source might sustain a useful "practical" wind energy system of at least 2 x 107 megawatts on the land area of the globe (2). That power is rather impressive, but the fact that seventy percent of the earth's surface is ocean plus the observation that the winds over the oceans are on average much more energetic than are those on average over land puts even more glitter on the size of the resource. There are oceanic regions over which very rich winds blow almost constantly, and that fact alone should excite the imagination of men who want to live in peace with nature rather than in open combat.

a chance for significant kinetic energy extraction

without violation of nature

When the estimate of windpower available for extraction by man was made it was done by simply summing up the rate at which winds must continually dissipate kinetic energy, that is, fritter it away via a myriad of friction processes into low grade heat, to maintain the global heat balance. In any vertical column of air one finds processes at various layers which either create or dissipate kinetic energy. There is almost always a net dissipation at the bottom of the column at the earth's surface. One of the more wonderful things about using windpower is that it appears that nature could care less whether that dissipation occurs in a man-made momentum exchanger or in kicking up dust or rocking trees back and forth. There thus appears to be a chance for significant kinetic energy extraction without violation of nature. There also appears to be a natural healing mechanism for the instance when kinetic energy in excess of the local surface dissipation rate is extracted: kinetic energy will then flow toward the surface to redress the balance. Two excellent recent estimates of the size of the extractable wind energy resource in two different regions have been published by Nelson and Gilmore for Texas (3) and by Wentink for Alaska(4).

Calculations in Terms of Annual Productivity

The resource is astronomical in size on a global base, is vast on a regional basis, but how "firm" is it? That answer in the first instance is rather disappointing: in the short term windpower is not firm at all, indeed it is capricious. And our forefathers who used the winds had to exercise some patience now and then. It is chronicled that there were even. millers who periodically would miss the seven o'clock CBS news because the winds might freshen at sixthirty. Our forefathers did realize, however, and we have since corroborated rather elegantly, that the total energy available in the winds in a region over a year or so was quite repeatable. Thus, those millers who were occasionally denied such essentials as the seven o'clock news could and did count on a certain number of productive milling

hours per year, and could predict with cold-hearted accuracy their charges and profits. Likewise, the sea captain in the Far East trade seldom knew what tomorrow's distance-made-good would be. but he could predict the total time of passage half way round the world with stunning accuracy. The windpower resource in a region can thus be assayed from an annual productivity point of view. That predicted energy resource can then be matched to energy markets via saleable products. Percy Thomas (5) was the first to couple this ability to predict reproducible annual energy content with expanded windpower usage.

For Agricultural Purposes

The most happy situation is the one in which the market, the product and the windpower system can all tolerate changes in wind velocity as they naturally occur. The largest of those situations today, around the world, is still the lifting of water for agricultural purposes using rather small, inexpensive windpumpers. The market, the soil, can usually accommodate a highly variable rate of delivery of product, water. And if the system is inexpensive enough, economics can accommodate a rather modest plant factor. Plant factors of the order of 0.10 to 0.20 are common in this situation. We in the United States have little interest in this situation (*) but the preponderance of the world's human population does. During the last two years ! personally have become very much aware of how large a role water-lifting might play in rice-culture, an operation that most people associate with adequate water, never requiring irrigation. To the contrary, even for one crop a year, windpowered water lifting could increase yields significantly. and alleviate considerable back-breaking labor. Where two crops per year are wanted (and this is one possible partial solution to the impending world food crisis) windpowered water lifting could be a crucial element, so long as the system's investment can tolerate low plant factors.

total available wind energy

in a region over a year

is quite repeatable

'Or do we? This month of April, 1975, brings word that over 1100 gaspowered 150 hp water well irrigation pumps in one of our most productive U.S. agricultural areas are soon to be cut off from gas supply. In fact, some 1,000,000 other water well irrigation systems in the US. southwest face that same lack of fuel in 2 to 20 years. Perhaps our own food supplies will need wind or solar pumped irrigation water even sooner than wilt those of the Less Developed Countries!

