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Discussion Starter · #1 · (Edited)
Has anyone looked into solar water heaters? I took a look today on Amazon and found this 24"x24" panel which is supposed to heat 5 gallons a day with a recirculating pump that can run off of a 5 watt 12 volt solar panel without battery. I don't suppose recirculating is necessary when there's no sun.

[ame]https://www.amazon.com/dp/B007F54PUY/[/ame]

I'm thinking if you add some plumbing and an insulated tank and maybe a small 12v immersion heater for supplemental heating run off house batteries and you could have a nice homemade alternative to propane systems. You can gang multiple panels together for additional capacity. Might need a control system, but I've designed those before.

I don't have a van yet, but I've always been interested in solar, so I'm tempted to buy a panel and a pump and start experimenting. If so, I'll let you know what I find out.
 

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Discussion Starter · #2 ·
Update: turns out the company (Heliatos) sells complete kits for rv and marine applications.

http://shop.heliatos.com/Kits-for-RVs-and-Boats_c24.htm

All you have to supply is the water heater. And I see Atwood sells a replacement 6 gallon aluminum tank 91059 for a combination gas/electric model. It comes with a styrofoam case and mount points for a relief valve and electric element. It's a 1400 watts 110 volt unit, and it has a thermostat separate from the propane half of the heater. So it may be easier to cobble a system together than I originally thought.
 

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Have you considered the Isotemp water heaters tied into the coolant loop?
Very effective and they also have a 750 watt element if you are not driving.
We have one in our Sprinter and only takes 30minutes of drive time to heat
the water in the 4 gallon tank. It stays hot for hours. I wouldn't want the hot
water tank inside the living space because it would add considerable heat to
the interior. Should be enough room to place a 4 gal unit under the vehicle
somewhere.

http://www.isotherm-parts.com/index...34_107&zenid=68f53afe69a026b5a4b4e30634f1a9ab
better price: http://www.marinewarehouse.net/Isotemp.html
 

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Discussion Starter · #4 ·
Interesting. I'm new to this and had assumed these were diesel units and not tied into the cooling system. I agree a 4 gallon tank would be easier to tuck in somewhere than a 6 gallon tank and a 750 watt immersion heater preferrable to 1400. Not sure about running hoses from the engine to this system. But with this sort of performance I'd probably forego solar altogether. Food for thought. Thanks!
 

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Ziggy Stardog,
You will still want solar electric I would suggest.
I have built several of the systems working on the principal of the ones you referenced. I currently have a 1 panel 4’X8’ on my home in AZ. It works amazingly well and produces about 90% of our hot water demand. In December and January we augment it with natural gas. My system is like the diagram in the thumbnail picture. Freeze protected, solar driven, and solar heated with a heat exchanger. It has been working for 18 years, flawlessly. Their kit price is fair. I have though about one for the van but without an internal shower our needs do not rise to the level it is worth it to me. Neither would the isotherm. Given the choice I would go Hein’s route I think. If I had a large class C or A motorhome I’d do solar.
For our use I have been thinking about the black solar tank with a shower fitting at the back of the van that was built by a poster here but for the life of me I cant find it.
 

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I wouldn't want the hot water tank inside the living space because it would add considerable heat to the interior. Should be enough room to place a 4 gal unit under the vehicle somewhere.
Hein, is yours under your Sprinter? Did you provide protection somehow?
 

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Our Promaster is the second camper we've installed an Isotherm inside a campervan and I don't believe there's any appreciable heat added to the living space and we recently drove and camped in some very hot weather in Illinois and Wisconsin.

I have the Spa model with the plastic shell over the insulated internal stainless steel shell and I'm typing this in the van now after driving several hours and the outer shell is not even warm to the touch. The insulation does a very good job keeping the heat in the tank.

I did add foam pipe insulation around the coolant hoses after they came up through the floor and the metal fittings as they did radiate heat.

Hein, thanks again for the tip about drilling the hole in the cover to reset the over limit switch to make the 110v element work after heating with the engine.

Had I know about that before, I wouldn't have thought the electric element in my previous camper was broken.
 

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Discussion Starter · #10 ·
Ziggy Stardog,
You will still want solar electric I would suggest.
Probably so. I'm a little leery of tapping into the cooling system. I read up on a cheaper Atwood/Dometic system and it requires mounting the tank at or below the engine. So under the hood or below deck seem the only straightforward options for these. Not sure if it's the same for the IsoTherm.

I was considering a layout akin to the Hymer Aktiv, with a small hot water tank under a second seat behind the driver with a wet bath behind that. I see plenty of small "point of use" water systems in small bathrooms and kitchens without thermal incident, but maybe I'm underestimating how thermally tight a van might be-- even with windows.

I'm interested that you went the glycol route. I live in Northern Florida, so I thought I might be able to get away with a water-based system and drain it during the rare freeze warnings. It seemed like you could always convert later and use an external heat exchanger. I guess I'd have to stick the expansion tank on the roof.

Right now I'm trying to come up with a suitable tank. My flexible half-pregnant option is a $300 Atwood/Dometic marine unit. It already has a heat-exchanger so I'd have all options: I could leave it disconnected and go all water, I could go with glycol for the solar for freeze protection, or I could bite the bullet and hook it to the engine cooling system.

