A Homemade Solar Water Heater

For one Florida family, it made more sense to build a homemade solar water heater before they actually had a home.
September/October 1979
http://www.motherearthnews.com/renewable-energy/homemade-solar-water-heater-zmaz79sozraw.aspx
The homemade solar water heater enables Bill and his family to clean up at the construction site, because he built the heater before he built the house!


PHOTO: WILLIAM J. WEBER

Last summer my family and I started digging out the foundation for our new home. However, after only two sweaty days of laboring under the Florida sun, I realized that we might be going about the whole project in the wrong order. Maybe, I thought, we should erect the solar water heater and shower — which we'd already planned as part of our new homestead — before constructing the house! Well, the more I considered this notion, and the more layers of grime built up on my tribe's bodies, the more that bit of backward logic began to make frontward sense.

As you can probably imagine, the whole family clapped and cheered when I proposed my topsy-turvy suggestion to them. So I sat down to research the current literature on solar water heaters. I studied every book and article I could find, but ended up more confused than educated! All the plans called for elaborate pumps, sensors, control switches and other complicated paraphernalia.

(Oh, I did learn one thing: we sure weren't going to buy a heater. Some of those commercial solar units cost over $2,000!)

It took a lot of time and sifting, but I finally devised a simple and inexpensive homemade solar water heater that I knew "us regular folks" would be able to build. In fact, my design involves only three steps:

First, build a glass-covered wood "hot box" to catch the sun's heat.

Second, install a manifold of copper water pipes inside this collector box so the gathered warmth will heat water.

Third, hook the outlets from the manifold to a storage tank (this container should be set above the heat collector) so the thermosiphon principle will move water from the collector to the tank. (That fancy-sounding phrase, "thermosiphon principle," simply means that, since hot water rises and cold water sinks, liquid heated in the closed loop system will move up toward our elevated storage container, while cooler water will circulate downhill toward the collector to soak up more sun.)

Glass, Wood, and Copper

We initially planned to construct a 48-by-96-inch collector box, but quickly scuttled those dimensions when I learned that a sheet of glass large enough to cover such a container would cost over $60! That price tag forced me to do some rethinking and to come up with an economical solution: I decided to make panels out of old aluminum awning-type windows! Several of the discarded 15-by-34-inch glass rectangles were lying around our homesite, and I was able to scrounge up a few secondhand panes for $1.50 each. Then all we had to do was adjust our collector size (we made it 34-by-90-inch) and line up six windows in a row to get $60 worth of glass cover for less than $9.00. (Besides, the lightweight aluminum units are a cinch to install and would be easy to replace from standard sources of supply if broken.)

A plumber friend gave me an old water heater to use for our storage tank, and I was able to "scavenge" all the black plastic pipe and odd fittings I'd need to connect all my units, and plenty of nails as well. Still, try as I might, I couldn't get around shelling out hard cash for my wood and copper materials.

The lumber costs weren't too severe. In fact, I bought all the wood I needed for the box's sides and support pieces, plus two sheets of styrofoam insulation and one of pegboard Masonite, for a very reasonable $25.59.

Our project did require one "killer expense," though: copper. I didn't want to spend any money I didn't have to, but I also figured that the outlay for our conducting medium was no place to cut corners. Copper is incredibly efficient at absorbing and releasing heat. And any less expensive collector material would have given us a "temporary gain but a permanent drain."

So, to build the manifold, I bought three 20-foot lengths of three-quarter-inch copper pipe, two rolls of 50-50 solder, one can of flux, and numerous fittings. That added up to an admittedly not inexpensive $75.72. (Of course, half-inch pipe and parts would have cost less, but such smaller diameter lines are too restrictive for good thermosiphon flow.)

I also paid $45 for a large 12-gauge copper sheet, which became the main "heat catcher" inside the box. This material is commonly sold in a 36-inch width, so, rather than cut off two inches of copper to meet my 34-by-90-inch requirement, my local sheet metal salesman kindly bent a one-inch border along each side, which made the piece both more rigid and easier to fasten.

To Work, To Work

At last we were ready to build. We made the 34-by-90-inch (measured on the inside) frame from two 12-feet long 2-by-6's. This rectangle had 2-by-2's spiked along its sides and 2-by-4's at its ends to support the collector plate. An extra 2-by-4 was nailed across the middle of the box as a brace. Then we covered the frame's "bed" with a piece of one-eighth-inch pegboard Masonite and two sheets of heat-holding Styrofoam insulation.

