Alternative Energy Sources: Solar, Wind, Hydroelectric, Geothermal and Passive Solar

Cutting-edge technologies could help break our fossil-fuel dependence.

| July/August 2006

Scientists overwhelmingly agree that the reliance on fossil-fuel energy sources, including oil and coal, has stressed our planet’s ecosystems and contributed to climate warming. They and other experts contend that developing and using non-polluting, renewable energy is the wave of the future. One (or a combination) of four technologies—solar, wind, hydropower and geothermal—might be right for your home.

Solar Energy

We can harness the sun’s power using several technologies. The first uses solar cells to convert sunlight (photons) directly into electricity (voltage), a process called the “photovoltaic (PV) effect.” This technology frees electrons from atoms, allowing them to flow through the solar-cell material and produce electricity. The cells usually are combined into modules mounted in “arrays,” or flat plates positioned flush on south-facing rooftops. Between 10 and 20 arrays provide enough power for a household.

A less noticeable form of PV is “thin film,” which allows solar cells to be used like regular rooftop shingles. They offer the same protection and durability as asphalt shingles, according to the National Renewable Energy Laboratory (NREL).

Another solar technology uses thermal panels, or collectors, to capture the sun’s heat. Tubing filled with water or antifreeze runs through a “flat-panel” collector, a thin rectangular box with a black bottom and a transparent cover. The liquid is heated as it flows through the tubing in the collector and into a storage tank. The hot liquid then can be pumped through coils and used to heat the entire home, the household water or a swimming pool. Solar collectors usually are mounted on the roof, and they’re heavier than PV modules, so it’s important to evaluate your roof’s load-bearing capacity before installing this kind of system.

Solar systems aren’t cheap—they can cost up to $20,000—but they’re becoming more affordable thanks to federal, state and utility-company rebates. Solar equipment dealers can tell you which technology is most cost effective for your home.

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