A system (100) comprises a cryogenic engine (16) and a power generation apparatus, wherein the cryogenic engine and the power generation apparatus are coupled with each other to permit the cryogenic engine (16) and the power generation apparatus to work co-operatively with each other in a synergistic manner. The cryogenic engine (16) and the power generation apparatus are mechanically and optionally thermally coupled with each other so that the output means is shared between the cryogenic engine (16) and the power generation apparatus and that the two systems can be operated in the most power efficient manner and may also thermally interact to the potential advantage of both performance and economy.