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Potentially the largest sources of energy worldwide are perpetual and renewable energy from the sun, wind, flowing water, biomass, and Earth’s internal heat.  Such resources- primarily hydropower and biomass- already supply 17% of the world’s energy and 9% of the energy used in the United States.  About 92% of the known reserves and potentially available domestic energy resources are coal (5%), oil (2.5%) , and uranium (0.5%).  Developing these mostly untapped resources could meet 50-80% of projected U.S. energy needs by 2030, and virtually all energy needs with improvements in energy efficiency.


The easiest, fastest, and cheapest way to get more energy with the least environmental impact is to cut energy waste.  There are two general ways to achieve this goal:

1.  Reduce energy consumption. Examples include walking or biking for short trips, using mass transit,
	putting on a sweater instead of turning up the thermostat, and turning off unneeded lights.

2.  Improve energy efficiency.  Examples include insulating houses, tuning car engines, building more
	energy-efficient cars, houses, heating and cooling systems, appliances...  Basing purchases on life-cycle costs not only saves money but helps sustain the earth.


Industrial processes consume 36% of the energy used in the United States.  

Cogeneration units recover about two-thirds of the energy wasted in a conventional boiler and use it to
produce both heat and electricity.  By 2000 cogeneration could produce more electricity than all the U.S.
nuclear power plants, and do it cheaper.  Cogeneration could also supply energy for local heating and
cooling systems by piping hot or chilled water or steam to nearby buildings.   

About 60-70% of the electricity used in U.S. industry drives electric motors.  Most of them run at full
speed with their output “throttled” to match their task- somewhat like driving with the gas pedal to the
floor and using the brake to slow the car down.  Each year a heavily used electric motor consumes 10
times its purchase cost in electricity-the equivalent of using $120,000 worth of gasoline each year to fuel a
$12,000 car.

Switching to high-efficiency lighting would be another energy saver.  Industries could also use computer
systems to turn off lights and equipment in nonproduction areas and to make adjustments.

Another way to save energy in industry would be to increase recycling and reuse and make products that
last longer and are easy to repair and recycle.

One-fourth of the commercial energy consumed in the United States is used to move people and goods

Today transportation consumes 65% of all oil used in the United States. Gasoline and other fuels accounts for 33% of total U.S. emissions of carbon dioxide, while leaking vehicle air conditioners put out 75% of chlorofluorocarbon emissions.  Thus the best ways to cut world oil consumption, slow ozone depletion in the stratosphere, slow projected global warming, and reduce air pollution would be to improve the fuel efficiency of vehicles, ride mass transit more often, and haul freight more efficiently. 

- An estimated 10-20% of the travel for commuting, business trips, and shopping in the United States could be eliminated by telecommunications.  Fax messages reduce the need for overnight delivery services.  Some state governments and private companies are encouraging a transition to increased use of the “electronic home office.”  Energy and time can also be saved by increased use of computerized home delivery services that allow people to shop from the home.

- Improvements such as more efficient engines and more lightweight materials would raise the fuel efficiency of the U.S. automotive fleet.
- Electric cars might help reduce dependence on oil, especially for urban commuting and short trips.

- Another way to stretch the world’s shrinking oil supply would be to shift more freight from trucks and planes to trains and ships.  Currently trucks burn 59% of the energy used to mover freight in the United States.

Manufacturers could also raise the fuel efficiency of new transport trucks 50% with improved aerodynamic design, turbocharged diesel engines, and radial tires.  And truck companies could slash energy waste and increase income by not letting trucks come back empty from their destination.

Sweden and South Korea have the world’s toughest standards for energy efficiency in homes and other buildings.   The 110-story, twin-towered World Trade Center in Manhattan is a monument to energy waste.  It uses as much electricity as a city of 100,000 people for about 53,000 employees.  Building a superinsulated house can improve the efficiency of residential space heating and cooling more than 75%, and save on l lifetime energy costs.  Such a house is heavily insulated and nearly airtight.

