As pegminer mentioned, you can use mirrors to concentrate the sunlight. The most popular example of this is the 11 MW PS10 station in Seville, Spain:
http://www.solarpaces.org/Tasks/Task1/PS10.HTM
There is a similar technology as well which does not rely on water to steam conversion, but rather just the simple fact that hot air rises. They heat up air at the base of the system, which rises through a tower and spins an electric turbine. You can read more about those here:
http://en.wikipedia.org/wiki/Solar_updraft_tower