It is thought that there might be large industrial processes in Europe and North America even today where intermittent wind power could be substituted (continued on next page]

Windpower

(continued from previous page)

for fossil-fueled energy inputs. The milling of grain might again to some level be subdivided back to smaller unit operations, manned in such a way that intermittent energy could be used. This might require a major experiment in manning. The typical U.S. working man operates at a plant factor of about 0.22. Would it be possible to disturb the now accepted workday pattern if so doing would assure 2000 hours of wages per year, guaranteed for a long career by a new industry made viable by release from the clenched fists of the fuel and electricity merchants? Could the wet milling operations, the various low-cost fermentation processes be rebuilt in a way that rather low return on capital could be offset by freedom from escalating energy inputs? I am particularly interested in the Maine Methanol Experiment. The textbooks on creation of methanol from wood waste warn against the need for a very high plant factor. They all required a return of capital in as few as five years, however, and a considerable input of very cheap coal, gas and electricity. If more kindly public concepts of capital return were used here say a 30-year return period instead of five - (*) plus intermittent energy from windpower, and some adjustment in manning, could this not be an inviting application for windpower whenever the wind does blow?

'Both in our public and private utility financing in this country, we insist on waiting 35 years to recover our invested capital. But, in any energyintensive new industry, private enterprise, the entrepreneur wants to recover all of his capital in as few as five years, no more than 10 years. Thus, the U.S. entrepreneur looks to the utilities for "cheap" electricity and other energy inputs rather than looking to his own process for somewhat more expensive home-made electricity or recovered heat. This bit of U.S. economic practice is probably the single largest reason for our being so cavalier toward investment in heat-recovery systems, bottoming cycles, etc. If somehow we as a society could arrange for the process industries to be able to (want to) use 35 year capitalization periods for en

ergy conservation systems, we might go a long way toward massive industrial energy savings.

Hydrogen Storage

A major candidate for the storable is hydrogen prepared by electrolysis of fresh water. Such a hydrogen storage subsystem then requires fresh water preparation, electrolysis, storage as a gas or liquefaction and storage as a cryogen, then reconversion or consumption of the hydrogen to generate electricity when required. The overall storage system efficiency could be as low as 30% using hardware available today. There are components already demonstrated in the laboratory and in the development stage which could boast that overall number to at least 50%. If the combination of electrolyzer and hydrogen consuming fuel cell is chosen, there is no carnot limitation to the subsystem efficiency which might rise into the 80's or 90's depending upon new inventions. If the combination of electrolyzer, in-earth or beneath water storage of gaseous hydrogen and oxygen, then stoichiometric recombustion plus water injection is used in a system like HOTSHOT, (7), an overall 60 percent subsystem efficiency might be achieved. That number is still not as good as the 64 percent for a highquality pumped hydraulic storage subsystem; but large quantity pumped hydro is simply not feasible in this country whereas large quantity storage in compressed or liquefied gases may be.

Compressed Air Storage

Compressed air may be used in the storage subsystem. This looks attractive if constant pressure variable volume air-compressors are driven directly (probably geared) by the windwheel and the air is stored in pressure balanced under water storage. In-ground storage of compressed air at pressure ratios of 4 to 20 have been shown to be economic for relatively small amounts of storage, but do not appear to be economic in a system where as much as 15 percent of the annual energy must be stored. The concept of storing compressed air economically, in the aquifer, has been patented, but it is not yet clear where that could be used to firm up large wind power systems. If demonstrated as practical, this method of storage might work well for large numbers of smaller systems.

Pumped Hydro Storage

Pumped hydro storage could be used for modest wind powered electricity systems where suitable terrain and water are available at acceptable costs. One acre-foot of upper pond 100 feet above a lower pond can store about 90 kWh. A farmer, rancher or rural resident in a reasonably windy area who happens to have terrain readily suited to creation of a pair of 10 acre-feet ponds, separated by 100 foot head can use his own wind-pumped hydro-electric system quite easily and very economically in the East or in a location expensively remote from the power line, if that potential energy is converted to electricity to an overall efficiency like that achiev

able via the Michell-Banki turbine (~80%).

