12. Saving energy at home and finding energy at your feet

Figure 12.1 Indian dwellings in Mesa Verde, Arizona, showed that the Anasazi understood the benefits of energy conservation, as did all early peoples. They had no choice—they lacked the abundant, cheap energy that we are accustomed to. The Anasazi in Mesa Verde built their houses on the south-facing slopes of cliffs, beneath an arch, so that they were shaded from the intense midday sun but warmed by the early-morning and evening sunlight at lower angles. This was only one of many ways that they lived with only small amounts of fuel. (Photograph by Daniel B. Botkin)

Key facts

• In many places in the world before the industrial/scientific revolution, homes and workplaces were designed to conserve energy. That changed in the 20th century. The buildings that we now consider standard and normal are actually novel in human history in terms of energy wastefulness.

• Cave dwellers many thousands of years ago made use of the ability of soil and rock to store heat from the sun, and many of the world’s peoples still do so today.

• We are rediscovering geothermal energy and realizing that it could be a major and relatively inexpensive energy source.

• Modern construction materials and careful architectural design can reduce energy use in buildings by 60% or more.

• Costs for these energy-efficient buildings appear only slightly higher than typical 20th-century designs.

Energy-efficient buildings

Long experience throughout human history shows without any doubt that thoughtful design of buildings can save large amounts of energy. The book A Golden Thread: 2500 Years of Solar Architecture and Technology, by Ken Butti and John Perlin, tells a beautiful and moving story of how the ancients from many cultures—probably all—designed and situated their homes and public buildings to make them as comfortable as their technology allowed and minimized the need for fuels.

You may be surprised to learn that people are not the only ones who build to make good use of solar energy. Huge termite mounds stand tall among the short grasses in the plains and savannas of East Africa. They not only are warmed by the sun but also have ventilation and even a kind of air-conditioning. Air passages extend from the base of the mound to the top. The sun heats the air at the top, causing it to rise, which in turn draws cooler, oxygen-rich air upward from the bottom. This is “design with nature” designed by nature (Figure 12.2).

Figure 12.2 The remnants of a large termite mound in the grasslands of Zimbabwe show that these structures take advantage of passive solar energy but also provide good ventilation and a kind of air conditioning. (Photograph by Daniel B. Botkin)

Recent architectural designs using the best of modern materials have led to new buildings that use much less energy than those characteristic of the Industrial Age. Building for energy conservation is often discussed today as if it is a new idea dreamed up in the most recent decades. But if there has been anything new in modern times—“new” in the sense of novel—it’s the way buildings were constructed in the developed nations during the 19th and 20th centuries, when fossil fuels were abundant and cheap. The old lessons were forgotten, and houses and commercial buildings were designed without a thought to energy conservation. With uninsulated or poorly insulated walls, ceilings, and floors, they required large wood-burning fireplaces and woodstoves to keep rooms livable.

I lived for a year in a classic example of this kind of house, a restored early-19th-century farmhouse in Acworth, New Hampshire. The house, situated on a hillside, had a thick skirting of open boards that separated the downslope side of the basement from the elements. In winter, the winds blew right through these and wafted up into the living room. A furnace had been added in the basement, but did not work, so we heated the house with a shallow fireplace in the living room, another in each of the bedrooms, and a wood-burning cookstove in the kitchen. It was a charming house, and it looked inviting on a summer afternoon, but it was far from cozy on a winter’s night.

All this is changing rapidly. Today, friends who live near that house are building houses of amazing new materials invented in recent decades. Imaginative architects and engineers have pursued their use, combining these new materials with the old lessons, lost for several centuries, of designing with nature and with the best of modern technology. Like many preindustrial buildings, these new buildings take into consideration where the sun shines, where the soil and rocks protect, where nature provides easy and convenient energy sources and energy storage, where and how vegetation makes buildings warmer, cooler, more pleasant—and a lot cheaper.

This combination of the new and the old has developed today into a sizable business with many projects, ranging from individual homes to housing developments and commercial buildings. There are many books on energy-conserving building designs; here I can only introduce the topic, focusing on the potential energy savings.

Among many recent examples is a house built in Denver, Colorado, by the National Renewable Energy Laboratory (NREL) in cooperation with Habitat for Humanity. The house makes use of active and passive solar energy and highly insulating modern materials (Figures 12.3 and 12.4). Since its construction in 2002, it has been studied by NREL, which has found that “when the energy efficiency features of the home are combined with solar water heating and solar electricity, the home saves about 60% of the total energy that would be used in an identical home built with standard features.”¹ The energy-saving features are grouped into passive and active methods.

