A few years back some car makers were looking at steam engines in view of proposed increased emissions; no doubt their lawyers and lobbying prevented the increase. The Stirling engine link I gave mentions the vast improvements in the burners (from CH boilers mainly) giving very low emissions. As a steam engine is external combustion also, the same applies.
There is no reason not to use Stirling or steam engines in slow moving town and city utility vehicles like: buses, delivery trucks used by utility companies, etc.
A Google will bring up lots on Stirling and steam engines. Lots of work is being done on Stirling engines, with many models readily for sale.
Stirling and steam engines cannot give instant power, giving quick acceleration, as the internal combustion engines can. This can be overcome by having a Stirling/electric or air motor hybrid. The electric or air motor is only used to assist in acceleration above a certain rate. Hybrid technology is here with Honda, Toyota and now Ford.
The Stirling is imminent to use in vehicles and Combined Heat and Power (CHP). Many points keep it from vehicle use: the industry is geared up for the internal combustion engines, no energy crisis driving up fuel costs (AMC made a Stirling engine car in the 1970s and were about to produce it when the fuel crisis waned) and exhaust emissions have not yet been lowered enough to preclude the internal combustion engine.
Some people want energy autonomous homes demanding little from the environment. The Vales attempted this with partial success. The problem is generating enough electricity and storing it. It would be simpler to:
- Construct a house that requires minimum energy demands. Superinsulate it with no thermal bridges, triple glazing and make it air tight, then concentrate on producing and storing solar hot water for DHW and CH (hopefully heating needs will be zero to minimal).
- Have minimal electrical use by using electrical appliances that consume as little power as possible, they are available, and use cheaper, and cleaner, to run gas appliances where possible (gas ovens and tumble dryers instead of electric, washing machines that take in hot water rather than heat it itself, and the likes).
This is a far more cost effective approach for a new build, or full renovation than trying to generate electricity.
The solar closets et al, are good retrofits to existing homes with some added insulation points, as: triple glazing or double with low "e" glass, make the house as air tight as possible, draught proof the windows and doors, put over 1 foot insulation in the loft, install porches on outside doors, etc.
The more a house is insulated and air-tight the less you need to generate heat.