In the Helianthos project, a cooperation of Shell Solar and Akzo nobel chemicals, roll-to-roll technology is being developed for cost competitive manufacturing of flexible PV modules based on thin film silicon. The resulting flexible lightweight PV modules allow for cost efficient integration and installation in PV systems. The manufacturing approach is based on the use of a temporary metal foil substrate which is removed in the course of the processing sequence and replaced by a commodity polymer carrier foil to obtain monolithically series-integrated PV modules. Laboratory cells and modules demonstrate the basic feasibility of the approach. Currently, a roll-to-roll R&D pilot line is being completed to demonstrate module manufacturing on kilometer-long foil substrates of 35 cm width.