Figure 12.3 A zero-energy house designed by the National Renewable Energy Laboratory and built in cooperation with Habitat for Humanity. Studies of the house by NREL show that it uses 60% less energy than a house built with standard 20th-century materials and methods. (Courtesy of DOE/NREL. Photo by Pete Beverly)²

Figure 12.4 Some key features of the zero-energy house designed by the National Renewable Energy Laboratory. (Reprinted from the National Renewable Energy Laboratory, NREL, 2009. “Zero Energy Homes Research: A Modest Zero Energy Home.” http://www.nrel.gov/buildings/zero_energy.html. Accessed December 29, 2009.)³

Passive methods are just that—they arise from the location of a building in relation to the environment, and from the way the building’s materials respond to that environment without any additional machinery. Among the passive features of the house are spray foam insulation in the walls, ceilings, and floors; skylights to reduce the need for artificial lighting; less window area on the east and west sides and more window area on the south side; light-colored roof tiles to reduce indoor temperatures in the summer; and adequate attic ventilation. This last feature is crucial; without it, the perfectly insulated building would be a toxic Thermos bottle. The optimum building design allows just enough air flow to provide the oxygen that people need and to prevent the buildup of air pollutants. Some of the cleverest designs have a two-way ventilation system, with air coming in through one set of metal pipes next to another set that allows air to leave. The exiting air can thus pass some of the heat it picked up inside the house to the air coming in, further reducing the need for heating fuels.

Active methods involve machinery to produce electricity and run pumps and other devices to move air and water and to control the use of energy. Active technologies used in the Denver house shown in Figure 12.3 include a 1.8-kilowatt solar-electric system that connects to the electrical grid and feeds energy to the grid when energy production on the rooftop exceeds home use; energy-efficient lighting (in this case compact fluorescent bulbs); and a radiant wall heating system (rather than forced warm air), using heat from a high-efficiency boiler to heat pipes in the walls.

The climate near the ground influences energy use in buildings

In the second half of the 20th century, people began to realize that they could reduce energy use within buildings by taking a new look at some ancient ideas that dominated building design in most civilizations before the availability of cheap fossil fuels. This led to the pursuit of more and better energy-conserving materials. Ecologists studying plants and non-human animals and their relation to their environment began to talk with climatologists and meteorologists about energy exchange, and with architects and landscape planners about human housing.

This has been mutually reinforcing and beneficial. Environmental scientists began to take an interest in local climatic effects and, perhaps most important, in the work of German scientist Rudolf Geiger, who wrote The Climate Near the Ground,⁴ which showed how very small variations in topography and in the vegetation that covered an area could affect local temperature, humidity, wind speed, and the water content of soil. This work attracted the attention of ecologists, who began in the 1960s to apply its findings to individual organisms, species and their habitats, and ecosystems. Climate was not just “climate, the big picture.” There was also microclimate—the average weather conditions right around an individual organism that affected the organism and was affected by it. The evolutionary adaptations of animals and plants to the microclimate were astounding and unexpected.

My own first research in ecology was about how trees in a forest adapt to their local climate and how they keep warm enough to survive and grow. One day, trying to place measuring equipment near the top of a small oak tree, I was struck by how different the leaves at the top of this tree were. They were thick, small, and waxy, quite unlike the leaves lower down and those shown in a standard field guide. The treetop leaves were adapted to hot, dry, bright conditions, which afforded all the sunlight they could use but required them to store water. In contrast, the leaves in the shade at the base of the tree were thin, large, porous, and shaped like those pictured in the field guide. (They were easiest to see, draw, and photograph.) These leaves took advantage of the cool, moist surroundings to exchange oxygen and carbon dioxide rapidly and to gather as much light as possible in the heavy shade.

David Gates, a physicist who left that field for ecology, wrote a path-breaking book, Energy Exchange in the Biosphere,⁵ that showed how an individual exchanges energy with its local surroundings, including how a person exchanges energy with the house where she lives. He explained that each organism has an energy budget, and he used mathematical equations to predict when a cardinal would have to fly out of the top of a tree because it got too hot and the bird’s internal cooling mechanisms could no longer keep its temperature under control.

