Ecological and Environmental Effects of Added Heat. — Possible environmental and ecologica effects include (l)the impact on the local flora and fauna of any significant increase in the experienced heat load caused by the rejection of waste heat at the receiving site and (2) “urban heat island” effects on the local atmosphere. Ecological effects can be evaluated by comparing energy losses from the receiving antenna with the energy environments characteristic of representative regions on Earth. To evaluate the possibility of a significant “heat island” effect, these losses can be compared with the energy consumption density for cities, on the basis that a significant heat island effect would be observed only if the energy loss rates were comparable to those experienced in cities where urban heat island effects have been suspected or observed. We have concluded that these environmental and ecological effects of heat are negligible. Thermal energy losses from the receiving antenna are very low in absolute terms, corresponding to mean heat losses in the range of 3 to 18 W/m2, depending on the size and efficiency of the receiver. More important, these energy losses are negligible when contrasted with the natural thermal energy flux occurring virtually everywhere on the surface of the Earth at any time of the year. Similarly, the loss is trivial when compared to the energy released by cities, and consequently there will be no urban heat island effect due to the presence of the receiver. The assumptions made and data supporting these conclusions are presented below. a. Receiving Antenna Heat Release A small fraction of the transmitted microwave power is absorbed in the atmosphere, and 90% of the remainder falls within the receiving antenna on Earth, which may vary from 3.85 to 7.5 km in radius. Assuming an 85 to 90% efficiency of rf-to-dc conversion, an energy loss totaling 5.6 to 8.4 x 108 watts will have to be dissipated at the receiving site, which corresponds to a mean heat loss in the range 3.22 and 18 W/m2, depending on size and efficiency. Power is not evenly distributed over the receiving antenna. Depending on the characteristics of the transmitter, the peak microwave power in the center of the beam could reach 330 W/m2, which corresponds to a peak heat loss of about 50 W/m2, assuming the lower conversion efficiency. The actual area of the heat transfer surfaces of the antenna has not been determined, but if the area is about 20% of the area covered by the antennas, exceedingly low heat transfer rates would be sufficient to dissipate the waste heat to the ambient environment. At this very low heat release per unit area natural air convection would obviate an environmental or ecological threat. b. Availability of Solar Energy The energy to be released from the antenna may be compared with the solar energy available at the surface of the Earth in latitudes from 20° to 60° N. This is equal to the solar energy available at the top of the atmosphere on a horizontal surface, less that absorbed in the atmosphere and that reflected back to space by cloud tops, and scattered by particles and other components of the atmosphere. Atmospheric losses and scattering from the atmosphere are extremely variable over the surface of the Earth, but average about 25% of the value of undepleted radiation. The latter varies
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