Because of its location, Iceland uses geothermal energy to meet a substantial portion of its energy requirements. Two-thirds of Icelandic homes are heated with geother­mal energy. In addition, most of the fruits and vege­tables required by the people of Iceland are grown in geothermally heated greenhouses. New Zealand, which is on a plate boundary in the South Pacific, also uses geothermal energy to generate much of its electricity.

Countries that arc increasing their use of geothermal energy include Italy, Japan, Mexico, the Philippines, and the United States. Currently, the world's total geothermal energy production is fairly small. A large nuclear power plant would produce more energy than all source of geo­thermal energy combined.

One of the environmental concerns associated with geothermal energy is that the surrounding land may subside, or sink, as the water from hot springs and their connecting underground reser­voirs is removed. Conventional geothermal energy also produces several pollutants, including hydro­gen sulfide and carbon dioxide. Also, geothermal energy becomes nonrenewable if the hot groundwater is tapped faster than it can be replaced by natu­ral processes.

Geothermal Energy from Dry Rocks Conven­tional use or geothermal energy relies on hot springs—that is, on groundwater bringing geothermal energy to the surface from subsurface hot rocks. Scientists at the Los Alamos National Laboratory

in New Mexico are investigating the feasibility of utilizing subsurface geothermal energy in dry areas. In 1986 they reported the production of enough geothermal energy from dry hot rock to produce electricity for a town of 2,000 people. They drilled a shaft to the subsurface hot rock, used hydraulic pressure to fracture the rock, and then pumped water into the fractured area under high pressure. When the pressurized water returned to the surface by way of a second well, it turned to steam, which drove an electric turbine.

The dry hot rock system has an additional ben­efit over conventional geothermal energy because it produces less pollution. Although this method requires the development of sophisticated technol­ogy if it is to become a practical reality, scientists are optimistic that it could be used in many loca­tions that cannot employ conventional geothermal energy.

Tidal Energy

Tides, the alternate rising am] tailing of the surface waters of oceans and seas that occur twice each day, are the result of the gravitational pull of the moon and the sun. Normally, the difference in water level between high and low tides is about 0.5 meter (1 or 2 feet). However, certain coastal regions with nar­row bays have extremely large differences in water level between high and low tides. The Bay of Fundy in Nova Scotia, for example, has the largest tides in the world, with up to 16 meters {53 feet) difference between high and low tides.

By building a dam across a bay, it is possible to harness the energy of large tides to generate elec­tricity. In one type of system, the dam's floodgates are opened as high tide raises the water on the bay side. Then the floodgates are closed, as the tide falls, water flowing hack out to the ocean over the dam's spillway is used to turn a turbine and gener­ate electricity.

Currently, three power plants that make use of tidal power are in operation, in the former Soviet Union, France, and Canada. The dam at La Ranee power station on the Ranee River in France utilizes the water-movement energy of both rising and fall­ing tides (Figure 12-20). As the tide rises, the dam's gates are opened. Water passing upstream through the gates turns 24 separate turbines to gen­erate electricity. At high tide, the water levels on both sides of the dam are the same, so no electricity can be generated, and the gates are closed. As the tide recedes, the gates are opened again, and water moving back toward the ocean turns the turbines and produces electricity. At low tide, the water levels are again the same on both sides of the dam, the gates are closed, and no electricity is generated.

Tidal energy cannot become a significant re­source worldwide, because few geographical loca­tions have large enough differences in water level between high and low tides to make power genera­tion feasible. The most promising locations for tidal power in North America include the Bay of Fundy in Nova Scotia, Passamaquoddy Bay in Maine, Puget Sound in Washington, and Cook Inlet in Alaska.

Other problems associated with tidal energy include the high cost of building a tidal power sta­tion and the potential environmental problems. The greatest tidal energy is found in estuaries, areas where river currents meet ocean tides. Because the mixing of fresh and salt waters creates a nutrient-rich environment, estuaries are the most produc­tive aquatic environments in the world. Fish and countless invertebrates migrate there to spawn. Building a dam across the mouth of an estuary would prevent these animals from reaching their breeding habitats. Estuaries are also popular sites for recreation, which would be severely curtailed by a tidal Jam.

