The Mojave sees a lot less sunlight at a lot less strength than an array in space would. An array in space can also beam the energy directly to a target point on the Earth, instead of having to transmit it along the surface, or relay it through orbiting relay satellites.

That being said, like Larry, I find it hard to believe that a Lunar facility would be more practical and economical than one built in geosynchronous orbit.

The technology would be quite safe. I did some work on concepts years ago, and a recieving antenna could be a relatively open flat mesh mounted on towers, like a net covering many acres many feet above the ground. Obviously, the area underneath would be shielded from the microwaves, and with the open mesh allowing in light, could actually be used for grazing or growing crops. I have also seen concepts for such large, flat arrays over bodies of water if land space is at a premium. If spread over a wide enough area, the microwave beam wouldn't even harm birds flying through it.