Power From Rain and Wind
BESIDES the direct methods of drawing on the sun’s energy, there are many ways to capture it indirectly. Running water has been used for more than 1,000 years to turn mills for grinding grain, thickening cloth, lifting water, and many other purposes. The water is carried back from the sea to the stream’s headwaters by the natural processes of evaporation and rainfall, all powered by the sun’s radiation. Thus it is continually renewable, a dependable source year after year.
The damming of large and small rivers has provided the means for a continuous supply of energy throughout the seasons, for generation of hydroelectric power. In some countries, running water is so abundant that it is the most important source of power. Norway gets almost all its electric power from falling water. But world wide, in comparison with other energy sources, it is less important. Only about 5 percent of mankind’s total consumption of energy is hydroelectric. In many parts of the world, much of the potential water power has already been harnessed, and not much can be added to quench the growing demand for energy.
The windmill is another age-old way of drawing energy from the environment. This also depends on the sun, because it creates the weather and the climatic differences that determine which way and how strong the wind blows.
Windmills used to be a familiar landmark in many parts of the world. The picturesque windmills of the Netherlands pumped water out of dike-enclosed lowlands. In the 18th century, they also supplied power for sawmills, grindstones, and for thriving industrial centers. Millions of windmills once dotted the plains of the central and western United States. They were used mostly to pump water from wells, but also as a source of electric power. In the 20th century, windmills were largely replaced by gasoline engines.
But now, with petroleum losing its dominant position, wind power bids to reclaim its popularity. Giving impetus to the renewed interest is the realization that the potential of the wind is much greater than had been believed. A University of California scientist claims, in a recent report, that, on a worldwide basis, man’s total need for energy could be supplied 20 times over with power only from the wind. Even in the United States, if the wind resources were fully exploited, there would be enough to supply 75 percent of the power now used. In many locations, the energy in the wind averages almost as much as that in the sunlight.
There is great variety in the form of machines being designed and tested to gain power from the wind. There are propellers with two or three blades, mounted on what looks like a small wingless airplane at the top of a tall tower. Such a machine with 63-foot (19-m) blades is now generating up to 200 kilowatts, enough for one sixth of the 1,300 homes in Clayton, New Mexico, when the wind blows—which it does 90 percent of the time. In 1978, the power cost three times as much as power from petroleum, but larger machines and mass production are expected to bring down the cost, even while petroleum is rapidly becoming more expensive.
Similar machines are being tested in several locations, and a 2,000-kilowatt generator, the largest yet, has been built on a mountaintop near Boone, North Carolina. A cluster of windmills is to be erected in a windy mountain pass in central California by a private firm. If it is an economic success, hundreds more will be set up at strategic locations.
Another type of windmill has curved blades attached top and bottom to a vertical shaft. Its appearance is something like a giant eggbeater. It does not have to be turned into the wind. As with other types, it works above a certain minimum wind speed, usually about eight miles (13 km) per hour, and can be shut off to prevent damage when the wind blows too fast.
Yet another unconventional machine has a stationary cylindrical tower with vertical vanes on all sides. These are opened at an angle on the windward side of the tower and closed on the leeward side. The wind entering the tower is directed into a spiral circulation pattern and moves upward, forming a miniature tornado. The low pressure in the center draws air in from the bottom through a relatively small-bladed turbine turning at high speed.
Still other designs are being invented and developed. The field is open for innovative ideas on how to get electricity from the wind, and no one can now predict which will finally produce the cheapest power. So vigorous research goes ahead on many competing designs.
One factor to be weighed in comparing wind power with other sources is the aesthetic one. An occasional windmill might be considered picturesque, but long rows of windmills could become a blemish on the landscape. There is also some concern that they may interfere with local television reception.
The present outlook is for wind power to come back at least to its former importance, and probably to share an even larger part of the energy picture. According to various estimates, between one and 10 percent of U.S. energy might be supplied by the wind by the year 2000.
Leveling the Peaks and Valleys
When the sun is not shining, or the wind dies down, the power from any device depending on them will be shut off. If this is an incremental part of another power system, say a hydroelectric or a coal-fired plant, this variability is no problem. The operators will simply adjust the output from the main generators to compensate for the varying solar or wind power in the same way as they do to meet changing demands during the day.
For some purposes, solar energy could be used by itself on a basis of “making hay while the sun shines.” If it is used to pump water into a reservoir, or in the electrochemical manufacture of aluminum, or the production of hydrogen, operations could proceed when the sun shines and be shut down when it does not.
