Renewable Energy Primer

 
What Is Renewable Energy?

 
Sources of Renewable Energy

 
 
Biomass Energy

Changing farming wastes, grasses, trees, bark, sawdust, and even trash or garbage into energy by burning it, changing it to a gas, or converting it to a liquid fuel.

When you burn a log in your fireplace or in a campfire, you are using biomass energy. Because plants and trees depend on sunlight to grow, biomass energy is a form of stored solar energy. Although wood is the largest source of biomass energy, we also use corn, sugarcane wastes, and other farming by-products.

There are three ways to use biomass. It can be burned to produce heat and electricity, changed to a gas-like fuel such as methane, or changed to a liquid fuel. Liquid fuels, also called biofuels, include two forms of alcohol: ethanol and methanol. Because biomass can be changed directly into a liquid fuel, it could someday supply much of our transportation fuel needs for cars, trucks, buses, airplanes, and trains. This is very important because nearly one-third of our nation's energy is now used for transportation.

The most commonly used biofuel in the United States is ethanol, which is produced from corn and other grains. Ethanol made from corn is currently more expensive than gasoline on a gallon-for-gallon basis. And even if we took all the corn that could possibly be grown in the United States and used it to produce ethanol, it would not make enough ethanol to power all our cars.

Like any fuel, biomass creates some pollutants when it is burned or converted into energy. The amount of pollution varies based upon biomass type and energy technology used. Some biomass uses produce worse pollution problems than fossil fuel use - for instance, burning wood in a stove or fireplace for warmth produces unhealthy soot and burning methanol produces health-endangering toxic gases.

 
Geothermal Energy

Energy obtained from heat under the earth's surface to produce power.

Geothermal energy starts with hot, molten rock (called magma) miles below the earth's surface that heats a section of the earth's crust. The heat rising from the magma warms underground pools of water known as geothermal reservoirs. Sometimes the water can even boil to produce steam. If there is an opening through the rock to the surface, the hot underground water may seep out to form hot springs, or it may boil to form geysers. Old Faithful in Yellowstone National Park is a one such geyser.

For thousands of years, people have been using hot springs for bathing and for cooking food. With today's technology, rather than waiting for hot water to come to the earth's surface we can drill wells deep below the surface of the earth to tap into geothermal reservoirs.

Geothermal energy can be used to produce electricity. Steam -- either pulled directly from the geothermal reservoir or from water heated to make steam -- is piped to the power plant. There, it rotates a turbine that generates electricity.

While geothermal energy is considered a renewable source of power, geothermal reservoirs can be depleated by drawing energy out of the them at a faster rate than they are replenished. Another problem with geothermals is that water from geothermal reservoirs often contain minerals that are corrosive and polluting. In addition, using a particular reservoir like a geyser may reduce its aesthetic appeal. For instance, if tapping into Old Faithful reduced its water output, it could lessen it value as a tourist attraction.

 
 
Hydropower

Energy produced by water flowing in rivers, streams and over waterfalls. The term is used to identify a type of electricity-generating station or any energy output in which the main mover is driven by flowing water.

Hydropower systems use the potential energy from flowing water to create electricity, usually by impounding it behind dams and then diverting it through a channel to a water turbine. Flowing water can also be used to mechanically drive machines in a direct fashion, for instance, using a water wheel. However, the most common form of hydropower uses dams on rivers to create large reservoirs of water.

Water released from the reservoirs flows through turbines, causing them to spin. The turbines are connected to generators that produce electricity.

Hydroelectric power plants in the United States generate enough electricity to power whole towns, cities, and even entire regions of the country. Hydropower currently is the largest source of renewable power, generating about 10 percent of the United States' electricity.

Hydropower is also inexpensive, and like some other renewable energy sources, it does not produce air pollution.

Hydropower does have several drawbacks. Among them, damming a river can change the ecology of the region, and reduce other ecological services that the river in its undammed condition provided. For example, the water below the dam is often colder than what would normally flow down the river, so fish sometimes die. Entire species of fish, for instance some salmon subspecies can be endangered due either to reduced water flow below dams or due to the fact that they are unable to reach their former breeding grounds due to a dam's blocking their path. In addition, the water level of the river below the dam can be higher or lower than its natural state, which affects the plants that grow along the riverbanks.

Another problem with hydropower is that while it is inexpensive to produce energy from a hydropower plant once it is built, building the plants is very expensive, requiring an enormous capital outlay and a relatively long time to build - which means that it will usually take a longer time to start seeing a profit from a hydropower plant than from other types of power plants. Also, there are a limited number of rivers on which dams are viable and almost all rivers and streams are publicly owned. All of these reasons have meant that most hydropower projects have been and will likely continue to be in the future, government built and publicly financed.

 
Nuclear Energy

Produced by fissioning or splitting certain heavy chemical elements like uranium or plutonium into lighter ones, thus releasing energy stored in the nuclear binding forces. Fission is induced when the nucleus of a suitable isotope (like uranium-235) is struck by a free neutron. Among the fragments from each fission event are some newly free neutrons. The freeing of those neutrons makes possible a chain reaction, which induce more fissions. Nuclear power plants operate by moderating or controlling the chain reaction.

There is some debate concerning whether nuclear energy is a renewable fuel. Technically it is renewable. In some countries, for instance France, nuclear energy is produced at so called "breeder reactors." Breeder reactors produce energy while reenriching (or reenergizing and recycling) used nuclear fuel rods. This produces, practically speaking, an unlimited supply of nuclear fuel. However, these reactors produce bomb grade nuclear material as a byproduct of reenrichment. In the U.S. the government has banned the use of breeder reactors for two reasons. Critics of breeder reactors have argued that producing more nuclear bomb material is in itself a provocative action. In addition, they have pointed out that with more bomb material available (in less secure non-military installations, no less) there is an increased liklyhood that some of the material will fall into the wrong hands through theft. Thus, breeder reactors are argued to pose a threat to U.S. national security. In sum, nuclear energy is not renewable in the U.S. for political, not technical reasons.

