At many points in that process the energy can be tapped to fuel our electric power systems, warm and cool our homes, drive our industries. The six technologies, therefore, involve different ways to make use of the sun's energy.

SOLAR HEATING AND COOLING

The most developed application of solar power so far involves the heating of buildings and the heating of wash water. Use of solar power for cooling is only a few steps behind. The process is simple enough. The sun's heat can be caught and held in thermal collectors-panels set up on or near a building and tilted to face the daily path of the sun across the sky. Typically, one of these collectors consists of piping mounted on a flat rectangular surface, all of it painted a dull black (black absorbs heat) and then surrounded by a deep frame to support one or two shielding sheets of glass, which will trap the heat the way a greenhouse does. Air or water or some other liquid (for instance, an antifreeze mixture where the outside temperature is likely to drop below freezing at night) is piped through the collectors, where it picks up the heat, and is then carried in pipes to a storage unit. The unit can use water, chemicals, rocks, even mud for storing the delivered heat; its purpose is to make the collected warmth last well beyond the time when the sun is shining. This heat can then be distributed to the building through air ducts with the help of a fan, or through pipes, as hot water, or be used to power air conditioning equipment (refrigerators and absorption airconditioners need heat to run). Basic versions of this system have been used for years in various parts of the world-for example, Japan, Israel and Australia, as well as California and Florida.

Over the last two years, the consulting firm of Arthur D. Little, Inc., Cambridge, Mass., has put together a consortium of 90 major companies in Europe, Japan and the United States to finance a cooperative analysis of the commercial possibilities. Last summer, Congress passed the Solar Heating and Cooling Demonstration Act-Mike McCormack's bill-which provided for the National Aeronautics and Space Administration and the Department of Housing and Urban Development to work on a wide range of development projects and practical applications for residential and commercial buildings. The project is expected, within three years, to show the value of solar-heating technology, and within five years to develop and demonstrate combined heating and cooling systems. This kind of Federal Government interest has made industry prick up its ears and start sniffing the air. During the American Society of Mechanical Engineers' annual meeting in New York in November, the group's solar-energy division and the University of Maryland's department of mechanical engineering offered two and a half days of sessions on solar heating and cooling; three years ago; the sessions could have been held in a hotel bedroom, but this time, they filled a ballroom. In 1974, PPG Industries Inc. (Pittsburgh Plate Glass) and Revere Copper & Brass Inc. each came on the market with solar-heat collecting panels. Several smaller firms are selling whole systems and even whole houses.

A few large school buildings-in Minneapolis, Minn., South Boston, Mass., Warrenton, Va., and Baltimore, Md.-have been fitted with experimental solar collecting panels, and plans for equipping major new buildings with the panels are multiplying. Arthur D. Little's vice president, Peter E. Glaser, who heads the solar study, predicts that solar heating and cooling will be clearly shown to be practical within the schedule set forth by Congress, and as early as 1985 will have grown into a billion-dollar industry in the United States, accounting for 1 per cent of the national energy market. The National Science Foundation, which until recently was the leading Federal agency in this field,* expects that if an accelerated program of study and application is followed, this technology could be meeting most of the heating and cooling demands of 12 per cent of the nation's buildings in the year 2000.

*The foundation has just relinquished its responsibility for supporting the development and demonstration of existing solar-power technologies to the recently created Energy Research and Development Administration. and will concentrate instead on encouraging research into new approaches. It is still not entirely clear, however, who in Washington will be in charge of overseeing solar-power development. It appears that nominal responsibility will pass to the Energy Research and Development Administration, which will also absorb a good deal of the National Aeronautic and Space Administration's role, but that the Office of Management and Budget which holds the Federal purse strings will play a crucial part by reflecting the Administration's attitude toward

