photovoltaic re-exposure

[DrMrLordX]

I have a general grasp of how photovoltaic cells work (and only a general one). You expose a PV cell to sunlight, and the following happens:

1). Most of the sunlight is reflected in some direction
2). Some of the sunlight is absorbed by materials in the cell/cell assembly and converted to heat which does nothing but make things hot.
3). A certain percentage of the sunlight stimulates production of electric voltage. Most commercially-available cells seem to be between 10-20% efficiency, with a few cells reaching as high as 40% using 20% efficient PV material plus lenses/mirrors/other optics for focusing purposes.

Now, what I'd like to know is, how much of that sunlight is absorbed and converted to heat? And if you could direct all the solar radiation reflected from the PV surface onto another identical PV cell, how much of the reflected radiation could produce voltage in the second cell? I would assume that PV cells absorb specific wavelengths better than others, so light that has already reached a PV cell might not be as useful for voltage production should it reach another PV cell.

 

[dogintub]

Originally posted by: DrMrLordX
And if you could direct all the solar radiation reflected from the PV surface onto another identical PV cell, how much of the reflected radiation could produce voltage in the second cell?

The light is scattered if not absorbed and couldn't be efficiently absorbed by another surface. I suppose you could collect some but it would be a diminishing return, probably the same effort could go only to improving optics and that would have a larger overall effect.

Originally posted by: DrMrLordX
I would assume that PV cells absorb specific wavelengths better than others, so light that has already reached a PV cell might not be as useful for voltage production should it reach another PV cell.

That is also probably true. The scattered light would be reduced in energy by the first partial absorption.

 

[CycloWizard]

Solar cells don't use heat to generate energy, so the material is selected such that when a photon hits it, it directly releases an electron. Maximizing the conversion of photons to electrons increases the efficiency, but it's not very clear how to do this as yet. There are currently efforts to develop materials utilizing multi-holes to release more than one electron per photon, but they are extremely crappy at this point (the one that I saw was only about 3% efficient IIRC, which is terrible).