Green power is another name for renewable energy - electricity generated from sustainable resources, by producing few or no hazardous emissions or pollutants, and having minimal impact on fragile ecosystems.
Why not all green, all the time? The answer is complicated, but it boils down to a few key factors:
There are five main types of renewable energy - hydro, biomass, geothermal, solar and wind - and each has its benefits and drawback.
Large-scale wind farms are becoming an increasingly common sight throughout the country, providing enough electricity to meet the needs of more than 18 million U.S. homes (Source: American Wind Energy Association)
Modern wind energy uses the same basic principles that have been around since the 1800s: the wind spins a rotor, which in turn spins a turbine inside a generator to produce electricity.
An ideal location for a wind farm is one that has an average annual wind speed of at least 14 miles per hour. The area also needs to be flat, with few or no surrounding structures. One large turbine requires about 1/4-acre of land; the rotor takes up most of this area, so 90 percent of the land remains accessible for farming or other development.
The advantages of wind power are obvious: the energy is free and completely renewable, there are no hazardous emissions, and there are no significant adverse environmental impacts.
Wind power is also becoming more economical to produce: technological innovations have brought the cost of wind power down from more than 30 cents per kilowatt-hour during the 1980s to less than 6 cents per kilowatt hour today. In addition, wind farms are modular, so additional turbines can be added if the need arises, and construction time is much shorter than a typical fossil fuel power plant.
You may never have heard the term " biomass " before, but it's the second most-common form of renewable energy we use today.
The word biomass means organic matter - biomass energy (or "biofuels") comes from natural material, such as wood products, municipal solid waste, agricultural crops and even landfill gases.
A few examples of large-scale biomass energy production include:
Biomass energy offers significant environmental advantages:
The use of biomass energy has a particular appeal in the Midwest, because the use of agricultural products can have economic benefits as well. The U.S. Department of Energy projects that energy crops like switchgrass or even fast-growing trees could provide more than 5,000 megawatts of electricity annually by the year 2010, supporting more than 170,000 jobs and diversifying local farming operations.
Instead of using steam to drive generator turbines, a hydro plant uses the force of falling or flowing water. Hydro power has been used to make electricity in the Midwest since the early 1900s, with many facilities built by the Works Progress Administration in the 1930s.
There are two types of hydroelectric power plants:
The benefits of hydro power are many: no hazardous emissions or solid waste, no fuel costs and it's entirely sustainable. Hydro plants are reliable, low maintenance and provide flood control.
Environmental groups have pointed out the drawbacks to hydroelectric power, especially from large-scale dams and reservoirs. The most dramatic is the impact on wildlife - the reservoirs can alter water temperature and prevent the migration of fish.
While "run of the river" hydro plants have a much smaller environmental impact, their use is constrained by the lack of control. The electricity produced at these plants cannot be increased or decreased according to demand, and the flow of the river is dependent on the area's precipitation.
Many of the nation's hydroelectric plants are aging, and flooding in recent years has irreparably damaged several in the Midwest. The initial costs of building or replacing a hydro plant are high, and usually not cost-effective in the Midwest, so most utilities are investing in other forms of renewable energy.
Geothermal technology uses the natural warmth of the earth to produce electricity, as well as heat and cool homes and businesses.
A direct-use geo system, also called a ground-source heat pump, works on a simple premise: the earth below a certain depth (the frost line - usually about four feet deep), remains a constant temperature of about 50 degrees year-round.
A geothermal system takes heat from the ground and transferred to the air in your home during the winter; the process is reversed during the summer.
Geothermal is gaining popularity because it is the most energy-efficient heating and cooling system available on the market - the only energy consumed is a small amount of electricity to run the pump.
Heating bills can be lowered by up to 50 percent, cooling bills by 30 percent. This can mean a payback in energy savings in less than seven years.
The environmental impact of a geothermal power plant is minimal, emitting no nitrogen oxides, very few sulfur dioxides, and 1,000 to 2,000 times less carbon dioxide than a fossil fuel plant. Geo plants also have a small "footprint," requiring less land than a typical coal or nuclear facility, and they boast 95-97% reliability. As with other types of renewable energy, the availability of geothermal power is limited by location.
A "geo" power plant works by tapping into steam or hot water reservoirs underground; the heat is used to drive an electrical generator. Most geo plants are located in the western U.S, where hot water reservoirs are common.
Thousands of homeowners are using solar power to heat their homes and their water, as well as provide natural lighting.
An emerging type of residential solar power is called photovoltaics. This technology uses semiconductor material to convert sunlight directly into electricity - if you have a solar calculator or watch, you're already using photovoltaics. More than 10,000 homes in the United States are entirely powered by solar energy.
The advantages of a photovoltaic (PV) system are numerous: it's non-polluting, there are no moving parts, it operates silently and requires little maintenance. Photovoltaic power can also be stored in deep-cycle batteries for evening or back-up use.
But economically, photovoltaics are rarely cost-effective for the average homeowner. A PV system produces low-wattage direct current electricity, compared to the 120-volt alternating current supplied by utility companies.
This means PV set-ups require different wiring, along with an expensive inverter to be able to run appliances. Sizing a PV system to provide enough power to run high-wattage appliances like refrigerators, air conditioners and stoves can quickly put it out of most homeowners' price range.
"Daylighting" is one of the easiest and most cost-effective ways to use solar energy at home. This technique involves building a house to take advantage of the sun's rays.
The architect and builder work together to "site" the house on the lot to bring in natural sunlight throughout the day. Windows are strategically positioned to provide adequate light without overheating the area, and the interior design is planned to diffuse the light throughout the room.
According to the U.S. Department of Energy, a home built with "daylighting" techniques can have lighting costs 40 to 60 percent lower than a typical home.
Solar water heating
Another "passive" method of using solar energy at home is a thermal solar water heater. These systems use the familiar flat glass or plastic panels seen on roofs and in backyards.
Sunlight passes through the panels and is collected by a dark absorber plate. The plate warms liquid passing through pipes - either the household water supply or an antifreeze solution that is used in a heat exchanger in the water storage tank.
Solar water heaters are popular in areas that do not have natural gas service - replacing an electric water heater with a solar model can reduce water heating costs by 50 to 80 percent every year. And over the 20-year lifespan of the equipment, more than 50 tons of carbon dioxide emissions will be displaced.
The initial cost of a solar water heating system ranges from $1,500 to $3,000; in many cases, the cost will be paid back in energy savings in less than eight years.
If you're interested in a solar water heating system, be sure to check your local building codes - many communities require a conventional water heater as a back up.