ENVIRONMENTAL ISSUES

Alternative Sources of Energy

Alternative Sources of Energy

Introduction

Renewable energy sources can be replenished in a single human lifetime, rather than over many lifetimes as with oil or coal. Renewables are therefore often cited by advocates of alternative energy as humanity's best hope for meeting the world's growing energy demands. Following are descriptions of the different types of renewable energy, their advantages and drawbacks:

Biofuels

The most common biofuel is ethanol, a form of alcohol made from vegetable matter (usually corn in the U.S.) and used to power cars. Ethanol--already widely used as an additive to gasoline--is considered renewable because its ingredients can be grown and harvested. In addition, because it is made from a type of vegetation, ethanol is considered by many to be environmentally cleaner than gasoline; although it releases carbon dioxide (CO2) when burned, this is offset by the CO2 absorbed during the growth of the vegetation from which it is produced.

Ethanol is criticized, however, for not being economically viable (it is heavily subsidized by the government) and for its production process, which some critics say involves substantial fossil-fuel use and generates significant CO2 emissions. Critics also say that farmers growing crops meant for ethanol production reduce the amount of land available for food crops, leading to scarcity of food and higher food prices (Passero, 2006).

Geothermal energy

The inside of the Earth contains abundant reserves of hot water, generating considerable energy. Geothermal power plants harness that energy to produce electricity in three different ways. The oldest method, known as dry steam, was first used in Italy in 1904. It takes advantage of steam from underground water to directly power turbines (structures resembling giant fans) that produce electricity. Flash steam plants, on the other hand, pump hot subterranean water into a low-pressure tank, causing it to "flash" into steam for electrical generation. A third type of facility, known as a binary-cycle plant, uses a secondary fluid with a lower boiling point than water. When moderately hot water is pumped out of the Earth, its temperature is still high enough to vaporize the secondary fluid, which then powers the turbine.

While geothermal energy is both abundant and environmentally cleaner than fossil fuels (dry steam and flash plants produce comparatively low carbon emissions, and binary-cycle plants produce almost none), there are some drawbacks. Currently, geothermal electrical production is expensive and relatively inefficient, and locating suitable sources of water can be difficult; areas in which hot water is close to the surface, such as sites containing geysers, are rare, and power companies often must undertake costly drilling to try to locate deeper reserves.

Hydroelectric power

In the U.S., the most common way to generate electricity from renewable sources is through water. Hydroelectric power, also known as hydropower, uses flowing water to rotate turbines, thereby generating electricity in power plants. The water used is often kept in a reservoir adjacent to a river, and its distribution is controlled by opening and closing a dam. Hydroelectric plants use more water at times of greater electricity ...