It wasn’t a big step to go from thinking about oaks and cardinals to thinking about one’s home. And meanwhile, architects and landscape planners were looking at nature around their buildings and wondering how animals and plants could survive very hot and humid and very cold climates.

We, too, radiate energy and are a source of heat

When we talk about heating a building, we rarely think of our own contribution, but as David Gates explained, we, like all physical objects, exchange energy with our surroundings. We do so in three ways. The first is by giving off heat from our skin directly to the air that touches it (or if the air is warmer than we are, taking up some of that heat). The second is by radiating heat energy—each of us radiates about as much energy as a 100-watt incandescent lightbulb. And the third is by exchanging energy-containing compounds with our environment. The most important of these compounds is water vapor, including what we breathe out and sweat in a warm room.

Whether we feel warm or cool depends on the total energy exchange between ourselves and our local environment—our climate near the ground, so to speak. By the end of the 20th century, standard heating systems blew warm air into a room, air that was not very hot but somewhat warmer than the local environment and warmed a person only if it came in direct contact with the body. But if you stand in a house in the middle of winter in a cold climate, you are also actively exchanging energy with the walls, floors, and ceilings. If they are a lot colder than you are, your body loses out in the energy balance—much energy from your body’s surface radiates to the cold walls, floor, and ceiling, and no matter how warm the air from the standard late-20th-century forced-air system, you rarely feel cozy. You can feel hot (and dried out) or chilly (and dried out), but not comfy.

In contrast, in a radiant-heating system, heat is supplied to surfaces, which in turn radiate heat to a room’s occupants and also feel warm to the touch. This is more efficient in several ways. I know this from working in the middle of winter in New Hampshire houses that were occupied only in the summer. Somehow nothing felt colder than being in a closed building with very cold walls; it felt warmer outside no matter what the temperature, as far as I was concerned.

I also know this from going into a barn on a dairy farm in the middle of a New Hampshire winter when the cows were inside quietly munching hay or chewing their cud. Because the bacteria digesting woody tissue in the cows’ complex stomachs generated a lot of heat energy, the cows were perfect radiant heaters (all the more so if their bodies were black, as a physicist will tell you, because a black surface makes the best radiator). No matter what the weather outside, it was always much cozier in the barn than in the little house I described earlier.

The take-home lesson here is that you feel a lot more comfortable using less energy with a radiant heating system than you do with a forced hot-air system.

But does an energy-smart, comfortable building save money?

In addition to the NREL’s formal study of the Habitat for Humanity house, friends and colleagues who have installed the kinds of passive devices just described tell me about amazing savings and increased comfort. One new house in New Hampshire, with modern insulation and high-tech windows, is kept warm, I’m told, with a single small woodstove even though some rooms in the two-story house are quite distant from the stove. In winter, that house uses about one-fifth the wood used by a typical mid-20th-century house of about the same size—two cords of wood compared to ten.

It has already been demonstrated that large energy savings can be achieved through careful design and placement of buildings and the use of the best modern technology. The only question is whether the added costs (if any) of constructing such buildings can be recovered through direct energy savings in a reasonable time, and whether the investment is cost-effective. The answer for retrofitting an existing building will be very different from the answer for a newly constructed building on a lot large enough to allow the best siting in relation to the sun and local topography. Although the general answer may be complicated, NREL states that “energy consumption of new houses can be reduced by as much as 50% with little or no impact on the cost of construction.”⁶

The Denver-Boulder, Colorado, area has become one of the major regions for energy-efficient homes, with some companies constructing entire housing developments and others offering to build on an owner’s lot. A 2008 article in the Denver Post said these houses are being priced 10–15% higher than the equivalent conventional houses.⁷ According to the American Institute of Architects (AIA), a comparison of 33 “green” buildings “from across the United States” showed an average cost increase of “less than 2%” versus conventional designs, and savings of $50–65 per square foot, or 20%, arising from energy, emissions, water, operations, and health improvements over a 20-year period.”^{8, 9} In addition to the features of the NREL-Habitat for Humanity house, some of these new housing developments use geothermal energy for heating and cooling (we discuss this later) and community solar electrical systems to increase energy independence.¹⁰

Machine Age buildings: the triumph of steel, glass, and cheap energy over human needs

