In this paper, energy consumption by the mankind is considered as a global process within the system of ‘Sun-Earth-cosmic environment’. The upper limit for the energy consumption rate is estimated, provided that the thermodynamic equilibrium in this system is retained. This viewpoint leads to the following principles of energy consumption: (i) the energy should be consumed from the renewable sources only; (ii) the amount of the consumed energy should not exceed the amount of energy coming to the Earth. Three major sources of the renewable energy are considered: a direct incoming solar irradiation, a chemical energy due to products of photosynthesis and, finally, an outgoing infrared (IR) radiation from the Earth as a heated body. It is shown that only the first source gives the most effective way of energy consumption from the viewpoint of the global energy conversion. The ranges of materials suitable for construction of energy converters from the last source are briefly reviewed. It is discussed that the proper use of the outgoing IR radiation on the large scale can be helpful in controlling the climate changes. It is shown that the energy consumption rate which meets the global thermodynamic balance and expected technical facilities cannot exceed a limit of 10¹⁴W, which is approximately an order higher of the contemporary rate of energy consumption by the mankind. The conclusion is made that we should learn how to restrict the energy consumption rate in the near future.

thermodynamic balance, renewable energy; consumption limit, IR radiation, -conjugated chromophores, donor–acceptor charge transfer chromophores