Active Passive

| 12/1/2009 9:45:32 AM

Passive SolarIf 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.

11/2/2010 3:58:46 AM

To Scott, who has a problem with this article: I don't want this to sound too oversimplified, but I'm sure if you presented a well-written article to Mother Earth News, outlining the details you believe the article should have, they would consider publishing it.

1/5/2010 9:56:17 AM

It can get complicated, Scott, but it doesn't have to. I've been in dozens of passive solar homes that were comfortable, efficient and easy to maintain. To discuss all the variables of architecture, materials and climate is the province of books, not blogs.

Scott Raney
1/4/2010 8:20:13 PM

The phrase "no-brainer" certainly applies to this article. Rather than an enlightened discussion of the pros and cons of passive solar technology, it provides a ridiculously oversimplified description of the concepts, no data on actual projects that work, and a brainless, feel-good conclusion about how wonderful the world would be if we all believed this drivel. Where is the discussion of the poor temperature regulation of passive solar houses? Or any mention of the expensive, complex, and intrusive movable insulation systems that are required to prevent the building from losing more heat during nights and cloudy days than it gains during periods of full sun? In my opinion, passive solar is the "Hybrid SUV" of energy technology, and articles like this have no more benefit to anyone than having them watch commercials for 20mpg hyrid SUVs when what the world needs (and should expect) are vehicles that get 3, 4, or 5 times that.

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