Future Solar Energy Utilization for Transportation
J. Richard Guadagno, Cimarron Technology, Ltd.
In my recent paper Transportation in the Post-Petroleum World, I stated that the direct conversion of solar energy into electricity was the only feasible way in which we would be able to gather sufficient energy to power the worlds future transportation systems. I also suggested that additional solar energy would have to be utilized for space heating and cooling when the nations natural gas supplies become exhausted. In view of these twin demands, which we will inevitably and simultaneously be facing around the year 2020, it behooves us to determine both whether such prodigious amounts of energy can be made available to us, and if so, how that energy can best be utilized. Since it was I who raised this issue, it would be irresponsible of me not to make an attempt to seek a resolution of the manner in which the proper answers might be found.
As to the matter of whether enough solar energy can be gathered, the answer is quite simple. The amount of solar radiation beamed from the sun to our planet each day is approximately 60,000 times the total amount of non-food energy consumed by mankind. Thus unlike the case for all other energy sources we enjoy quite a surplus of solar energy. Even a continuation of todays uncontrolled population growth could not significantly reduce its availability, since other overpopulation-related factors such as a shortage of tillable soil are likely to do us in long before that could happen.
Thus we need concern ourselves only about how to utilize this vast and totally renewable energy supply. We must begin by determining how much we need. In the case of the Integrated Transportation System (InTranSys) the only proposed dual-mode system which has seriously considered energy efficiency as a primary design component it has been calculated that solar panels covering only the surface of the track structure could provide more than half of the required energy. Values close to this may also apply to other techniques which employ super-efficient linear synchronous motors (LSMs) for propulsion. These figures are based on the average value of insolation (the amount of solar energy striking any particular area) for the 48 contiguous states. Since the total area taken up by this collection option is quite insignificant, it is obvious that the remainder could easily be acquired either by simply enlarging these solar panels above the overhead track structure, or by installing additional solar cells somewhere else including on existing rooftops alongside the tracks.
In fact, the latter option rooftops, plus perhaps building walls in Alaska to catch the low-angle sun there suggests a solution to virtually all of the nations future energy problems. If solar panels were to be installed on every rooftop in America, we could provide all of our energy needs. Whether these panels should be photovoltaic (producing electricity) or thermal (producing heat) would depend on a sites geographical location. For example, a person living in warm, sunny Miami would need only enough thermal energy to heat water for bath, kitchen, and laundry purposes, while one dwelling in cold, cloudy Buffalo would require many times more than that just to stay warm during the winter months.
Since space heating is a different but related issue, I will concentrate here solely on the conversion of solar energy into electrical power for transportation. The most efficient way to do this is direct conversion through the use of photovoltaic cells. And the biggest obstacle which must be overcome in this venture is the fact that the sun does not always shine precisely at the time and place where this energy is needed. Insolation across the United States varies from extremely high values in the southwest desert regions to only a minor fraction of that in the northeast corner of the country. This problem is further compounded by the fact that the population density and therefore the demand per unit area is still much higher in the energy-poor Northeast than in the Southwest. Moreover, in any area solar energy can be gathered only during the daylight hours. In addition, regions with seasonal precipitation patterns, like the West Coast, also receive far more solar energy during their respective dry seasons.
Thus it is not enough merely to state that there is sufficient solar energy available to supply all of our ground transportation needs. Some means must also be designed to collect this energy where and when it is available, and to use it where and when it is needed. This implies a need for two additional types of facility whose functions are just as critical as those of the collectors: a viable means for electrical energy storage, and another for energy transmission. Thus we must address these three components of a complete solar-energy-powered transportation system with equal thoroughness.
1. Solar Energy Collection.
There are four regions of the United States which can be expected to produce significant amounts of surplus energy from photovoltaic cells: the Southwest deserts, from the Texas coast to California; the Great Basin, including Nevada and portions of all the states surrounding it; the Great Plains, from Montana and the Dakotas (at least seasonally) south to the Oklahoma and Texas panhandles; and Florida and the coastal southeast although in the last case, other demands for land may necessitate that panels have to be largely confined to rooftops.
