Energy Conservation and Efficiency

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Energy Conservation and Efficiency


While scientists and engineers search for alternatives to fossil fuels that are clean, abundant, safe, and inexpensive, other important alternatives are available to businesses, governments, and other energy consumers: finding ways to reduce energy use and using energy more wisely and efficiently. For the foreseeable future, solar power, wind energy, and other alternatives are likely to function mainly as supplements to fossil fuels. That is, they can meet some percentage of the world's energy needs, but the potential of these alternatives in the early 2000s is limited by cost, environmental considerations, and even simple geography. Wind power, for example, can become a major power source only in those parts of the world that have sufficient wind.

In the short term, the world will continue to rely on fossil fuels. One way to stretch the supply of fossil fuelswhile at the same time reducing the pollution caused by mining, transporting, and burning themis to burn less of them. The cost of fossil fuels is likely to increase as reserves diminish and it becomes increasingly expensive to mine or drill for less-readily available supplies. However, energy consumers can reduce their dependence on fossil fuels and their energy bills by finding new ways to use less energy. Among the best ways to accomplish these goals are increasing energy efficiency and energy conservation. The first includes redesigning vehicles, buildings, appliances, and the likeboth by building them with materials that require less energy to produce and by designing them in such a way that they require less energy while in use. The second includes the many ways in which the average person can make lifestyle choices that conserve energy, such as drying clothes on a clothesline rather than using a dryer; eating less meat; setting thermostats lower in the winter and higher in the summer; maintaining water heaters at lower settings; carpooling, using public transportation such as subways or buses, walking, or biking to work or school; purchasing smaller, more energy efficient vehicles rather than larger vehicles like SUVs; and choosing to replace incandescent light bulbs with compact fluorescent light bulbs. Some experts argue that energy conservation among consumers is a cheaper and more environmentally sensitive option to increased energy production from either fossil fuels or alternative sources.

Words to Know

Carbon sequestration
Storing the carbon emissions produced by coal-burning power plants so that pollutants are not released in the atmosphere.
Climate-responsive building
A building, or the process of constructing a building, using materials and techniques that take advantage of natural conditions to heat, cool, and light the building.
Drag coefficient
A measurement of the drag produced when an object such as a car pushes its way through the air.
Green building
Any building constructed with materials that require less energy to produce and that save energy during the building's operation.
Hybrid vehicle
Any vehicle that is powered in a combination of two ways; usually refers to vehicles powered by an internal combustion engine and an electric motor.
A measure of the amount of light, defined as the amount of light produced by one candle.
Sick building syndrome
The tendency of buildings that are poorly ventilated, lighted, and humidified, and that are made with certain synthetic materials to cause the occupants to feel ill.
Thermal mass
The measure of the amount of heat a substance can hold.
Trombé wall
An exterior wall that conserves energy by trapping heat between glazing and a thermal mass, then venting it into the living area.

Conserving oil and gas

Scientists and energy officials agree that the need for conservation and greater fuel efficiency is pressing, although they debate just how urgent it is. In the 1990s the Intergovernmental Panel on Climate Change (IPCC) conducted investigations that led in 1997 to the Kyoto Protocol, a worldwide plan designed to reduce fossil-fuel consumption, with the goal of reducing global warming. At that time the IPCC estimated that the amount of oil remaining in the ground was about 5,000 to 18,000 billion barrels. The panel also estimated that world production of oil and gas would begin falling in about 2050. At that point the cost of oil and gas would become painfully high. Meanwhile, according to the World Energy Council, the world consumes over 71 million barrels (one barrel equals 42 gallons) of oil and natural gas per day.

In 2003 a team of geologists from the University of Uppsala, Sweden, presented findings that differed from those of the IPCC. The good news, according to the Swedish scientists, is that global warming, caused in part by pollutants emitted from vehicles, will never reach disastrous proportions. The bad news, however, is that global warming may be less of a threat than previously thought because the amount of fossil fuels remaining is dangerously low and the world will run out of these fuels before global warming becomes a critical problem. This team of scientists believes that the remaining supply of oil is only about 3,500 billion barrels and that production will begin to fall in about 2010 rather than 2050. Furthermore, about 80 percent of the known oil and gas reserves are in regions of the world that are politically unstable, so reserves could be sharply reduced or even cut off entirely as a result of political unrest.

In general, energy experts fall into two camps, the optimists and the pessimists. The pessimists believe many countries have exaggerated their figures about proven oil and gas reserves and that all the world's major oil and gas discoveries have already been made. Thus, the pessimists believe that the world is faced with declining oil and gas supplies. In this case, energy conservation and energy efficiency are necessary because world supplies will not support the use of energy at current levels for very long. The optimists, on the other hand, believe that technological advances will lead to the discovery of more oil and gas and, more importantly, enable engineers to tap that oil and gas in ways that were thought impossible in past years. In this case, energy conservation and energy efficiency are necessary because, with the discovery of more fossil fuels, the environmental impact of using them continues to grow.

Conserving coal

Coal reserves are more abundant than oil and gas. Many experts say that the amount of coal reserves in the worldjust over a trillion metric tonsis enough to last for about 200 years. The primary issue with coal, however, is that it is dirtier than oil, contributing significantly to the emission of carbon dioxide, the chief pollutant behind global warming. While the amount of carbon dioxide produced by burning coal differs with the type and quality of the coal, the U.S. Department of Energy provides this analysis: When coal is burned, the chief element that provides heat is carbon. During the combustion process, one pound of carbon combines with 2.667 pounds of oxygen to produce 3.667 pounds of carbon dioxide. Thus, if the carbon content of a particular grade of coal is, say, 78 percent, and burning a pound of it produces about 14,000 British thermal units (BTUs) of heat, then producing 1 million BTUs of heat releases about 204.3 pounds of carbon dioxide into the atmosphere. This figure is about twice that of natural gas and about 50 percent more than that of oil, according to the U.S. Department of Energy.

Carbon Sequestration

Some scientists argue that the key to using coal without emitting huge amounts of carbon dioxide into the atmosphere is a process called carbon sequestration. Carbon sequestration refers to several methods of removing or slowing the concentration of ("sequestering") carbon dioxide in the atmosphere. According to the U.S. Department of Energy (DOE), natural sequestration occurs in various ways, including the absorption and storage of carbon by vegetation, soils, and the oceans in carbon "sinks." The DOE, many environmental groups, and some power companies support enhancing natural sequestration with methods such as the reforestation of agricultural or urban areas and restoration of wetlands, though research is needed in order to create larger, longer-lasting carbon pools in various ecosystems. Another method in development includes the capture and injection of carbon dioxide at deep sea level, though the long-term effects of injecting carbon dioxide into the oceans are unknown. In addition, several countries, including the United States, China, and England, are funding research into the capture and storage of carbon in underground or undersea geologic formations such as depleted crude oil and natural gas reservoirs, unmineable coal seams, and deep saline reservoirs. The DOE states that not only does carbon storage in depleted oil reservoirs reduce carbon dioxide levels, the pressure created can force out additional oil.

Proposals have been made in England, the United States, and other countries to rely more on carbon sequestration. England has abundant coal reserves that could provide a significant percentage of the nation's energy needs for many decades, if ways can be found to deal with the carbon dioxide. Some British experts believe that there is enough space under the North Sea to store the United Kingdom's carbon emissions for a century.

Currently, coal is used almost exclusively in the production of electricity, while oil, after it is refined into gasoline, is the primary fuel source for cars and trucks. It is possible to design and build cars and trucks that are powered by electricity, but doing so would increase demand for electricity. This increased demand would require the combustion of increasing amounts of coal, which in turn would lead to the emission of more carbon dioxide.

Conventional energy sources can be conserved in various ways by individuals, for example consumers can make conscious choices to meet rather than exceed their needs in terms of the size of their homes and automobiles. Consumers can buy smaller homes to decrease home square footage, cutting the overall energy consumed by heating, cooling, and lighting. People can decrease dependence on automobiles by utilizing public transportation, carpooling, walking, or biking. Even with minimal changes to everyday life, consumers can take steps to reduce their energy consumption by making minor improvements in their homes, such as upgrading old inefficient heating systems and installing storm windows; relying on more energy-efficient lighting and appliances; and by changing their driving habits. There are also ways in which consumers can reduce energy use by requiring the housing and automotive industries to construct climate-responsive buildings; use "green" building materials; and design and build "hybrid" vehicles that use less gasoline. Any of these can significantly cut an energy consumer's bills, reduce pollution, and help stretch the world's energy supplies.


