Disadvantages

The biggest disadvantage of the Stirling engine is that the start is so complicated that it is not applied in vehicles such as cars and trucks. There are also technical problems to be solved, regarding the sealing system that prevents leakage of fluid, especially when it is used inert gases as helium and hydrogen, because it’s very difficult to set under high pressure without escape to the outside.

Moreover, as these engines are unknown technology, the costly acquisition and maintenance is  still high.

However an improved Stirling engine called sonic motor (efficiency 18%), is under consideration to replace thermoelectric generators (7% efficiency), currently in use in spacecrafts.