Q. We have teenage daughters who take long showers. Our water heating costs are sky high. We are on a tight budget, but want to use some solar water heating. Is there a system we can make ourselves?
A. For a typical family of four, heating water can account for about 20 percent of its annual utility bills. If you have two daughters taking long showers, yours may be somewhat higher.
Don’t expect a solar water-heating system to cut your water heating costs to zero. A target savings of 40 to 50 percent is reasonable for a simple system.
Using solar energy to heat water is generally more economically feasible than for space heating. Your family uses hot water year-round, so the savings continuously pay back the initial investment. By contrast, a solar space-heating system is used only about six months a year, so the payback period is often much longer.
Before you consider using solar or any other efficient water-heating methods, install low-flow showerheads with shutoff tickle valves. Also talk with your family about taking shorter showers. This not only reduces water heating costs. It also conserves our fresh water supply.
Unless you are an accomplished craftsman, I suggest you make a simple batch solar water heater. This is called a
passive system because the water moves through it due to the incoming line pressure or temperature differences, yet it can be quite efficient and effective.
Attempting to build an active solar system— with collectors on the roof, plumbing, pumps, control systems and storage tanks—is beyond the skill level of most
homeowners. I am a mechanical design engineer and don’t think I could build an active system from scratch. There are kits available, but it takes a high skill level to
install and set it up properly.
A batch solar system is used as a preheater for your existing water heater. The incoming cold water flows through the solar preheater before going to your water
heater. Each degree the water is warmed in the preheater reduces the amount of electricity used by the water heater. This also reduces your peak electricity demand
for your electric utility.
The simplest batch solar system is called a breadbox design. It uses a horizontal metal water tank inside of a box with a clear top. The sun shines in through the clear top to heat the water. A slightly more efficient option uses a tall box tilted at an angle to face the sun. This allows the warmer water to be drawn first from the top of the tank.
You can buy a stainless steel water tank especially designed for this application with the inlet and outlet water fittings. If you can find an old water heater that is not leaky, strip off the metal skin and insulation to use the inner tank. Paint it flat black to absorb more of the sun’s heat.
It helps to insulate the solid sides and bottom of the box, especially if you plan to use it most of the year. Very heavy insulation is not needed because the tank
will not get extremely warm. One-inchthick foil-faced rigid foam sheets should be fine. Attach them inside the box so they reflect the sun’s heat to the tank.
Install water valves and plumbing so the solar tank can be drained and bypassed during cold weather. Install heavy insulation around any exposed pipes and bury as much as possible underground.
The following companies offer solar kits and components: Alternative Energy Store, 877-878-4060, www.altestore.com; Solar Components, 603-668-8186, www.solar-components.com; Build It Solar, www.builditsolar.com; and Solar Direct, 800-333-9276, www.solardirect.com.