Heating water for our homes is one of the largest drains of energy

Heating water for our homes is one of the largest drains of energy, but for those who have had a cold shower on a chilly day, hot water is non-negotiable. This is one sacrifice even the greenest of green people aren’t generally willing to make. Luckily for them (and the planet), with a little forethought and ingenuity, it is possible to create a hot water heater that runs on the sun alone.

We might as well acknowledge that most of us aren’t going to re-plumb our homes to run on solar-generated hot water, which is understandable. However, that doesn’t mean this information can’t apply to you. Japanese-style outdoor showers have become quite the rage, and these could be the perfect opportunity to try out a solar hot water heater.

Outdoor showers are another great way to enjoy nature. More practically, they are good for cleaning up after a dirty day’s work without tracking it all through the house. Plus, for those who use bio-degradable soaps and shampoos, the water can be drained right into a garden or food forest.

The basic design of solar water heaters is to install tubing in an insulated box. The sun will heat water inside the tubes, and the insulation will keep it hot — sometimes scorchingly so — until it is drawn from the tap. Obviously, like solar power, these systems do require some sunlight to make the magic happen, but some designs, like evacuated tube collectors, are reported to work in overcast and sub-freezing temperatures. The sun’s radiation is just magic that way.

For those who just want to experiment with solar water heating, there is a very inexpensive and surprisingly effective way of doing so. Put water in a clear or black plastic bag (a manageable tank or five-gallon bucket would be a more permanent way of doing this), and put it out in the sun. After about an hour, the water will heat up, and even on relatively cool days, it’ll be warm enough to have a pleasant shower.

While the cheap and easy way might work for fun or for camping, most of us — if we are installing an outdoor shower in our garden — will be looking for something a little more substantial and permanent. That’s where the box-work will come in. And, here’s what you’ll need.

It begins with building a wooden box. Something about four feet by six feet should work fine (size can be adjusted to the materials available), and that would require a board for the back, two-by-fours as the sides, and glass to cover the top (look for used windows and be willing to cover the top with a couple of separate panes, if necessary). Black tubing will work, but copper piping is the best option for transferring and holding heat from the sun to the water. The inside of the box will require black paint and possibly (for a deluxe model) a copper plate. Then, it’s just fittings to connect water pipe in and out of the box, and there should be a water collector (or big bucket) leading into the heater, and a tank (five gallons or more) holding the heated water.

The box is very easy to build.

Simply screw the two-by-fours along the edges of the backboard so that they form sides. If you’ve gone the copper plate option, install it on the inside of the back board. If not, just go directly to painting the inside of the box black.
Install the inlet and outlet fittings into the box, and connect the coil of copper (this should be painted black, too) or black plastic tubing. About 50 feet of ¾” piping should work, but put as much as possible or is affordable.
Before sealing the box, connect water to it and test that there are no leaks.
Then, install the glass top. The feeder tank should be lower than the hot storage tank, and the hot water storage tank above the water heater, feeding the shower head.
The box needs to be in a sunny place, with the most sun being available when the box is angled to face the south (if you’re in the northern hemisphere). Consider using the box as a roof for the shower or possibly a sheltered changing area. In really sunny places, it’s not uncommon to need a cold water line to balance the water temperature.