To study concentrator photovoltaic modules with GaInP/GaInAs/Ge triple-junction solar cells we used the measurement capabilities of a solar simulator accompanied by a computer simulation. The comparison of values of parameters for a module, Fresnel lens and triple-junction solar cell, obtained both experimentally and computed by means of the computer simulation, demonstrated good matching of results and high precision of calculations using the software. This allows to use both methods simultaneously to explain processes of radiation conversion in the system concentrator–solar cell and predict the values of module parameters under various external focusing conditions. The utilization of both methods revealed the impact of lateral currents on the total photo current of solar cells inside a module. For the system Fresnel lens–multi-junction solar cell we determined the possible cases of power loses associated with internal resistance of the cells. Output parameters of the module under varying spectrum of incoming radiation has been calculated using software.