Solar Water Heating - Fiberglass RV


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Old 07-17-2007, 11:35 AM   #1
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My propane water heater needs to be replaced, and because I am thinking of adding a solar panel to recharge my batteries, I was thinking that maybe I could also use the panel to heat up water.
Any thought or suggestions on this? I believe I would be looking at something about 60watts.
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Old 07-17-2007, 12:03 PM   #2
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It takes a lot of energy to heat water and solar panels just don't put out much. I have one of those electric water heaters to heat 4 cups of water in 5 or 6 minutes (110 volt). It is over 1,000 watts. They do make 12 volt rods for a small electric water heater (they replace the 110 volt versions of the rods), but they are 600 watts. To give you an idea of what that means, your 60 watt panel x 6 hours of daylight = 360 watt hours. That means it could run the 600 watt electric water heater for 1/2 hour if you used the total output of your solar panel for the entire day. You would need much more solar power and would also need a good sized battery pack to store the energy to even consider doing something like that with solar. Propane is much better suited to run a water heater in a trailer or RV. One option that some people use is to forgo the water heater entirely and get a solar camp shower (I believe Coleman makes one). It is basically a black plastic bag that you hang in the sun and you can have a hot/warm shower that way. I haven't used one so I don't know how well they work.

Good luck with your project,

John
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Old 07-17-2007, 12:13 PM   #3
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My propane water heater needs to be replaced, and because I am thinking of adding a solar panel to recharge my batteries, I was thinking that maybe I could also use the panel to heat up water.
Any thought or suggestions on this? I believe I would be looking at something about 60watts.
Without doing the math, I think you'd find that to raise a gallon of water by 50 degrees using 60 watts of electricity, it would take on the order of a week.

Off the top of my head.
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Old 07-17-2007, 12:24 PM   #4
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Those black plastic water bags do work IF you are prepared to wait till mid afternoon (usually) to get any decent kind of warm water from them (at least in our latitudes up here). rendering them almost useless. ( ....and forget about a 'shower')
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Old 07-17-2007, 01:28 PM   #5
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It takes a lot of energy to heat water and solar panels just don't put out much. I have one of those electric water heaters to heat 4 cups of water in 5 or 6 minutes (110 volt). It is over 1,000 watts. They do make 12 volt rods for a small electric water heater (they replace the 110 volt versions of the rods), but they are 600 watts. To give you an idea of what that means, your 60 watt panel x 6 hours of daylight = 360 watt hours. That means it could run the 600 watt electric water heater for 1/2 hour if you used the total output of your solar panel for the entire day. You would need much more solar power and would also need a good sized battery pack to store the energy to even consider doing something like that with solar. Propane is much better suited to run a water heater in a trailer or RV. One option that some people use is to forgo the water heater entirely and get a solar camp shower (I believe Coleman makes one). It is basically a black plastic bag that you hang in the sun and you can have a hot/warm shower that way. I haven't used one so I don't know how well they work.
Good luck with your project,
John
I have never ventured into solar, but I didn't think it was feasible because I searched on the web and found nothing, except solar water heating for your home, a totally different set-up. Plus if John's math is even close, I don't think my wife would wait a week for a shower.
Back to replacing my conventional propane heater.
Thanks guys
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Old 07-17-2007, 02:39 PM   #6
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I have never ventured into solar, but I didn't think it was feasible because I searched on the web and found nothing, except solar water heating for your home, a totally different set-up. Plus if John's math is even close, I don't think my wife would wait a week for a shower.
Back to replacing my conventional propane heater.
Thanks guys
Solar hot water systems have three important components, a collector panel with tubes of water (or more exactly a water-antifreeze-type mix) that collects the heat of the sun, an exchanger where the heat from the antifreeze-water mixture is transferred to drinkable tap water (some systems skip this part), and an insulated storage tank (because, even mid-day in Arizona a collector would likely turn merely tepid water if it ran directly to a shower). All of this stuff is heavy, and a water-filled collector on the roof of your RV would make your trailer very tipy.

