One of society’s most important goals for the coming years and decades is to reduce greenhouse gas (GHG) emissions. A successful energy transformation includes the switch from fossil fuels to sustainable energies. Hydrogen will play a key role in this as a versatile energy carrier. In the case of electricity and heat generation, decentralized generation without the emission of greenhouse gases will become much more important than it has been so far. Combined heat and power plants (CHP) operated with H2, will be used on a large scale. To enable our customers to switch from fossil fuels to hydrogen, Rolls-Royce Power Systems is developing a solution for the easy conversion of already installed mtu Series 4000 natural gas CHPs to run on 100% hydrogen. This paper provides an insight into the development of the conversion kit based on Series 4000 stationary natural gas engines. It explains how the key components mtu-turbocharger, injection valves as well as the engine electronics and control system were adapted for operation with 100% hydrogen. The combustion process was developed on a single-cylinder unit in such a way that the strict EU emission limits can be met without exhaust gas aftertreatment. The successful validation was carried out on a 12-cylinder full engine.