Volvo Construction Equipment is one of the leading construction machinery manufacturers in the world. To stay amongst the leaders, research and development projects for new technologies are crucial. The most important path of development today is the reduction of emissions produced by these heavy duty vehicles. To tackle this challenge, several technologies are already used in industry. One example are hybrid machines that combine a conventional diesel engine with batteries, resulting in reduced engine size and pollutants. Another option are full battery-electric vehicles, which can reduce the on-site emissions to zero. The electrochemical processes within batteries are however comparable slow and result in long recharge times. A new focus of development within the industry are hybrid systems combining fuel cells and batteries. Since hydrogen can be refueled almost as fast as convenient fuel, it solves the issue of long recharge times. Additionally, the reaction is emission free, since there is no combustion process and the only byproduct that is emitted from the fuel cell is chemically clean water. This thesis aims to propose an architecture and packaging solution to replace the diesel engine in a large size wheel loader with a fuel cell power system. This also includes all respective auxiliary systems, i.e. energy storage, cooling and electric systems. Achieving the same performance as a conventional large size wheel loader as well as keeping the spatial envelope the same are the main objectives of this work. To achieve these goals, an extensive study on the most common drive cycles is carried out to understand the power demand of the machine. After the selection of an energy storage system based on a MATLAB simulation script, a cooling system is modelled and scaled to fulfill the operating requirements of the different components. Eventually, all systems are modeled and installed into the wheel loader in CATIA V5. The study showed, that the new system architecture of the vehicle can be fitted into the existing engine bay with a slight extension of the rear frame and hood. Two power optimized batteries are combined with one fuel cell. Hydrogen tanks with a filling volume of 478 [L] can be installed in the machine, covering 50% of the customer population curve without degradation of performance. This includes one refill of the wheel loader during the day. The performance parameters match the conventional machine up to a high degree, concluding that the conversion of a large size wheel loader into a fuel cell powered wheel loader is feasible.