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Figure 7. Solar Power Satellites Can Be Installed on the Necessary SCALE Figure 8 shows again the historical cost trend for electric power in the United States and also a band of extrapolation between escalation levels of five and fifteen percent per year. It is probable that this band contains the future electrical energy trend. The predicted price for electric power from solar power satellites is also shown, along with a band to allow for uncertainties. Note that in the 1990's there is good probability that electric energy from solar power satellites may be lower in cost than energy from conventional sources. A properly maintained solar power satellite should have an almost indefinite life. After amortization of the purchase price the absence of fuel costs may allow an energy price of approximately 1¢ per kilowatt hour. Thus the SPS energy price trend is downwards.
The cost of electrical energy from solar power satellites was estimated by investigating contributing factors to this cost such as the cost of ground receivers, the cost of the satellite hardware itself, the cost of transporting this equipment to space, and the cost of transmission of the electrical energy overland from the receiving point and its distribution to the ultimate users.
Ideally we should have solar power satellites today, but of course we cannot. A development phase remains ahead. Our studies have indicated however that expeditious development could lead to initial operation in the early 1990's; if solar power satellites were then placed in serial production, by the year 2000 they could be contributing nearly half of our current electric energy consumption. The use of electrical energy within the United States increased by over 6% in 1976. Shown in Figure 9 is a band of estimates of future electricity utilization. Serial construction of solar power satellites using four to six orbital construction bases could allow solar power satellites to become our primary energy source,
Preliminary investigations of solar power satellite receiver siting have indicated that these receivers can be placed relatively near their demand points, as shown in Figure 10. Hence, solar power satellites are not a regional energy solution, such as ground solar power which clearly best performs in the southwest, or ocean thermal energy conversion which is probably best off the southeastern United States. The 200 antennas shown here would be adequate for an output of approximately one million megawatts or about twice the current U.S. generating capacity.
(POWER SATELLITES ARE NOT A REGIONAL SOLUTION)
- RECEIVING ANTENNA
(200 SHOWN - 1,000,000 MW CAPACITY:
TWICE CURRENT U.S. CAPACITY)
Figure 10. Solar Power Satellites Deliver Energy to the Right LOCATIONS
Table 4 discusses environmental factors relative to solar power satellites. SPS studies have indicated that solar power satellites may have the lowest environmental impact of any potential new energy solution. The land area requirements for the ground receivers appear large; however, the land area required for a SPS is smaller than that required to strip mine the coal to produce the electrical energy which such a satellite can produce in only 20 years of operation.
Table 4. Solar Power Satellites Will Have MINIMAL ENVIRONMENTAL IMPACT
· RADIATES WASTE HEAT OF POWER GENERATION TO SPACE, NOT TO THE ENVIRONMENT.
*LAND AREA REQUIREMENTS ARE COMPARABLE TO OTHER SYSTEMS; EARTH RECEIVERS
THE MICROWAVE BEAM WILL BE SAFE. AT THE PERIMETER OF THE EARTH RECEIVING AREA,
CONTRIBUTION TO AIR POLLUTION IS ROCKET EXHAUST, WHICH IS PRIMARILY WATER,
Criticisms of the solar power satellite concept have centered on the microwave beam which would be used to transmit energy from space to the ground. However, it appears this beam can be made completely safe.
Figure 11 illustrates a cross section of such a beam which carries 5.9 million kilowatts. At the center of the beam the strength is approximately 23 milliwatts per square centimeter, about one quarter of the strength of desert sunshine. Approximately half way from the center of the ground receiver to its edge the beam strength has fallen to 10 milliwatts per square centimeter (the current U.S. microwave exposure standard). Nearer the edge the signal strength has fallen to 5 milliwatts per square centimeter, the current standard for microwave oven leakage. At the edge of the receiving array, where it is no longer economically practical to install receiving antennas, the signal level is at 1 milliwatt per square centimeter or 1/10 of the U.S. continuous exposure standard. A fence to exclude the general public is shown 8/10 of a mile from the receiver edge. At this fence, the signal level of the beam from space will be 1/10 of a milliwatt per square centimeter or 1/100 of the U.S. microwave exposure standard. There will be some additional peaking, or concentrations, of microwave energy in rings surrounding the ground receiver. However, these peaks are quite weak and never exceed the level at the fence. Consequently, people in these regions would not be exposed to high microwave levels and would in fact probably encounter higher microwave levels from other electronic devices which they use in their normal day to day activities. Aircraft would probably be routed around these microwave beams.
The seven factors described above thus contribute to the overall suitability of solar power satellites as a national energy solution.
Development and implementation of a new clean energy source suitable for perhaps centuries of utilization will not come lightly in terms of either human effort or dollars. To put this in perspective consider these recent energy costs: In 1976 the United States spent nearly $23 billion for new electric power plants, overland transmission, etc., the total price for the electricity consumed within the United States was approximately $55 billion and, as previously stated, $45 billion was sent overseas in 1977. A national energy solution can therefore be expected to be relatively expensive.
In the lower portion of Figure 12 are repeated the cost trends from Figure 8, showing the crossover point where, after approximately the mid 1990's, electric energy from solar power satellites becomes lower in cost (with a decreasing trend). Above this SPS line are dollars which might be spent if solar power satellites are not developed. The total in this shaded area is well over one trillion dolars for the time period 1995 to 2025. The total cost to not develop satellite solar power is greater than the cost to develop it.
Figure 12. What Can a "National Energy Solution" be Expected to Cost?