Passive Solar Energy Technology Guidelines

Solar energy innovators Jon Hammond, David Bainbridge, Harold Hay, and Steve Baer provide MOTHER EARTH NEWS readers guidelines to using their passive solar energy creations.

| November/December 1975

Solar energy innovators Jon Hammond, David Bainbridge, Harold Hay, and Steve Baer share their solar energy creations with MOTHER EARTH NEWS readers. 

Passive Solar Energy Technology Guidelines for Homes

Solar Heating and Cooling Guidelines for Windows by Jon Hammond and David Bainbridge

The windows on an average house here in the United States are responsible for about 50% of the building's heat gain during the summer and 50% of its loss in the winter. Anyone interested in solar heating and/or cooling a residence, then, would be wise to pay particular attention to making the windows on his or her home do exactly what he or she wants them to do. Luckily, some rather minor changes can be made to windows to markedly improve their thermal performance.

A great deal of a building's summer heat gain comes in through its east and west windows. You can control this temperature buildup to a large extent by putting a screen of vegetation, a bamboo shade, a bris-de-soleil, or an extra pane of glass right over (but a little distance from) the glass already in the opening. This can, of course, become somewhat expensive if you have a large number of windows to cover . . . since the necessary trellises and/or framing must be built strongly enough to withstand wind, rain, etc.

For this reason, you may find it easier and less costly to fit your east/west windows on the inside with insulated shutters made of either fiberglass or urethane foam. That's shutters, not drapes. Interior drapes are less effective and can even increase heat gain within a house unless they're well-sealed around their edges and across the top and bottom.

South windows are a different story. If properly protected by an overhang, they can be shaded from the high summer sun and allowed to admit Ole Sol's warming rays when the sun is low in the winter sky. You can calculate just how far such a projection should extend out over any window by multiplying the height (in inches, feet, meters, or any other unit of measurement) of the opening to be protected by your home's latitude and then dividing by fifty. The overhang can then be constructed of either solid material or slotted . . . or covered with vegetation.

The colder the climate in which you live, the fewer north windows your house should have. Cover the ones you don't need — inside and out — with insulation and board them over. Or fit them with insulated internal and/or external shutters which can be opened during the summer but tightly fastened against frigid January winds.

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