Climate-responsive building is sometimes called green building or sustainable building. In a broad sense, each of these terms refers to the same philosophy of building design and construction. This philosophy emphasizes the construction of buildings that use resources efficiently, both during their construction and once completed. Another goal is to minimize the impact of the building on the surrounding natural environment.

In this chapter the term climate-responsive building will emphasize issues pertaining to the siting (the placement), design, and layout of a building in order to take advantage of local weather conditions to reduce energy-use during the building's operation. The term green building will be used to emphasize the use of alternative construction materials that reduce energy demands. Sustainability is a more general term that refers to any technique, whether applied to construction or to such activities as agriculture, that enables the human community to "sustain" the natural environment for the future by using building materials and sources of energy that are renewable. These terms, though, all overlap. The design of a climate-responsive building emphasizes, in part, the use of green-building materials, and green-building practices are likely to be, at least in part, climate-responsive. The goal of both is sustainable building design.

Climate-responsive history

The history of climate-responsive buildings dates back at least to the ancient Greeks. Around 500 BCE the Greeks in many areas of the country were running out of firewood. To heat their homes, they began positioning them in a way that would take advantage of the sun's rays and provide passive solar heating. Even the philosophers Socrates and Aristotle used their influence to call for construction that took advantage of solar heat during the winter by facing transparent mica windows toward the sun. (Mica refers to a number of transparent silicates that easily separate into thin sheets.) The Greeks also began to use dark floors and other building materials that absorbed heat during the day so that buildings would stay warmer at night. They began to use window shutters to trap the day's heat, and they built structures in clusters so that each building would get some protection from cold winds.

Later the ancient Romans used similar building techniques. Moreover, the Romans were the first civilization to use glass greenhouses not only for growing plants and vegetables but also to trap heat. The Romans built bathhouses that took advantage of the sun, and whole cities were laid out to provide each resident with access to the sunaccess that was protected by law. In the American Southwest, the Anasazi Indians, in a similar way, constructed villages that took into account the changing angles of the sun throughout the year.

In more modern times scientists and engineers developed new climate-responsive building techniques. In eighteenth-century Switzerland, physicist and geologist Horace-Benedict de Saussure (17401799) designed the first solar water heater. It consisted of a wooden box with a black base and a glass top. The water in the box could reach a temperature of 190°F (88°C). Other scientists focused on other ways to exploit solar energy in building construction or for commercial purposes. In 1878, for example, solar energy was focused to power a steam-operated printing press in France. However, much of modern construction after that point paid very little attention to climate-responsive building. Instead, humans focused on developing artificial means of heating and cooling using fossil fuels.

In the twenty-first century, architects and design engineers have rediscovered some of these techniques. Rather than simply putting buildings anywhere and relying on fossil fuels to heat, cool, ventilate, and light them, these designers are paying more attention to local climatic conditions to make buildings far more energy-efficient. They are learning to see buildings not just as collections of steel, glass, wood, and other materials, but as systems that interact with their natural environment. By paying attention to that environment, buildings can consume less energy while still providing for the comfort of their occupants.

The need for climate-responsive buildings

Use of energy in commercial buildings is huge, so one place to start with energy conservation and efficiency is to design and construct such buildings with the principles of climate responsiveness in mind. Energy use within commercial buildings in the United States is actually higher than within the sectors of industry and transportation. And consumption of electricity within buildings doubled in the 1980s and 1990s and was expected to increase another 150 percent by 2030. As of the late twentieth century, 66 percent of the electricity used in the United States was that in commercial buildings.

In addition, buildings produce a considerable amount of carbon emissions. Buildings are responsible for 35 percent of all U.S. carbon emissions. On-site burning of fossil fuels accounts for 11.3 percent, while electricity usage accounts for 23.7 percent. Buildings also produce 47 percent of U.S. sulfur dioxide- and 22 percent of nitrogen oxide-emissions. Climate-responsive buildings can cut both this energy consumption and the greenhouse gas emissions. Such buildings can also contribute to a more healthful working climate for the building occupants.

Climate-responsive building techniques

Some of the most common climate-responsive building techniques include the following:

  1. Available solar energy can be used for heating and lighting. This would include daylighting, or using natural sunlight to provide for lighting needs; solar ventilation preheating, which makes use of greenhouses, atriums, and solar buffer spaces to provide some of the building's heat; solar water heating; and photovoltaics, or the use of photovoltaic cells to provide electricity. Using daylighting and solar energy for heating and lighting requires intelligent placement of the building relative to the sun. Solar water heating and photovoltaic features can be built right into the skin and roof of the building, as well as into skylights, shingles, roofing tiles, glass walls, and even ornamental features. In fact, buildings that are constructed with built-in photovoltaics can even become net energy producers, creating surplus power that can be sold to the local energy grid or traded for power the building needs during periods when the sun does not shine.
  1. Controllable shading can prevent overheating and glare. In hot-weather climates coatings can be placed on windows to block heat from entering the building while still allowing light to enter.
  2. Using external wind pressure and solar radiation can power ventilation systems, serving as a supplement to fan-powered ventilation systems.
  3. Using thermal mass and shading to help control internal temperatures reduces the demand for artificial heating and cooling.
  4. In private homes, some builders construct Trombé walls, named after French inventor Felix Trombé (19061985), who conceived the design in 1964. Trombé walls are built facing the sun from materials such as stone, adobe, concrete, or even water tanksany material that has high thermal mass (an ability to store and give off energy). The walls also have an air space, insulated glazing, and vents. As sunlight passes through the glazing and strikes the wall, the wall absorbs heat, in turn heating the air between the wall and the glazing. This warmer air then rises and is channeled through the vents into the home; cooler air from the home, which sinks, flows through vents at the bottom of the interior walls and into the air space. Heat can be retained on cloudy days by placing insulation between the air space and the thermal mass.

While incorporating energy-saving features into a building's design is beneficial, modern architects who design climate-responsive buildings make it clear that to derive the maximum possible benefit, it is important to take a "whole building approach," seeing a building not just as a collection of parts but as a living, breathing system. Further, architects point out that what works in one locale or part of the country might not work in another. A major concern in Minneapolis, Minnesota, is heating a building in winter, while residents of Phoenix, Arizona, are more concerned about cooling, especially in the summer. In the Midwest and Deep South, expelling humidity is a major concern, while in the dry air of the Rocky Mountain region, the concern is just the opposite. Architects and designers take these differing conditions and needs into account, then by integrating solar, wind, thermal mass, and other features, they can create designs that cut energy consumption significantly.

Proving this is a pair of buildings in San Diego, California. The Ridgehaven Building, a commercial office building, is located next door to a nearly identical building of the same size. The Ridgehaven Building was built using climate-responsive techniques and with green materials; the neighboring building was constructed using traditional techniques and materials. The Ridgehaven Building uses 65 percent less energy than the neighboring building, saving the building's owners $70,000 a year in utility bills.

Sick Buildings

In addition to providing energy savings, climate responsive (and green) buildings have an additional benefit: They tend to be more healthful for the occupants, including workers in a commercial building or students in a school building. Sometimes, a building can be the site of specific illness, such as Legionnaires' disease, an illness caused by the legionella bacteria, which is thought to be spread through cooling systems.

Buildings, though, often suffer from what is called "sick building syndrome." This syndrome became more apparent after the rise in energy costs in the 1970s, when people started to become more aware of air leaks in buildings and sealed them to reduce wasted energy. While sealing the air leaks saved energy, it also trapped toxins and stale air inside, giving rise to a host of physical problems for the occupants, including eye, nose, and throat irritation; dryness of the skin, throat, and nose; breathing difficulties; headaches; fatigue; and even rashes.

According to the World Health Organization (WHO), sick buildings typically have forced-air ventilation, are constructed with light-weight materials, have indoor surfaces covered with fabrics, especially carpet, and are airtight. These features create uncomfortable temperatures, humidity levels that are too low, noise, and reliance on artificial lightingespecially fluorescent lighting that can "flicker" and cause headaches. They also trap molds, spores, dust mites, and other microorganisms. Some equipment such as photocopiers and printers may have toxic solvents in their toners, while carpeting and adhesives release toxic vapors such as formaldehyde.

