It has been shown that in the case of multi-junction PV
arrays with a non-uniform spectral distribution of light, the
optimal location to split the spectrum cannot be calculated
using detailed balance methods only. The optical
efficiencies of the system need to be taken into account in
order to assure that the optimization is accurate.
We have also shown that any combination of diffraction
grating and band gaps for a 2 cell solar array can only
slightly beat the single cell solar cell optimal efficiency.
This efficiency is also optimistic in that ideal diffraction
gratings are not physical and a real diffraction grating
would introduce more inefficiency. However, we also
believe that because the diffraction grating has the same
effect on efficiency whether more band gaps are used or
not, that more cells could be used to raise the efficiency.