To keep prices low for buyers, builders often skimp on energy-saving features.  When lifetime costs are considered, however, these energy-inefficient houses cost owners 40-50% more.  A superinsulated house costs about 5% more to build than a conventional house, but this extra cost is paid back by energy savings within five years and can save a homeowner $50,000-$100,000 over 40 years.  Sadly less than 1% of new homes in the United States are superinsulated, mostly because of a lack of consumer demand.  Moreover, builders and owners of rental housing have little incentive to make their units energy efficient when renters pay the utility bills.

One-third of the heat in U.S. homes an buildings escapees through closed windows-equal to the energy in all the oil flowing g through the Alaskan pipeline every year.


Currently home refrigerators consume about 7% of the electricity used in the United States.



A passive solar heating system captures sunlight directly within a structure and converts it into low-temperature heat for space heating.  Super windows, greenhouses, and subspaces face the sun to collect solar energy by direct gain.  Thermal mass (heat-storing capacity)- such as walls and floors of concrete, adobe, brick, stone, salt-treated timber, or tile- stores collected solar energy as heat and releases it slowly throughout the day and night.  Some systems also store heat in water-filled glass or plastic columns, black-painted barrels filled with water, and panels or cabinets containing heat-absorbing chemicals.  Roof-mounted passive solar water heaters can supply all or most of the hot water for a typical house.

Solar-powered air conditioners have been developed but thus far are too expensive for residential use.

In an active heating system, specially designed collectors absorb solar energy, with a fan or a pump used to supply part of a building’s space-heating or water-heating needs.  Several connected collectors are usually mounted on a roof with an unobstructed exposure to the sun.  Active solar collectors can also supply hot water.

Both active and passive technology are well developed and can be installed quickly.  No carbon dioxide is added to the atmosphere, and environmental impacts from air and water pollution are low.  Land disturbance is also minimal because passive systems are built into structures and active solar collectors are usually placed on rooftops.

Active systems cost more than passive systems over their lifetime because they use more materials, need more maintenance, and eventually deteriorate and must be replaced.

There are disadvantages.  Higher initial costs discourage buyers who are not used to considering lifecycle costs or who move every few years.

Owners of passive and active solar systems also need “solar rights”, laws against building structures that block access to sunlight.


Several systems are in operation that draw on solar energy to generate electricity and high-temperature heat.  In one such system huge arrays of computer-controlled mirrors, called heliostats, track the sun and focus sunlight on a central heat-collection tower or on oil-filled pipes running through the middle of curved solar collectors.  This concentrated sunlight can generate temperatures high enough for industrial processes or for producing steam to run turbines and generate electricity.

Today these plants are used mainly to supply reserve power for daytime peak electricity loads, especially in sunny areas with a larger demand for air conditioning.

The impact of solar power plants on air and water is low.  They can be built in 1-2 years, compare to 5-15 years for coal-fired and nuclear power plants.  Solar power plants need large collection areas but use one-third less land than a coal-burning plant.


Solar energy can be converted directly into electrical energy by photovoltaic cells, commonly called solar cells.  Most solar cells consist of layer s of purified silicon, which can be maid from inexpensive, abundant sand.  When traces of gallium arsenide or cadmium sulfide are added, the resulting semiconductor emits electrons and produces a small amount of electrical current when struck by sunlight.

Today solar cells supply electricity for at lest 30,000 homes world-wide (20,000 in the United States) and for whole villages in LDC’s, including 6,000 in India.

Solar cells are reliable and quiet, have no moving parts, and should last 30 years or more if encased in glass or plastic.



Hydroelectric power, or hydropower, supplies about 20% of the world’s electricity and 6% of its total commercial energy.

In large-scale hydropower projects high dams are built across large rivers to create large reservoirs.  The stored water then flows through huge pipes at controlled rates, spinning turbines and producing electricity.  In small-scaled hydropower projects a low dam with noreservoir, or only a small one, is built across a small stream.  Since natural water flow generates the electricity, out put can vary with seasonal changes in stream flow.