Ocean Currents and Salinity Gradients

Oceans cover 71 percent of the Earth's surface and are in constant motion. Great currents, which are driven by the Earth's rotation and by wind, circle around the edges of the oceans. A tremendous amount of energy occurs in these currents because of their size; however, the currents flow slowly, so the amount of energy in any given small portion of the ocean is unimpressive. In other words, the ocean currents have low energy density. This makes it difficult to harness their energy.

Salinity gradients, or differences in salt con­centration at different depths in the ocean, have only recently been recognized as a potential energy source. The technology to harness this energy is not currently available, but some scientists are in­terested in developing it, both to provide energy and to desalinize brackish water.

energy conservation {moderating or eliminating wasteful or unnecessary energy-consuming activi­ties) and energy efficiency (using technology to accomplish a particular task with less energy). As an example of the difference between energy con­servation and energy efficiency, consider gasoline consumption by automobiles. Energy conservation measures to reduce gasoline consumption would include carpooling and reducing driving speed, whereas energy efficiency measures would include making more fuel-efficient automobiles. Conserva­tion and efficiency accomplish the same goal— saving energy.

    Energy conservation and efficiency could he considered the most promising energy "sources" available to humans, because they not only save energy for future use but also buy us time to explore new energy alternatives. Energy conservation and efficiency also cost less than development of new sources or supplies of energy. A system that sup­ports energy conservation and efficiency makes good economic sense, as well. The adoption of en­ergy-efficient technologies creates new business opportunities, including the development, manu­facture, and marketing of those technologies.

    In addition to economic benefits and energy resource savings, there are important environmen­tal benefits from greater energy efficiency and con­servation. For example, using more energy-efficient appliances could cut our carbon dioxide emissions by millions of tons each year, thereby slowing global climate change. Energy conservation and efficiency also reduce air pollution, acid precipitation, and other environmental damage related to energy production and consumption.

Energy Consumption Trends and Economics

Energy consumption in developed countries did not increase between 1975 and 1990, as had originally been projected; it actually decreased during that period, partly because of improved energy effi­ciency. Technological improvements in the paper-making industry, for example, make it possible for us to use less energy to manufacture paper today than we used just a few years ago. Similarly, new aircraft are much more fuel-efficient than under models. The energy savings from such improve­ments in efficiency translate into greater profits. For the companies employing them. It has been esti­mated that the United States is approximately Z5 percent more efficient in its energy use today than it was in the early 1970s. This means that the United States uses 25 percent less energy to gener­ate each dollar of its gross national product.

    A country's or region's total energy consump­tion divided by its gross national product gives its energy intensity. Despite gains in

efficiency, the energy intensity of the United States i> -till considerably higher than that of Japan or Western Europe.

The Challenge in Developing Countries Per-capita consumption of energy in developing na­tions is substantially less than it is in industrialized countries, although the fastest increase in energy consumption today is occurring in the developing nations. As developing nations boost their eco­nomic development, their energy demands will continue to increase. This is partly because the "new" industrial .and agricultural processes being adopted in developing countries often represent older technologies that are less energy-efficient. Also, the burgeoning populations in developing countries will raise energy demands.

    Developing countries are faced with the need for economic development and the need to control environmental degradation. At first glance, these two goals appear to be mutually exclusive. How­ever, both goals can be realized by the use of tech­nology now being developed in industrialized na­tions to achieve greater energy efficiency. For example, it would cost Brazil $44 billion to build power plants to meet its projected electricity needs for the near future; this cost could be avoided by investing $10 billion in more efficient refrigerators, lighting, and electric motors. The energy efficiency approach in Brazil would not only cause fewer envi­ronmental problems but also foster and expand the growth of manufacturing industries devoted to en­ergy-efficient products.

Energy-Efficient Technologies

The development of more efficient appliances, au­tomobiles, and buildings has been a major factor in the recent reduction of energy consumption in developed countries. Compact fluorescent light bulbs, introduced in the mid-1980s, require 25 percent of the energy used by regular incandescent bulbs and last nine times longer; the energy-efficient bulbs do cost more, but them more than pay for themselves in energy savings. New condensing furnaces require approximately 30 percent less fuel than conven­tional gas furnaces. "Superinsulated" homes in Sweden and the United States use 68 to 90 percent less heat than do homes insulated with standard methods.