Each of these areas is large enough that we can afford to be selective as to which portions of it should be utilized for this purpose. Thus we can easily avoid areas of intensive agriculture; scenic, recreational, and wildlife value; and high-density population (except for rooftops). As an example of what can be done, I would like to refer to an 880-mile solo backpack trip I undertook several years ago across the Southwest, beginning in southwestern Arizona. While on this journey, I traversed some spectacularly beautiful mountain and canyon terrain, with abundant wildlife and varied vegetation. But often, while crossing the gaps between these areas, I found myself slogging across vast stretches of monotonous, flat to gently sloping desert almost totally dominated by a single plant species creosotebush. This is a spindly shrub which grows in a widely spaced pattern, maintained by the poison which its deep roots inject into the soil around them in order to stifle competition. Virtually all of the wildlife in these areas was concentrated in the occasional dry washes, where other plant species could grow. I walked mostly on auto-pilot during these intervals, observing little because there was so little of anything to observe.
Rectangular panels of photocells, each tilted downward toward the south at the optimum angle for its latitude, could be placed in these areas, arrayed in north-south rows spaced so that the ground itself would receive about half of the light it now gets from the westerly moving sun. This would accomplish several things all beneficial. Vast amounts of electrical energy would be produced. The ground surface would be cooled and the evaporation rate of the little moisture that falls there would be reduced. Plants other than creosotebush, resembling the richer growth of the nearby mountains, would take root. Wildlife habitat would be greatly improved. And we would still have far more creosotebush left than we or any other species could ever need.
There are comparable areas, including numerous dry lake beds scattered across southern California and Nevada and culminating in Utahs huge salt flats, where virtually nothing grows due to the high salinity of the soil. These could be similarly treated, although in such places the panels would have to be sufficiently elevated on corrosion-resistant stilts to stay above the temporary water brought in by rare storms. Many of the other broad valleys across Nevada and extending into adjacent states, which support a very sparse growth of sagebrush or other desert vegetation, could offer similar opportunities. Most of the land of this type, throughout the West, is now owned by the U.S. Government, and is now used (if at all) solely for grazing (most mining takes place in the mountains). This use which now has very little economic value could continue beneath the panels. In fact, there is a very good chance that it could even be improved by the reduced evaporation of moisture and consequent enhancement of forage.
The drier portions of the Great Plains could also provide suitable sites far more than we will need for similar photocell plantations. It is very likely that the grass now growing there would be improved or at least not badly damaged by such treatment. Test plots could provide more precise evaluation. All of these areas desert and grassland alike share a single optical feature: a very high albedo, causing most of the incoming solar energy to be reflected back into space, unused and unusable. Thus tapping this resource for electric power would have very little effect on the planets overall energy balance or climate. Solar electric energy thus stands as the closest thing to a free lunch that the human race can ever enjoy.
Other potential sites for photocells, covering smaller areas but perhaps with even greater corollary gains, would be the huge water storage reservoirs in the Southwest and northern Great Plains. These could harbor large floating rafts of individual panels tied together and anchored with cables to keep them in place. In the Southwest, water is likely to be even more in demand than energy in the future. And yet vast amounts of this invaluable resource are now unnecessarily evaporated from the surfaces of these reservoirs. As an example, Utahs Lake Powell alone evaporates more Colorado River water than all of the consumptive use in the states of Colorado, Utah, and Wyoming combined.
Rafts of floating photovoltaic panels covering most of the area of these reservoirs (while still leaving enough for recreation around their edges) would eliminate a major fraction of these huge water losses. They would not only reduce the area exposed to sunlight and dry air, but also cool the water, thus greatly reducing the "normal" evaporation rate of more than 80 inches per year. In addition, they would slow the high winds which at times whip the surface into whitecaps and evaporate even more. The same rafts which support the solar panels could also be used for a grid of windmills, thus taking advantage of these winds to produce even more energy. Moreover, the shading provided by the rafts would greatly improve fish habitat, compensating for the lost recreational opportunities for high-speed power boat use. But then these boats (and virtually all other recreational vehicles) will be hard-pressed to find fuel when the oil runs out, anyway. This is a matter of concern only for the vehicles users, however, so lets not worry about it. Californias manmade (although accidentally) Salton Sea, which has an annual evaporation rate even higher than that of Lake Powell, would also be a suitable site for such floating arrays of panels. This site could serve the nearby city of Los Angeles.
Yet another opportunity for combined energy and water production lies in the covering with solar panels of the vast network of huge open canals serving irrigated lands, especially in Arizona and California. These panels would be spaced more closely, allowing only a minimum of light through. At intervals, simple bridges could be installed to allow passage of pedestrians, wildlife, and livestock (on my hiking trip, I had to walk miles out of my way to cross one of these canals, which I promptly dubbed the Great Barrier Rift).
