Trolleybus systems may be a sustainable and cheap alternative to diesel and battery buses. However, to improve sustainablity, the trolleybus system must be powered by renewable energy sources. In this work, a case study on the Arnhem trolleybus grid is performed. First the bus power demands and bus traffic are constructed for the whole system, afterwards Photovoltaics and wind energy sources assited by ESS are sized to investigate the effects on renewable power utilization. It was found that for the Arnhem trolleybus system, a centralized approach with equal shares PV (51%, 4.3 MWp) and wind (49%, 1.75 MWp) and diurnal energy storage (5MWh - 10MWh) can provide a 72% to 78% of the total trolleybus load. This system will reduce the CO2 emissions by 80% over a 30-year lifespan.