WIND ENERGY CONVERSION

Commercially competitive products to derive usable power from the wind are also possible within five years. It may seem strange that they are not available already, because man has been tapping wind energy for centuries; the earliest windmill written about was built a fine bit of historical irony-in Iran in the seventh century A.D., and wind-energy machines have been used since to mill corn, pump water and even, in this century, to make fairly large amounts of electricity. A few wind generators are now produced in the United States, and other equipment can be imported from abroad. Last year, Grumman Aircraft Corporation bought the rights to a windmill design developed at Princeton University and began to study it, along with other designs, looking for a marketable item. The problem now is that windmill systems cost too much. The power that comes in over utility lines now costs the consumer anywhere from 2 cents to 8 cents a kilowatt-hour including any fuel-adjustment "tax." The Solar Wind Company of East Holden, Me., which distributes wind-power equipment, estimates that if you buy one of the home systems now available and figure on amortizing the capital costs over a period of 15 years, the power you get out of it will cost 10 to 25 cents a kilowatt-hour, depending on the equipment you buy and the local wind conditions. That may already be attractive if you have a grudge against your local utility or if you are building a new home a considerable distance from existing utility lines. You might decide to forgo the high cost of stringing in a line and spend the money instead on a wind turbine, the tower to mount it on, the storage batteries to supply a steady amount of power and the equipment for transferring the wind-generated power to the batteries.

The wind-system costs could be cut somewhat by improving the efficiency of the equipment, but not by much. "If you took a good windmill of today," says Louis V. Divone, program manager for wind-energy systems at the Energy Research and Development Administration, "and got it theoretically perfect, you would improve its performance only by about 20 per cent." Efficiency could be improved by simplifying the machinery, making it lighter and stronger, reducing the likelihood of breakdowns, insuring the long life that makes a system economic, and then mass-producing it.

No one foresees any overwhelming difficulty in achieving this. Eventually many homes may have their own wind turbines-to produce power and perhaps to drive "wind furnaces" for heating. It is possible that platoons of huge wind machines will march across the Great Plains and float at anchor off the Northeast coast and the Aleutians, areas of consistent strong winds. The floating generators could produce large blocks of electric power that could be cabled ashore directly or else, in an electrolytic process, used to separate hydrogen gas from sea water. The hydrogen could then be piped or shipped ashore for burning in generating plants or fuel cells. If the technology is pushed, according to the National Science Foundation, the United States might by the year 2000 be generating about one-fourth of the electric power it will need with windmills. This amount would equal half the electricity we use today and would meet 6 per cent of our total energy needs at the turn of the century.

BIOCONVERSION

It is possible to grow crops-a basic result of sunlight on the planet-specifically for burning to produce power. These can include trees, sugar cane, marine plants, many things. Plant products can be heated in a vacuum (the method is called "pyrolysis") to make gas and oil-"fossil fuels"-thereby cutting a few million years off nature's schedule for doing the same job. Or, after plant products have passed through some initial process-a natural one, as in the digestive tracts of animals and humans, or a mechanical one, as in production of paperthey can be burned as fuel. (Dry cow dung has been used that way in India for centuries, and the buffalo-chip fire warmed many an American plainsman in the last century.) These materials can also be converted to gas, oil or a solid fuel; so can the waste food in your garbage pail.

The development of economically viable bioconversion systems seems likely in the near future. The National Science Foundation believes that pilot plants should now be built and tested for several bioconversion approaches, including direct combustion of vegetation as well as the burning or converting to methane and methyl alcohol of vegetable wastes, municipal refuse, sewage and wastes from animal feedlots. The Environmental Protection Agency has been backing

a demonstration project in St. Louis, where the Union Electric Company feeds burnable solid wastes-shredded-into a boiler furnace along with coal; the process has been so successful that Union Electric is now moving to enlarge it to handle most of the solid waste produced in the seven-county St. Louis area. Similar systems are being built in Chicago; Ames, Iowa; Bridgeport and New Britain, Conn.

A number of other cities are planning to follow suit. The environmental agency is also helping finance two pyrolysis demonstration plants, in Baltimore and San Diego. The Baltimore facility, which will make gas for firing steam plants to heat and cool downtown buildings, is finished and will start up early this year; the San Diego plant, which will make oil for sale to a utility, is scheduled to be ready in two years. Under an accelerated implementation program, bioconversion might be providing as much as 8 per cent of the nation's energy by the year 2000, according to the National Science Foundation.

PHOTOVOLTAICS

Solar-cell collectors have produced the electricity for all our space satellites. They consist mainly of pieces of semiconductor-a material whose ability to conduct electricity is somewhere between that of copper wire and that of an insulator such as rubber or porcelain. A semiconductor can be specially treated so that when light strikes it a voltage is created-the so-called photovoltaic effect. This current can then be stored in batteries or used directly. At the moment, photovoltaic technology is economical only for remote applications-powering satellites or certain navigation lights and telephones. There are relatively cheap semiconductors available, but they deteriorate quickly and must be replaced frequently.

