Here are "already" two, maximum electric power:
a) Stirling Sunmachine: 3kW electric in cogeneration 10,5KW thermal max.
Presentation (German): https://www.econologie.com/forums/moteurs-st ... t5703.html
Datasheet (French): https://www.econologie.com/cogeneration- ... -3867.html
Info and doc: http://www.sunmachine.de/download.htm
They also have a solar model to discover here in video: https://www.econologie.com/moteur-stirli ... -3856.html
b) KWB: 1kW electric but, brilliant, it's an "SPM module" kit that can be integrated into an existing boiler (for the moment only for KWB brand boilers ... but ökofen being a shareholder this should happen for other boilers soon)
By integrating an SPM module into a KWB pellet boiler, the user will be able - from the renewable energy resource that is wood - to produce both heat and electricity!
Info and documents: http://www.stirlingpowermodule.com/