Much of the hydropower potential of North America and Europe has been developed.  

Currently the United States is the world’s largest producer of hydroelectricity, which supplies 10% of its electricity and 3-5% of all of commercial energy.

Hydropower has a moderate to high net useful energy  yield and fairly low operating and maintenance costs. Hydroelectric plants rarely need to be shut down, and they emit no carbon dioxide or other air pollutants during operation. 

However, , hydropower also has adverse effects on the environment.  The reservoirs of large-scale projects flood huge areas, destroy wildlife habitats, uproot people, decrease natural fertilization of prime agricultural land in river valleys below the dam, and decrease fish harvest below the dam.

Also, during drought periods these plants produce little if any power.


Twice a day water flows in and out of coastal bays and estuaries in high and low tides.  In perhaps two to three dozens places in the world, a bay mouth is narrow enough, and the difference in water height between high and low tide large enough, that kinetic energy in these daily tidal flows can be used economically to spin turbines to produce electricity.  Currently two large tidal energy facilities are operating, one at La Rance, France, and the other in Canada in the Bay of Fundy.  China has built several small tidal plants.

The benefits of tidal power include a free energy source ( the moon’s gravitational attraction), low operating costs, and a moderate net useful energy yield.  Also, no carbon dioxide is added to the atmosphere, air pollution is low, and little is disturbed.  However , most analysts expect tidal power to make only a tiny contribution to world electricity to world electricity supplies.


The kinetic energy in ocean waves, created primarily by wind, is another potential source of electricity.  Japan, Norway, Great Britain, Sweden, the United States, and the former Soviet Union have all built small experimental plants to evaluate this form of hydropower.  None of these plants has produced electricity at a competitive price, nut some designs show promise.


Ocean water stores huge amounts of heat from the sun, especially in tropical areas.  Japan and the United States have been studying the technological and economic feasibility of using the large temperature differences between the cold deep waters and the sun-warmed surface waters of tropical oceans to produce electricity in ocean thermal energy conversion (OTEC).  


Saline solar ponds-usually located near inland saline seas or lakes in areas with ample sunlight-can be used to produce electricity.  The bottom layer of water in such a pond stays in the bottom when heated because it has a higher salinity and density ( mass per unit volume) than the top layer.  Heat accumulated during the daytime in the bottom layer can be used to produce steam that spins turbine, generating electricity.


Worldwide, by 1993, there were over 20,000 wind turbines, most grouped in clusters called wind farms, which fed power to a utility grid and produced 2,7000 megawatts of electricity.  Most are in California (17,000 machines) and Denmark ( which gets about 2% of its electricity from wind turbines).  Most are located in windy mountains passes and ridges and along coastlines, which generally have strong and steady winds.

California wind farms in mountain passes produce enough electricity to meet the residential power needs of San Francisco.

However, the development of this energy resource in the United States has slowed since 1986, when federal tax credits and most state tax credits for wind power were eliminated.

Wind power has a number of benefits.  It is am unlimited source of energy at favorable sites, and large wind farms can be built in only three to six months.  With a moderate to fairly high net useful energy yield, these systems emit no carbon dioxide or other air pollutants during operation; they need no water for cooling; and their manufacture and use produce little water pollution. The land occupied by wind turbines can be used for grazing cattle and other purposes, while the leases to use land for wind turbines can provide extra income for farmers and ranchers.

However, wind power is economical only in areas with steady winds. When wind dies down, backup electricity from a utility company or from an energy storage system becomes necessary. 


Biomass is organic plant matter produced by solar energy through photosynthesis. It includes wood, agricultural wastes(including manure), and garbage, Some of this plant matter can be burned as solid fuel or converted into more convenient gaseous or liquid biofuels.  Biomass, mostly from the burning of wood and manure to heat buildings and cook food, supplies about 11% of the world’s energy- 4-5% in Canada and the United States- and about half of the energy used in LDCs.

