Dr. Glaser. I will show some slides to help the flow of the discussion. Let us first examine the total amount of solar energy reaching the Earth. Perhaps the most important consideration is that solar energy is a diffuse form of energy which, in order to be converted on Earth, requires large areas to be covered with capital-intensive devices. At best we receive around midday 1 kilowatt per square meter, or about 1 horsepower per square yard. Furthermore, we have to contend with weather and we have to accept the night-and-day variation which prevails on our Earth. Therefore, if we wish to use solar energy on a large, worldwide scale, I propose that we seek another way of doing it—that is by using a satellite solar power station in synchronous orbit where sunlight is available to us nearly 24 hours a day. The objective of the satellite solar power station, or SSPS for short, is that it be able to provide power on Earth on a large scale and be cost-competitive, resource conserving, compatible with the environment and of benefit to society. Three technical considerations are involved: We have to learn how to convert the vast amount of solar energy available in space into electricity, how to beam the electricity back to Earth and then how to convert the beam to useful power on Earth. One possible way of doing this is the concept that the team of Arthur D. Little, Raytheon, Grumman, and Spectro Lab has been studying, that is the conversion of solar energy directly into electricity by a photovoltaic process, using solar cells. As illustrated, the satellite functions by using solar cells to convert the solar energy into electricity, conducting the electricity to microwave generators—which form part of a transmitting antenna—where it is converted into microwaves which are then beamed back to Earth where they can be effectively and safely reconverted directly into electricity. We are considering a large satellite because of the geometric requirements of a transmitting antenna capable of directing a low-density beam to the receiving antenna back on Earth. A typical output of power on the ground is about 5,000 megawatts, therefore, for our studies we developed baseline SSPS design with this power output. Now, why should we actually go into space? Why should we consider this kind of large project? The primary advantages of power from space are that even if we were to place solar energy conversion devices in a region with copious sunshine, we would need 6 to 10 times the area on Earth. Furthermore we have a very favorable operating environment in space; we have more options for siting the receiving antenna on land or offshore; we have the potential with one satellite to generate very substantial power for use on Earth. And finally, such a project allows us to industrialize space, building on the first step that this Nation is taking through its commitment to the Space Shuttle. A number of other methods are also feasible for converting solar energy for use on Earth. You will be hearing more about the thermalelectric conversion, for example—I will be discussing, therefore, primarily photovoltaic energy conversion. There are reasons why solar cells are of interest—they have been widely used in the space program, they can be improved to have an adequate efficiency to do the job as we foresee it, they can be mass produced, they operate passively in their operation, and they allow the design of the SSPS to be reasonably flexible.
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