Do-it-yourself Solar Heating

All of the heat energy used in our homes comes directly or indirectly from the sun. Some of it, such as oil, gas, or coal, has stored the sun’s energy over millions of years. Residential solar systems use the sun’s heat as it shines on houses each day.

Be realistic in your expectations for using free solar energy to heat your home. Trying to provide 100 percent of an existing home’s heating needs with solar is difficult to do while maintaining acceptable comfort. An initial target of a 10 percent savings is reasonable for a do-it-yourself project.

Just having the sun shine in a large window is effective passive solar heating, but it can be made more efficient by providing an adequate thermal mass in the room. This mass captures the sun’s heat so the room does not overheat or lose as much of the heat back outdoors. Once the thermal mass warms up, it slowly dissipates stored heat back out into the room once the sun is no longer shining.

Two projects for the home
The best solar option is to build a solar Trombe wall, consisting of stacked bricks or concrete blocks very close to a window. The stack gets warmed by the sun, which creates an upward warm air current. This circulates warm air throughout the room while it also stores heat for nighttime.

Another project is to make a shallow, flat solar heater that rests against the outside wall facing the noon-to-afternoon sun. A size of 4×8 feet is good because it makes the most efficient use of inexpensive standard lumber. The box has to be only the depth of standard 2×4 studs.

Construct a plywood box and attach foil-backed rigid foam insulation on the inside with the foil facing inside and painted flat black. Cut one hole in the back at the top and one at the bottom and install duct stubs. Cut holes in your house wall so the duct stubs come through to the indoors.

Cover the box front with a sheet of clear acrylic plastic and seal it. The solar-heated air will flow out into your room. Make airtight indoor covers to seal off the duct stubs at night.

EFFICIENCY IDEA

Building more thermal masses
There are several ways to provide a thermal mass. You can make planters with concrete blocks or bricks or pour your own concrete planters using tinted concrete similar to concrete kitchen countertops. A large terrarium with damp soil has a reasonably high thermal mass and adds humidity to the air.