Floating rafts of panels could also be installed in the huge reservoirs along the Missouri River in Montana and the Dakotas. These lakes unlike those in the Southwest freeze up in the winter, however, and preventing ice damage to the rafts may require a more sophisticated design. Moreover, production of power during the shorter winter days there would be considerably less than that further south. These dams also unlike those in the Southwest were not constructed for irrigation, but primarily for barge traffic. Since this demand has failed to materialize, these dams may be at least partially dismantled, since the value of the land they have inundated is far greater than any benefits they have brought. Their sole advantage is that they lie closer to the relatively sun-starved Northeast.
Throughout the country, photovoltaic panels mounted on the roofs of existing buildings have the potential of adding greatly to the local power supply. Laws are already on the books which allow and sometimes require compensation when such contributions are made a part of the nations power grid. Each owner would have the choice of using his roof space for the production of electricity or heat. But in low-insolation regions, it is likely to prove insufficient for both. This problem will be tackled when we examine the other two critical components of a nationwide solar-powered transportation system.
On a worldwide basis, other areas of similar nature can be found at many serendipitous locations. The vast Sahara Desert could supply all of the necessary energy not only for Africa but also for Europe, providing that transmission lines can be built beneath the Strait of Gibraltar. The Middle East has comparable potential. In China, the sparsely populated Gobi and Tarim Deserts could provide the needs of the 90% of the population which lives along the east coast. Other deserts from the Arabian peninsula to Rajasthan could serve Indias billion people. Australias outback could supply its own needs plus those of the rest of Southeast Asia, again through the use of undersea transmission lines.
It is a matter of interest that the greatest potential for the worlds future energy supplies lies in regions which are now largely considered wasteland, and which are very sparsely populated. Many of these areas are also among the worlds poorest. But this could all change as these same regions become the exporters of the planets most valuable future commodity.
Solar energy is not just the potential source of electricity for future transportation systems; it is also the source of the energy for all of our present fuels, except for nuclear fission. But the efficiency with which this solar energy can be converted into electricity by photovoltaic panels is many times greater than that for such means as biomass (including alcohol derived from it), fossil fuels, wind, and hydroelectric power all of which operate at overall efficiencies of tiny fractions of one percent. The efficiency of producing synthetic hydrocarbon fuels from minerals such as oil shale or tar sands rank even lower. Thus photovoltaic conversion ranks far above any other process for utilizing solar energy, and it is the only one which can possibly provide all of the electrical energy we will need for our future transportation and other needs.
But which of the many potential photovoltaic collector types and materials will be most suitable for transportation? Today there are several choices available, and in the near future there will be many more. At the high end of the conversion efficiency spectrum are some high-tech panels, made from some rather exotic and not too abundant materials, which can convert more than 40% of the incoming solar energy into immediately usable electricity a remarkable number considering that not too long ago the first viable photocells produced only about 0.6 % conversion. But these may be reserved in the future for applications where low weight is of critical importance, such as for operating in outer space.
The current favorites for domestic use are the somewhat less efficient, but far cheaper, large-crystal silicon panels, which are doped with very small amounts of less abundant elements. Less expensive amorphous silicon can currently be used to produce a somewhat reduced efficiency. Both of these are made from the most abundant solid material on earth. I once had someone tell me that we could never depend on solar energy because we didnt have enough silicon! But this element comprises fully one-fourth of the Earths crust, and a single large quarry located anywhere on the globe could supply enough panels to cover the entire planet. But other possible options are also being developed rapidly. These include thin films of layered materials, plastics which can be coated on the back with adhesive and applied directly to existing smooth surfaces such as metal roofs, and the latest entry into the competition: semi-conductor materials.
The final decision as to which collector material (or materials) will be used will probably be a compromise depending on a number of factors: conversion efficiency, the abundance of the material, the cost of producing the cells, ease of application, expected lifetime, and the availability of space at the collection site. It seems likely that moderately efficient but relatively cheap cells, made from abundant materials, will eventually provide most of our future energy. The decision as to which option shows the most promise for any particular application can wait until the precise needs of that application have been better defined.