Methanol Storage

As mentioned earlier, methanol prepared from wood waste might be an excellent wind system storable on the medium to large scale, perhaps even on the small scale, if we can reinvent a modern electrical equivalent of the dirt-cheap woodfired methanol retort that French farmers used one hundred years ago to prepare a saleable by-product from their carboniferous barnyard and woodlot wastes. On the grand scale the oxygen and part of the hydrogen produced by wind driven electolyzers could perhaps be combined with dirty coal to prepare a clean storable fuel, liquid preferably.

amount storable depends

on the shape of the

product delivery pattern

There are hopes that the super flywheel may be developed and marketed in sizes and at costs that will make it attractive to windpower systems. For small wind electricity systems, flywheels with power ratings of 5 to 30 kW and energy storage as large as 500 to 1500 kWh, would be very useful if they could be sold at reasonable prices.

The amount of storable required in any system will depend on the shape of the product delivery pattern can (particularly if that pattern can be bent out of its usual shape without uneconomic consequence) and the specific power of the wind machines used in the system. The specific power in turn is a function of the wind regime, the swept area and the power rating of the generator (or air compressor or hydraulic pump) attached to the windshaft. If the wind regime is rich and/or economics permit a relatively large swept area to driven generator ratio, storage requirement can be made quite low indeed. On the other hand, if the system attempts to wring out every possible kWh from a lean to mediocre wind regime and to do this with a small wind wheel, the storage fraction can be quite large. The relationships among annual productivity, annual plant factor and storage fraction as functions of a specified wind regime, swept area and driven generator can be examined parametrically rather easily (7). Wind regime in turn is a function of geography and height above surface, so tower or support costs can enter the computation easily. Rather good guidance toward most economic or best-suited wind systems including storage can thus be obtained analytically when wind regime descriptors are available.

Infinite Number of Wind Generators

Wind system conceptual designs prepared at the University of Massachusetts have to date spanned the broad field from cloth-and-wood home-built pumpers capable of reducing the backache of a

single peasant farmer all the way up to a grand scale Offshore Wind Power System conceived to deliver 360 billion kilowatt hours of electricity on demand for New England. All of the storage subsystems enumerated above have been looked at (some only prefunctorily) and some significant effort to inject circa 1970-1975 technology and materials into each of the major subsystems has been expended. Preliminary studies of the horizontal axis high-speed low-solidity propeller type momentum exchanger in sizes from six feet diameter to 200 feet diameter and in metal, wood and composites have been made. Analyses and laboratory tests of the S-rotor vertical axis machines have been made. Several high-solidity fan mill horizontal axis configurations have been studied and a number of unique cross-flow vertical axis machines are under consideration. The electrical portion of the work has just begun: it can be stated that the solidstate power devices available today at such high reliabilities and efficiencies as well as reasonable cost make 1975 wind system electrics much more flexible and attractive than they were in 1939-1945 during the Smith-Putnam experiment, during the 1945-1951 work by Percy Thomas and during the 1950-1954 production efforts by Allgaier in Germany under Hutter's guidance. It is just possible that wind generated electricity systems may help stimulate industry to convert more of the US electric power engineering hardware into the kinds of "power electronics" hardware already flowing out of Sweden, Holland and Japan. It is nothing less than exciting to realize that an "infinite" number of wind generators, each turning at a different speed in a different energy flux can be made to spill their paralleled outputs into one common high-voltage d.c. collector cable at very high efficiency, at very reasonable cost, and with no moving parts other than the rotors of the wind generator. Space Heating

The University of Massachusetts team is also involved in development of windpower systems planned for the provision of heating (and perhaps cooling) of buildings. Studies have shown that wind generated electricity delivered to resistive heaters in a water storage tank could be added to existing fossil-fired or electric-furnace heating plants in a very economically attractive way. This concept is called the "Wind Furnace" concept, and research was started in 1972. As of March 1975 the National Science Foundation has agreed to support completion of the project, and a single residence demonstration of the system should be available on the Amherst campus by December 1975.

