Feedback on 12V water heater element as solar diversion load

[ewarnerusa]

My solar charge controller has a diversion load feature where excess current can be diverted to a load once batteries are full. The manual discusses using a water heater element and this sounds like a clever way to do something with excess solar harvest that would otherwise be wasted. I recognize that this is not a primary method for heating the water, just a way to doing something rather than nothing with excess solar harvest. Does anyone do this and have feedback? I found an old thread posted by "msiminoff" with a cool project doing this with a custom element.
https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/25824208/srt/pa/pging/1/page/1
Otherwise, there are existing 12V heating elements that can do this.
https://windandsolar.com/9-3-8-inch-dual-power-submersible-water-heating-element/

[Cptnvideo]

"IMO, in order to actually use excess solar capacity, add battery storage capacity so the excess power can be used when needed."

Exactly. That is the correct thing to do.

[rjstractor]

enblethen wrote:
My thought you are wasting time and money for the small amount of energy you possibly save.

Exactly. Especially considering that the OP wants to use the excess capacity for resistive heating appliances. The entire output of the OP's system (280W) doesn't even come close to the power required to make either a space heater or electric water heater work with any efficacy. IMO, in order to actually use excess solar capacity, add battery storage capacity so the excess power can be used when needed.

[stevenal]

ewarnerusa wrote:
Then we have the kind of online gambling shopping when trying something from Ali Express. The 1/2" NPT size means it could swap with my 1/2" NPT thread drain plug, right? This would be ideal, maintaining my OEM 120V AC 1400 watt heating capacity.

Dernord Immersion Cartridge Heater Hot Rod Heating Element Replacement with 1/2"NPT Thread 12V 24V 1...

Just make sure you have the needed depth.

[Grit_dog]

^You’re still barking up the wrong tree. No, 1 280W panel won’t power a space heater either.
At best 100% solar power being absorbed, it will kick out 8-9amps at 12v +-
Good luck. I know you so want to “make this work” but the practicality of it is of seriously diminishing returns.

[ewarnerusa]

StirCrazy wrote:

ewarnerusa wrote:

Chum lee wrote:
As previously hinted at, if you have a 2/3 way absorption type fridge, why not divert the excess power generated to that and save some propane? Clearly, if you have a 2 way fridge, you'll need an efficient inverter capable of generating at least +-500 watts on a duty cycle of at least 50%. Just keeping your 1500 watt PSW inverter online full time may be enough to waste enough excess power to solve your issue doing nothing else. IMO, 280 watts of solar wont be enough to run the fridge full time, but hey, it's a start. You'll be spending a lot of time doing load management.

Chum lee

A different take on this idea^^ I wonder if instead of a 12V water heater element I could explore a refrigerator 12V element? Is there harm in adding variable/inconsistent heat (less than the OEM 300 watt AC power element) to the ammonia in an absorption fridge? This is just a brainstorm, I definitely don't want to swap out the AC side of the fridge.

EDIT: I clearly don't know exactly how the ammonia is heated in an absorption fridge, just that this is part of the process. But first google search showed a promising success for a similar idea. This is a Dometic fridge, mine is Norcold. https://www.escapeforum.org/forums/f8/adding-12v-heating-element-to-rm2510-fridge-16224.html

my 3 way on 12V is 12 amps. thats a lot of power to be chucking out for the return on propane savings.. I can go probably between 1 and 2 months on just my fridge with a 20lb bottle, but as soon as your solar stops producing over the amprage for the 12v heater then you have to turn your fridge back to propane or you start eating battery capacity. Idealy you want somthing that you don't have to interact with in my opinion. the hot water element would be great, in my case the space heater would be good but in the summer you would have to be able to turn it off and you would still be not using all your potential when its hot... maybe a combanation of the water heater and space heater so you can use which ever one you want.

Steve

Thank you for this. Do you think both a water heater element and a space heater could be paralleled on the diversion load circuit each with an on/off switch?

