Much recent work on thermodynamic energy conversion efficiencies is here presented ab initio and from a unified point of view. New considerations are offered and previous work is analyzed in light of the unified presentation. The energy conversion processes discussed include, for example, the conversion into light in a laser or light-emitting diode and the direct or indirect conversion of solar radiation into work. The thermodynamic limiting efficiencies of these various processes are derived by applying simple balance equations to a generalized energy convertor. The new work includes the distinction between temperatures based on fluxes and temperatures ∂U/∂S based on standard thermodynamics, etc., and their application in the correct context. Also the use of standard entropy formulas is justified without relying on thermodynamic equilibrium and the results are then applied to nonequilibrium situations in energy conversion.

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Abstract— An energy conversion model descending from, and generalising, models due to BjoUrn, Calvin, Knox. Ross and others has been developed. It uses three sets of levels between which radiative, non‐radiative and storage transitions are possible. Maximisation of the rate of power storage with respect to the absorption threshold yields wavelengths of the order of 680 nm is in good agreement with the absorption peak of chlorophyll a. Departure from the experimental spectra, for example by the substitution of equivalent black‐body spectra, and passage to two sets of levels only, tends to destroy this agreement, which presents chlorophyll a as a materia! optimised through evolution for a maximum rate of power storage in day light. Various meteorological conditions are considered. The results found are not very sensitive to cloud cover. The simplified model for two sets of levels yields an interpretation in terms of transition probabilities of the parameters which occur in the simple solar cell theory. Both types of conversion are thus covered by the same theory. The model is also general enough to deal with photochemical or photovoltaic conversion in undersea conditions.