Twelve and a half square miles of solar panels --> Produces 1/3 the power of one coal burning power plant.

Two Large Solar Plants Planned in California

That means to get the same output from a solar power facility as you would from a coal plant, that inhabits a few acres, you would need a facility in the neighborhood of 35 square miles.  That's a lot of space to have set aside for generating power.

What is the environmental impact comparison between the two?

The quote at the very end of the article is telling:

Neither approaches the economy of fossil-fuel burning plants, said Ms. Zerwer, the spokeswoman for Pacific Gas & Electric. But they will be competitive with wind power and with power from solar thermal plants, which are equipped with mirrors that use the sun’s heat to boil water into steam. And prices will fall, she predicted.

Then why build them?