I recall reading about a Spanish solar plant that was storing extra heat from their grid in a salt mass, and using the stored heat to continue steam generation for the turbines will after the sun set.
Molten salt can store vast amounts of heat for many hours....long enough to boil water for a turbine at night.
A solar facility near Las Vegas uses a simlilar concept via a heat storing oily-gell material.
Andasol 1 & 2, in the Andalusian Sierra Nevada.
http://www.abb.com/cawp/seitp202/cfbd3e0344fc81dbc125754e004d7f2e.aspx
Each power plant has its own 50 hectare solar field containing 624 parabolic troughs arranged in 156 loops. The fields produce up to twice the thermal energy that can be absorbed by the plants’ steam turbines. The excess energy is stored in liquid salt tanks for up to seven hours, thereby ensuring a continuous and stable supply of electric power to the grid – even in the middle of the night.