This 1 Kw/M^2 is valid ONLY at the equator, at local apparent noon (from 11:15 to 12:15 each day), on a cloudless day, with a perfect absorber/reflector/transmitter/receiver/converter. (In space.)
No matter how you play with your umbers, solar power is 40-75% more expensive than conventional. Even using the unreasonable assumptions of this advertisement.
Solar power is more expensive, in most cases, than gas/coal/hydro/nuke.
It is much cheaper the further one gets from the installed power line base. A full blown home solar system has a much cheaper installation cost than running a even couple miles of power lines, and is essentially free to operate.
As fuel costs continue to rise solar becomes more cost effective. It isn’t there yet, but will be fairly soon.