» "Available energy" redirects here. For the meaning of the term in particle collisions, see Available energy (particle collision). In thermodynamics, the exergy of a system's the maximum work possible during a process that brings the system into equilibrium with a heat reservoir. When the surroundings are the reservoir, exergy's the potential of a system to cause a change as it achieves equilibrium with its environment. Exergy's then the energy that's available to be used. After the system and… (More on Exergy)