Solar cells from crystalline silicon wafers have been dominating the photovoltaic market so far due to the availability and stability of c-Si and the decades of Si technology development which were leading to two orders of magnitude in cost reduction. However, conversion efficiencies are limited for single-junction c-Si devices and efficiencies exceeding 25% in production are hardly achievable. Therefore, it becomes increasingly important to find solutions how to increase performance by moving towards more advanced technologies. But at the same time such technologies may significantly benefit from building on the success of c-Si solar cell devices. The EU-funded project SiTaSol developed a next generation III-V/Si tandem solar cell with a target conversion efficiency of 30 %. It answered important questions for reaching low manufacturing costs and low environmental impact. III-V/Si solar cells are attractive not only for the PV power market but also for the growing market of mobile applications where solar cells are integrated into cars, wearable electronics, unmanned vehicles, or consumer devices to extend grid independent operation. Furthermore, the project leads the way to lower cost manufacturing of conventional GaAs based devices like LEDs, sensors, transistors, switches, and photodetectors which are the basis of growing markets for “Smart” technologies.