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.
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.
It’s important to note that solar systems actually might make you money if you can sell back to your local utility any excess power your system produces.
Passive Solar Heating
Another way to use the sun’s energy to warm your home is through passive solar heating. If your house has large, south-facing windows, you’ve already experienced this phenomenon. By adding walls and floors made of concrete, brick, tile and other masonry materials that absorb heat, your home essentially becomes its own heat source. These surfaces heat up during the day and slowly release the heat throughout the night; dark colored materials are most effective.
A key to passive solar design is incorporating shading elements, such as overhangs, on the south side to keep the house cool in summer. If you’re considering building a solar home, architects who specialize in passive solar design can help.
Wind-energy systems create electricity using turbines and generators. Air flows past the turbine’s rotor, which looks like an airplane propeller, causing it to spin. This drives the generator shaft, producing electricity.
If you decide to build a stand-alone wind-energy system for your home—which can cost up to $25,000 installed—monitor the wind on your property for at least one year before construction. Experts say adequate wind speed must be at least 16 miles per hour.
Because of the cost and complexity, it probably makes sense to construct your own full-blown system only if you live in a rural area where the cost of connecting to your local utility grid is prohibitive or, if you’re connected to the grid, you live in an area that’s windy enough to produce more energy than you need. If so, you might be able to sell your excess power back to your local utility.
Turbines in your back yard may be out of the question, but check to see if your local utility has a program that allows you to receive some or all of your home’s energy from wind. For example, Xcel Energy, which supplies power to 10 U.S. states, has a program called Windsource that allows customers to pay a premium to receive energy derived from its wind farms.
With rising natural gas prices, wind power is cheaper than conventional because its prices remain fixed. Xcel Energy reports that in fall 2005—when natural gas prices soared—homes using 100 percent Windsource energy saved an average of $10 per month over a similar home using conventional power.
If a stream or small river runs through your property, you might be able to use water to generate electricity. Your stream needs a sufficient quantity of year-round, falling water. With this system, turbines and generators convert energy from flowing water into electricity or mechanical energy. So-called micro-hydropower systems can generate up to 100 kilowatts (kW) of electricity; 10 kW provides enough power for a large home.
Most micro-hydro systems are “run of the river,” meaning they don’t require dams or storage reservoirs. These systems divert stream water through a pressurized pipeline, called a penstock, which delivers water to a rotating turbine that powers a generator or an alternator to produce electricity. The systems can stand alone or connect to your utility’s electricity grid.
Like most renewable energy, hydropower comes with high construction costs, but it lasts a long time and maintenance typically is inexpensive. State and local incentives might lessen the sticker shock; if you’re connected to the grid, you might be able to sell excess electricity back to your local utility.
You also can get power directly from the earth. Renewable geothermal resources can heat and cool your home, saving you up to 80 percent over fossil-fuel energy.
One popular way homeowners tap geothermal energy is with a heat-pump system buried beneath the earth’s surface. The systems work well in North American latitudes where the upper 10 feet of ground maintains a constant temperature of between 50°F and 60°F. Heat exchangers and air-delivery systems distribute warm air from underground to the home during winter; cooler air is brought up during summer.
Another way to tap into geothermal energy is through a “direct use” system, which requires drilling a well into a geothermal hot-water reservoir and using heat exchangers and piping to circulate the hot water to deliver heat. Direct-use systems can be used only where geothermal reservoirs exist; most are located in the West, Alaska and Hawaii.
Increasingly, utility companies are investing in geothermal energy. Between January and May 2005, utilities companies produced as much power from geothermal systems as from wind. Check with your local utility to see if it offers geothermal power.
How Your System Can Pay for Itself