Windpower

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time lag between the heat loss and the wind energy. In contrast, the plot of expected yield from a solar flat-plat collector optimized for heating season productivity at that site is quite flat, indeed slightly hollow when heat is required the most. Paper studies suggested at least four models of the wind furnace involving several combinations of flat plate collector, wind generator, water storage tank, a heat pump, and a wind driven mechanical water heater. Ten professors and as many students are now continuing this investigation, theory, analysis, design, hardware fabrication and hardware test. The computer runs tell us that the first model with no storage at all is very wasteful so it will probably receive little test. They also tell us what we had surmised: water should be stored at at least two different temperatures in at least two separated (insulated from each other) tanks. The demonstration facility will hopefully be inside a very specially designed low-cost dwelling which we think should in future supplant the present poorly insulated mobile home.

Ocean Winds

There are two other wind energy systems essentially without storage systems in which some effort has been expended over the past three years. Both involve the winds over the oceans, the strong to very strong winds that intensify as they are drawn toward the persistent low pressure regions of the seas (8), or, those which would use the rather gentle but steady trade winds (9). He who will go to sea to use the winds will be able to accomplish great things for mankind at essentially no cost to the rest of everything in our biosphere.

appears feasible for

ships to return to the sail

The first of these sea-going systems is for the propulsion of ships. It is perhaps a sign of the times, just another mark of how topsy-turvy the world has become, to realize that oil tank ships designed to speed along at 15 to 21 knots cannot now afford burn oil to make those speeds. There are other factors contributing to this situation, like the fact that occasionally more oil is available in tankers at sea than can the world markets afford to buy and consume. Many tank ships are forced into a wait-for-a-customer posture in which they have no need at all for high speed. All of this added up (and it may add up this way for the entire remainder of the petroleum era) has many of these large ships loafing along at 4 to 5 knots quite willfully. As few

as 40 years ago a speed of advance of 5 to 10 knots was quite acceptable in ninety percent of the world's merchant navies. But who would have predicted that moon-conquering homo sapiens would be reduced to circumstances where their great merchant fleets were constrained to crawling let alone walking. Well, the same kind of nut who believes in the efficacy of windpower might have predicted a return to slow speed and thence a return to sail. If those ships were rigged for sail and manned for sail, the sail canvas market would be very prosperous today. We at UMass like sail, but we think that windwheel propulsion would be superior in many ways. A wind system called the "Power Mast" is on the boards. The Power Mast rises as a stayed pole mast 225 feet above deck and supports a structural grid in which four columns and 4 rows (16') of 35 foot diameter wind wheels, each given a 50 foot diameter working circle, are suspended. A seventeenth wind wheel is supported on the top of the mast in skysail fashion.

ammonia-manufacturing, seagoing vessels could make use of wind energy

Each 35 foot wind wheel drives a 60 kW constant pressure variable displacement hydraulic pump. A Power Mast can be fitted in each 250 foot length of ship, shrouds and stays rigged so that the yards can be swung at least 120 degrees. Each Power Mast is thus capable of delivering one megawatt of power, and five could be stepped on a 1200 foot long tanker. The hydraulic power is to be collected and delivered below to a variable-stroke hydraulic motor connected to the propulsion shaft via clutch and silent chain drive. In a new design it would be very desirable to have a controlled pitch propeller fitted so that low-power propulsion efficiency could be enhanced. Wherever a reasonably efficient propeller (open water efficiency of at least 40 percent at half rated advance coefficient) exists, this ship will do very well on all points of sailing including sailing dead into the wind. The best speed will be achieved with the wind just slightly forward of the beam in a gentle breeze, or with the wind on the quarter in a strong breeze or gale. The usual petroleum trade routes between the Atlantic, Pacific or Gulf ports and the Arabian oil fields would provide a good passage all the way except astride the tropical zone. There some fuel oil would probably have to be burned. A very few naval architects have persistently held the view that sailing merchantmen could compete in the right trade: perhaps the OPEC nations have given new life to that thesis.

The other sea going wind system is to be a factory ship, a drifting ship of unusual configuration which raises a number of wind wheels up into the