According to SolarReserve the plant would use an array of 15,000, 25 foot-wide, tilting mirrors which would direct sunlight to a solar collector sitting a top a 600 foot tower. Inside the collector would be molten salt. The mirrors would heat the salt to over 1,000 degrees Fahrenheit.
From energyboom.com & cnet.com
Image from power-technology.com via energyboom.com