Finally a reasonable and informative comment. Also a retrodirective transmitting array can be used to stay targeted automatically using a pilot signal. Additionally the beam can be defocused if the pilot signal is lost.
Here is an analogy.
If a I have a flashlight that puts out a million watts, it would burn you if you stood a foot in front of it right? Now what if you were standing a mile away, you would be receiving much less power and you would be perfectly safe. But the light energy doesn't just disappear, it is spread across a large area. Now, if you build a large collector several miles wide you would absorb all that light. Assuming nothing in between the flashlight and the receiver to block/absorb energy, then you just transmitted 1 million watts a distance of 1 mile to a receiver and it is perfectly safe to stand in the beam because the energy density is so low.
This SPS works the same way. The receiving power density would be less the limits set by the government for exposure to electromagnetic radiation. A large rectenna would collect all that energy over a wide area at >85% efficiency. Walking in the low power density beam is harmless.
Exposure limits: http://www.astrosurf.com/luxorion/Radio/table-power-field.gif
Notice the limit is lower at about the point that a half wavelength is about the same height as a human...
You answered your own question. It cant produce a narrow beam, which is the same reason why it cant cook anybody. You have a large diameter beam (kilometers in diameter) at a low power density (similar to the energy density of sunlight) and a huge rectenna array (say, covering many farmers fields by being upheld on stilts). Yes, this works. I have studied it. Smarter people than you or I have studied it. I swear to god NOBODY on slashdot understands power density. Every frikin time this subject comes up its always "its a weapon!"
Now economic viability and possible electronic interference you can go and argue all you want.
I have a theory that it's impossible to prove anything, but I can't prove it.