Silicon solar cells, which have a virtually infinite life, are exceedingly expensive to make at the moment, and the method used to make them does not lend itself well to mass production. A home could today be powered with 1,000 square feet of long-life solar cells, but it would cost $300,000 to buy them. However, Tyco Laboratories in Waltham, Mass., has developed a way of producing— in the laboratory-silicon solar cells in the form of fine ribbon as thin as a human hair, and that appears to point toward a mass-production technique that will lower the costs dramatically. Mobil Oil Corporation thinks the Tyco process is so promising that it has joined forces with Tyco to develop the technique and will spend up to $30-million on it between now and the end of 1981. If that or some other research effort pays off, the National Science Foundation projects that the first demonstration plants could be operating by 1985, and that by the year 2000, 4 per cent of the nation's energy demands could be met by this technology.

The foundation is concentrating on terrestrial uses for solar cells, but Peter Glaser of Arthur D. Little has proposed putting huge solar-cell collectors-arrays six miles long and two and a half miles across-into orbit and beaming the power they generate back to earth on microwaves. This is not really Buck Rogers stuff; everything that goes into such a system has been shown to work. It is "futuristic," however, because of its scale, and because the collectors would have to be constructed in space, with the help of a new generation of space vehicles. But Glaser believes that the first of these orbiting power stations could be supplying electricity before the turn of the century.

OCEAN THERMAL DIFFERENCES

Half of those 3,600 quintillion B.T.U.'s that reach the earth each year land in the tropics. Since the tropics are largely ocean, most of the heat is soaked up and stored in the surface water of the sea. It is possible to tap that energy, too, by using the stored heat alongside "stored cold"-water pumped up from the cooler depths. The proposed mechanism is extremely simple: An electricitygenerating turbine is turned by the force of some fluid that becomes a gas and expands when it is warmed to the relatively low temperature of the surface seawater. Propane will do that, for example. So will ammonia. Then the gas is condensed back to a fluid by cooler water pumped up from the depths of the ocean and the fluid is cycled back to be evaporated again.

The ocean-thermal-differences idea is almost a hundred years old, having first been conceptualized in 1881 by the French physicist Arsène d'Arsonval. An experimental model was tested in the twenties, but nothing similar has been built since then. Nonetheless, William E. Heronemus, a University of Massachusetts

professor who has done extensive research in both wind-power and ocean. thermal technology, believes that if we wanted to, we could have the first commercial-sized ocean-thermal-differences power plant in place and making electricity in the Gulf Stream off Florida within six to eight years. The National Science Foundation, which is funding two industry studies of the concept, suggests that the process may take a decade, but that by the turn of the century strings of these plants in the Gulf Stream could be making 260 million kilowatts of electricity. A good deal of that power would probably be used to electrolyze water to produce hydrogen gas. The hydroger could then be piped ashore over long distances or shipped in containers. In all, the foundation estimates, the process could be supplying about 4 per cent of the nation's energy in the year 2000.

SOLAR THERMAL CONVERSION

Still another way to make large amounts of electricity from sunlight is to trap the heat in vast arrays of collectors, and make steam with that heat to turn turbines. Or other vast arrays-of mirrors-could be used to focus the sun's heat on a boiler, set atop a tall "power tower," again to make steam and thus electricity. This is a space-taker, requiring on the average a square mile of land covered with collectors or mirrors for every 25,000 kilowatts of electricity produced; but it is estimated that if 10,000 square miles-about 10 per cent-of the supersunny California-Arizona desert were planted with this sort of collecting and generating equipment, solar thermal conversion alone could produce more than twice the electricity generated today in the United States. By the year 2000, solar thermal-conversion installations won't be anywhere near that extensive, but they might be making some 80 million kilowatts-a lot of kilowatts, and a meaningful contribution to the power needs of the American Southwest, though still less than 1 per cent of the nation's expected energy demand. Researchers are also giving a good deal of attention to what they call "total energy systems," in which solar thermal-conversion plants would generate electric power for military bases, shopping centers, industries, perhaps whole communities; the leftover heat of which there would be plenty-would then be used to warm and cool buildings and run certain kinds of equipment, instead of being thrown away into the atmosphere.

