Direct to water heating.

[efficientPV]

I think the confusion is the 120V, meaning AC not DC directly from the panels.

I had a natural gas tank start to leak and used a 30 gallon 3500W electric tank to replace it temporarily till I got another gas unit. Only had 120V AC nearby so connected that to the heater. So, only about 750W. My buddy at Lowes never came thru with a discount gas unit and I used that for years without an issue. Finally connected a NYLE external HPWH to that tank. Running low power all day with solar is a viable option to high current elements.

 

[z80]

I let the factory thermostats do the work. Usually the top element thermostat interrupts the power to the lower element thermostat when it's on, so I bypassed that by hooking both the top and bottom thermostats directly to 120v. If I'm feeling skiddish about my SOC at the time I just turn off the breaker to it.

edit: should've chose my words more carefully and said thermostats instead of elements. The elements are using their factory installed thermostat.

Put a 10uF/450v capacitor across the thermostat terminals if using a DC voltage....else contacts will fuse together and hot water will never turn off.
Then there will be a big...BANG

 

[copec]

If anyone is using AC coupled solar with varying frequency for SoC, I found this programmable load manager that can drop load at a programmable frequency between 50-62hz, with a programmable timeout between 1 second and 10 minutes. It says 50-60hz on the page, but I talked to them and it is actually 50-62hz.

SAK-60 & SAK-60C In 3R Enclosure - PSP Products

www.pspproducts.com

 

[Isla]

Solar collector panel, storage tank, expansion tank, control system.

 

[GLC]

What I have found out is that dc elements have a less resistance in ohms therefore they are more efficient in heating water vs ac elements.

 

[K W]

What I have found out is that dc elements have a less resistance in ohms therefore they are more efficient in heating water vs ac elements.

Ya can't improve on the efficiency of turning electrical power into heat. I's always 100%.

 

[K W]

Yes,dc element has heating resistance wire.For example:https://www.heatdas.com/ProductInfoCategory?categoryId=471698&PageInfoId=0

Both so called AC and DC heating elements use resistance wire. If you attach one to AC, it's an AC heating element. Attach the same element to DC, and it's a DC heating element.

Nor is there an issue with electrolysis using AC or DC, as long as the heating element is electrically connected to any metal in the tank, including the tank itself, and the tubular structure around the resistive element doesn't leak.

Galvanic corrosion would be an issue if the metals are are at significantly different potentials on the galvanic scale, but that has nothing to do with powering it with AC or DC.

 

[TRW]

Both so called AC and DC heating elements use resistance wire. If you attach one to AC, it's an AC heating element. Attach the same element to DC, and it's a DC heating element.

Nor is there an issue with electrolysis using AC or DC, as long as the heating element is electrically connected to any metal in the tank, including the tank itself, and the tubular structure around the resistive element doesn't leak.

Galvanic corrosion would be an issue if the metals are are at significantly different potentials on the galvanic scale, but that has nothing to do with powering it with AC or DC.

Glad you added your info and facts. There is some level of mystery when it comes to heating with DC, and I guess it comes down to more arc on breaking the circuit.

 

[GLC]

Correct, only difference between AC and DC elements is that you can power an AC element with DC current but due to higher resistance it does not work efficiently. You do not want to try powering a DC element with AC current, it will not last very long. Been there, done that.

 

[Hedges]

The element itself isn't going to care if DC or AC, what matters is applied voltage and voltage rating of element.
I commonly connect 120VAC to a heating appliance meant for 240VAC. This cuts power to 1/4, so a 2400W water heating element draws 600W, just takes longer. The thermostat and over temperature switches work fine on lower voltage AC.

"DC" elements are typically for lower voltage, like 48V or 12V, so lower resistance to produce reasonable power dissipation. Of course any heating element will fail quickly if operated well above its intended voltage.

Some water heater elements sold for DC have a thermostat built in, to take care of the issue that an AC thermostat will arc and fail on DC. Only problem is, one forum member had it fail. Turned out that by "48V" the vendor meant absolute max, not nominal 48V system which can be 60V.

The forum member disassembled the device and what to his wondering eyes should appear ... but a thermostat clearly marked for AC, not DC.

Caveat Emptor.

Safest way to heat with DC is use an inverter to power an AC heating element. That isn't likely to fail with welded contacts in the over-temperature switch.

 

[TRW]

The element itself isn't going to care if DC or AC, what matters is applied voltage and voltage rating of element.
I commonly connect 120VAC to a heating appliance meant for 240VAC. This cuts power to 1/4, so a 2400W water heating element draws 600W, just takes longer. The thermostat and over temperature switches work fine on lower voltage AC.

"DC" elements are typically for lower voltage, like 48V or 12V, so lower resistance to produce reasonable power dissipation. Of course any heating element will fail quickly if operated well above its intended voltage.

