The basic Stirling engine is a device which converts heat into mechanical power by approximating the thermodynamic cycle known as the “Stirling cycle.” The cycle and engine, which bear his name, were invented by the Scottish Reverend Robert Stirling around 1816.

The first Stirling cycle engines delivered mechanical power through a rotating shaft which was connected to an internal crank mechanism attached to two moving pistons. These “kinematic” Stirling engines enjoyed initial success as an alternative to the inefficient and dangerous steam engines which were widely used at the time. However, improvements to steam engine safety and decreasing fuel costs meant the Stirling engine found no wider application. Ultimately, with the development of the Otto cycle engine (gasoline internal combustion engine) and Diesel cycle engine in the late 1800’s, the steam engine was relegated into a historical curiosity.

Throughout the twentieth century, various groups were attracted by a potential for very high efficiencies, quiet operation and heat input/fuel flexibility of the Stirling engine compared to other well established power generation technologies such as Otto cycle or Diesel cycle engines.

In 1964 William Beale, a professor of Mechanical Engineering at Ohio University in Athens, Ohio, invented the “free-piston” Stirling engine (FPSE) which eliminated the need for the complicated crank mechanism. Sunpower has successfully developed its FPSE technology into the current range of patented, state-of-the-art, highly efficient, low mass, reliable Stirling machines.