Some experts, such as those at the Renewable Energy Policy Project (REPP), argue that sick building syndrome has a distinct economic cost and that climate-responsive buildings can lessen those costs. According to the REPP, such features as daylighting and natural ventilation can reduce employee sick days, boost the achievement of school students, and even increase sales in retail outlets. The REPP says that a ten-percent improvement in the productivity of employees can actually pay back the entire cost of a building over a ten-year period.


Closely related to climate responsiveness is the concept of using "green" building materials. "Green" is a word that is used in connection with environmentally sustainable building materials and practices. It does not refer to the actual color of the materials. Rather, because green is the predominant color of the natural world, the word has become a figure of speech to refer to any environmentally sound practice that reduces the impact of human activity on the natural environment.

The need for green building materials

Many green building practices have goals other than energy efficiency. For example, using products made out of natural materials can reduce the level of toxins and other harmful substances in a building. These substances are emitted by such materials as synthetic carpets, adhesives (e.g., glue used to bind two elements together), and fiberglass insulation. Substituting materials made from natural products (like insulation made from recycled paper) can contribute to the health, and therefore productivity, of employees working in a commercial building. Other green building practices are designed to reduce water consumption, for example toilets that use less water and landscaping that does not require large amounts of water. Still other practices are designed to minimize waste. One simple technique is to design buildings with dimensions that use entire 4- by 8-foot (1.2- by 2.40-meter) sheets of particleboard rather than creating large amounts of scrap. Also, using other green building materials that are made from recycled materials. Roof shingles, for example, can be made from recycled vinyl and sawdust.

Many green building practices, however, have energy efficiency and conservation as their primary goal. Many green construction materials save energy not only in the day-to-day operation of the building but also in its construction, because producing and transporting the materials are less energy-intensive activities. Furthermore, some green building materials are more durable than their traditional counterparts. This represents a form of energy conservation because the structure will last longer. A good example is cement composite house siding. Used more and more in place of wood, the cement composite can last fifty years or more with virtually no maintenance, primarily because it is not only tough but the color is mixed into the composite rather than applied on the surface, so it does not have to be painted. Though the initial production of cement is more costly in terms of carbon dioxide emissions than wood, the energy-efficiency of a building made with cement composite may save more carbon dioxide emissions over the lifetime of the building than were used making the cement.

Common green materials

Below are some twenty-first century green building materials. Most of these are more practical for houses than they are for commercial construction such as office buildings. Nonetheless, the impact of using these materials in large numbers of homes could be considerable.

  1. Adobe: Adobe is one of the world's oldest building materials. Essentially, adobe is nothing more than earth that has been mixed with water and shaped into bricks. Sometimes chopped straw is added to give the adobe additional strength. Adobe is most durable when the content of the earth is about 15 to 30 percent clay, which binds the material together. The rest is sand or aggregate (small bits of rock). While adobe is commonly used in the southwestern United States, it can be used in most areas of the country. The chief advantage of adobe is that it provides good thermal mass, meaning that it absorbs heat during the day, then slowly releases the heat during the cooler nighttime. Some homeowners use adobe because the walls absorb heat during the day, then transfer the heat to the main portion of the house at night. The chief disadvantages of adobe are that it is structurally weak and is not a good insulator. Thus, adobe homes are often built very thick and may include a layer of insulation. A variation of adobe is called cast earth, which consists of blocks made of a mixture of earth and plaster of Paris. The plaster gives the blocks greater strength, so the amount of clay is unimportant. Cast earth has a strong aesthetic appeal to some builders because of its stone-like appearance.
  2. Cob: Cob, which was commonly used in nineteenth century England, is similar to adobe, but it has a much higher straw content. Because of the additional straw, it works better as an insulator than adobe does, though cob is often much thinner than adobe construction it is also becomes rather brittle over time. Another difference is that while adobe is typically fashioned into bricks, cob is applied in a more freeform manner, similar to plaster. This can give structures a more artistic look. A variant of cob is called light straw. With light straw the primary component is the straw itself, which is bound together with an adobe-like mixture. Light straw has even higher value as an insulator. It is more fragile, though, so it has to be used with a timber frame to bear loads.
  3. Rammed earth: Rammed earth is another very old construction technique. Much of the Great Wall of China consists of rammed earth. Rammed earth construction again is similar to adobe in that it makes use of local materials. Rather than shaping the earth into bricks (as with adobe) or applying it like plaster (as with cob), rammed earth refers simply to the process of compressing large amounts of earth into thick walls. Often, a stabilizing ingredient, such as cement or even asphalt, is added to the earth to make it more stable and durable. Wooden or metal forms are used to give shape to the walls, in much the same way they are used in pouring a concrete foundation. Like adobe, rammed earth provides a great deal of thermal mass but is not a good insulator. Another disadvantage is that rammed earth is very labor-intensive, usually requiring considerable use of heavy equipment.
  4. Earth bags: Some builders are experimenting with bags of earth, similar to the sandbags that are used for flood control. Builders fill the bags with adobe material or use crushed volcanic rock, which provides greater insulation. The bags are laid in courses, similar to brick, then covered with some sort of plaster-like substance. Many builders are turning to a covering called papercrete, which consists of shredded recycled paper mixed with cement.
  5. Straw bales: Bales of straw are one of the most common green materials used in home construction, primarily as an insulator. The home is constructed using traditional framing methods. The chief difference is that much more space is left between the interior and exterior walls. This space is filled with bales of straw rather than fiberglass insulation, which is made from petroleum and therefore depletes petroleum reserves. Not only is the straw a good insulator, but many homeowners like the thick walls and deep windowsills that result from straw bale construction. Straw bale homes are also quiet, because the straw acts as a sound insulator. The chief disadvantage is that great care must be taken to prevent water from getting into the walls and to prevent the buildup of condensation, because moisture can cause the straw to rot.

Thermal Mass

Energy experts always refer to thermal mass, which measures not the flow of heat but the amount of heat that a substance can hold. Thermal mass is important primarily in areas where there are wide temperature swings throughout the 24-hour day, such as the southwestern United States and parts of the Rocky Mountain region. During the day, as outside temperatures rise, the temperature of the outside of a house is higher than that of the inside. Thus, following the laws of thermodynamics, the heat flows from outside to the cooler inside. During the night, when temperatures tend to fall dramatically (primarily because in these regions the air is drier, so there is no blanket of humidity to trap the day's heat), the heat flow reverses. Heat now flows from the warmer inside of the house to the cooler outside. But thermal mass is always responsible for a time lag. It might take up to eight hours for heat to move from outside to inside in the daytimebut by that time, the sun has set and the heat flow has stalled and starts to reverse. Likewise, it might take up to eight hours for heat to move from outside to inside, but by that time the sun is rising, so once again the heat flow is reversed. The key point is that thermal mass, as in an adobe home, helps to keep the inside temperature relatively constant, so that it changes far less than the outside temperature. A building with a great deal of thermal mass "holds" the heat rather than transferring it.

Thermal mass is a much less important consideration in areas of the country where the temperature does not swing as dramatically. In the north, for example, the daytime high temperature in the winter is almost always lower than the indoor temperature; similarly, in the summer the nighttime low temperature is very often higheror nearly sothan a comfortable indoor temperature. Because the heat flow does not reverse itself under these conditions, thermal mass is less important.

In addition to these common green building materials, builders have experimented with many other types of materials, all with a view to reducing energy consumption and recycling materials that would otherwise find their way into landfills. Some builders, for example, build walls out of recycled tires. They fill the tires with earth, stack them, then plaster over the walls so that the tires do not show. This type of construction, in combination with other methods such as passive solar design and bermed (mounded or piled up) earth on the north side of the house, contributes to very low energy bills for the homeowner.

Embodied energy

In addition to focusing on the energy savings of new climate responsive buildings and use of green building techniques, the "embodied energy" of existing structures must be taken into account. Embodied energy is basically all of the energy (beyond that of the operating costs such as heating and lighting of the building itself) used during a building's life cycle. This would include things such as recycling or removing previous structures; harvesting wood or other resources used in the building; manufacturing other materials used in the building; and transporting materials to the site. In many cases, older buildings contain large amounts of embodied energy, so it consumes less additional energy and is more environmentally friendly to upgrade or restore the older building than to demolish and rebuild, even if green materials are used in the new construction.

