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Passive Solar Hot Water Heating
#11
(01-02-2019, 05:16 PM)Motrukdriver Wrote: Yeah, that might be much...  How about this one?

https://www.supplyhouse.com/AO-Smith-EJC...gIS7fD_BwE

The 120v version of that takes 1500 watts. I helped install a Bosch on demand that had a 2 gallon tank and pulled 1440 watts but it too was 120v.
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#12
(12-31-2018, 11:18 AM)TrainChaser Wrote: The problem with a system like that rooftop one is when the water gets too hot, and there's no way to add cool water.

Good point. I am considering two tanks, hot and cold, on the roof. I’ve held off because of the weight sloshing around up there and the hassle of a ladder.
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#13
The HotRod or Camco Hybrid electric water heater kits come ready to go in a RV hot water heater. They could be adapted for another hot water heater if one has a diy system with a different tank. Or as Mo pointed out there are 12 volt heating elements available with 1” npt thread they fit directly into a off the shelf hot water heater. Wiring a DC water heater is extra work and expense. I have a miniature 800 watt@12 volt water heater I haven’t used. That’s about 65 amps load and 4 gauge wire. It came from off a big truck I think. Water is meant to flow through it as it only holds about a half gallon.
I just keep thinking it would be nice to have some passive water heating. Maybe for preheating water going to a electric water heater? The performance of my flat mounted solar POV panels is poor for heating water alone. I don’t get much power. And it’s hard to test the panels when they are mounted flat on a roof. I prefer things that are sited on the ground. I saw somewhere the military has solar that can be deployed rapidly on the ground. More tax dollars at work.
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#14
(01-02-2019, 05:34 PM)justjim Wrote:
(01-02-2019, 05:16 PM)Motrukdriver Wrote: Yeah, that might be much...  How about this one?

https://www.supplyhouse.com/AO-Smith-EJC...gIS7fD_BwE

The 120v version of that takes 1500 watts. I helped install a Bosch on demand that had a 2 gallon tank and pulled 1440 watts but it too was 120v.

Replace the 120vac element with a 12vdc element.  Be sure it's a true 12vdc too.  Seems there are a bunch of nefarious element resellers that are melting the element plastic where the specs are printed and selling them as 12vdc.
  [Image: 414097000.jpg]
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#15
Correction: meant to write PV, as in photovoltaic, not “POV”.
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#16
I looked at 12 volt water heaters before I got the Hott Rod. First it is hard to find one with a thermostat. Second is running heavy gauge wire, switch and fuse would just add to the cost and make it take longer before the propane savings paid for the gear.

Honestly, unless you are going to go without a inverter I don't see why the hassle is worth it. Yes my water heater would take less if it were 12 volt due to the loss at the inverter. That said, if you are THAT worried about power you shouldn't be running a water heater in the first place.

I find this misinformation a lot. People that want a design and think that just because a device is 12 volt that it uses no power. My water heater on 12 volt still pulls 450 watts. My Engel set as a freezer uses lots of power. So much so that I really believe I would have been better off getting a 3 foot 120v freezer. The compressor would have used more power but the insulation would have kept it from running so much. Use a load sensing inverter and the loss is even less.
[-] The following 1 user says Thank You to justjim for this post:
  • Roadtripp (01-05-2019)
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#17
I hear that regarding the devilish details of hot water and energy . This van dweller forum has a mix of vehicles and applications and folks. I like that. My stuff is currently very steam punk and experimental vans and buses. Someday I can see trying the newer RV’s that are much lighter than the older ones.
I have only just begun researching refrigeration again. My solar mentor super insulated a conventional fridge. Wrapping 6” of insulation around a fridge helps a bundle. But he has a relatively big house.
Making ice involves a “phase change” of water. That can take energy. Hot water to steam is a phase change I believe. But steam is hazardous. So be careful. The expansion and heat can be dangerous. It’s against code to ever put a shut off valve in between the heat source and the relief valve.
I’m surprised to hear the Engel used so much power as a freezer. Human nature keeps me looking for a easy solution. But I’ve been wondering about a conventional freezer chest also.
I like my inverter but for now will continue looking for ways to reduce relying on it. I’d like my space heater and water heater to run straight from the sun as possible. That why I’m still interested in a passive heater or preheated.
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