Equipment to generate themicrowaves is therefore inexpensive and readily available, though higher frequencies have been proposed as well. It could be designed to let light through, so that crops, or even solar panels, could be placed underneath it. The amount of power available to consumers from one such SPS is 5 billion watts. The US standard for industrial exposure to microwaves is 10 milliwatts per square centimeter, while up to 5 milliwatts per square centimeter are allowed to leak from microwave ovens. US standards are based on heating effects.
Stricter standards are in effect in some countries.
Nevertheless, even the peak of the beam is not exactly a death ray. Underneath the rectenna, microwave levels are practically nil. The reason that the SPS must be so large has to do with the physics of power beaming. The smalle rthe transmitter array, the larger the angle of divergence of the transmitted beam. A highly divergent beam will spread out over a great deal of land area, and may be too weak to activate the rectenna.