Some water heater elements sold for DC have a thermostat built in, to take care of the issue that an AC thermostat will arc and fail on DC. Only problem is, one forum member had it fail. Turned out that by "48V" the vendor meant absolute max, not nominal 48V system which can be 60V.

The forum member disassembled the device and what to his wondering eyes should appear ... but a thermostat clearly marked for AC, not DC.

Caveat Emptor.

Safest way to heat with DC is use an inverter to power an AC heating element. That isn't likely to fail with welded contacts in the over-temperature switch.

This info is what I have been looking for, and tells it just like it is. Thanks for the input!

 

[FilterGuy]

I commonly connect 120VAC to a heating appliance meant for 240VAC. This cuts power to 1/4, so a 2400W water heating element draws 600W

@Hedges makes an important point. The power dissipated by a fixed resistor is *not* a linear function of voltage, it is a squared function.

​

So.... if you cut the voltage in half, the power is divided by 4. Conversely if you double the voltage the power goes up by 4 times. Keep this in mind if you are trying to repurpose a heating element at a different voltage than it is designed for.

 

[GLC]

I have used a DC element for about a year now and it works great. I do this without controller, batteries or inverter. I tried different DC elements from12 to 48 volts. 36 volt worked the best. The DC element I choose has dual elements. I connected 3 - 305 watt solar panels to one side and the same to the other. I positioned 3 panels to the east side of my house and 3 panels to the west side of my house. I have solar heating through out the day. This is installed in the lower portion of a 40 gallon hot water heater. I kept the AC element in the top of the unit just incase I had days of no solar gain. I rarely have it come on.

 

[Hedges]

Have a link to that element?

What are the PV panel ratings? Wattage rating of 36VDC element? I would think that Vmp and Imp of the array matching resistance of the element would give most heating. Have to think a little harder about the power curve of array throughout the day, but I'll bet I could do better connecting the two arrays in parallel (possibly adjusting panel configuration or element rating.)

 

[TRW]

This thread keeps making interesting points and ideas.

 

[GLC]

I have it linked somewhere on here in an original post, let me see where i can find it. I put it together last year. Its been working so good I haven't thought about it. I had tried multiple configurations last year when i was putting it together and what I am using worked the best for me. Panels in the east and west got the water heating in early am and continued through the day vs just in the afternoon.

 

[GLC]

Here is the element and the thermostat I am using. You got me thinking now if I wound up using the 36 or 24 volt element. Don't really remember right now, will have to check.

Yokshop Thermostat for DC water heater element Water Overheat 140 Degrees Fahrenheit - - Amazon.com

Yokshop Thermostat for DC water heater element Water Overheat 140 Degrees Fahrenheit - - Amazon.com

www.amazon.com

Amazon.com : CHUANG Water Heating Element Screw Plug Tube Immersion Screw-in Tubular DC 24V 600W 1 INCH NPT DN50 : Patio, Lawn & Garden

Amazon.com : CHUANG Water Heating Element Screw Plug Tube Immersion Screw-in Tubular DC 24V 600W 1 INCH NPT DN50 : Patio, Lawn & Garden

www.amazon.com

Amazon.com

 

[TRW]

I will study this tonight when I have time, but I like the idea of heating water for several reasons with excess solar.

 

[GLC]

If you want to look at my evolution go here, it has good things that worked and those that did not.

I will study this tonight when I have time, but I like the idea of heating water for several reasons with excess solar.

DC water heater element?

Has anyone tried these? Just wondering if they actually work. I was wondering what to do with extra energy from the panels I have.

diysolarforum.com

 

[efficientPV]

There is successful and then there is really successful. With enough space and panels heating water isn't a problem. I do diversion heating directly from array voltage and not using a battery or charge controller by diverting any increment of unused power not needed for charging. I have a 40 gallon tank in the garage just used for the clothes washer. All laundry cycles use hot water, it's free. This is excess diversion from diversion system that heats the house water. This is just an example of what can be done. I know there are lots of used panels, but think of how that separate hot water array could be used for household needs.

12V panels with a 12V heating element is always a bad match. A heating element closer to 18V or higher should be used. 24V panels will match closer to 36V elements. You don't want to over voltage elements. Dual element heaters can be placed in series instead of parallel shorting bars. This increases your resistance options. I use 2,000W 120V elements, these are 500W at 60V. There is an ideal resistance, but that is only useful if you live where there are no clouds. If the panel can produce 10A max, 7.5A would seem pretty good. Fact is the power has dropped to 50%. At 5A it id down to 25%. Some studies have shown increasing ideal resistance 50% does not affect daily power production that much and is a big help on those partly cloudy days.

I use power point control to always get what the panels can produce. I have very limited space. A number of panels are not even on my property. I keep them at a low angle almost flat so they can't be seen. All the panels suffer from extreme shading and I have to clean off twigs every morning because they are under trees. It is a site that shouldn't work art all. And I have hot water.