In the framework of the FAE "Fotovoltaico ad Alta Efficienza" ("High Efficiency Photovoltaic") Research Project (PO FESR Sicilia 2007/2013 4.1.1.1), we have performed electrical and optical characterizations of commercial InGaP/InGaAs/Ge triple-junction solar cells (1 cm2) mounted on a prototype HCPV module, installed in Palermo (Italy). This system uses a reflective optics based on rectangular off-axis parabolic mirror with aperture 45×45 cm2 leading to a geometrical concentration ratio of 2025. In this study, we report the I-V curve measured under incident power of about 700 W/m2 resulting in an electrical power at maximum point (PMP) of 41.4 W. We also investigated the optical properties by the electroluminescence (EL) spectra of the top (InGaP) and middle (InGaAs) subcells. From the analysis of the experimental data we extracted the bandgap energies of these III-V semiconductors in the range 305÷385 K.