11.1.5.5 Heating of the Atmosphere by the Rectenna Waste Heat Heating effects of the atmosphere by the rectenna will decrease with higher latitudes because nearly the same amount of power is distributed over a larger area. In the following we compare the waste heat density for 40° and 60° latitude. The rectenna areas have already been calculated in section II. 1.4. For reasons of simplicity we assume equal losses for all latitudes. So the overall waste heat for one 5 GW rectenna is approximately 790 MW. This results from the conversion losses and the grid interfacing losses. For a 40° rectenna the waste heat is distri- 2 buted over 113 km . This results in a waste heat density of 6.99 W/m^. The waste power density of a 60° rectenna is 3.45 W/m^. A comparison with the average insolation data (fig. 1.7) shows that the waste heat remains below 4.5 % in both cases. We do not expect perceptible weather changes due to the total waste heat of a rectenna. The differences between 40° and 60° appear to be insignificant. II.1.5.6 Radio Frequency Disturbances by the Microwave Beam Out of the three categories of RFI, - direct RFI at 2.45 GHz or harmonics thereof, - mutual interference with geosynchronous services, and - RFI as a result of ionospheric excitation, only the latter might change with higher latitudes. The reason for this kind of RFI is ionospheric excitation by microwave power as reported in part I of this study. With a lower angle of incidence of the microwave beam on the ionosphere the total number of electron - excitations is increased.One can estimate an increase of electron temperature of approximately 45 % of a beam directed towards a 60° latitude rectenna compared with a 50° rectenna. Radio communications which depend on properties of the natural ionosphere might be increasingly affected. It should be noticed, however, that the understanding of the micro- wave/ionosphere interactions is currently in its infancy and many estimates are speculative.
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