Thermographic methods are widely established to detect shunts in photovoltaic technologies. In all methods the cell has to be directly accessible to determine quantitative shunt values. In this manuscript a precise method is presented to determine shunt values in solar modules consisting of series connected bulk-heterojunction organic solar cells without the need to access the single cells separately. It will be shown that, although parallel resistances in organic solar cells show a strong dependence on the illumination intensity, the shunts that are detected using illuminated lock-in-thermography are strongly ohmic and therefore can be assigned a distinct ohm value. (c) 2014 Elsevier B.V. All rights reserved.