Buildings designed in the industrial/scientific era of the 19th and 20th centuries differed in another important way from most of the shelters people have built during our species’ time on the Earth. Buildings came to be viewed primarily as outside of nature, separate from nature, just as people were assumed to be, and just as industry, civilization, towns, and cities were perceived. As such, they were built not just to insulate people from the worst weather and climate, but also to reinforce the triumph of modern technology over nature. Buildings became structures to be admired independent of their surroundings, like the Eiffel Tower in Paris, which demonstrated, with its mathematically determined shape and bare-bones steel structure, that the Machine Age was here, and not just surviving within nature but prevailing. It seemed for a while that the long debate about where people stood in relation to nature was over. With steel and concrete and our fossil-fuel-powered machines, we had prevailed and risen above nature. Nature was no longer our concern—we didn’t need it; it didn’t matter.

Lewis Mumford, the great 20th-century historian of cities, wrote at length about this aberration in modern designs in such classics as The City in History and The Pentagon of Power, the latter criticizing the worst of the hubris of the Machine Age. Buildings became objects of art, and by the late 20th century an architect could become famous simply for the beauty of his designs and his drawings, whether or not his buildings worked well for people.

The classic example of this was Yale University’s Art and Architecture Building designed by the then head of Yale’s School of Architecture, Paul Rudolph. When completed in 1963, the building was praised for being avant-garde, somewhat in the tradition of Frank Lloyd Wright and in the cubist and Bauhaus style. But by the early 1970s it had become infamous. At the time, I was on the faculty of Yale’s School of Forestry and Environmental Studies and was invited to participate in a course in the newly fashionable field of ecology at the School of Art and Architecture. The faculty and students told me their woes about the building.

Rudolph had given the architecture students a large work space, with a cathedral ceiling and huge windows. But the drapes were like large fishnets, and their open weave pattern cast constantly moving shadows onto desks and papers, making it difficult for people to focus on their work. He put the sculptors in the basement, where the ceilings were too low for them to do any really large pieces, and where even moderately large stones or statues could be moved in and out of the studio only by an elevator, which was not built for the job and usually ceased to work after transporting a massive stone. This was design-without-nature and design-without-design, and everybody I talked to who worked in the building hated it. The story is told that Rudolph claimed his building was indestructible, built primarily of cement. But much of it was ruined by a fire that became uncontrollable, in part because the stairwells formed open chimneys that allowed the fire to spread.

Green buildings

During the time that steel, glass, concrete, electricity, and modern plumbing, along with cheap and abundant energy, allowed the development of architecture as only art, and of buildings meant to isolate people from their surroundings, another, contrary approach developed. It had its beginnings in the landscape design of Frederick Law Olmsted and in the plans and designs of cities and suburbs by Ebenezer Howard and others. Howard believed that the city and the countryside—that is, the city and its local environment—should be designed together. The idea was to locate garden cities in a set connected by greenbelts, forming a system of countryside and urban landscapes.¹¹ The names remain, as in Greenbelt, Maryland, and Garden City, New York. Olmsted’s use of the natural landscape in designing city parks and Howard’s garden city still influence city planning today.¹²

Both Olmsted and Howard saw people as within nature, and saw nature playing an important role even in city life. Olmsted wrote that vegetation in cities played social, psychological, and medical roles; hence, nature within a city was necessary for the best style of life, rather than a city in which the buildings loomed over and dominated people and their surroundings. As Charles Beveridge, the editor of the Frederick Law Olmsted papers and the leading authority today on the history of landscape design, has written:

The primary purpose of the urban park movement in the 19th century was neither aesthetics nor biological conservation, but was part of a series of sanitary reforms by which those governing cities sought to counteract the threat of ill health produced by industrialization and rapid urbanization. These were pragmatic developments. Among the leaders in the 19th century was Frederick Law Olmsted, who designed New York City’s Central Park and had a great deal to say about planning. Olmsted’s goal was not aesthetics in itself—he had no interest in beauty for beauty’s sake—he was interested in public institutions that met urban psychological and social needs.¹³

The green building idea continues and expands this vision. It takes us beyond a minimalist view of the energy problem—the view that we should all be energy misers, that our only role in nature has been to sin against it, and that we must, like all sinners, pay the price.

