A solar Stirling Engine takes advantage of the fact that concentrated sunlight is a fantastic heat source, and as such can be used to generate electricity more efficiently than photovoltaic solar panels
The Stirling Engine was developed in 1816 by Robert Stirling in order to offer an alternative to the frequently explosive early steam engines. Basically a closed cylinder containing a piston and helium, nitrogen or hydrogen gas is heated at one end by concentrated sunlight, and cooled at the other end by air or water.
More: How does a Stirling engine work?