I have seen home-grown systems that people who don't move around often (or at all) have set up with a collector/exchanger/storage tank on the ground of the sunward side of their trailer-shack. The few I've seen have a part-still, part science-experiment kinda look to them.

--Peter
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Old 07-17-2007, 02:52 PM   #7
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I have a solar shower I bought a number of years ago. I think it was one of the first. It's a vynil bag, one side clear, the other black on the inside. I haven't seen one like it in while, maybe because the water gets too hot.
You fill it with about 5 gallons of water. Lay it in the sun, clear side up. In a couple hours you've got hot water.
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Old 07-17-2007, 03:08 PM   #8
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My propane water heater needs to be replaced, and because I am
About 10 years ago I installed a tankless propane instant water heater in the camper I had at the time. It worked very well. When I decide which trailer I am going to keep for ever, 13' Scamp or 4500 Trillium, I am going to install another tankless propane heater.
You can find them much cheaper than the standard RV water heater and you only use gas when the hot water is on.
If you only camp in full service campgrounds they make small point of use electric tankless water heaters. I just installed a whole house electric tankless water heater in my home and it would fit in the cubicle that your water heater is now in.

Just a thought,
John
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Old 07-17-2007, 07:38 PM   #9
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John, I like the tankless (or demand) heater idea... but I don't recall seeing a recommendation for a specific model which is either so inexpensive or well-suited to RV installation. Can you give us a make and model?
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Old 07-17-2007, 07:50 PM   #10
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The sunshine to electricity to heat scheme is handicapped by the inefficiency of the solar panel. That, and the cost of panels, is why the domestic solar water and space heating systems don't go through the electrical stage.

Herb, I couldn't come up with a number off the top of my head, and just had to know how close your (deliberately exaggerated) value would be...

1 gallon = 3.8 litres = 3.8 kg
50 degrees F = 5/9x50 C = 27.8 C or K
heat capacity of water: 4.186 J/(g-K) or 4186 J/(kg-K)
so one gallon heated up by 50 F by 60 watts takes
3.8 x 27.8 x 4186 / 60 = 7370 seconds, or 122.8 minutes

Well, two hours isn't a week, but it might as well be. If it takes full sun on a $500 panel to get just one gallon of lukewarm water, I wouldn't be taking a lot of showers or doing a lot of dishes...

Interesting idea, though. In very sunny locations if a lot of panel is available and hot water demands are modest it could actually work.
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Old 07-17-2007, 09:15 PM   #11
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John, I like the tankless (or demand) heater idea... but I don't recall seeing a recommendation for a specific model which is either so inexpensive or well-suited to RV installation. Can you give us a make and model?
A friend of mine bought a water heater off of ebay. He has had it almost a year now and is very satisfied with it. It is the one I will buy. Item #110150132355 on ebay is the unit my friend has.
With shipping it is about $200.00.

John Perry
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Old 07-18-2007, 09:03 AM   #12
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A friend of mine bought a water heater off of ebay. He has had it almost a year now and is very satisfied with it. It is the one I will buy. Item #110150132355 on ebay is the unit my friend has.
With shipping it is about $200.00.
John Perry
Interesting, I looked into tankless water heaters a while back and the cost were $800 - $1000 (probably for home use). One product specifically for RV's was around $600.

Here is another one I just found that does not have to be shipped from China.
http://www.omega2000group.com/tankless-wat...eater-p-30.html

Thanks for the info John, installing a tankless water heater is definitely the route I am going to go.
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Old 07-18-2007, 06:14 PM   #13
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We purchased a Coleman Hot Water On Demand it works really well. Runs on propane and has a 5 gal water bag which hooks up to the unit. Turn the spout out and turn the knob to anything from cool to hot. We love it. You can get a hose adapter or a shower adapter hose. Just a thought go to the Camping World site , they carry them.
Maggie
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Old 07-21-2007, 08:16 AM   #14
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We purchased a Coleman Hot Water On Demand it works really well.
Thanks for the info. I have seen those at Canadian Tire, and considered that option. I would perfer something mounted in the trailer. If using the adapters, I can hook it up to the water pump and shower I may consider it again. Now I am getting too many choices. Better too many than none at all.
MIke
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