Antenna states of the absorber particles

Let us consider these particle states in a radiant energy absorber, transitions between them result from the absorption of photons. The states of atomic particles or their groups, as well as energy transitions between them, are called "working" if they take part in performing work. It is known that solar energy conversions are not always working processes. The states of atomic particles and the energy transitions between them are said to be "antenna" ones if they take part in the absorption and emission of radiant energy without work production, i. e. in the photon reemission. Carnot cycles are examples of working processes, while cycles described below involving the photon reemission are examples of antenna processes.

It is clear that antenna and working states are equilibrium ones if cycles of the radiant energy conversion are not accompanied by entropy production, i. e. if it takes place along line LB on Fig. 9 with an efficiency from Eq. (5). Let us take their total amount to be 100%. Now assume that the conversion of radiant energy consists of reversible working processes with an efficiency цо from Eq. (2) for matter, with an efficiency цas from Eq. (5) for radiation and irreversible with an efficiency ци from Eq. (1) for irreversible antenna processes, i. e. that the conversion of radiant energy corresponds to line CEB. In this case, the ц-coordinates of all points belonging to the line CEB divided by ^ are equal to the fraction of working states, while 1-ц/^ is equal to the fraction of antenna non-equilibrium states.

Fig. 9 shows that the number of antenna non-equilibrium states in solar cells decreases as the efficiency ц grows along lines CE and CF. The isothermal growth of the efficiency ц implies that the total amount of antenna states remains constant, but certain antenna states have become equilibrium states and that reversible transitions that do not generate work have appeared. If the temperature dependence of ц is determined by experiment, Fig. 9 becomes in our opinion an effective tool for interpreting and modeling the paths along which work is performed by solar cells. We can consider Fig. 9 as the reversibility diagram of the conversion of solar heat into work.

image424

Fig. 9. Comparison of the efficiency ц l of Landsberg engine (the LB line) with the efficiencies of combined engines (the CEB, CFB lines). A difference between the efficiencies and цоцоци is that in the first case radiation working cycle is not a Carnot cycle. Lines CEB and CFB are practically coincide at temperatures used for operation of solar cells.

Obviously, knowledge of physical and chemical nature of antenna states of particles is important for revealing optimal schemes for radiant energy conversion. The question about technical realization of antenna states is not subject of this chapter. This is a material science problem. One only should note the model of absorber with antenna states does not contradict to thermodynamic laws and represents a way of solution of following aim: how to separate any given cycle into infinite number of infinitely small arbitrary cycles.

Updated: August 23, 2015 — 2:44 am