Active Passive

Reader Contribution by Staff
article image

If wind-power is a no-brainer, what about passive solar power? It’s ubiquitous, clean, renewable and free. Our homes could cut their heating requirements dramatically simply by capturing the solar energy that lands on the house naturally. Imagine if all new homes had a row of tall, insulated windows on their solar exposure (the south side, if the home is north of the equator). Then, we add a heat-absorbing concrete floor in the room with the windows. All day long the sunlight warms the house and heats up the concrete. At night the concrete radiates warmth.

The basics of passive solar architecture are simple.[1] First, the building needs what the engineers call an “aperture” through which the sun can shine – in other words, a window. If the sun shines into a window in your home or office, then you have a passive solar collector.

Second, if you want to store some of that solar energy you need an “absorber,” some “thermal mass” that can be heated by the sun. Dense substances like stone, concrete or adobe are very good for storing thermal energy. Sometimes a water tank is used to store thermal energy with the added benefit of being able to distribute the warmth in pipes. Less dense materials – like wood or carpet – can’t effectively store heat.

Third, for a building to be effectively warmed by passive solar energy there needs to be some way of distributing the warmth through the house. In an Earthship, nearly every room has its own solar aperture and thermal mass, so there’s no distribution problem. In more complex structures, fans, ducts and blowers may be used to circulate warm air.

And passive solar buildings need some control mechanism to regulate their temperature – open windows, broad eaves that block the summer sun, insulated shades.

It’s fun to think about homes heated entirely by the sun, but the larger benefit today could come from a tiny alteration in the way we think about site design and construction. Very minor changes can orient buildings more efficiently and place some thermal mass in the sunlight. Every calorie of solar energy captured on a cool day preserves a calorie of fossil fuel. If all our new construction was designed with solar energy in mind, imagine the global benefit. The reductions in energy consumption and carbon emissions are incalculable – but they would be enormous.

Today most new homes are sited without any reference to solar energy at all. A few builders are catching on, however, and making the simple adjustments necessary to turn new houses into solar collectors. They are adding big insulated windows, facing them toward the sun and painting And homeowners are pouring concrete pads under their new sunrooms so they can harvest free heat from nature, in the simplest way possible.

Bryan Welchis the Publisher and Editorial Director of Ogden Publications, the parent company of MOTHER EARTH NEWS. Connect with him on.

For further optimistic discussion about our future, read Beautiful and Abundant by Bryan Welch and connect with Beautiful and Abundant on Facebook.

Photo courtesy the National Renewable Energy Library/Tierra Concrete Homes

[1] U.S. Department of Energy. Technologies. Passive Solar Building Design. Sourced October 30, 2009.