In the development of each of these technologies were to proceed at a rapid pace, and if all the other circumstances remain favorable (particularly if oil supplies remain short and high-priced), we might see some power produced with each of them 10 years from now, and in 25 years be meeting about one-fourth of our energy needs with solar power. The likelihood, of course, is that things won't work out that well. Progress will probably be a good deal slower and have a smaller impact on our energy situation at the end of the century.

Why no more, and why no faster? There is a raft of reasons. The first of them is money. “Even if they all did get through [the research and development programs] on schedule," says Lloyd Herwig, director of Advanced Solar Energy Research and Technology for the National Science Foundation, "there's no way that you can implement all six at the maximum rate, because it takes a hell of a lot of capital for each one."

The second-despite the fact that we already know how to do most of what we want to do-is technological. There could be no better friend of solar power than James J. MacKenzie of the Union of Concerned Scientists, a member of the Joint Scientific Staff of the Massachusetts and National Audubon Societies; yet Dr. MacKenzie declared recently that if someone came knocking on his door today and offered to put a solar heating system on his home for $2,000-a low cost he could make up in about six years with saved fuel bills-"I'd tell him to go jump in the lake, because I wouldn't believe him." To convince Dr. MacKenzie as a homeowner, it would take "a thorough economic and engineering study of the system's performance over a period of at least one or preferably two heating seasons. You've got to know these things work, that they work not for weeks but for years." When the homeowner or builder can buy the solar-heating equip ment for a reasonable price at Sears, Roebuck, and it comes with warranties, a service contract and a guarantee of available replacement parts for everything, then it will sell, and in principle the same rule applies to all the solar-power technologies. For their part, the major manufacturers have to be convinced, too; they've got reputations and other product lines-to protect. And that kind of progress takes time.

Wouldn't more Government money help? Some, but it wouldn't solve everything. "There is a concept," says A. I. Mlavsky, the Tyco executive who heads

the Mobil-Tyco photovoltaic project, "-it's engrained in the American ethosthat if you put enough guys and enough money to work on something, you can do anything. It's baloney. It'll work on certain kinds of things. It worked for the Manhattan Project. But they finished up with two bombs. That was enough to finish the war. If they had wanted to make 10,000 of those things, each as alike as peas in a pod, it would have taken another 10 or 20 years."

Besides financial and technical hurdles, there are others. Primary among them is competition with other energy sources, notably petroleum, natural gas, coal and nuclear power. The search for more efficient ways to use them will continue to divide the resources available for energy development, including the dollars of consumers long accustomed to these traditional sources. And there will no doubt be a lot of competition among the various solar technologies themselves. The next 25 to 30 years will probably see something like the first boom decades of the automobile, when hundreds of companies came into being to make hundreds of different kinds of cars-gas buggies, steamers, electrics. It was an unsettled shake-out period, and solar power will probably go through the same kind of process.

Since setting up a new power network is a tricky undertaking, there will also be logistical problems. Where do you put what kind of equipment to make the most efficient use of the sun's energy? There are certain areas in the United States where hydropower provides plenty of cheap energy, and it will be some time before even the best of the solar technologies are cheaper; other places simply don't have a lot of sunlight in the periods when they need the most heating; everywhere, the sun is on the other side of the earth half the time; the wind is fickle in a great many areas and highly consistent in others. At least in the beginning, solar power systems will have to be backed up with conventional systems.

And of course there are the human factors. Just as the automobile caused a transformation of society, so would the need to adapt to solar energy on a huge scale, and such social transformations do not occur without strain. Even the environmental movement, long a champion of solar power, will have some adjustments to make. How about covering 10,000 square miles of the great American desert with mirrors and power towers? And do you want a wind-energy farm in your neighborhood-a hundred shiny wind turbines sitting there, whistling away? These would not be the weather-beaten gray structures of the picture books; instead, they could be huge machines sitting on towers "bigger than oil derricks." as Mike McCormack put it.

And so, if solar power is clearly on its way to becoming some sort of reality, the most immediate problem may be that it will be oversold. "The solar field is a young field," cautions Tyco's Mlavsky. "It's neophytic. It's receiving a lot of attention. It will not provide major solutions to our energy problems in a short time, and those-including myself-who sometimes get sucked into thinking that it will are wrong. It shouldn't be expected to produce a major impact on our energy economics in a period of just a few years, because nothing else we do moves that fast either. And if in 20 or 25 years-by the turn of the centurywe can be replacing, with solar energy, a significant fraction of the energy now made by conventional sources, we'll have done a hell of a job."