When a building is demolished, all of the non-renewable energy used to create the original building is lost and more must be used to rebuild. There are several reasons why remodeling older buildings for efficiency may be a better environmental choice than destruction. The demolition and removal of materials can take up huge amounts of landfill space. Reusing old materials prevents the destruction of more trees, saves the energy used to transport them to mills and create new construction materials, and keeps more green space from development. And, since the energy used to create the original structure has already created pollution, especially with materials such as concrete, which is responsible for large amounts of carbon dioxide during production, tearing down the old structure means that all of the pollution created in building the original structure will be followed by more pollution caused in the creation of a new building.


Energy experts estimate that up to one-quarter of a typical homeowner's energy bill is for artificial lighting. While climate-responsive building techniques can help lower energy use by situating homes and buildings in a way that takes more advantage of natural light, doing so may not be possible for existing buildings, which have to continue to rely on artificial lighting. Further, even the best positioning of a home to take advantage of the sun is of little use on a cloudy day or after the sun has set. Nonetheless, building occupants can take steps to conserve energy on lighting.

Incandescent lightbulbs

Until Thomas Edison invented the incandescent lightbulb in 1879, artificial light was produced primarily by candles and oil lamps, which were not only inefficient but also produced a fire hazard. For years during the nineteenth century, inventors experimented with ways to produce artificial light by passing electricity through some sort of filament in a vacuum. These experiments, however, repeatedly failed because the filament quickly crumbled as a result of the intense heat that made them glow. After numerous experiments testing about a thousand materials, Edison finally came up with one that worked: a carbon-based filament. His earliest lightbulbs burned for an average of about 170 hours before the filament crumbled.

Did Thomas Edison "Invent" the Lightbulb?

The short answer to this question is "yes and no." In 1860 British physicist and electrician Joseph Wilson Swan (18281914) invented an incandescent bulb using a carbon paper filament, but the bulb did not work very well. He abandoned the pursuit for 15 years, but he returned to the problem in 1875. In 1878, a year before Edison, he demonstrated a working incandescent lightbulb with a carbonized thread as a filament. Edison receives all the credit for the invention of the incandescent lightbulb because he developed the first bulb that was commercially successful.

When it was pointed out to Edison that most of his experiments were failures, he famously commented that they were not failures but successes, for he had successfully discovered that the substances he tried did not work.

Today the typical incandescent bulba design that has not changed much since Edison's daylasts about from 750 to 1,000 hours, although more expensive long-lasting bulbs can last 2,500 hours. The bulb consists of a thin, frosted-glass "envelope" that houses the filament, which today is made of the element tungsten, as well as an inert gas (argon). Inert gases are used to fill the bulb for two reasons. One, the bulb cannot contain any oxygen; if it did, the intense heat of the filament would set the bulb on fire. Two, because a gas like argon is "inert," meaning that it does not combine with other elements, tungsten atoms that evaporate from the filament bounce off the argon and most are redeposited on the filament, making the bulb last longer. The filament in a 60-watt lightbulb is about 6.5 feet (2 meters) long, but only about one one-hundredth of an inch thick. It is wound into coils so that it can fit into the bulb. Electricity is applied to the filament, exciting the atoms and producing light. A bulb eventually burns out because the tungsten in the filament evaporates and some of it deposits on the glass. In time, the filament develops a weak spot where it breaks.

Incandescent lightbulbs have a number of advantages. They are inexpensive and easy to use, and the quality of the light they produce is good. (They are so inexpensive that before the energy crises of the 1970s, some electric companies provided lightbulbs to their customers free, usually exchanging new bulbs for burned-out ones.) They can also be used with dimmer switches. But a chief disadvantage is that they are not energy-efficient. After an incandescent lightbulb has been on for a brief period of time, it becomes hot to the touch. This is because the electricity heats the filament to 4,500°F (2,500°C). In other words, most of the electrical energy going into the bulb is converted into heat rather than light. In this respect, an incandescent lightbulb is little different from an electric space heater or a toaster. This production of heat is a double disadvantage in hot-weather climates, where buildings have to be air-conditioned, because a large number of incandescent lightbulbs add to a building's interior heat, placing greater demands on the air-conditioning system. Thus, electricity is being wasted twice.

In the Limelight

The traditional lightbulb is not the only form of incandescence. Incandescent light can also be produced by a rod of lime (a highly flammable solid) surrounded by a flame fueled by oxygen and hydrogen. In the nineteenth century this type of light was the brightest form of artificial light known. Its primary use was to light stages in theaters. This is the origin of the expression "in the limelight," or being in the public's attention.

A more recent innovation is the halogen lamp. The basic technology of a halogen lamp is similar to that of the incandescent bulb. A halogen bulb uses a tungsten filament, but it is encased in an envelope made of quartz rather than glass. Further, this envelope is positioned very close to the filament, but since it is made of quartz, it does not melt. The quartz envelope is filled with gases from the halogen group, consisting of fluorine, chlorine, bromine, iodine, and astatine. What is unique about these gases is that they combine with tungsten vapor. As the tungsten of the filament evaporates, its atoms combine with the gases and then are redeposited on the filament. Thus, halogen lightbulbs last much longer than incandescent lightbulbs. Combined with a parabolic reflector, they produce a high-intensity, crisp light, making them useful for such items as car headlights, most of which are now halogen. The chief disadvantage is that they are energy wasters, for they get even hotter than incandescent bulbs, creating up to four times as much heat. Halogen lamps can be a serious fire hazard in a home, especially if they are too close to draperies or other flammable materials.

Fluorescent lightbulbs

Fluorescent lightbulbs were first invented in 1896. Today they are more commonly used in commercial buildings than homes, although many homeowners use fluorescent bulbs in basements, workshops, and laundry rooms. They tend to be less popular in the living areas of a home for three reasons. First, they often have a subtle flicker, which at best is an annoyance and at worst can cause headaches for some people. Second, the quality of the light they give off tends to be less "warm" than that emitted by incandescent bulbs, which give off more light from the red end of the light spectrum and less from the blue end, in contrast to fluorescent bulbs. For many people, fluorescent lighting has a kind of "sickly" look, although modern fluorescent light has largely overcome this problem. Third, they tend to be a bit noisy, emitting a low hum, although this disadvantage, too, has been overcome by recent technology. The chief advantage of fluorescent lighting is that it is much more energy-efficient than incandescent lighting. Further, fluorescent lightbulbs last 10-15 times longer than incandescent bulbsoften up to 10,000 hours or more.

To measure that efficiency, a distinction is made between watts and lumens. A watt is a measure of electrical usage equal to 1/746th of a horsepower, or one joule per second. (A joule is a unit of energy equal to the work done by a force of one newton acting through a distance of one meter; a newton is the amount of force needed to impart an acceleration of one meter per second per second to a mass of one kilogram.) Typically, the size of an electric lightbulb is measured in watts. Thus, found throughout a typical home are likely to be bulbs of different wattages, such as 40- or 60- watt bulbs where less light is needed and 75-, 100-, and 120-watt bulbs where more light is needed, especially for reading or similar activities.

Wattage, though, measures electrical usage. It is not a measure of the amount of light the bulb produces, although higher watt bulbs are likely to produce more light. Light output, on the other hand, is measured in lumens. Defining a lumen is much easier than defining a watt. One lumen is equal to the amount of light emitted by one candle. The 40-watt incandescent bulb made by one major manufacturer emits 475 lumens, the 60-watt bulb emits 830 lumens, and the 100-watt bulb emits 1,550 lumens.

Fluorescent bulbs produce the same number of lumens as incandescent bulbs with about one-fourth to one-sixth the amount of wattagethat is, electricity. Thus, fluorescent bulbs are far more energy-efficient than incandescent ones. They achieve this greater efficiency because they do not produce nearly as much waste heat, so per watt of electricity consumed, they produce more lumens.

Fluorescent lightbulbs are easily recognizable because rather than being shaped like bulbs, they are tubular. This sealed glass tube contains mercury and an inert gas (such as argon). The inside of the tube is coated with phosphor powder, a substance that emits light when its atoms are excited. At each end of the tube is an electrode that is wired to an electrical circuit. When the current is turned on, the voltage across the electrodes causes electrons to move from one end of the tube to the other. The energy converts the mercury from a liquid into a gas. The electrons collide with the mercury atoms, exciting them so that their electrons move to a higher energy level and higher orbit. As the electrons move back to their original orbits, they emit light.

