Exergy
![Higher exergy content tends to mean higher energy prices. Here the costs of heating (vertical axis) are compared with the exergy content of different energy carriers (horizontal axis) in Finland. Energy carriers included are district heating (D), ground-source heat pump (G), exhaust air heat pump (A), bioenergy meaning firewood (B), heating oil (O) and direct electric heating (E). Red dots and trend line indicates energy prices for consumers, blue dots and trend line indicates total price for consumers including capital expenditure for the heating system. [20]](/uploads/202501/12/Cost_and_exergy_for_heating_energy_in_Finland2814.jpg)
In thermodynamics, the exergy of a system is the maximum useful work possible during a process that brings the system into equilibrium with a heat reservoir. When the surroundings are the reservoir, exergy is the potential of a system to cause a change as it achieves equilibrium with its environment. Exergy is the energy that is available to be used. After the system and surroundings reach equilibrium, the exergy is zero. Determining exergy was also the first goal of thermodynamics. The term "exergy" was coined in 1956 by Zoran Rant (1904–1972) by using the Greek ex and ergon meaning "from work", but the concept was developed by J. Willard Gibbs in 1873.