I am not an expert but this is what I understand after researching this on and off for quite some time (10 years): Stirling engines are not great for uses in cars and other applications where you want to regulate the output on demand. The nature of the engine is such, that in practice it will probably lose a great deal of energy with heat loss, heat transfer etc. Most of the engines require maintenance because of the inner atmosphere (the gas used for transfer). It is and was used rather to supply a constant output with a regulated heat input. That is why it is suitable for solar applications and waste heat generators, for which it has been used (on a small scale) for some time. It is not used in large applications, because apparently you get better efficiency with CCGT (combined cycle gas turbine). Generally, I've seen engineers use steam turbines where one would imagine a stirling engine. I have no idea why, but I imagine they have a good reason for that (cost, maintenance, input and output regulation etc.). Due to the nature of the engine, I have allways dreamed of a stirling powered by biomass and this year I have found two projects where this is done: http://www.okofen-e.com/de/pellematic_smart_e/ http://www.microgen-engine.com/buy-engage/ Both use a sterling engine from the same company. One costs around 23000 Euro, the other 11000 Euro. They use waste heat from the fireplace. One has a buffer tank which is used to store warm water, runs on pellets and is automated. The other is just a fireplace. The advantage is that the heat that is not used by the engine is used to heat the house and water. I am not sure how well these will work in the long run and what the maintenance costs will be, but they bassically represent what a sterling engine is suitable for (collecting waste heat and converting it into energy).