The process, though, does not stop there. The light that is emitted is in the ultraviolet wavelength range, so it is not visible. This is where the phosphor powder coating goes to work. The photons created during the first step in the process collide with the phosphor atoms, again exciting them and causing their electrons to move to a higher energy level. Once again, when the electrons return to their normal energy level, they emit photons. These photons have less energy than the original photons; this is because some of the energy is released in the form of heat. But these lower energy photons now give off light that is visible, so-called white light that the human eye can detect. By using different combinations of phosphors, bulb manufacturers can alter the color of the light.

For many years, one of the problems with fluorescent bulbs was that it took them several seconds to light up. "Rapid start" lights have been developed to overcome this problem. In these lights a mechanism called the ballast maintains current through the electrodes. When the light is turned on, the electrode filaments heat up very quickly to ionize gas in the tube. Modern ballast mechanisms have also helped to reduce or eliminate both the flicker and noise that earlier ballasts created.

Compact fluorescent bulbs

Traditional fluorescent bulbs are long, thin tubes rather than actual "bulbs," making them unsuitable for use in floor and table lamps and even in many wall and ceiling fixtures. For this reason, they have been used primarily in special ceiling fixtures in commercial buildings, as well as in certain areas of the home. Further, they cannot be used in regular lamps or fixtures because of the nature of the plug, which consists of pairs of pins at each end rather than the metal screw portion of an incandescent lightbulb.

In the 1980s these shortcomings were corrected with the development of the compact fluorescent lightbulb (CFB). This type of bulb works in exactly the same way that a traditional fluorescent bulb does, but rather than being packaged in a long tube, the tube is smaller and folded in such a way that the bulb resembles a traditional incandescent bulb. Further, rather than pins at each end, the bulb screws into the light fixture in exactly the same way incandescent bulbs do (although occasionally some of these bulbs require special fixtures because the screw portion is a different size).

What this means is that fluorescent lighting can now be used throughout a home or other building, with the potential for enormous energy savings. The California Energy Commission estimates that a single 20-watt compact fluorescent bulb used in place of a 75-watt incandescent bulb (remember that fluorescent bulbs produce more lumens per watt than incandescent bulbs do) will save 550 kilowatt-hours of electricity over its lifetime. It takes about 500 pounds (227 kilograms) of coal to produce this much electricity, and burning this amount of coal releases about 1,300 pounds (590 kilograms) of carbon dioxide and 20 pounds of sulfur dioxide into the atmosphere. That is just one bulb. It has been estimated that if every American used CFBs, the nation could save 31.7 billion kilowatt-hours of electricity each year. A typical coal-fired power plant produces about 500 megawatts, or about 3.5 billion kilowatt-hours, of electricity per year. To generate this electricity, it has to burn about 1.43 million tons of coal, releasing 10,000 tons of sulfur dioxide and about 3.7 million tons of carbon dioxide. Converting all home lighting to CFBs would in effect eliminate the need for roughly nine of these power plants.

CFBs have one disadvantage. While a typical incandescent bulb costs about $0.75, CFBs average about $11. The tradeoffs, though, are significant energy savings over the life of the bulb, combined with the fact that the bulb is likely to last up to ten times longer.


Climate responsiveness and the use of green building materials are options for new home construction. Most people, however, do not have this option because their homes were constructed years ago before these innovations were widely used. Nonetheless, homeowners can take many steps to lower their energy bill by saving energy. Some of these steps involve changes they can make to the home itself to conserve energy; others involve steps they can take to reduce personal energy use or use energy more efficiently.

Energy conservation

Experts recommend the following as ways to conserve energy in the homemany of these same steps can be taken in commercial buildings as well.

  1. Phantom loads. Many electronic devices use electricity even when they are turned off. Such items as videocassette recorders, televisions, microwave ovens, and computers, as well as business machines such as copiers and faxes, all consume energy when they are not in use. A simple way to lower energy use with these devices is to plug them into a power strip, which can be turned off when the device is not being used. Another way is to unplug wall transformers (such as those used to charge a battery in a power tool or a cell phone) when they are not needed. A wall transformer, even if a tool or appliance is not plugged in, still operates and is warm to the touch. This warmth represents wasted energy.
  2. Hot water. A major component of a family's energy bill is for hot watertypically about one-seventh of a home's energy bill. Hot water tanks, especially older ones, can be insulated with kits available at hardware stores. Point-of-use hot water heaters, which operate only when the hot water tap is turned on, reduce the need for a standing tank of hot water that is not being used. Most manufacturers preset the temperature on hot water heaters at 140 °F (60°C), but 120°F (49°C) is sufficient for most households (and reduces the risk of scalding by water that is too hot). Lowering the thermostat temperature on a hot water heater by 10 degrees can save 3-5 percent on hot water costs. Moreover, low-flow shower headsthose that flow at a rate of 2.5 gallons (9 liters) per minute or less rather than the 4-5 gallons (15-19 liters) per minute of older shower headsreduce the consumption of hot water, saving energy. One commonsense way to reduce hot water consumption is not to let the shower run for long periods of time while preparing to get in.
  3. Heating and cooling. Thermostats can be turned down at night and when the family is away for the day. A programmable thermostat can be set to turn the heat down at night or during times when no one is at home, then warm the house up just before the family gets up in the morning or just before they are scheduled to return home at the end of the day. Also, the style of indoor dress can be changed slightly so that indoor temperatures can be set lower in winter and higher in summer. In the summer, fans may be used to compensate for decreasing the use of air conditioning. Weather stripping can reduce heat loss around leaky doors and windows. Insulated curtains can help reduce heat loss through windows at night. Double-paned thermal windows allow the warmth of the sun to enter the home when the sun is low in the winter sky but block the sun's heat when the sun is high in the summer sky, reducing the need for air conditioning. Rooms that are not being used can be closed off and the heating in the room turned off (or the hot air duct closed). Changing filters on furnaces and having the furnace serviced each year can reduce energy consumption.
  4. Insulation. Because heat rises, most heating energy is lost through a home's roof. An investment in a few hundred dollars' worth of insulation can reduce home heating (and cooling) bills by as much as 30 percent. Insulation can be installed in ceilings. Contractors can even insulate existing exterior walls by blowing insulation through small holes drilled between wall supports.
  5. Landscaping. Well-placed landscaping can reduce heating and cooling bills. Deciduous trees (those with leaves) can be placed so that they block the sun, especially on the south side of a house, during the summer. The trees then lose their leaves in winter, allowing sunlight through to warm the house. Windbreaks, consisting of a row of trees or bushes, especially on the north side of a house in most areas, can block winter winds, lowering heating bills. According to Colorado State University researchers, windbreaks in some areas can reduce heating bills by as much as 25 percent.

Energy efficiency

One major way to conserve energy is to use energy more efficiently. Using compact fluorescent lightbulbs, double-paned thermal windows, and insulation conserves energy by enabling homeowners to heat, cool, and light their homes more efficiently. But another way to conserve energy is to use appliances that consume less energy.

Beginning in the 1980s the United States Congress passed several laws mandating minimum energy efficiency for appliances such as refrigerators, freezers, washers, dryers, ovens, water heat-ers, and pool heaters. Smaller manufacturers make many of the most efficient appliances, which tend to be more expensive. But even the major manufacturers have models that are far more energy efficient than appliances used to be. Here are some guidelines that promote energy efficiency in appliances:

  • Refrigerators: Models with the freezer on top are generally more efficient than side-by-side models and those with the freezer on the bottom. Refrigerators that have to be defrosted by hand use about one-half the energy of automatic-defrost models. The most efficient refrigerators tend to be in the 16- to 20-cubic-foot range. Generally, though, it is more efficient to run one large refrigerator than two smaller ones.
  • Washing machines: Many homeowners overuse the hot wash cycle. The warm and cold settings are adequate for most laundry. Energy-efficient washers automatically control the water level for the size of the load. Also, the spin cycle, in which the machine spins quickly to eliminate as much water from the clothes as possible, is faster in energy-efficient washers. Thus, more water is expelled from the clothes, and they do not have to spend as much time in the dryer. Horizontal axis machinesthat is, front loadersuse far less water and soap and are much more efficient than vertical axis machines, or top loaders. The cost of running a front loader is about one-third that of running a top loader. One major manufacturer makes a washing machine that communicates with the dryer and presets it to deliver the most efficient results.
  • Clothes dryers: The most energy-efficient clothes dryer is the sun and a line to hang the laundry on. In rainy or cold weather, racks for drying laundry can be used indoors, and the humidity the drying clothes add to indoor air is an added plus.
  • Dishwashers: One way to boost the energy efficiency of dishwashers is, of course, not to use them as often and only for full loads. Many dishwashers have a "no-dry" cycle that saves energy; the dishes air-dry instead of being dried by heat produced by the dishwasher itself. Also, many dishwashers have water heaters so that only the water going to the dishwasher is being heated.