Next we started on the main task: welding our copper pieces together. The first stage of this "penny metal" work involved constructing the pipe manifold, a "jail-door" structure that had four "bars" inside a frame-fitting rectangle. (Since each interior pipe section had to be fastened to the top and bottom pipe lines by three-quarter-inch T's, we did a lot of cutting and soldering at the manifold's ends.)

After that job was done, we laid the $45 copper collector sheet on a level concrete surface (so the heated material wouldn't warp) and brazed the manifold to this backing. Then we put the pipe-to-sheet assembly in its wood and Styrofoam frame bed, soldered the supply, discharge and relief valve lines in place, and topped the finished structure with the six awning windows.

A Trying Moment

To test the airtightness of our manifold, we plugged the collector's intake line, attached a garden hose to the top outflow opening, and trickled water into the pipeworks until air quit coming through the relief valve outlet. Then we tightened up the release mechanism, opened up the hose spigot and let 'er have it!

Sixty pounds of water pressure rushed into our lines. The pipes held for about ten minutes, then a small trickle started running down the collector, so we drained the conduit and resoldered the leaky seal. We left the equipment under pressure all night for its second test, and — thank goodness — when we examined our "sun catcher" the next morning, not one drop of H20 had escaped.

Hot Times

The last construction steps were to paint the collector sheet and manifold flat black, coat the exposed wood with a protective oil-based covering, set the water heater in place (at a 45 degree angle), attach the storage tank and rig up our outdoor shower.

That was that. For about $160 in materials, we'd built a solar heater that now gives my whole family an abundant supply of free hot water. (In fact, we actually had to add a cold water line to our shower stall to keep from getting scalded on especially sunny Florida days!)

Now I'll admit that our fresh air facility does look kind of silly perched by itself on the side of a hill, but we're all as blissful as bluebirds over our outdoor showers. After all, it may take us more than two summers to finish our house, but we're enjoying the pleasures of sun-heated bathing right now!


Bill of Materials

Lumber

(2) 2" x 6" x 12'              $6.30
(2) 2" x 2" x 8'                1.50
(1) 2" x 4" x 10'               2.31
(1) 1/8" x 4' x 8' pegboard     6.98
(2) 1" x 4' x 8' styrofoam      8.50

Copper

(1 ) 36" x 90" 12-gauge sheet  45.00
(3) 3/4" x 20' pipe~ type M    52.20
(11) 3/4" T's                   6.50
(5) 3/4" L's                    1.50
(3) 3/4" male adapters          1.32
(2) rolls 50-50 solder         13.02
(1) can solder flux             1.15

Miscellaneous

(6) l5" x 34" awning windows    9.00
(1) relief valve                4.50
(2) metal insert adapters       1.50
Total Cost                   $161.31

EDITOR'S NOTE: While we congratulate Bill for his clever design, and acknowledge that Mr. Weber's homemade water heater is perfectly suited to his family's needs, we should also add that his device won't be appropriate for everyone because there's no feature in Bill's collector to keep the water in his pipes from freezing! Since such a mishap would obviously damage the unit, any folks who want to copy William's ideas, yet live in colder climates than the Floridian enjoys, should include some method of preserving their pipes. 

One solution to this dilemma would be to use Bill's solar collector in the summer and a wood-burning stovepipe system in the winter. This approach is explained in "Use Your Wood Stove as a Water Heater."  

The most common "collector-protector" technique, though, is to install a heat exchanger in the storage tank so that fluid coming from the collector warms water in the tank but remains, itself,  within a closed heating circuit. The sun-grabbing liquid in this sort of rig can be mixed with antifreeze to protect it from bitter weather. Two examples of the method are discussed in [1] "Doyle Akers' $30 Homestead Solar Water Heater" (Doyle used salvaged air conditioner coils to build his exchanger), and [2] "More Ways to Recycle Old Refrigerators Into Low-Cost Solar Water Heaters" (MOTHER EARTH NEWS' researchers recycle a gas-fired hot water tank into an efficient heat exchanger. The article also displays a passive no-heat-exchange unit that our inventors designed. This particular model is protected from frostbite because it can be closed up at night!) 

Several examples of direct heaters that, like Bill Weber's model, are inexpensive do-it-yourself solar devices but don't have any freeze protection appear in "The Khanh Solar Water Heater,"  "Build a Simple Solar-Heated Shower," and "Recycle a Refrigerator Into a Solar Water Heater. 

Lastly, a good explanation of the solar thermosiphon principle can be found in our interview with David Wright.