There is one thing of which we can be absolutely sure: it is clearly possible for us to power a completely solar-powered ground transportation system using only todays technology. Tomorrow can only make things even better. But if this is true, why arent we using solar energy in this way today? There are two major reasons; one is that the introduction of supply-side economics during the Reagan administration the philosophy that the producers of goods, and not the consumers, should be allowed to make all economic decisions was responsible for a severe decline in serious government-sponsored photocell research in this country. Behind this decision was a fear that home photovoltaic systems could be controlled entirely by their individual users, and that the power companies which have for so long depended on these users dependence on them would be left out of the profit loop. The second reason is that the installation of solar panels requires the investment of a considerable amount of up-front money. This can easily be justified by the fact that these panels, once installed, can be expected to last for decades, and will produce absolutely free energy over that entire period. But this meant nothing to those entrenched commercial interests who were responsible for the crippling of solar research, because they traditionally consider only this years balance sheet. The truth is that we must make such an investment in our future. If we dont, we wont have any.
2. Electrical Energy Storage
There are a number of factors which dictate a need for electric energy storage facilities. Some areas which enjoy high insolation rates can produce more solar energy than they need, while others with low insolation cannot match their demand. The average insolation value for any given area is affected by seasonal variations in both the length of the day and the amount of cloudiness. The sun shines (obviously) only during the daytime. Day-to-day weather variation also affects the momentary opportunity for utilizing solar energy for electricity production. Thus we cannot depend solely on the fact that there is sufficient energy available. Provision must also be made for diurnal, day-to-day, seasonal, and geographical variations in the availability of such energy. These problems can be solved only if we have suitable energy storage facilities which will enable us to gather energy at one time and one place and then use it later at another time and another place.
Today the only facilities which are currently used for this purpose aside from storage batteries for home photovoltaic systems are pumped storage installations. In this method, electrical energy is provided by conventional power plants during off-peak hours to pump water out of one reservoir and into another which is located nearby but at a higher elevation. Then when the next peak demand period occurs, this stored water is run down through turbines to the initial reservoir, with the ensuing output being added to that of the conventional plant. But such facilities are fraught with limitations, most of which are associated with the fact that pumped storage is a very low-grade system.
Let us pause here to define what we mean by this nomenclature. The grade of any energy production or storage system can be defined in two ways. The first of these is the mass of material which must be utilized to produce (or store) a given amount of energy. The second is the volume of that material. The lowest grade supplies are those which depend on mechanical (kinetic) energy, including hydroelectric (gravity-induced flow), windmills, and flywheels. Either enormous amounts of material or very high speeds are needed to contain significant amounts of energy in each of these cases.
By comparison, a comparable amount of chemical energy can be found in a far tinier amount of a suitable material. This is why the internal combustion engine has served so well for transportation in the past. Liquid fuels derived from petroleum, including gasoline, Diesel oil, and jet fuel, allow the storage of a great deal of energy both in a small weight and in a small volume. Moreover, they are very easily transported, both to the vehicle and within it. Gaseous chemicals like natural gas or hydrogen rate very high on a mass basis, but very low when the required volume is considered. Another quantum leap in grade comes from nuclear fission, which allows the conversion of tiny amounts of matter into prodigious quantities of energy. Even higher is nuclear fusion, which in the sun is the ultimate source of all of the lower-grade energy sources covered in this and the preceding paragraph. If controlled nuclear fusion ever succeeds on Earth, it might rank even higher than photovoltaic collectors as a producer of electric power for transportation. But we cannot risk our future on such an unknown quantity at this critical juncture in human history.
Pumped storage rates very low according to both mass and volume measures of energy grade. First, it depends on gravitational energy, and secondly, it employs a low-density material water which means that it requires the movement of a vast volume of material in relation to the amount of energy stored. Such plants thus require large tracts of land for reservoirs capable of containing sufficient amounts of water. They can only be installed in areas which enjoy large elevation differences over short distances. They cannot be used where the reservoirs are likely to freeze over in winter. And they operate with a huge energy deficit, since the energy losses suffered in operating both pumps and turbines are quite significant. This means that more energy must be produced than if auxiliary power plants, operated only during peak periods, were to be used for the same purpose. Pumped storage is a process which is energetically uneconomical, but it can be justified financially if and only if the extra cost of building a new conventional auxiliary plant exceeds that of the extra fuel which must be burned in the existing one.
The amount of energy storage needed for a nationwide solar-powered transportation system will be many times as great as that which can be supplied by such facilities, and the storage units must be available along the entire system. But this seeming disadvantage is overwhelmed by the fact that once proper storage facilities are built, the "fuel" they consume will be not only free, but it will also be available forever. Moreover, other prospective types of storage units unlike conventional power plants can be built in virtually any size.
