Alternative Energy Sources in America

Renewable resources can be a big part of an energy generation portfolio.

Whether motivated by a desire for energy independence, the need to reduce human influence on the local and global environment or by the logic of simplicity, there is an increasing push towards meeting energy needs with alternative sources. Biofuel, geothermal, solar and wind power are all parts of the alternative energy portfolio.

Biofuels

Bacteria eat organic materials in trash, releasing methane gas.

Municipal solid waste (MSW), or as it's more casually known, garbage, is dumped in the ground. If the landfill is properly covered, a special class of bacteria, called anaerobes, literally eats the organic matter and excretes methane. This is good news for renewable energy, because methane is a hydrocarbon, the primary component of natural gas. It's possible to collect the methane gas, burn it and run a generator or an automobile. The same basic process is used for generating energy from cow manure and other biofuels. The energy content of methane is relatively low, but the alternative to its controlled capture and utilization is its release into the atmosphere, where it is a powerful greenhouse gas.

Geothermal

Hot steam, heated by the the thermal energy of the Earth itself, can be tapped to produce electricity.

Water circulating under the Earth's surface comes into contact with heated rock and heats up. The water is trapped in between layers of rock, where the pressure builds, letting the underground reservoirs reach temperatures up to about 400 degrees Centigrade. In geothermally active regions, the heated water is close to the surface, and pushes through seams and cracks to appear on the surface as jets of steam or bubbling hot springs. To reliably tap this energy source, a pair of wells is drilled --- one to let the steam up and one to recirculate water back down into the underground reservoir. On the way, the steam drives a turbine, either directly or by heating an intermediate exchange fluid.

Solar

Solar cells convert about 15 percent of the incident light into electricity.

The sun is a gigantic fusion generator that's been around for five billion years, and is expected to hang in there for another five billion. All the energy on the Earth comes from the sun, one way or another. Solar energy is a more direct method of harvesting sunlight, either by converting it directly to electricity in photovoltaic cells or indirectly by heating a fluid and driving a turbine. Unlike biofuel or geothermal power generation, solar power is an inconsistent resource, disappearing every evening and reducing its output in cloudy conditions. On the other hand, it's convenient and generally available. Solar technology is rapidly advancing, making it the fastest-growing segment in the renewable energy portfolio.

Wind

Wind turbines placed in high wind areas can produce reasonable energy output.

Humans have ridden the wind, literally and figuratively, for thousands of years. Now wind turbines from Maine to Hawaii supply about 35,000 MWh per year. Especially when installed in regions with average wind speeds above 6.5 meters per second (about 14.5 miles per hour), wind farms can be an effective component in an energy generation portfolio. Like solar energy, wind is inconstant, rising and falling in speed throughout the day and varying over the seasons. There are also concerns over hazards to birds and, in populated areas, noise pollution. But wind turbine technology is rapidly advancing, making it an economical choice for future energy needs.

Water, Water, Everywhere

Hydroelectric facilities generate electricity from water---about as clean as it gets.

Hydroelectric is generally classed as a renewable energy resource, but it may not be considered "alternative," as it is well-established. Hydroelectric facilities annually supply the U.S. with more than 270 million MWh of electric power. They are dependent upon rainfall, but there is a long history of water management experience to ease that task. But not all is rosy; there are some environmental concerns resulting from modifying a river's course by building dams. But there is more to be tapped---the Department of Energy estimates that output could be doubled just by upgrading the hardware at existing facilities.

Big Possibility in Small Power

Distributed power generation has been around for a long time.

Each renewable technology described above can also be applied on very small scales. Individual buildings or homes can be, and are, powered by small scale biomass, geothermal, solar or wind generators. On the one hand, this distributed generation can be considered the ultimate realization of the promise of alternative energy --- generation scaled to immediate use and nothing wasted on distribution networks. On the other hand, without a unified approach and unified control over distributed resources, the flexibility of the overall power grid is not enhanced with small-scale distributed generation. Either way, any facility that powers itself doesn't present an additional load to the power distribution system --- meaning fewer demands for added traditional power plants.

Resources

• Department of Energy: Wind & Water Program
• Geothermal Education Office: Geothermal Energy Facts
• Solar Central: Solar In-Depth