusk if no clouds. replicating the v through the heater elements. From this observation I'm going to run directly to my inverter from the pv's since it's range is 10-15v with diodes to prevent backfeed.

Other lights run off a VHM-009 low battery unit setup for 15v on 12.8v off - with a relay that connects the - of the leds to the pv - thus no amperage through the pwms(common +)
 
Now that I've added another 600w 12v element and another set of 6 180w panels to the east we seem to be running in unison except at 12v rather than 24v.

What may be of interest is I've run a cable from the PV to another set of 12v led lights on my fishtank. These come on at sunrise and go off dusk if no clouds. replicating the v through the heater elements. From this observation I'm going to run directly to my inverter from the pv's since it's range is 10-15v with diodes to prevent backfeed.

Other lights run off a VHM-009 low battery unit setup for 15v on 12.8v off - with a relay that connects the - of the leds to the pv - thus no amperage through the pwms(common +)
So have you checked the voltage from the panels to the element. What is it reading on the element connections as far as voltage? What is it reading as far as amps when sun is at its best orientation facing the panels with most solar gain?
 
So have you checked the voltage from the panels to the element.
From https://diysolarforum.com/threads/dc-water-heater-element.11699/page-2
Readings at 10am: PV end of cable 39.7amps 11.57volts At element 9.13v ....362w output of element

This was from 4 panels/element. I ended up with 6 to get the 12v at the single 600w element.

The poly housing used for the single element has been replaced with galv, steel when the 2nd element was added.

I'll make a proper record of the latest readings over the next few days.
 
Looks like that element can be pushed a little harder. Are your panels in parallel or in series? Still have about 1/2 the headroom to push either more volts or amps through it to get it up or over 600 watts. I have a double 600 watt element that i am pushing about max on each side with 3, 305 watt panels at 38 volts / 8 amps per panel wired in parallel on each one.
 
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Looks like that element can be pushed a little harder
Thats with the 4 panels. There is 6 now and the v at the elements is 12v.
These things get hot! i will make sure over the next few days that the alternative connection to the inverter keeps under the 15v before connecting.
 
Inverter? You are hooking up DC elements to an AC inverter? Or are you talking about an solar converter? I have mine hooked directly to the panels bypassing everything.
 
So you have double wires on the heating element? So you have direct wires from the panels and from the load side of your controller? Or something else?
 
So you have direct wires from the panels and from the load side of your controller?
Direct wires from the pv to element. They are completely separate from the main system.
The panels have been split in half electrically to use the 12v elements.
Unmodified panels with a Voc of 36 - 40 will need a 24v element.
 
Ok, that is what i had done also. I just did not quite understand what you stated. Pretty good setup. Mine is working great.
 
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