Via Jonathan Adler:
The [two new solar] plants will cover 12.5 square miles of central California with
solar panels, and in the middle of a sunny day will generate about 800
megawatts of power, roughly equal to the size of a large coal-burning
power plant or a small nuclear plant.
I don't know this exact location, but you can see from here, the best one can probably expect from central California is about 6 peak sun-hours per day (more explanation here). This means that even in a very good solar location, the plant will produce over the course of a year 25% (6/24) of nameplate capacity. This means that to actually replace a large coal-burning power plant, 50 square miles of solar panels would be required (assuming that one has a 100% efficient way to store power for non-sunny times, a technology that does not currently exist).