Hi Bobby R-
That exhaust driven alternator I showed may not be in production yet but would be great if it was. Let us know if you get a response from them.
I got interested when remembering that my turbochargers on heavy equipment that I owned were exhaust driven. There was a small oil line from the main engine to supply oil to its bearing. I am supposing because of the tremendous heat that regular sealed bearings would cook up and malfunction.
One could place gates in the exhaust flow that would shut off when the battery becomes charged and thus not lose any power turning stuff unneccessarily unlike our cars where we keep running belts and pulleys.
The steam option sounds fun too though. Let us know how that info develops for you.
Best