In all but a few places, space considerations dictate that higher-grade storage facilities must be used in place of pumped storage. This inevitably dictates that chemical energy, where the same amount of energy can be stored in a much smaller quantity of material, must provide the basis for the system. Among those candidates which I have evaluated, I found two which appear to show the most promise. Both of these were originally proposed as alternative propulsion systems for mobile use specifically, for electric vehicles. Ironically, for this purpose they both have drawbacks which appear to be insurmountable. However and very serendipitously these disadvantages do not exist when applied to stationary storage facilities. These two prospects are sodium-sulfur batteries and hydrogen-oxygen fuel cells (it should be pointed out that other battery alternatives may eventually prove to be even more feasible).
The basic reason why a search has been made for alternatives to the common lead-acid battery and the reason for current electric cars limited performance and range is the great weight of the lead which must be carried around to supply a given amount of energy. But there is another reason why lead-acid will probably not be suitable for solar energy storage. Like petroleum, lead is not really a common material; its long history of use is due to the ease with which the ore can be found and processed into metal. Thus there are serious questions about whether our planet has enough of it to satisfy the greatly magnified demand which will be generated by the switch to solar energy. By contrast, both sodium and sulfur are among the more common elements in the Earths crust. Both of them are also quite light in weight when compared with lead. But they havent caught on for mobile use for two reasons. First, both materials have to be in a liquid state for the batteries to work properly. Thus, if they were used for vehicles, they would have to be elevated to these temperatures before the car could start and this takes both time and energy from some other source. The second drawback is a matter of safety: both elements, when raised to the proper temperature, are extremely chemically reactive. If exposed to moisture and/or oxygen, sodium spontaneously bursts into flame, while sulfur forms highly corrosive (and dangerous) sulfuric acid. Thus in case of a vehicular accident which caused the protective shields to be punctured, there would be a very serious chance of both fire and severe human danger.
For stationary purposes, on the other hand, these matters are of little concern. Huge banks of individual cells could be contained within a single large building, offering ample energy storage capacity. It would be encased by strong walls and thick insulation. The light weight of the materials would permit the use of high-rise structures requiring little land space. The entire building could easily be maintained at the required temperature at all times. It could also be sealed off from the atmosphere and filled with an inert gas such as nitrogen under a small positive pressure, so that no air could leak in. What little routine interior maintenance is necessary could be conducted by suitably designed robotic machines, although with no moving parts (other than electrons) to worry about, this would be a rare occurrence. And if a case did arise where air and water somehow entered the facility, the two products of reaction sodium hydroxide and sulfuric acid would ultimately neutralize each other, and the resultant inert products could be contained quite safely if the building were properly designed.
Hydrogen has a number of advantages as a fuel for road-driven vehicles, but at the same time it introduces other problems. Burned as a fuel, it can produce far more power per unit weight than gasoline, but it does so by operating at a much higher temperature, requiring that the engine be built of rather exotic and costly refractory materials. Even higher efficiency can be achieved by producing electricity by means of hydrogen-air fuel cells. But in either case, it is the size and/or weight of the hydrogen container, rather than the fuel or engine, which is critical. This must either be prohibitively large, with the increased air drag undoing any fuel efficiency, or else the gas (hydrogen cannot practically be liquified in such applications) must be contained at extremely high pressures. Whether it is made of high strength steel or composite materials, the fuel tank would still have to be quite large and heavy to withstand the internal pressure of the fuel plus any forces which might be experienced in case of a severe collision. It would also have to be attached to the vehicle by a comparably strong (and also heavy) structure in order to avoid becoming a lethal projectile itself in such instances. And if a collision were severe enough to rip open the tank, a serious explosion or at least a huge fireball could occur.
As in the case of sodium-sulfur batteries, the use of hydrogen as an energy storage medium at stationary sites would largely eliminate these problems. To begin with, hydrogen-oxygen fuel cells can be used in place of hydrogen-air. These operate at much higher efficiencies, but have not been considered for vehicles because of the extra need to carry an oxygen tank around as well as hydrogen. Secondly, the entire operation, like that of a sodium-sulfur battery installation, could be enclosed within a strong-walled structure to protect it from outside influences, including sabotage.
