A solar water heater for an RV? Is it possible? Wouldn't it be cool to unroll a small rubber collector on the roof of your RV, adhere it to the roof, plumb it into your small-ish water heater and have LOTS more hot water, while using less propane and/or electric to heat it? Sounds like a Free Lunch, doesn't it?
Nope. Not this time.
In a simpler system we have a collector of some kind (more on that later) on the roof and it feeds the hot water heater/tank directly. So there's no anti-freeze in the system, just water. Of course you'd have to make sure that it is drained in the winter (if you actually HAVE winters!) or have some way of draining water back into your water system and out of the collector if there was a danger of freezing. So far, so good. Since this project is really in the planning stages, I am not sure what temperatures the water will get to from the collector, so I will have to test some different configurations. I'm hoping I can set up a simple recirculating system that feeds my little Atwood 6 Gallon water heater.
I'll put bypass valves on both sides, so I can disconnect the collector from the hot water system. I mean, if it's cold, why heat all that extra water! That brings up another good point, since the collector has to have water in it to heat, then it stands to reason that you could have more gallons of hot water to use. I'm looking at adding a 6-10 gallon collection system so I should be able to have that much more hot water.
How do you get the water up to the collector? Good question....yes, I know I'm talking to myself, but that's okay. I figured a small 12v water pump near the inlet of the hot water heater running from power I get from my solar panels (or you could install a small one amp solar panel) with a manual switch or perhaps a flow switch or temperature switch or even a pressure switch wired in for automatic operation. Since the system only needs to pump water up to the collector and that will only happen when the sun is up, it won't really affect my solar charging or power consumption. I'll have to make sure the pump will lift water to the height of the roof. The one pictured will lift water 2.5 meters or 8.2 feet and will pump 350L/hr or 92.5 gallons/hr of water. It uses 450mA of current. Gravity will be used to get the newly heated water back down to the hot water heater.
Now, on to the roof! I'm looking at a flat, tubular style of rubber or polypropylene collector. These get connected to "manifolds" that if needed can be daisy chained together to form the basic collector. From the manifolds they will be connected to flexible hoses leading down into the coach, probably through the refrigerator roof vent opening.
I've got to figure out how much square footage of collector we'll need to feed the water heater. Since it's flat and will be a few square feet in size the weight of the water will be spread out. that's a good thing because it weighs 8.4 lbs/gallon. I try to be as nice to my roof as possible. Roof leaks kill so many RV's.
I am waiting for several manufacturers to get back to me with some real technical specs of the collector material. Mainly, I'll need the amount of liquid they hold per square foot and how much they will heat water at a given sun level. Then I'll be able to calculate how much area the collector will have to cover to make this work.
Of course, since it's WINTER here, I can't really do any heavy, "real world" testing, but I will assemble the test system now and plan on writing a second article as more information is available.
Be seeing you...Down the Road,
Rich "The Wanderman"