E nergy sources are at the core driving force in most sciences. Photosynthesis drives the growth of plants, nuclear energy sources drive the evolution of stars, and chemical energy drives chemical reactions. Better energy sources may stimulate economic growth and may help to reduce the pollution of the environment. Therefore, finding new sources of energy and efficient energy conversion has been an important research topic for a long time. In recent years, energy efficient forcing of nonlinear systems was studied systematically [1][2][3][4]. It was found that nonlinear dynamical systems react most sensitively to perturbations that complement the natural dynamics of the system [1]. In this case there is a perfect impedance match [2] and the energy transfer is most effective. In quantum systems as well, the energy transfer is most effective if the forcing function matches the spontaneous radiation of the system [3][4][5]. The most important application in Condensed Matter Physics are quantum dot transistors with extremely low power consumption [6,7].A topic that has received much less attention is the extraction of power from dynamical systems. Power generators such as wind mills, steam engines, and car engines extract mechanical energy from fluids. They can extract a large fraction of the energy stored in coherent patterns, whereas only a much smaller fraction can be extracted from less coherent motion such as a turbulent flow.If the wind is steady, wind farms are most efficient in converting energy of the air into electrical energy. The efficiency is much less for wind gusts, and the energy stored in the irregular microscopic motion of the gas molecules is not extracted [8 -11].The energy of a system is due to coherent and irregular motion, ranging from large convection cells to molecular chaos. Heat, or more precisely, thermal energy, is the part of energy due to irregular motion. Energy stored in irregular motion is hard to retrieve, because most energy extraction processes require knowledge about the current state of the system and its immediate future. Hence, energy stored in molecular chaos is generally considered to be thermal energy. In the following we divide energy into two parts, thermal energy and the rest, which we call coherent energy or extractable energy. The distinction between thermal energy and extractable energy depends on the given information about the state of the system and the quality of forecasting algorithms.This can be illustrated with a simple thought experiment. We consider a 1-cm 3 container with one gas atom. It is assumed that the container walls are movable as in a piston, have a rough, irregular surface, and do not conduct heat. If the position of the atom is known with uncertainty x, for instance x ϭ 1 mm, the size of container is rapidly reduced around the atom to a volume of size x 3 . Finally, the container is slowly expanded to its original volume while the atom is bouncing against the inside