Abstract: The ecological meaning of the thermodynamic concept “Exergy” is discussed and the applications of the maximum exergy principle and Darwin's theory of “Survival of the fittest” in the evolution of ecosystem are explored. The study indicated that the ecosystem is to evolve to the direction, in which the exergy of ecosystem is increasing and the system will continuously select the species that can contribute most to the maintenance or even growth of the exergy of the system. The exergy has the following advantages compared with the other thermodynamic concepts: 1)It is an energy term which is easily interpreted; 2)Exergy is easily computed in the model;3)It is directly related to Darwin's theory and the application of exergy has therefore an ecological interpretation; and 4)It is dependent on the environment but is not a variable state as entropy. These advantages make the exergy to be better used in ecology.

Key words: sunken solar greenhouse, soil wall, temperature, heat flux, thickness.