One of the most efficient uses of solar power is solar hot water heating. A portable solar hot water heater will provide hot water for free during times when the sun is shinning, or slightly overcast. A portable solar hot water heater is handy for those times where you are on the go and seriously need a hot shower.
We take our portable solar hot water heater on camping and rafting trips. Lately, as our outdoor work increases our portable solar hot water heater is seeing more use. It would seem that building an outdoor shower would be in order, however that is another article.
You can build a portable solar hot water heater from materials you may already have. DIYers can build this solar water heater or a version of it in an afternoon. To get started you will need:
1/2 inch sheet insulation
20 foot copper tubing (1/2 inch) or black rubber hose
1/2 inch paddle bit
camping stove for carbon blacking
scrap sheet metal flashing
Plexiglas or picture frame glass
Roll your copper tubing into a tight coil free of kinks. The copper piping needs to be completely flat without overlap. To bend a spiral easier you can cap off the end's of the pipe after you have filled it with water. Using this method you can achieve a smooth bend. Garden hose can be used in place of the copper pipe. Spray paint the hose black to ensure proper heating. Using a garden hose, as a substitute for copper pipe, in a portable solar hot water heater will yield adequate amounts of hot water.
Make a box from scrap lumber big enough to hold your heating coil. Scrap 2x4's ripped on center or any other scrap lumber you have will work great for the box. Two holes need to be drilled in the side of your box to allow for piping to enter and exit. The bottom hole is where the water will enter and the top is the exit. You can build a portable hot water heater however big or small you like. Consider your water heating needs and choose your size accordingly. Remember to keep this unit portable.
Attach a piece of plywood to the back of your box and insert a piece of polystyrene insulation. Batt insulation can be used in a test unit, however I do not recommend it for long term wear and tear. Paint the solar hot water heater box using a flat black spry paint. The surface will absorb light when a flat spray paint is used. Gloss paint reflects light and won't give the same performance.
Plexiglas, an old window, or picture frame glass can be used on a portable hot water heating unit. A great place to find materials for this build is a Habitat Restore in your area. Use a glass cutter to size the glass for a custom fit to your homemade solar water heater.
When using copper pipe a solar water heating unit will work better if the pipe has had carbon blacking applied. Using a camp stove heat the copper pipe until it begins to carbon black. Carbon blacking the pipe is more effective than spray painting the pipe, it allows more heat to be absorbed.
Install the pipe in your box and place the glass on top for a test run. You can run a solar hot water heater by using a solar water pump or by simply allowing the unit to thermosyphon. A solar water pump will provide better performance and eliminate the need for priming.
Once you have tested the unit and are happy with the build you can seal the glass top. Use a clear silicone bead to seal the glass to the solar hot water heater box. Clear silicon will allow you to access the unit if there is ever a problem.
A portable solar hot water heater is great addition to an RV or camping trailer. Free hot water can be had on those long trips of rest and relaxation.