The guidelines for energy efficiency focus on conventional appliances, like those that can be purchased at such places as department stores. For consumers who want to achieve even greater savings on their energy bills, specialty products are available. Examples include solar-powered hot water heaters (especially heaters for smaller quantities of water, enough, for example, for one person to take a shower); solar cookers that focus the sun's rays to produce enough heat for cooking purposes or straw ovens that store the heat in the heated food to cook it; washing machines that require no electricity, relying instead on soaking and using a hand crank to wring out water; and point-of-use water heaters that activate when the hot water tap is turned on and heat just the water that is being used rather than a tank of standing water.

One conventional appliance that has potential for significant energy savings is the refrigerator, which on average uses about nine percent of the energy consumed in homes. Standard refrigerators and freezers use about 3,000 watt-hours per day, although it is possible to find commercial models that use just 1,500 watt-hours per day. Some manufacturers, however, build superinsulated refrigerators that use only about 750 watt-hours per day, depending on the size and model. Smaller superinsulated refrigerators use only 200 watt-hours per day. These types of refrigerators are ideal for people who run their homes primarily on solar power. Fewer solar panels have to be added to the home to power the refrigerator.


Energy savings in the home and in commercial buildings makes a vital difference in the total amount of energy consumed. Still, the energy used to power cars and trucks represents a major portion of energy expended. Just in the United States, drivers consume about 360 million gallons of gasoline each day, or about 131 billion gallons of gasoline each year. If one gallon of gas, when burned, releases about 5-6 pounds (roughly 2.5 kilograms) of carbon dioxide into the atmosphere, then U.S. drivers are releasing about 2 billion pounds of carbon dioxide into the atmosphere each day. While U.S. drivers consume about 45 percent of the world's gasoline, they are not responsible for the entire problem with vehicle gasoline consumption. As of 2005, for example, the number of private cars in Beijing, the capital of the People's Republic of China, was 1.3 million, up 140 percent just since 1997. In 2005 China consumed about 252 million gallons of gasoline per day, but that figure was predicted to double to 504 million a day by 2025. Meanwhile, according to the World Bank, sixteen of the twenty most polluted cities in the world are in China, and vehicles cause most of that pollution.

Energy Star Ratings

Energy experts urge consumers to look for the Energy Star label when they shop for appliances. The label appears on appliances such as refrigerators, washing machines, dishwashers, water heaters and heat pumps, and even on windows. The label indicates that the energy efficiency of the appliance exceeds that required by federal regulations. Appliances that earn the Energy Star label are at least 13 percent more efficient than normal machines, but many are 15, 20, and even 110 percent more efficient. For example, Energy Star washing machines use 50 percent less electricity than those that do not have the Energy Star label.

Before the energy shortages of the 1970s, Americans tended not to care very much about what kind of gas mileage their cars got. Large, "gas-guzzling" cars were the norm, and gasoline was relatively inexpensive, so little attention was paid to gas mileage. In the 1960s it was not uncommon for a family car to get as little as 10 miles (16 kilometers) per gallon or even less. Beginning in the 1970s, though, efforts were made to improve the gas mileage of cars by making them smaller and lighter and by introducing technical innovations that enabled them to burn gas more efficiently. While cars became more efficient in the following years, Americans also developed a taste for larger, heavier vehicles such as sport utility vehicles (SUVs). Thus, by the year 2000 many Americans were driving vehicles that got the same gas mileage as those that they drove 25 years earlier.


The early 2000s saw the introduction of so-called hybrid vehicles. A "hybrid" of any sort is a combination of two or more features that produces a benefit. In the case of vehicles, a hybrid combines two technologies for using energy in a way that reduces energy consumption. While conceivably any two technologies might be used in hybrid vehicles, the most common is to combine a conventional internal combustion engine with an electric motor and batteries that power the car with electricity. In the future, hybrids are likely to make use of other technologies, including hydrogen fuel cells and possibly even steam power.

Hybrid vehicles are not entirely a new concept. The moped, a motorized pedal bike, is a hybrid vehicle that combines a gasoline motor with pedal power. Locomotives are diesel fuel-electric hybrids, as are many giant trucks used for mining. Submarines, too, are hybrid vehicles using diesel-electric and in many cases nuclear-electric combinations. In 1899 German automaker, Ferdinand Porsche (18751952), engineered a hybrid car. The current generation of hybrid vehicles uses a combination of gasoline and electricity for power, as did Porsche's car.

The hybrid design overcomes the chief disadvantages of all-electric cars. Cars powered entirely by electricity have to be plugged in to a power source when they are not in use. These cars have limited rangegenerally about 100 miles or sobefore the electrical power stored in the car's batteries is depleted. Moreover, the process of "refueling" is time-consuming and inconvenient. In a hybrid car the gasoline-powered engine and the batteries work with one another. Typically, an electrical motor, powered by batteries, powers the car's engine. The internal combustion engine provides a power boost when necessary, especially when the car is accelerating. The gas-powered engine keeps the batteries charged, so the car does not have to be plugged in. On some models, when the car is idling, the internal combustion engine does not operate, so no gas is being consumed. This feature makes hybrid cars very quiet when the car is stopped at an intersection.

The components of a hybrid vehicle

A typical hybrid vehicle consists of the following components:

  • Gasoline engine: A hybrid has a gasoline-powered engine similar to that found on a standard vehicle. This engine, however, is small and more fuel-efficient than the engine on a normal vehicle, boosting gas mileage and lowering emissions.
  • Fuel tank: The hybrid has a tank for storing gasoline.
  • Electric motor: Hybrid vehicles use sophisticated motors to provide some portion of the power the vehicle needs and to recharge the batteries.
  • Generator: In some hybrids the motor acts both as a motor and as a power generator. In others a separate generator produces electrical power.
  • Batteries: A battery pack stores energy produced by the motor and braking system. One major problem with electric vehicles is that gasoline is much more energy dense than batteries. That is, one gallon of gasoline contains as much energy as 1,000 pounds (454 kilograms) of batteries. The advantage of hybrids over all-electric vehicles is that the battery pack does not need to be as large because the motor is continually recharging the batteries.
  • Transmission: The transmission of a hybrid is similar to that on a standard car, although some manufacturers have introduced more sophisticated transmissions that can be powered both by the electric motor and by the gas-powered engine.

Advantages of hybrid vehicles

Hybrid vehicles have at least two advantages. First, a hybrid's internal combustion engine is generally much smaller and more fuel-efficient than the engine of a standard car. This is because the engine does not do all the work. It is assisted by the batteries that supply power to the car's drive train. Generally, the internal combustion engines of standard cars are much larger than they need to be. A standard car might be capable of 200 horsepower or more, but a car generally needs only about 20 horsepower to overcome drag as the car pushes its way through air, to compensate for the friction produced by the tires and transmission, and to power such accessories as the power steering and air-conditioning. All the extra power is used primarily for sudden acceleration or to climb an uphill grade, but that extra capability is used only about one percent of the time the car is on the road. Therefore, in contrast to big, high-horsepower engines, hybrids use smaller, lightweight engines. One model's engine weighs only 124 pounds (56 kilograms), has only three cylinders (as opposed to the six or eight cylinders on many larger vehicles), and produces just 67 horsepower. By using small engines and designing them so that they operate at close to their maximum load, hybrid vehicles cut down on gas consumption.

