In this paper we present a methodology that uses the detailed balance method to determine the optimum bandgap combination of III-V triple-junction solar cells for the highest yearly energy production. As an example of the methodology, we analyze two geographical locations on Earth with distinct spectral conditions. For these places the monthly average of the measured aerosol optical depth and the precipitable water are used to calculate direct solar spectra with a discretisation of one spectrum per hour. The model is used to analyze the spectral sensitivity of the bandgap design of four practical III-V triple-junction solar cell structures. Furthermore, the ideal bandgap combination for a maximal energy harvest is calculated for each location. It is shown that the metamorphic solar cell structure of Ga(0.35)In(0.65)P/Ga(0.83)In(0.17)As/Ge with transparencies optimized for the standard AM1.5d reference spectrum leads to the highest energy harvesting efficiencies and shows the lowest spectral sensitivity. The standard lattice-matched structure of Ga(0.50)In(0.50)P/Ga(0.99)In(0.01)As/Ge shows the highest spectral sensitivity with up to 10%(rel) difference in the yearly energy harvesting. (C) 2010 Elsevier B.V. All rights reserved.