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In your question you already have the answer, photovoltaic cells. They are not heat engines but change the black body electromagnetic radiation of the sun to electricity. Of course this depends on the fact that the black body temperatures of the cells are much smaller than the black body temperatures coming from the sun. As @ThePhoton says , note the ...


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The gray model results from starting with the assumption that we have a plane-parallel slab: The light ray from the source (i.e., the star's atmosphere) travels at some angle, $\theta$, from normal, $z=0$. Since the light is coming from an angle, we need to account for that by modifying the radiative transfer equation to have a vertical optical depth, ...


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The cross section $\sigma$ is related to the absorption coefficient $\alpha$ by: $$ \sigma = \frac{\alpha}{N} $$ where $N$ is the number density of the scattering medium i.e. the number of particles per unit volume. This is described in more detail in the Wikipedia article on the absorption cross section. If you want $\alpha$ in units of cm$^{-1}$ you ...



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