Today, we recognize four basic environmental goals for a city: to reduce energy use; to reduce and remove pollutants; to help create a pleasing environment; and to aid in biological conservation. Individual buildings can play a role in each of these—for example, with skyscrapers becoming nesting sites for peregrine falcons in New York City and San Francisco.¹⁴

Olmsted also thought about individual houses. For example, traveling to Los Angeles, he wrote about how vegetation could benefit those who lived in a city within a semiarid, semidesert environment such as the Los Angeles Basin. “Plantings should be concentrated close to houses, providing an atmosphere of lushness, green and shade, while blocking out the dusty middle distance and setting off distant views so that the dryness and dustiness were not evident, even in a drought season,” he wrote. “If such an approach were carried out on hillsides like those at Berkeley, the plantings around the house of one’s neighbor below would become a green ‘middle distance’ in the outlook from one’s house, and one’s own plantings would do the same for neighbors above.”¹⁵

Research by ecologists helped to stimulate work by the architect Ian McHarg, founder and head of the Department of Landscape Architecture at the University of Pennsylvania, and author of another important book, Design with Nature.¹⁶ McHarg became a friend and colleague of some of America’s leading ecologists, including Murray Buell, my major professor. In the 1960s, the idea of designing with nature became popular, and among the most famous attempts to accomplish this were Reston, Virginia, and Columbia, Maryland. In the 1970s, with funding by George Mitchell, McHarg designed and built The Woodlands, a suburb of Houston, Texas, where he employed his ideas extensively, focusing on building a connection between people and their environment, so that one’s home and town were within a naturalistic setting that minimized negative effects on the environment. The Woodlands has a population of more than 80,000, making it one of the largest towns designed and built in the second half of the 20th century for both people and nature, and for the best interaction between the two.

Today, interest in and actual construction of green buildings has become so much a part of architectural practice that the American Institute of Architects gives annual awards to the ten best green buildings.¹⁷ In 2008 these ranged from Yale University’s Sculpture Building and Gallery to condominiums in various cities¹⁸ and the Cesar Chavez Library in Laveen, Arizona. The Green Building Council, a nonprofit corporation, has established a green building rating system called Leadership in Energy and Environmental Design (LEED) to determine how well a building meets accepted green building conditions. In 2005 the state of Washington passed a green building law requiring all new public buildings greater than 5,000 square feet to meet the LEED standards. The expectation was that energy savings would be 20%.¹⁹

Energy at your feet: geothermal energy

One of the features advertised for some energy-efficient buildings is the use of geothermal energy—energy from the heat of the Earth. There are two kinds of geothermal energy: the spectacular venting of deep-earth hot gases and liquids, such as the hot springs and geysers at Yellowstone National Park; and low-density, shallow-earth “geoexchange”—the less exciting but for most of us more useful solar energy stored in the earth’s soils and rocks, which can be recovered and used.

At present, the first kind of geothermal energy, from deep-earth-heated materials, is used to run steam-electric generators that provide about 7,500 megawatts of generating potential in the United States. This is 7.5% of today’s total energy-generating capacity from all the U.S. renewable energy sources, less than half of a percent of the total energy capacity of our nation.^{20, 21}

It is the second kind of geothermal energy that is advertised for most energy-efficient buildings.²² The idea is simple. The Earth’s surface—soil, bedrock, and the water stored within these—is warmed by sunlight (and a tiny, tiny bit by deep earth heat generated within the Earth’s core). Because these earth materials can store a lot more energy than the atmosphere can near the ground, over time these have become warmer and, just as important, much less variable in their temperature than the air above. If you dig down, you find that as you go deeper, the soil and bedrock very gradually get warmer (in temperate and cold climates), and the temperature varies less from day to night, from season to season, from year to year. That’s why sod huts are warmer than cabins built above the prairie (Figure 12.5). It’s also one of the reasons why prehistoric people liked to live in caves, such as the famous caves of southern France and Spain, where today we find their 15,000-year-old paintings. Those caves are in limestone hills that are especially good at holding onto the sun’s heat.

Figure 12.5 Claus Braseth’s sod house in North Dakota. A pioneer’s sod house on the prairie made good use of passive solar energy and energy conservation. (Used with permission of the Braseth Family)²³

Although the preindustrial way to make use of this geothermal energy was to live in sod houses and caves, the modern way is to put long plastic or metal tubes or hoses down a few feet into the earth and spread them out, sometimes vertically, but more commonly horizontally, sometimes over quite long distances (Figure 12.6). During the winter, the temperature of the soils and rocks is a little warmer than the air; in summer it is slightly cooler. The density of the heat energy stored within the upper surface of the Earth is low, but if you bury long pipes and hoses deeply enough, you can gather a lot of energy.