There's the sub $200 6 gallon Atwood replacement "inner tank" I'd already mentioned. Comes with most everything I'd need, aside from a mounting solution. And there are a number of domestic units in the 4-7 gallon range priced from $130-$200. Some of these are a little taller than I'd like. Decisions, decisions.
 

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Discussion Starter · #11 ·
Encouraging news about the Spa unit. I see that there's a requirement that it be mounted below the engine. Is it possible to do this in the cabin of the PM? I was thinking of locating the heater on the floor below a second seat.

Still leery about plumbing the engine coolant. I'm wondering if it's feasible to use the heat exchanger with a glycol loop to one of the solar panels instead. I guess the expansion chamber would have to go somewhere like the roof for that. Was considering the Atwood marine units, but read some reviews that questioned the longevity of aluminum and the Spa unit isn't much more costly for stainless steel. Not sure how the lower temperatures of solar would mix with the mixing valve and thermostat arrangements.
 

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That solar panel would return 180º water to the tank, same as the radiator heat. I use RV antifreeze in my home solar loop because it is non toxic and code requires a double walled heat exchanger to use glycol. I change it out every 5 years as the manufacturer suggests. The expansion tank can be small (size of a quart jar) if you can find a tiny one. The pump needs to be very low flow as the efficiency of all this stuff works better if the Delta of the temperatures is high. Pushing a lot of water through the panel doesn't let the fluid get hot enough so slow is better. The best part of such a system is it just makes hot water. Nothing to run from your batteries, no differential thermostats, no monitoring, one moving part!
Personally I would think it was great to have someone do a system.
 

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That solar panel would return 180º water to the tank, same as the radiator heat. I use RV antifreeze in my home solar loop because it is non toxic and code requires a double walled heat exchanger to use glycol. I change it out every 5 years as the manufacturer suggests. The expansion tank can be small (size of a quart jar) if you can find a tiny one. The pump needs to be very low flow as the efficiency of all this stuff works better if the Delta of the temperatures is high. Pushing a lot of water through the panel doesn't let the fluid get hot enough so slow is better. The best part of such a system is it just makes hot water. Nothing to run from your batteries, no differential thermostats, no monitoring, one moving part!
Personally I would think it was great to have someone do a system.
Hi RD,
It actually turns out that higher flow rates give better collector efficiency. You get less temperature rise for each time the water flows through the collector, but the water goes through the collector more times and net result is higher efficiency and higher tank temperature after a given amount of time with higher flow rates. Reason is that almost all the loss in effciency on a solar thermal collector is heat loss from the hot absorber out the glazing, and running higher flow rates through the collector reduces average absorber temperature and this reduces heat loss out the glazing.

Numbers to support this on this page: http://www.builditsolar.com/References/ColFlowRate.htm#Best
Its not a huge deal as efficiency drops from about 50% with 0.07 gpm/sqft down to about 45% with only 0.01 gpm/sqft of collector.


You can make these water heating collectors yourself for about $5 a sqft:
http://www.builditsolar.com/Experimental/CopperAlumCollector/CopperAlumCol.htm






I'm using this one on my house to provide hot water and some space heating:
http://www.builditsolar.com/Projects/SpaceHeating/DHWplusSpace/Main.htm





A nice thing is that the solar thermal collectors are about 3 times more efficient that PV panels.

!!! Build It Solar !!!​

Gary:)
 

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Discussion Starter · #14 · (Edited)
Personally I would think it was great to have someone do a system.
Sure, I'm game. Just have to get a van first. I see plenty of off-lease ones and I can have any color as long as it's white. I'm looking at two-tone paint or a partial wrap if I go that route.

Just waiting for the 2018s to start arriving so I have more negotiating power. I tend to buy all my vehicles around Halloween for just this reason.
 

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Thanks GaryBIS,
In our experience controlling the fluid rate improves the temperature of the storage tank so we get a supply of HOT water where faster flow results in WARM water as monitored by a thermometer on our return line from the panel. I have done no study of the total heat recovered but prefer to have a nice hot shower with the stratified hot water in the tank as opposed to a tepid shower from a whole tank of sort of warm water. I know technically this is not efficiency (my bad) but having the exit temperature of the panel at 160º+ in full sun is more satisfying than 90º. Our relatively small single panel is designed and aimed for mid-winter AZ. If we return in September there is no need for hot water (my panel is covered) as the shallowly buried supply water comes into the house about 135º so your “cold” faucet is now the HOT water and most residents use the hot faucet from the turned off water heater to get the temperature of the water DOWN to a comfortable temperature! In June we have a “changeover” time when we go back to that. In the winter we use the hot for hot just like you. I leave and arrive to miss both changeover times if I can.
 

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Hmm... would an automotive one work? Or do I need a fancy-pants one? I'm having trouble finding anything under 2 gallons.
RV systems have accumulators for the pump which I expect work like bladder water tanks and should provide the same function as an expansion tank, BUT need to be rated for 200º water.

[ame]https://www.amazon.com/Seaflo-SEAFLO-Pre-Pressurized-Accumulator-Tank/dp/B01MVA6GCC/ref=sr_1_2?ie=UTF8&qid=1502540551&sr=8-2&keywords=RV+accumulator+tank[/ame]
 
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