Biomass is a renewable energy resource as long as trees and plants are not harvested faster than they grow back.  However, it takes a lot of land to grow biomass fuel- about 10 times as much land as solar cells need to provide the same amount of electricity.


One way to produce biomass fuel is to plant large numbers of fast-growing trees, shrubs, and water hyacinths in biomass energy plantations.  After being harvested these “BTU bushes” can be burned directly, converted into burnable gas, or fermented into alcohol.

Such plantations can be located on semiarid land not needed to grow crops, although lake of water can limit productivity.  They can also be planted to reduce soil erosion and can help restore degraded lands.  In Sioux City, Iowa, buses are running on a fuel made from vegetable oils such as soybean or canola.

There are several drawbacks to this form of biomass fuel.  The industrialized approach to biomass production usually requires large areas of land as well as heavy use of pesticides and fertilizers, which can pollute drinking water supplies and harm wildlife.


Almost 70% of the people living in LDCs heat their dwellings and cook their food by burning wood or charcoal.

The forest products industry (mostly paper companies and lumber mills) consumes almost two-thirds of the fuelwood used in the United States.

Total energy use from wood in the United States is probably at least 3% of total U.S. energy use.

Although burning wood produces virtually no emissions of sulfur dioxide, it does release carbon monoxide, solid particulate matter, hydrocarbons, and unburned residues that pollute indoor and outdoor air.

Fireplaces can also be used for heating but usually result in a net loss of energy from a house.  The draft of heat and gases rising up the fireplace chimney exhausts warm air and pulls in cold air from cracks and crevices throughout the house.  Fireplace inserts with glass doors and blowers help but still waste energy compared with an efficient wood-burning stove.  Energy loss can be reduced by closing off the room and cracking a window so that the fireplace won’t draw much heated air from other rooms.  A better solution is to run a small pipe from outside into the front of the fireplace so it gets the air it needs during combustion.


Is agricultural areas crop residues (such as stalks left after harvest and processing refuse) and animal manure can be collected and burned or converted into biofuels, as can coconut shells, peanut and other nut hulls, cherry pits, and cotton stalks.  By 1985, for example Hawaii was burning bagasee, the residue left after sugarcane harvesting and processing, to supply almost 10% of its electricity (58% on the island of Kauai and 33% on the island of Hawaii).  Brazil gets 10% of its electricity from burning bagasse and plans to use this crop residue to produce 35% of its electricity by 2000.

This approach makes sense when residues are burned in small power plants located near areas where the residues are produced.  Otherwise, it takes too much energy to collect, dry, and transport the residues to power plants.

An increasing number of cities in Japan, western Europe, and the United States have built incinerators that burn trash and use the energy released to produce electricity or to heat nearby buildings.  For example, New England obtains about 2% of its electricity from 20 trash-burning plants.


Plants, organic wastes, sewage, and other forms of solid biomass can be converted by bacteria and various chemical processes into gaseous and liquid biofuels.  Examples include biogass (a mixture of 60% methane, the principal component of natural gas, and 40% carbon dioxide), liquid ethanol (ethyl, or grain alcohol), and liquid methanol (methyl, or wood alcohol).

After the biogass has been separated, the solid residue is used as fertilizer on food crops or, if contaminated, on trees.  India has about 750,000 biogass digesters in operation.

Methane gas, produced by anaerobic decomposition of organic matter in landfills, can be collected by pipes inserted into the ground, separated from other gases, and burned as a fuel.  Eighty-two U.S. landfills currently recover methane, but 2,000-3,000 U.S. landfills have the potential for large-scale methane recovery.  Burning this gas instead of allowing it to escape into the atmosphere methane causes roughly 25 times as much atmospheric global warming per molecule as carbon dioxide.

