Economy Solar To Go

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Also, there should be no obstructions—including coniferous trees—in the vicinity of the window. (Since this is a cold-weather heater, deciduous varieties growing a dozen yards or more distant shouldn't present a problem, because their bare trunks will cause little solar blockage.)

LOCAL TUNING

Start the project by figuring out what collector angle is best for your locale and situation. Generally, the tilt on a winter-only solar collector varies between 50° and 70° from horizontal, depending upon the latitude (northern areas require the more upright angles). Because the collector panels also serve as a lean-to storage shelter, they'll probably have to be fixed closer to the maximum angle to provide headroom. A 60° pitch, like ours, is a good compromise, since even a surface cocked 25° out of square with the sun's direct rays will absorb over 90% of the available energy.

With your face angle roughly established, check the siding panels around the window. Make certain there are no dryer vents, service hookups, or protruding casement frames that might get in the way of the flush-mounted collector framework, which will cover an area approximately 8' wide and 7' tall. Then, relying on our descriptions and illustrations as guides, gather your materials and prepare to assemble your collector.

DUCTS IN A ROW

The foundation consists of stacked 8" concrete blocks joined with Surewall surfacebonding cement (made by the W.R. Bonsal Co., P.O. Box 38, Lilesville, NC 28091, and available at contractors' supply houses) and set in a level, hand-dug footing trench. The number of courses will depend, naturally, on how high you need to position the collector platform and framework.

To economize on materials and provide a flush floor surface, we incorporated the coolair return duct right between the 2 X 4 joists that support the 3/4"-plywood floor. At its forward end, the duct feeds the two collector-panel inlets through a short connector. At the rear, it's tied in to the window plenum with a length of insulated-board duct. Notches cut at the front of the floor joists support the lower edge of each collector panel.

Because we wanted ambient lighting available to the upper sash of the window, we faced the stud-frame enclosure walls with Sun-Lite HP, a fiberglass-reinforced plastic glazing. A compact door allows access to the inside. The upper corners of the wall sections are joined together with a hollow, three-sided structural member that serves as a header and panel support, and a warm-air supply duct. Two openings cut into the face of that manifold are sealed to the collector-panel outlets with caulking . . . and a third hole at the bottom connects to the supply half of the window plenum through a second insulated duct.

The window plenum is simply a plywood box sized to fit in the sash opening and split into two chambers. The return side houses a closable air register, a filter, a 465-cfm squirrel-cage blower, and a line-voltage thermostat. The supply side merely connects to a 3" X 12" wall-mounted duct that runs through a partition and into the living area, where it's capped with a diffuser grille.

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