Though nuclear energy use produces no air or water pollution or greenhouse gases - it is among the cleanest of all fuels in this regard - there are serious waste and cost problems associated with nuclear energy use. Exposure to radiation from nuclear plants would be deadly without protective measures. In the U.S. no deaths have ever been successfully attributed to nuclear energy use. Even the worst nuclear accident in U.S. history at the "Three Mile Island" nuclear reactor caused no deaths due radiation poisoning. This safety record is in part the result of the high safety standards and technological safeguards in place at nuclear reactors. These safeguards come at a high price, however, making the cost of a new nuclear plant prohibitively expensive to build. The capital cost of a nuclear plant are only exceeded by large hydroelectric projects. So while the marginal cost of energy production at nuclear plants is among the lowest in the industry, the price of nuclear energy is quite high.

In addition, nuclear energy produces radioactive wastes. There are two types of waste: high-level and low-level. Low-level waste can be safely incinerated. By contrast, high-level waste must be stored for thousands of years. Improper storage could be dangerous, and the storage process is proving to be quite costly. Nuclear plants are rapidly running out of storage space, and the federal government had promised to find a permanent repository of spent nuclear fuel. Unfortunately, there are very few sites that offer adequate protection for nuclear waste and of those sites available, no locality or government wants the nuclear waste stored in its area. Finding a location to safely store used nuclear fuel is both a technological and political problem.

 
  Solar Energy

The electromagnetic radiation generated by the sun. Solar radiation may be converted to useful forms of energy in several ways by thermal conversion or through high temperature collectors (solar panels, boxes or rooms that trap the sun's rays to produce heat). Solar energy is usually captured in the form of heat, and is therefore best used for a variety of heating purposes. The sun's energy can be used to warm and light homes, heat water, and provide electricity to power our lights, stoves, refrigerators, and other appliances.

The photovoltaic process converts solar radiation directly into electricity. Thermal conversion is a process whereby the sun's energy is concentrated to heat water and produce steam, which is used to produce electricity.

Like wind power, hydro power and nuclear energy, solar energy is touted by its advocates as a safe, non-polluting source of power of unlimited potential. However, the widespread use of solar power has several limiting factors that its promoters have yet to overcome. The production of solar panels, solar fuel cells and photovoltaic batteries creates pollution.

Solar power is very expensive, due, in part, to the fact that it is unreliable. Nightfall and cloudcover are among the factors that interupt solar power production - thus a second, usually fossil-fuel-burning power supply is necessary to supplement solar power when necessary (dual or redundant facilities are rarely efficient). In addition, solar power simply isn't feasible in many parts of the world due to space or daylight limitations. Large solar powered electric projects are only feasible in desert locations, but there they disrupt desert ecosystems.

 
 
Wind Energy

Energy that is tapped from the natural movement of the air. Wind energy is considered a form of solar energy because wind is caused by variations in the amount of heat that the sun sends to different parts of the earth. It may be converted into electricity or mechanical power through the use of a wind driven turbines (i.e., a turbine driven by blades). Windmills were an early form of wind driven power supply.

For centuries, the wind has been used to sail ships, grind grain, and pump water. Now, people use the wind to generate electricity. The windmills built long ago had many blades, but today's wind turbines usually have just two or three blades that turn when the wind blows. Wind turbine blades can be up to 82 feet (25 meters) long!

The blades drive a generator that produces electricity, much like steam turbines. The longer the blades and the faster the wind speed, the more electricity the turbine generates. Wind turbines are placed on towers because the wind blows harder and more steadily above the ground.

To produce the most electricity, wind turbines need to be located in areas where the wind blows at a constant speed, which it does not do in all parts of the world. Wind speed is described by seven "classes." For example, Class 7 winds are extremely strong, while Class 2 winds are mild breezes. Generally, Class 4 winds and above are considered adequate for wind turbines to produce electricity.

Large groups of wind turbines, called wind farms or wind plants, are connected to electric utility power lines and provide electricity to many people.

In theory, wind systems can produce electricity 24 hours every day. However, even in the windiest places, the wind does not blow all the time. So, while wind farms don't need batteries for backup storage of electricity, small wind systems do need backup batteries. Like solar power, because of the inconsistent nature of wind power, power plants that rely on wind energy need redundant or additional power supplies - usually generation systems that use fossil fuel.

Wind farms are very expensive to build and maintain. Wind power, like almost every other source of renewable energy is more expensive than non-renewable energy sources. Resources spent above and beyond what is absolutely necessary to produce a needed amount of energy are wasted in the sense that they are unavailable for use in the pursuit of other worthwhile and important social and private goals.

Wind farms pose a number of environmental problems. They require a great deal of land and many people see them as a blight on the landscape. In addition, they are very noisy (noise pollution is a nationally recognized problem). The noise is so great that people find it difficult to live in the vacinity of a wind farm.

From an environmentalist's point of view, perhaps the worst environmental problem caused by wind power is the number of birds that wind turbines kill each year. The most viable locations for wind farms are also critical flyways for many migratory bird species and prime habitat for several endangered raptor species. Most of these birds are "protected" by treaties or laws. However, every year thousands of birds in Europe and America are killed when they fly into the turning blades of wind turbines. Raptors are drawn to their deaths by prey species cowering at the bases of wind turbines. On more than one occassion, the bodies of the killed birds have ignited and started fires on the windfarms, not only killing other animals, but also interrupting the power supply.

 
 
Tidal Energy