Methane can also be produced by anaerobic digestion of manure form animal feedlots and sludge from sewage treatment plants.

Some analysts believe that liquid ethanol and methanol could replace gasoline and diesel fuel when oil becomes to scarce and expensive.  Ethanol can be made from sugar and grain crops (sugarcane, sugar beets, sorghum, and corn by fermentation and distillation.

Gasoline mixed with 10-23% pure ethanol makes gasohol, which burns in conventional gasoline engines and is sold as super unleaded or ethanol-enriched gasoline.  Gasohol now accounts for about 8% of gasoline sales in the United States-25-35% in Illinois, Iowa, Kentucky, and Nebraska.  The ethanol used in gasohol is made mostly by fermenting corn.  Excluding federal taxes it costs about $1.60 per gallon to produce.

Growing grains to make alcohol fuel could cut into cropland needed to grow food.  For example, about 40% of the entire U.S. corn harvest would be needed to make enough ethanol to meet just 10% of the country’s demand for automotive fuel.

Another alcohol, methanol, can be produced from wood, wood wastes, agricultural wastes (such as corn-cobs), sewage sludge, garbage, coal, or natural gas at a cost of about $1.10 per gallon-more than twice the cost of producing gasoline.


Heat contained in underground rocks and fluids is an important source of energy.  Over millions of years this geothermal energy from the earth’s mantle is transferred to underground concentrations of dry steam (steam with no water droplets), wet steam  (steam with no water droplets), and hot water trapped in fractured or porous rock at various placed in the earth’s crust.  If geothermal sites are close to the surface, wells can be drilled to extract the dry steam, wet steam, or hot water.  This thermal energy can be used for space heating and to produce electricity or high-temperature heat for industrial processes.

The United States accounts for 44% of the geothermal electricity generated worldwide.  The most accessible, high-temperature geothermal sites in the United States lie in the West, especially in California and the Rocky Mountain states.  Iceland, Japan, New Zealand, and Indonesia are among the countries with the greatest potential for tapping geothermal energy.
Geothermal reservoirs can be depleted if heat is removed faster than it is renewed by natural processes.  Thus geothermal resources are nonrenewable on a human time scale, but the potential supply is so vast that it is often classified as a potentially renewable energy resource.  There are four sources of this type of geothermal energy: dry-steam reservoirs, wet-steam reservoirs, hot-water reservoirs, and geopressurized brines.
Without pollution control, geothermal energy production causes moderate to high air pollution from hydrogen sulfide, ammonia, mercury, boron, and radioactive materials.  It also causes moderate to high water pollution from dissolved solids (salinity) and runoff of toxic compounds of heavy metals such as arsenic and mercury.  Noise, odor, and local climate changes can also be problems.
Hydrogen is produced easily by passing electrical current through water, which decomposes into oxygen and hydrogen gases.
When hydrogen burns it combines with oxygen gas in the air and produces nonpolluting water vapor.  Hydrogen has about 2.5 times the energy by weight of gasoline, making it an especially attractive aviation fuel.
Unlike gasoline solid metallic hydrogen compounds will not explode or burn if a vehicle’s tank is ruptured in an accident.  Years’ worth of hydrogen compounds stored in deplete oil or gas wells or underground areas.
Currently it would cost about $1.40 to produce hydrogen gas with the energy found in 3.8 liters of gasoline.  However, the current price of gasoline does not include its numerous pollution and health costs, which add at least 50 cents per gallon to its true cost.  Thus even today hydrogen is cheaper than gasoline and other fossil fuels when the overall societal costs are considered.
A solar-hydrogen revolution over the next 50 years would eliminate the air and water pollution caused by extracting, transporting, and burning fossil fuels, and would reduce the threat of global warming.  It would also reduce the threat of wars over dwindling oil supplies.  Furthermore, nuclear power could be phased out.  Finally, individuals would be able to produce most, if not all, of their own energy, instead of having to rely on oil and utility companies.


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