Solar Power

Passive solar, or passive solar gain, is a method of using the sun's energy into usable heat or to cause air movement, while employing limited or no other technology. Solar energy systems that use photovoltaics or a pump to move heated water or air are considered active solar methods, since they employ technology to increase the usable heat from a given solar energy generation method.

You've experienced passive solar heating when you've walked by a large, sunny window or sat beneath a skylight. The glass magnifies the sunlight, creating a warmer area near the window or skylight. The reverse is true if the glass is treated to block the sun's rays-that area then feels cooler than its surroundings.

Passive solar utilizes the design of a space and the natural flow of energy, rather than mechanical heating or cooling methods. Especially if employed in the design and construction phase of a building, passive solar techniques can reduce energy costs while increasing the "livability" of the building. For instance, utilizing natural daylight not only reduces energy costs by allowing artificial lighting to be turned off, but the daylight is full-spectrum, much better than incandescent or fluorescent light.

Because passive solar utilizes no-tech or low-tech, it's amazingly easy to use. Some buildings are constructed with a solar chimney or thermal chimney, which is simply a vertical shaft painted black. During the day the black paint heats up, as does the air inside the chimney.

We all know that hot air rises, and as it heads up the chimney it pulls warm air within the building along for the ride. Cooler air from lower elevations comes in to replace it. The combination of cooler air and the draft of moving air creates a fresher environment within the building.

Many homes have been constructed with a passive solar attic venting system. A hot attic increases air conditioning costs in warm climates, and therefore energy costs and pollution. By tying a solar chimney to the attic space, the attic heat helps speed up the chimney convection and keeps the house below cooler.

A variation on the solar chimney is the evaporative down-draft cooltower. Water is allowed to evaporate near the top of a tower that's located next to or built on to a house or business. Air comes in an opening near the top of the tower, passes over the water, and is cooled.

The cool air then descends through the tower and enters the building, cooling everyone inside. A solar chimney can be used on the opposite side of the building to increase airflow and allow easier escape of hot air.

Another element of passive solar design is thermal mass, or a material that can retain heat and slowly release or radiate it. A concrete wall or stone floor typically comprise a thermal mass area in a passive solar home. Many times these are built of dark materials or painted a dark color to better collect heat during the day.

You have probably seen black or dark-colored plastic water storage tanks, especially if you've been around "off the grid" homes. Water stores twice as much heat as masonry, but of course requires a container, support (water is heavy) and periodic treatment to keep bacterial and microbial growth from contaminating the water.

Passive solar has so many applications, and is so inexpensive, that even a modest investment in it can reap large rewards for homeowners and business owners alike.