Figure 12.6 Heat and cooling right under your feet. How a geoexchange system works.²⁴ (Reprinted from National Renewable Energy Laboratory Technical Report, NREL/TP-840-40665)

Some condominium high-rises in Florida make use of this for air-conditioning. One that I know of uses the cool water a few feet below the surface that maintains a pretty steady temperature of about 67°F throughout the year. Instead of having to use a lot of fossil-fuel energy and standard refrigeration equipment to separate cooler air from warmer air, these systems provide air-conditioning simply by passing water or air through pipes cooled by the groundwater, then pumping this air or water through pipes into the apartments. Farther north, doing just the opposite—pumping colder air or water from a wintry surface down into the ground through pipes and hoses—warms the air and water, which then is circulated in a building to provide heat. The only energy we have to expend to get this heating and cooling is for pumping the air or liquid through the circuit of pipes and hoses, which requires much less energy than heating or cooling air or water with a fuel.

Because Earth’s soils and rocks are so massive compared with us and our belongings and buildings, vast amounts of geothermal energy exist everywhere on the land (Figure 12.7). This energy is potentially available to us through geoexchange, and indeed an industry is developing to provide geoexchange devices. Proponents say these devices can reduce home heating and air-conditioning bills by as much as 70% and 40%, respectively, although installation costs currently may be about $3,000 more than for a standard air-conditioning and heating system.²⁵

Figure 12.7 Geothermal energy in the United States. This map shows the potential for the two kinds of geothermal energy: intense heat from volcanic and other earth activity (dark shaded areas) and geoexchange, which uses the solar energy stored in surface and near-surface rocks and soil (the lightest tone). The darker the color, the higher the temperature. (Source: National Renewable Energy Laboratory²⁶)

The U.S. National Renewable Energy Laboratory estimates that our country could obtain more than 1 million megawatts from geothermal energy, about ten times the amount of energy obtained today from all renewable energy and about 60% of the total energy used today in the U.S. (Figures 12.7 and 12.8).²⁷ Remember, this would be a nonpolluting, nongreenhouse-gas-emitting energy source, whose only potential kinds of pollution would come from the manufacturing of the pipes, hoses, and pumps, whatever that might be. However, installing these systems over the entire land area of the United States would pose many problems, including disruption of parks, nature preserves, and cropland, so it is unlikely that their maximum energy potential will ever be realized.

Figure 12.8 Wind, solar, and geothermal energy offer vastly greater potential for U.S. energy independence than do fossil fuels, conventional nuclear power, and waterpower. (Source: National Renewable Energy Laboratory²⁸)

According to the NREL, “Today’s U.S. geothermal industry is a $2-billion-per-year enterprise involving over 2,800 megawatts of electricity generation capacity, about 620 megawatts of thermal energy capacity in direct-use applications such as indoor heating, greenhouses, food drying, and aquaculture, and over 7,300 megawatts of thermal energy capacity from geothermal heat pumps.” The NREL also says that “U.S. geothermal generation annually offsets the emission of 22 million metric tons of carbon dioxide, 200,000 tons of nitrogen oxides, and 110,000 tons of particulate matter from conventional coal-fired plants.”

About half of the energy used in a typical American home is for heating and cooling, so a transition to local geothermal could result in a significant reduction in energy use with no change in lifestyle or comfort (Figure 12.9). And of course, this would result in a great decrease in the production of carbon dioxide.

Figure 12.9 U.S. energy use by type. (Source: Energy Information Administration, Annual Energy Review 2008)²⁹

The bottom line

• Energy-efficient buildings and green building designs are major ways that we can reduce per-capita energy consumption and achieve energy independence without sacrificing the quality of our lives. In many cases, the quality of life will likely actually improve.

• Geothermal energy is one of our best bets for energy independence and for inexpensive energy. Geoexchange systems can reduce heating bills as much as 70% and air-conditioning bills as much as 40%.

• Because geothermal energy is locally produced, it also requires fewer expenditures for a national grid, pipelines, or other means of transporting fuels.

• One estimate is that within the lower 48 states this local geothermal energy could provide an energy capacity of a million megawatts.