DC Electric Hot Water Pre-Heater

[TheDroidsYouAreLookingFor]

Im not trying to give offense but a solar panel with 40v and 15 amp would be a 600watt panel. If your numbers are 40v and 45amp between all 3 panels the math says you have 1800w total panel wattage available. Also if the heating element in fact reads 30 volts and is drawing 20 amps your element is producing only 600 watts on a 1200 watt element with 1,800watts attached to it. See what i mean now?

 

[GLC]

Im not trying to give offense but a solar panel with 40v and 15 amp would be a 600watt panel. If your numbers are 40v and 45amp between all 3 panels the math says you have 1800w total panel wattage available. Also if the heating element in fact reads 30 volts and is drawing 20 amps your element is producing only 600 watts on a 1200 watt element with 1,800watts attached to it. See what i mean now?

No offence taken, I am only giving you real world data. Your math is correct but it is just that math, not real world results. As far as the heating element, it is a 1200 watt heating element but it is a double element, 600 watts per element making it 1200 watts. And yes , math tells you that there may be possible1800 watts available open circuit voltage with . That is with nothing connected to the panels if: Panels are actually producing rated watts. Sun in peak location. Panels are cool not over heated. You have minimal loss of amps through wiring.

Just checked, I did make a mistake, the panels are rated only 305 watt each -36.8 volts-8.30 amps each open circuit, my bad. This would put them at around 900 watts open circuit.

As far as rated vs actual, my two solar arrays are composed of 4 - 305 watt panels which should produce by math calculations1220 watts. But in the real world they have only produced appx 900 watts max through the solar controller at peak periods .

 

[TheDroidsYouAreLookingFor]

Ohh I did not know you meant open voltage. Wattage would be calculated under load so it would be 0 watts @ 40v or 8amps @ 36v which aattage could then be calculated. Seems like you are making quite a bit of heat after reading through your post. I am going a similar route but trying to get it all in the tank if i can. I have a 100 gal preheat tank.

 

[GLC]

I will eventually go with a preheater tank too just to keep the wife happy. Last weekend for some reason the upper 240 volt element thermostat tripped. Wife kept saying that the water was not as hot as usual but would work. So at that time we were 100 percent on solar total for showers, laundry and baths so that was nice to see it working. I found the issue and reset the thermostat. I do think in the future, I will be 100 percent on solar with a preheater tank and 4 dc heater elements.

 

[TheDroidsYouAreLookingFor]

I figure a 100 gal water heater is a really inexpensive battery that can be charged during non peak hours and can be used during peak hours. Right now we have 6 people and a single 40 gallon water heater. Having more capacity and a faster tank reheat time is almost the most important part, saving energy is just a bonus and its fun to tinker around.

 

[GLC]

Yes sir, i started out just planning a small setup for emergency lighting and it got a little out of hand. Now the house is about 85 percent on solar.

 

[TheDroidsYouAreLookingFor]

I have 3,000 watts of grid tie DIY and my electric bill is regularly over $500 monthly. Electric everything so no propane or gas and on a private well. Mother in law house is on the same meter so 2 washers 2 driers ect... if i could just get out of tier 2 power i always say... LOL

 

[GLC]

A month ago my electric bill was like $56. All electric home, 2100 sq ft. Yes, I also have a well but it is 220 volt. My system is not grid tie. I have picked 10 circuits that i can switch back and forth from solar to grid power. Just FYI, worst culprit for power consumption is the dryer, then, oven and cook top and then HVAC. I put a kilowatt meter on those circuits and figured that out. I may try eventually change setups to a 220 setup but haven't made that decision yet. I do have a 9000 watt back up generator that I can plug in if i lose power and need 220.

I have 2 mirrored setups of 1200 watts each that feed my setup with 8 batteries,

 

[efficientPV]

Ok I am back at it. Picked up 10(ten) 4 year old never used panels from an installer for very little money. 30 volts 9 amps 255ish watts. I picked up a 36v heating element and plan to hook up directly while i work on a plan to get my panel voltage to a steady 12ish volts for the 600 watt element.

I have an idea but unsure how well it will work. I was thinking i could get an mppt controller and a 12v wall recepticle. Attach the wall recepticle to the battery leads in parralel with the heater. I know the heating element would try to use all the wattage but im wondering if the mppt wouldnt then stay running and think that the battery needed to charge at all times. When it provides amperage it could be set at whatever voltage matches the element best. Is this crazy or would it give me mppt tracking, monitoring (victron ect) and efficiency at the expense of pulling 12v @ 1 amp 24/7... seems it would be worth it in total investment.

I have serious doubts that this will work. But, it would be interesting to find out. Especially at these low voltage currents.

 

[TheDroidsYouAreLookingFor]

I also noticed that the load terminals of the low amp victron units are "short circuit proof" according to the manual. I read a few places that the load terminals can handle whatever the amperage is of the rated unit ie. 15 amp can use 15 amp load and 20 amp can use 20 amp load. So possibly just put a lifepo mini pack on there and dump the load out of load terminals all day at whatever float voltage i choose. I havent seen configuration for dump load on these units but its something to think about. Some other brands tend to micro cycle the batteries attached with dump loads so maybe even a cap bank with the same external charger. Just thinking out loud here.