[ewarnerusa]

Bobbo wrote:

ewarnerusa wrote:
I think the only thing "running" when an absorption refrigerator duty cycle is on is that an element is heating the ammonia. So I think I would be bypassing any refrigerator thermostat and just applying a bit of heat to the ammonia. Since the diversion load current wattage would never be even as much as the OEM 120v element, I'm not sure if it really gets hot enough to achieve the cooling cycle. I don't fully understand the systems, just the high level idea.

Which, since it accomplishes no effective work, is still wasting that energy while at the same time adding to the degradation of the heating element over time.

If all the diversion load would accomplish in this scenario is to preheat the ammonia rather than boiling it, that is still offsetting work the propane burner would have to do to get it boiling once the thermostat calls for it.
I'm not really considering the fridge element as a candidate, it seems like the hot water tank is a much better sink for extra current turned to heat. It was more of a brainstorm of another place to dump it.

[Bobbo]

ewarnerusa wrote:
I think the only thing "running" when an absorption refrigerator duty cycle is on is that an element is heating the ammonia. So I think I would be bypassing any refrigerator thermostat and just applying a bit of heat to the ammonia. Since the diversion load current wattage would never be even as much as the OEM 120v element, I'm not sure if it really gets hot enough to achieve the cooling cycle. I don't fully understand the systems, just the high level idea.

Which, since it accomplishes no effective work, is still wasting that energy while at the same time adding to the degradation of the heating element over time.

[ewarnerusa]

I think the only thing "running" when an absorption refrigerator duty cycle is on is that an element is heating the ammonia. So I think I would be bypassing any refrigerator thermostat and just applying a bit of heat to the ammonia. Since the diversion load current wattage would never be even as much as the OEM 120v element, I'm not sure if it really gets hot enough to achieve the cooling cycle. I don't fully understand the systems, just the high level idea.

[Bobbo]

ewarnerusa wrote:
The different idea on the refrigerator is with the diversion load, where there is no input on my end. The heating element gets some diverted current whenever it is available, which in my head means it gets turned into refrigerator cooling and therefore propane offset. Same logic as the water heater, where heat is being added to the water just because there is spare current available and there is no "control" of it. Just "here I have some extra energy, want it?"

I have a question. Since the idea is to use the extra energy generated so it doesn't go to waste, won't the refrigerator idea fail to do that half the time? If the refrigerator is at temperature and not running, that energy is STILL being wasted. You wouldn't want to run the refrigerator's heating element if the refrigerator is already cold enough. Forcing the refrigerator to keep running, just to use solar energy, when it is already at temperature is a recipe for freezing everything in the refrigerator.

[Cptnvideo]

Interesting, Don. My 20cf residential fridge draws a max of 20 amps DC.
But I don't have the option of running on propane. 😞

[pianotuna]

My fridge draws 34 amps on 12 volt setting. However, due to voltage drop it only works well on 12 volt *if* the converter is on.

My converter is a back up for the Magnum inverter charger, so it is never on.

[ewarnerusa]

enblethen wrote:
My thought you are wasting time and money for the small amount of energy you possibly save.

Sometimes it is just about tinkering. I certainly don't expect to notice any change in my propane expenses. But if it works, I will like seeing my amp meters show full solar harvest potential happening even when it isn't needed right then for the battery charging and other loads. And I will have learned something about off-grid solar design to apply to future projects.

[enblethen]

My thought you are wasting time and money for the small amount of energy you possibly save.

[ewarnerusa]

Then we have the kind of online gambling shopping when trying something from Ali Express. The 1/2" NPT size means it could swap with my 1/2" NPT thread drain plug, right? This would be ideal, maintaining my OEM 120V AC 1400 watt heating capacity.

Dernord Immersion Cartridge Heater Hot Rod Heating Element Replacement with 1/2"NPT Thread 12V 24V 1...

[ewarnerusa]

The different idea on the refrigerator is with the diversion load, where there is no input on my end. The heating element gets some diverted current whenever it is available, which in my head means it gets turned into refrigerator cooling and therefore propane offset. Same logic as the water heater, where heat is being added to the water just because there is spare current available and there is no "control" of it. Just "here I have some extra energy, want it?"