A tandem solar cell architecture of silicon and germanium solar cells in a mechanical (stack like) arrangement is evaluated to increase the efficiency of light absorption in the far infrared region from 1107 nm to 1907 nm wavelength, which constitutes about 14.5% of the power intensity in the solar AM 1.5 spectrum. In this work, the technical feasibility of tandem solar cells is investigated. Here, we report on detailed electrical and optical simulations of this structure quantifying the various theoretical and practical loss mechanisms in the encapsulation, interfaces, and in the device and indicate that a relative efficiency improvement of 20% may be attainable with silicon and germanium solar cells in this configuration. The optical and electrical parameters for silicon and germanium simulation models were extracted from experimental devices and material vendors. The developed simulation models were validated by comparing the performance of stand-alone silicon and germanium solar cells with experimental devices reported in the literature.