A solar furnace is a means of concentrating solar energy, normally by focussing one or more parabolic mirrors or by directing the reflected energy from multiple plane mirrors onto the same area (see http://en.wikipedia.org/wiki/Solar_furnace). 

This concentrated energy can be used directly, e.g. in a solar oven, or to heat the working fluid in an external combustion engine, such as a Stirling engine, a Cyclone engine, a steam engine or a turbine.  Mirrors can also be used to direct additional solar energy onto a photovoltaic (PV) array.

Mirrors are much cheaper, both financially and environmentally, than PV arrays, but there is a question as to whether an economical way of maintaining the focus of a mirror array on a pitching and rolling platform can be achieved.