A second advantage is that hybrid vehicles make use of what is called a regenerative braking system. Such a system is based on the laws of thermodynamics, which say that energy cannot be created or destroyed but can only change form. When a car is moving down the road, it burns gasoline, releasing energy that is converted into the mechanical energy of the car's drive train. Some of the energy is lost to friction where the tires meet the surface of the road, as well as in the transmission. But much of a car's energy is lost when the brakes are applied, converting the kinetic energy of the moving car into friction, which is released in the form of heat in the car's brakes. (This explains why cars periodically need a brake job to replace the brake pads, which have been worn down by heat.) A hybrid vehicle recaptures some of this otherwise lost energy and sends it off into the car's batteries, where it is recycled to power the car. The end result is vehicles that generally get much higher gas mileageup to 60-plus miles (97 kilometers) per gallon for some modelsand that release one-tenth the amount of pollution into the atmosphere compared to standard vehicles.

Hybrid manufacturers incorporate other ways to increase the fuel efficiency of their vehicles. They recover energy and store it in the battery and allow the gasoline-powered engine to shut down when the car is idling. In addition, they use advanced aerodynamics to reduce drag. The chief way this is accomplished is by reducing the front area of the vehicle so that the volume of air the car has to push through is reduced.

Automakers have even found ways to reduce the drag caused by objects such as mirrors that stick out from the vehicle. Some have replaced side mirrors with small cameras. Others partially cover the rear wheels to reduce drag and also enclose parts of the undercarriage (the underside of the car) with plastic panels. The result is a very low drag coefficient, sometimes as low as 0.25. Hybrid makers often install low-rolling resistance tires. These tires are stiffer and inflated to a higher pressure than standard tires, two aspects that reduce drag by as much as half. Finally, hybrid manufacturers make use of lightweight materials, such as aluminum, so the vehicle needs less energy to accelerate.

Hybrid vehicles have other advantages. In 2003, 2004, and 2005, buyers of hybrid vehicles were entitled to a $2,000 federal income tax "clean fuel" deduction, the government's way of promoting interest in hybrid vehicles. As of 2005 that deduction was scheduled to be reduced and then phased out. Supporters of hybrids, naturally, were working to get legislation passed to extend the deduction.

Drag Coefficient

Engineers use the term drag coefficient to refer to measurements they make of the amount of drag a vehicle generates as it pushes air out of the way while it is in motion. Engineers can calculate the drag coefficient of various shapes under normal conditions. Thus, the drag coefficient of a sphere is 0.47; of a cube, 1.05; of a long cylinder, 0.82; of a short cylinder, 1.15. The most aerodynamic shapethat is, the one with the lowest drag coefficientis the streamlined "teardrop" shape with the pointed end at the front, at 0.04. Energy-efficient vehicles cannot use a pure teardrop shape, but they can use something that approaches it by reducing the front area of the vehicle.

As of 2005 at least fifteen states gave tax credits to hybrid vehicle buyers, and thirteen other states were considering doing so. Oregon offered a state tax credit of up to $1,500; Connecticut waived the 6 percent sales tax on the car, and Colorado offered a tax credit of up to $4,713. Hybrids can also go on some toll roads free. In some cities, such as San Jose and Los Angeles, California, hybrid car owners do not have to feed parking meters in city lots or on the streets. Some states allow hybrid cars with just the driver and no passengers to use car-pooling lanes. And some states release hybrids from emissions inspections. In London, England, hybrid vehicle owners pay the lowest amount of tax on their cars and do not have to pay a "congestion charge," a tax levied on all other vehicles in the city.

Types of hybrid vehicles

Hybrid vehicles come in two basic types: series and parallel. In a series hybrid, the first generation of modern hybrids, the gasoline-powered engine never powers the car directly. Rather, the gasoline engine turns a generator, which powers an electric motor that in turn powers the drive train, or it recharges the batteries. In a parallel hybrid, the second generation of modern hybrids, the gasoline-powered engine and the batteries power the car at the same time. In these cars, both the gasoline-powered engine and the electric motor are attached, independently, to the car's drive train. A third generation of hybrids is being developed. These vehicles use a differential-type linkage and a computer to allow the vehicle to be powered by the internal combustion engine, the electric motor, or both. The computer shuts off the gas engine when the electric motor is providing enough energy.

Other terms are frequently used to describe various sorts of hybrids. Sometimes the terms strong hybrid or full hybrid refer to the third-generation vehicles that can be powered by the gas engine, the electric motor, or both. The term assist hybrid refers to vehicles in which the battery and electric motor are used to accelerate the vehicle in combination with the gas engine. Plug-in hybrids, sometimes called gas-optional or griddable, have larger batteries and are able to run entirely on electricity from the electric motor and batteries. These vehicles can be recharged by plugging them into the power grid. The vehicle can rely on this electricity for short hops and daily commuting, but it also has a gas-powered engine for use during longer trips. Mild hybrids are often sold as hybrids, but they are not true hybrids because the electric motor never powers the vehicle. They are able to achieve greater fuel efficiency, however, because a starter motor spins the engine to the number of revolutions per minute it needs to operate before fuel is injected. These vehicles also use "regenerative" braking, and their engines do not run when the vehicle is coasting, braking, or idling.

The future of hybrid vehicles

As of 2005 only about one percent of new cars purchased were hybrids. In 2004, however, the number of hybrid registrations was up 81 percent from the year before, to just over 83,000. Many car industry observers believe that momentum is building in the hybrid industry and that consumer demand is growing enough to encourage manufacturers to design and build them. In the early 2000s the three hybrid cars available in the United States were the Honda Civic Hybrid, the Honda Insight, and the Toyota Prius. In designing its cars Honda aimed for the highest gas mileage possible, and its cars can get up to 68 miles (109 kilometers) per gallon. Toyota, on the other hand, aimed primarily for pollution reduction. The gas mileage of the Prius is in the mid- to high 40s.

Other car manufacturers made plans to release hybrid models. Scheduled for release in 2005 were hybrid vehicles from Daimler-Chrysler (Dodge and Mercedes), Ford, and General Motors (Chevy, GMC-Sierra, and Saturn). In the early 2000s many conservationists were growing concerned about the large and growing number of SUVs, which are classified as trucks and therefore are not required to get gas mileage as high as that of cars. Accordingly, some manufacturers are designing hybrid trucks and SUVs. In 2005 Toyota and Lexus were both planning to release hybrid SUVs, and Chevy scheduled offerings of two models of hybrid pickup trucks. Industry observers believe that the number of hybrids sold in 2005 could equal the total number sold in the four preceding years combined.

Some experts question the value of hybrid cars, at least from a strictly economic standpoint. While they support efforts to reduce pollution, they point out that, as of 2005, the higher price of hybrids offsets much of the energy savings. The magazine Consumer Reports calculated that it would take about 21 years of energy savings to offset the higher price of one popular hybrid model without the tax deduction. With the tax deduction, it would still take about four years for the buyer to break even. These estimates, however, assume that gas prices will remain consistent. In 2005, and early 2006, gas prices rose dramatically, thus making the payback period for hybrids shorter. For the near term, industry experts are also concerned about the resale value of hybrids, given that improvements are continually being made in the technology. Further, auto industry experts note that it is possible to achieve nearly similar energy savings with standard cars, some of which cost much less. Driving a stick shift vehicle as opposed to one with an automatic transmission can achieve gas savings of up to 18 percent.

