Let’s face it, this isn’t rocket science. Paint any container black and put it in the sun. Of course the amount of heat you get will vary a lot depending on location, time of year and cloud cover, but they are easy to build and provide a hot shower with a small investment. I started experimenting to make a lightweight portable unit to give me a hot shower while primitive camping. I have a pop-up slide in a truck camper, but it doesn’t have hot water or a shower. If you are building one for a cabin you can build it into an insulated collector box and boost the efficiency.
I have built two different heaters and I am happy with both styles. The first one is the easiest to build. I checked the plumbing aisle at the home store to get the most tubing for the least price. I found 100′ coil of 3/4″ black poly tubing for $20. I would rather have 1″ tubing to increase the volume, but the price jumped up too high. You can keep an eye on Craigslist for cheap tubing left over from a construction company. Short pieces can be joined together. I formed the tubing into a flat coil and secured it with wire ties to a scrap length of pvc pipe to hold it’s shape. I inserted a plastic hose barb with 3/4 npt threads in each end of the tubing. A standard garden hose can be tightened onto the 3/4 threads. You can spend a few more dollars for garden hose fittings, but I just snug the hose onto the npt threads with a pair of pliers. I wanted to use garden hose for the connections so I can park the camper in the shade and put the heater in the sun. I can add more hose as needed.
I put the coil in the sun and filled it with cold ground water. It was a sunny 75-80 degree day. 4 hours later the water came out too hot to hold your hand under it. I didn’t make any exact measurements, but I was happy with the results. I needed to make a mixing valve to temper the water. I had a couple hose cocks laying around and they were perfect because the garden hose will screw right on. I attached the hose cocks to a tee and added a ball valve to the other end of the tee. I picked up a cheap shower head and removed the low flow restrictor. I attached the shower head to the ball so I could take a “navy shower”. Now I could open the hot valve and wait for it to reach the shower head. I can add cold water as needed and use the ball valve to shut off the flow without the need to readjust the temperature. It gave me enough hot water for one person to easily shower and probable enough for two if you wash fast. When it runs out of hot water the changeover to cold takes place fairly slowly. It allows enough time to hurry up and finish before you have to freeze.
The second heater I built was made out of two 10′ lengths of 4″ pvc pipe. I had some drain pipe here so I used it. It’s not meant to be under any pressure, but since it was just collecting dust in the loft I figured I had nothing to lose if it cracked. If I were buying the pipes new I would get standard pvc or abs pipes. The abs would not need to be painted. I clamped both pipes next to each other on a couple boards. I drilled and tapped 4 end caps to take 1/2″ npt adapters. You can buy reducer fittings if you don’t have a tap. I used 1/2″ pvc pipe to make all of the connection. You can use 3/4″ pipe for more flow. Cold water is supplied to one end of the pipe. There is a tee to feed both pipes with cold water. The hot water exits the other end of the pipe through the 1/2″ npt adapters. It tee’s back together and supplies hot water to my garden hose. This heater holds much water than the coil and has less surface area exposed to the sun so it takes longer to heat up. It can supply a comfortably warm shower after sitting in the sun on an 80 degree day. I didn’t need to be tempered, but it will need it in warmer weather.
I set up a 12v utility pump so I could shower if running water wasn’t available. I have a whole house water filter to remove any debris and a tee to supply hot and cold water to my shower head. I added a pressure gauge just so I could have an idea what is going on in the system. Now I can draw water from a stream or any other fairly clean source. If you have an off grid hunting cabin you could supply it from a rain collection barrel. As you start making the connection with the garden hoses you might run into a problem connecting two male end together. You can pick up a couple female/female connectors, but I used washer machine hoses because I had some here. My pump/filter system, shower head and valves and a couple hoses all fit right into a rubbermaid container for storage.
The coil or the pipes could be mounted to the roof of your rv or camper. Even if you have a water heater this could increase the time you can boondock and save enough fuel to pay for itself quickly. You don’t have to copy my system exactly. Use it as a guide and put together something with the parts you have on hand. I have been thinking of a good way use this system seasonally in my house. I want to leave the existing plumbing in place and add a second shower head. I want to be able to have conventional hot water if needed while still taking advantage of the sun’s green energy during the summer months.
This article included several photos. Be sure to view them all.