Photovoltaic energy generation is envisaged as an efficient, natural and valuable energy source not only for outdoor but also for indoor applications, even if it is often difficult to give an adequate description of the indoor illumination conditions, and till now no (international) norms regulate the characterization of solar cells under the particular indoor conditions. In this work commercially available photovoltaic modules have been measured under artificial light conditions using an appositely designed experimental set-up, and under mixed natural/artificial illumination in real indoor conditions. These modules are based on completely different physical and chemical concepts, from semiconducting amorphous p-i-n junctions to photoelectrochemical cells based on TiO2 nano-particles, to semiconducting polymers, to crystalline silicon micro-spheres. Aim of this work is to compare their performances in view of possible indoor applications for low-power devices. (c) 2012 Elsevier Ltd. All rights reserved.