Tips for more fuel-efficient driving

Though hybrid vehicles offer promise for reducing the U.S. reliance on fossils fuels, they are not the only solution. There are many other ways in which people can immediately reduce the amount of fossil fuels used by making personal choices to limit their own use of traditional automobiles. Drivers can also take a number of steps to increase the fuel efficiency of their existing vehicles or to use less fuel, whether the vehicle is a hybrid or not:

  1. Use your legs. People can bicycle or even walk to many of their destinations, a solution that is better for both for the environment and an individual's health in general.
  2. Utilize public transportation when possible. Public transportation is an option in many larger cities, though the structure of many U.S. cities (or their urban sprawl) needs to be addressed in others. One city bus can keep 40 or so vehicles off the road and save over 21,000 gallons (79,493 liters) of gasoline each year.
  3. Car-pool. Car-pooling not only saves fuel by taking vehicles off the road, but it also reduces traffic congestion. Many cities encourage car-pooling with special lanes set aside for cars with two or more passengers.
  4. Plan efficient trips. For long-distance trips, drivers can save fuel by taking the most efficient route, which may not necessarily be the shortest route. Taking a bypass around a city might add miles, but it eliminates the stop-and-go driving of cities and suburbs that uses more gasoline.
  5. Avoid short trips when possible. A vehicle reaches its peak operating efficiency only after it has warmed up for a few miles. Short hops of under a few miles use more fuel per mile than longer trips. Drivers can save fuel by combining errands in the same trip. In winter, combining errands can also reduce the number of cold starts the car has to make.
  6. Reduce quick accelerations and stop-and-go driving. Cars consume the most fuel when they are accelerating. Fast accelerations waste fuel, and racing up to stoplights or stop signs, applying the brakes, then racing on to the next stop is especially wasteful. By anticipating stops, coasting, then gently accelerating, drivers can save fuel. One test showed that "jackrabbit" driving, or driving with quick starts and hard braking, saves only 4 percent of a driver's time (two-and-a-half minutes for a one-hour trip) but consumes 39 percent more fuel.
  7. Slow down. Driving at 55 mph (89 kph) can produce gas mileage gains of 15 percent compared to driving 65 mph (105 kph).
  8. Reduce idling. Most drivers tend to let their car idle when it is stopped. Many believe that it takes more gas to restart the car than is consumed by idling. Tests, however, show that this is not true if the idle time is more than about 10 seconds. Turning the car off when a long delay is anticipated (for instance, at a railroad crossing, when waiting to pick someone up, or when waiting in line at drive-through windows) can save significant amounts of fuel. Idling a car for long periods of time in order to warm it up in cold weather wastes fuel. The best way to warm a car up is by driving itagain, avoiding quick acceleration, especially when the car is cold.
  9. Use engine-block heaters in cold weather climates. For a short trip a car can use up to 50 percent more fuel in cold weather than in warm weather. Plug-in engine-block heaters allow a car's engine to reach peak operating efficiency in cold weather much faster, saving fuel.
  10. Reduce weight. Two ways to reduce weight are to clear snow and ice off the car, including ice that builds up in the wheel wells, and not to carry around excess items in the trunk or in the bed of a truck. Removing items such as ski racks and bicycle racks when they are not being used can increase fuel efficiency by reducing both weight and aerodynamic drag. Airlines discovered that they could save thousands of dollars per year in fuel costs solely by switching from glass to lighter plastic bottles for beverages on jumbo jets.
  11. Keep tires inflated. A tire that is underinflated by just two pounds per square inch can increase fuel consumption by one percent. Tire pressure drops in cold weather, so it is especially important to check the tires' pressure in winter.
  12. Service the vehicle. Such things as fouled spark plugs and dirty air filters can reduce fuel efficiency. A periodic wheel alignment can increase gas mileage by up to ten percent.
  1. Use tires appropriate for conditions. Most city and suburban drivers do not need snow tires, which are softer and increase fuel consumption. For these drivers all-season radial tires are sufficient. On the other hand, drivers in rural areas, where roads can often be snow-packed, might achieve greater fuel efficiency with snow tires because they can reduce slippage.
  2. Shift up. With manual transmissions shifting into a higher gear as soon as possible saves fuel. Manual-transmission vehicles get up to 18 percent better gas mileage than automatic-transmission vehicles.
  3. Turn off the air-conditioner. Minimizing the use of air-conditioning, which is powered by the vehicle's engine, increases fuel efficiency, especially at lower speeds, when the amount of aerodynamic drag is not significantly increased by opening the vehicle's windows.


Though innovation and creativity in creating energy efficient buildings, cars, and appliances and using renewable energy sources will begin to reduce the use of fossil fuels in the future, the choices that people make today, in their everyday lives, can also make a major difference. Every person on the planet leaves a "footprint" on the Earth, a demand on nature that includes the energy taken to support a person's consumption habits, whether they are choosing food, housing, utilities, transportation, or other goods and services (like clothing, recreation, and cleaning products). For the Earth to support a growing population, there must be a balance between increasing human needs and wants and nature's ability to sustain all of the energy requirements placed on the planet's resources.

There are daily actions beyond those mentioned above that everyone can take to reduce the overall energy footprint on the Earth and to help stay within the planet's capacity for regenerating energy, food, and materials, including:

  1. Limiting excess consumption. People can make choices not to buy items they do not need, to purchase recycled or secondhand items, or, if a new product is necessary, to purchase non-disposable items that require little or no packaging. Energy is used to make any product; thus, the fewer products people buy, the less energy is used. Many times, a secondhand item, especially a durable good such as a piece of furniture, is just as good as purchasing a new item, and will be cheaper for the consumer as well. The excess packaging of items affects energy consumption in several ways, including in the production of the packaging itself and the fuel necessary to power the dump trucks that must take the additional garbage to the landfill. Rather than buying a product that is contained in both a box and a plastic bag, people can choose items that have less packaging or are not packaged at all.
  2. Recycling. Many items that go into landfills can be recycled into products to save energy. Waste paper can be made into insulation. Plastic can be turned into a host of products, such as durable carpeting for use in cars. In the United States, about 250 million automotive tires are scrapped each year. In 1989 only about 10 percent of those tires were recycled, but by the 2000s, that percentage had increased to 80 percent. The tires are commonly shredded to provide fill in building projects, mulch for gardens and under playground equipment, and as an ingredient in road asphalt. Soda pop bottles can be recycled to make the synthetic fleece common in winter jackets. Aluminum cans are 100 percent recyclable. In 2003, 54 billion aluminum cans were recycled, saving an amount of energy in aluminum manufacture equal to about 15 million barrels of crude oil.
  3. Lighting. Artificial lighting is a major consumer of electricity. Energy can be saved by turning off lights that are not in use, relying on natural lighting during the day, and attaching motion sensors to outdoor lighting so that the lights come on only when they are needed for outdoor activity. The use of compact fluorescent lightbulbs throughout a home can cut energy usage for lighting by about three-fourths.
  4. Food choices. Eating a diet with fewer animal-based and more plant-based products generally requires less energy, land, and other resources. Planting a garden or choosing locally grown goods rather than buying items that must be transported cuts down on energy and pollution from shipping, packaging, fertilizers, and pesticides. Buying items that are not processed saves energy used in the canning, freezing, or packing industries.

Even if it seems that the actions you take are small and will not affect the planet, your contributions over your lifetime can make a difference. You can also ask your parents, other family members, and friends to take some of the steps listed above, and work together to encourage changes in energy efficiency and conservation.

For More Information


Frej, Anne B. Green Office Buildings: A Practical Guide to Development. Washington, DC: Urban Land Institute, 2005.

Husain, Iqbal. Electric and Hybrid Vehicles: Design Fundamentals. Boca Raton, FL: CRC Press, 2003.

Hyde, Richard. Climate Responsive Design. London: Taylor and Francis, 2000.

Kibert, Charles J. Sustainable Construction: Green Building Design and Delivery. New York: Wiley, 2005.

Wulfinghoff, Donald R. Energy Efficiency Manual: For Everyone Who Uses Energy, Pays for Utilities, Designs and Builds, Is Interested in Energy Conservation and the Environment. Wheaton, MD: Energy Institute Press, 2000.


Feldman, William. "Lighting the Way: To Increased Energy Efficiency." Journal of Property Management (May 1, 2001): 70.

Motavalli, Jim. "Watt's the Story? Energy-Efficient Lighting Comes of Age." E (September 1, 2003): 54.

Web sites

"Driving and Maintaining Your Vehicle." Natural Resources Canada. (accessed on September 28, 2005).

"Ecological Footprint Quiz.;rdquo; Earth Day Network. (accessed on February 6, 2006).

"Energy Efficiency and Renewable Energy." U.S. Department of Energy. (accessed on September 28, 2005).

"Green Building Basics." California Home. (accessed on September 28, 2005).

"Incandescent, Fluorescent, Halogen, and Compact Fluorescent." California Energy Commission. (accessed on September 28, 2005).

"Introduction to Green Building." Green Roundtable. (accessed on September 28, 2005).

Nice, Karim. "How Hybrid Cars Work." (accessed on September 28, 2005).

"Thermal Mass and R-value: Making Sense of a Confusing Issue." (accessed on September 28, 2005).

Venetoulis, Jason, Dahlia Chazan, and Christopher Gaudet. "Ecological Footprint of Nations: 2004." Redefining Progress. (accessed on February 8, 2006).