The selection and assessment of single-photon detection modules is a crucial problem in satellite-based QKD systems. The system's overall efficiency, secure key rate and quantum bit error rate are all significantly influenced by single-photon detection modules. There is a knowledge gap about the practical performance of commercially available single-photon detectors because existing research frequently relies on theoretical characteristics. This paper introduces a study on the effect of the parameters of three commercial single photon detection modules from ID Quantique company: ID Qube, ID100, and ID281 on certain Bennett-Brassard 1984 protocol parameters such as secure key rate, mean photon number per pulse, quantum bit error rate, link efficiency and zenith angle with the presence of link and geometrical losses for a downlink geostationary satellite. The study accounts for link and geometrical losses, zenith angle, and mean photon number per pulse. Results indicate that the ID281 detector outperforms the other two in maintaining a better secure key rate and quantum bit error rate, while ID100 shows superior performance in shorter wavelength ranges suitable for downlink operations. The findings suggest that global quantum key distribution coverage is achievable using geostationary satellites. To the best of our knowledge, there has been no prior study that has introduced using real parameters of commercial SPDMs to evaluate secure key rate for quantum key distribution systems based on downlink geostationary satellite
