Optical modelling of one folded tandem solar cell and four types of stacked tandem solar cells has been performed, using the finite element method and the transfer matrix method for the folded cell and the stacked cells, respectively. The results are analysed by comparing upper limits for short circuit currents and power conversion efficiencies. In the case of serial connected tandems all of the five cell types may be compared, and we find that the folded cells are comparable to stacked tandem cells in terms of currents and power conversion efficiencies.