LonnieJohnson

60% efficiency
http://www.popularmechanics.com/science/earth/4243793.html That will change if Lonnie Johnson’s invention works. The Atlanta-based independent inventor of the Super Soaker squirt gun (a true technological milestone) says he can achieve a conversion efficiency rate that tops 60 percent with a new solid-state heat engine. It represents a breakthrough new way to turn heat into power.
 * 4,724,683, 2/16/1988, Johnson tube, a thermodynamic heat pump

A Stirling engine using air, StirlingEngine achieves 15% efficiency. The hydrogen based one achieves 30%. Parabolic trough systems combined with a turbine achieves 15%. With a 60% efficiency the unit area is reduced by 4 to achieve the same output power. See:

http://www.popularmechanics.com/science/earth/4243793.html That will change if Lonnie Johnson’s invention works. The Atlanta-based independent inventor of the Super Soaker squirt gun (a true technological milestone) says he can achieve a conversion efficiency rate that tops 60 percent with a new solid-state heat engine. It represents a breakthrough new way to turn heat into power.

patents by Lonnie Johnson
* http://www.patentstorm.us/patents/4724683/fulltext.html Johnson tube, a thermodynamic heat pump. * http://www.patentstorm.us/patents/6489049/fulltext.html Electrochemical conversion system