But for many uses, some means of storing energy must be provided. Electricity can be stored in batteries, as we have long done in our automobiles. However, the number and bulk of the ordinary lead-acid cells needed to serve the power requirements of an average home would be cumbersome and expensive. Fortunately, recent research promises new types of solid-electrolyte batteries that may be able to store large quantities of electric energy in a small volume.
If such batteries become a reality, electric automobiles will be much more practical than they are today. The motorist would keep his car plugged into the power outlet at home or in the parking lot where he works or shops. With improvements in solar cells as well as in batteries, it may become practical to mount solar panes on the car top, to charge the batteries while the car is traveling as well as while parked. Such an automobile is now being tested in Florida. An enterprising inventor in California has even attached a battery to solar cells mounted in the wings of a light airplane, and demonstrated that it will fly on sun power.
For large power plants, it may be more practical to convert energy to other forms for storage. For instance, excess power generated during sunny days, or when the wind blows, could be used to pump water uphill into a reservoir. Then, by reversing the flow, the power could be used at night or during a period of calm. Another proposal is to pump air under pressure into natural underground spaces. Or mechanical energy could be stored in the rotational momentum of giant flywheels. This diversity of ideas indicates that there will be changes in the ways we use energy if solar and wind power become common.
Bottled Sunshine
Photochemical production of fuels by sunlight is another way to use solar energy. A natural process of this kind is photosynthesis. Green plants use the sun’s light to make energy-rich compounds such as carbohydrates. Man’s earliest use of solar energy was burning firewood to cook his food and warm his domicile.
By fermentation, another natural process, alcohol can be made from many plant materials and extracted for use as fuel. From 10 to 20 percent alcohol can be mixed with gasoline in automobiles without altering the engine. Engines can also be converted to burn pure alcohol. Up till now, alcohol has been more expensive than gasoline, but the picture is changing, and motorists have begun using the mixture called “gasohol.” Brazil has undertaken an intensive project to produce alcohol and become independent of petroleum imports. For commercial production, various kinds of quick-growing plants are being studied in a search for more economical processes. Such methods for using solar energy are classified under the term “bio-mass.”
Some forward-looking scientists would like to use sunlight to decompose water directly into hydrogen and oxygen. Of course, this can be done by electrolytic decomposition, but they are looking for a photochemical method. What is needed is a suitable catalyst for the reaction, something that will work the way chlorophyll serves to produce sugar from water and carbon dioxide. If this can be found, compressed hydrogen may come to be used as a fuel for automobiles in the future.
Such fuels as alcohol or hydrogen, produced with sunlight, have a great advantage over hydrocarbons. They do not pollute the environment. Furthermore, they do not disturb the balance of carbon dioxide in nature as do fossil fuels, because each year’s supply is cycled from and back to the atmosphere.
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One scientist claims that man’s total need for energy could be supplied 20 times over by the wind
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In some areas the energy from wind averages almost as much as that from the sun
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It may become practical to mount solar panes on the tops of electric cars, to charge batteries while the car is being driven or while parked
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Alcohol can be made from plant materials and used as fuel; it burns without polluting
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Power from Inside the Earth
Besides nuclear energy, there is another source of energy that does not come from the sun, either now or in the past. It is the earth’s own internal heat. It has long been known by those who drill deep holes into the earth that the deeper you go the hotter it gets. There are also local hot spots near the surface. The spectacle of a volcanic eruption, spewing molten rock down its sides, is the most dramatic demonstration of this. A lesser manifestation is that of geysers, which spurt steam and boiling water high into the air. Milder yet are the hot springs that attract people to spas.
Scientists believe that the earth’s heat resulted from the gravitational compression of the metallic and rocky materials of which it is made. Presumably all parts of the earth have been molten at one time or another; the crust cooled off but the interior is still hot. The remaining heat is always flowing toward the surface, faster in some places than others. This primordial heat is augmented by the radioactive decay of such elements as potassium, uranium and thorium in the earth’s crust.
At those places where the earth’s heat is accessible, it provides a useful source of energy. At Larderello, Italy, there are steam vents that have been harnessed to electric generators since 1904. A larger plant near Geyserville, California, generates over 500,000 kilowatts from dry steam.
Superheated water drawn from a bed of hot rocks is also a source of steam when it is piped to the surface and the pressure is relieved. New Zealand and Mexico have tapped hot water for power production. The first plant of this kind in the United States is now being built near El Centro, California. It is to produce 50,000 kilowatts, and it is estimated that the geothermal field there will support expansion to 10 times that capacity.
Geothermal energy is so vast that it is practically limitless in comparison with man’s needs. But it can be tapped at relatively few locations. Its useful potential at present is quite small compared with the thousand times greater potential of sunlight and wind, which are available over all the earth’s surface.