    The National Appliance Energy Conservation Act sets national appliance efficiency standards for refrigerators, freezers, washing machines, clothes dryers, dishwashers, air conditioners, and water heaters. The energy cost that consumers will save as a direct result of energy savings required by this law is estimated at $28 billion by the year 2000.     Automobile efficiency has improved dramati­cally as a result of the use of lighter materials and designs that reduce air drag. A Japanese prototype automobile with special design features and materi­als, for example, achieved 98 miles per gallon. Using current technology, automobiles with fuel efficiencies of 60 to 65 miles per gallon could be routinely manufactured before the year 2000.

Cogeneration One nontraditional energy technol­ogy with a bright future is cogeneration, which is a way of recycling waste heat. Cogeneration is cur­rently being used on a small scale, but its use is increasing. Modular cogeneration systems enable hospitals, hotels, restaurants, and other businesses to harness steam that would otherwise be wasted. In a typical cogeneration system, electricity is pro­duced in a traditional manner—that is, some type of fuel provides heat to form steam from water. Normally, the steam used to turn the electricity-generating turbine would be cooled before being pumped back to the boiler to be reheated. In co-generation, after the steam is used to turn the tur­bine, it supplies energy to heat the building, cook food, or operate machinery before it is cooled and pumped back to the boiler as water. Cogeneration can also be accomplished on a large scale. Prince Georges County, Maryland, plans to build a natural gas-fired power plant that will sell electricity to the local utility. The waste steam produced in the generation of electricity will be used to operate a soft-drink carbonation plant adjacent to the power plant. A similar cogenera­tion plant in North Carolina supplies electricity to utilities in two states and steam to an adjoining textile company.

Energy Savings in Commercial Buildings

Energy costs often account for 30 percent of a company's operating budget. Unlike cars, which are traded in every few years, buildings are usually used for 50 or 100 years, so a company housed in an older build­ing normally does not have the benefits of new en­ergy-saving technologies. It makes good economic sense fur these businesses to invest in energy im­provements, which often pay for themselves in a few years.

    To get businesses to install new energy-efficient technologies, many energy-service companies (com-

ciency) offer their assistance in such a way that the business makes little or no financial outlay. Here's how it works. An energy-services company makes a detailed assessment of how a business can improve its energy efficiency. In developing its proposal, the energy-services company guarantees a certain amount of energy savings. It also provides the fund­ing to accomplish the improvements, which may he as simple as fine-tuning existing heating, ventila­tion, and air conditioning (HVAC) systems or as major as replacing all existing windows and lights. The reduction in utility costs is used to pay the energy-services company, but once the bill is paid, the business benefits from substantial energy sav­ing.

Energy Savings in Homes

When buying a new home, a smart consumer should demand energy ef­ficiency. Although a more energy-efficient house might cost a little more, depending on the technol­ogies employed, the improvements usually pay for themselves in two or three years. Any time spent in the home after the payback period means substan­tial energy savings. Energy efficiency will almost certainly be an important part of the design of homes of the future.

    Some energy saving improvements, such as thicker wall insulation, is easier to install while the home is being built. Other improvements, such as installing thicker attic insulation, installing storm windows and doors, caulking cracks around windows and doors, replacing inefficient furnaces, and adding heat pumps, can be made in older homes to improve energy efficiency and, as a result, reduce the cost of heating the homes.

    Many of the same improvements also provide energy savings when a home is air conditioned. Additional cooling efficiency is achieved by insu­lating the ductwork for the air conditioner (espe­cially in the attic), buying an energy' efficient air conditioner, and shading the south and west sides of a house with trees.

    Other home improvements that result in sub­stantial energy savings include replacing incandes­cent bulbs with energy-efficient compact fluores­cent light bulbs and wrapping insulation around water heaters and water pipes.

    How does a homeowner learn which improve­ment will result in the most substantial energy sav­ings' In addition to reading the many articles on energy efficiency that appear in newspapers and magazines, a good way to learn about your home is to have an energy audit done. Most local utility companies can send an energy expert to your honk to perform an audit for little or no charge.

What about Energy Conservation?

Simple measures such as lowering your thermostat during the winter and raising it during the summer, turning off lights when you leave a room, and driv­ing more slowly result in small energy (and cost!) savings. You also contribute to energy conservation by making use of carpools or public transportation. The cumulative effect of many people taking similar measure is substantial.

    Energy conservation and efficiency are sound ideas for all of us. Energy saved today will be avail­able for our grandchildren. The energy we save now will help to slow down climate change and envi­ronmental degradation so that our consumption will not become an overwhelming burden on future generations. The energy we save now will give us additional time to develop and improve alternative energy sources.