Such a facility would probably have the following layout. At one end of a central corridor there would be a water hydrolysis chamber, which would not have to be very large. Here direct current electricity coming from photovoltaic cells arrayed along the track structure and elsewhere would separate the water into its two components: hydrogen and oxygen. This would take place at two adequately separated electrodes, with the gases rising through the water and being collected in the tops of two chambers. The two gases would immediately be pumped into large storage tanks placed on opposite sides of the separator. These tanks would be moderately pressurized to reduce the volume, perhaps only by heavy weights placed on top of the containing chamber (this system has long been used for the storage of natural gas in urban areas). Small leaks from these tanks would not be serious, since the oxygen would only join that already in the air, while the hydrogen would rise rapidly and be quickly dispersed.
Also in the corridor between the two tanks or perhaps at an exterior location would be a battery of hydrogen-oxygen fuel cells, into which the two separated gases would be fed when power is needed. The ensuing direct current would then if it is to be consumed locally be fed to a converter of some type, perhaps a motor-generator set or a mercury-arc inverter, located either at the facility or elsewhere along the track, in order to transform it into the alternating current needed for the A.C. magnets of the LSMs used to propel the vehicles. From there it would be conducted to the power lines of the nearby track, while the water produced by the fuel cells would return to the separation chamber to be reused. If the energy is instead intended for transfer to some distant point, it would remain as high-voltage D.C. in order to reduce transmission losses.
3. Power Transmission.
For people living in Phoenix, nearby solar cell arrays could easily produce all the power they needed, plus a lot more. For the residents of Buffalo, on the other hand, the wintertime "lake effect" coming steadily off of unfrozen Lake Erie shrouds them in almost constant cloudiness. Thus we must find a way to transport the energy produced in one part of the country to other regions, with the distance to be covered perhaps being as far as from the Southwest to the Northeast.
A number of very serendipitous features of a solar-powered automated transportation system can easily make this feasible. To begin with, photovoltaic cells produce direct current. For large-scale applications like this, the collection array is made up of many separate cells. These can easily be wired together either in series or parallel, allowing us to produce virtually any voltage that we desire. Transmission losses for either A.C. or D.C. decline rapidly as the voltage goes up; thus the maximum feasible voltage would also be the optimum. Transmission losses in D.C. power lines are far lower than those for comparable A.C. voltages, allowing the use of conductors with only half the cross-sectional area (and therefore half the weight). Thus it would be logical to use the D.C. output of the solar cells directly for all long-distance transmission. This energy can then be used directly (perhaps with voltage controllers) to charge sodium-sulfur batteries or to produce hydrogen and oxygen for fuel cells at the energy storage facilities at the receiving end of the line.
In the case of InTranSys, the optimum design of the cable-tensioned concrete track structure includes a continuous, enclosed and unused chamber at the top. This would be an ideal site for the location of high-voltage transmission lines. The sturdy concrete walls will protect the conductors from damage from outside. The equally sturdy bottom of this chamber which also forms the top of the open channel along which the vehicle carriers travel will separate the D.C. conductors from the A.C. ones needed to power the moving LSM magnets. This design also has the significant advantage that both those power lines carrying electricity from solar collectors to storage facilities and those lines carrying electricity from the A.C. converters to the vehicles on the track will be completely protected from all adverse weather conditions. This means that power outages like the ones which frequently plague conventional open-air transmission lines such as the ice storm which completely paralyzed much of Quebec for many days just a few years ago can be totally eliminated from future automated transportation systems. Even a terrorists bomb which destroyed a given section of track would have a very limited effect, since interconnecting lines in all other branches of the overall network would continue to supply power to all but the immediately affected segment.
The next question is: should conventional wire conductors or superconducting materials be used to transmit this electrical energy? The ultimate goal of superconductor researchers is to produce a room-temperature superconducting material. If they succeed, so much the better. But even if they dont, and refrigeration is needed to keep the conductors cold, InTranSyss closed chamber could still provide the ideal location. There would be plenty of room for whatever amounts of cooling coils and insulation are required. And the power to run any refrigeration units which might be needed is already at hand. This option could allow a variety of superconductors to be considered, and the relative abundance of the requisite materials could enter into the final decision. One advantage is that superconducting cables can be very small, thus reducing the amount of any scarce material needed.
Another advantage of the interconnected network design of InTranSys is that a melange of conducting materials could be employed, both conventional and superconducting, depending on the location. For example, short spur tracks or connecting links added to the overall system could employ conventional conductors, since the distance the power is transmitted would never be very great. At the same time, the main lines of the system, which cover much greater distances could use superconductors.
Last modified: November 27, 2000