This lead me to an interesting Google search around engine efficiency. I always knew that engines are imperfect engine transfer devices, but I didn't realize how much is lost.

Seems like in most scenarios you're getting at best 40% energy efficiency in gasoline engines and somewhere between 17% to 40% in steam engines.

Even at 17% efficiency using the sun to generate steam power seems to hold lots of potential. The trick will be to get it working at scale and able to produce a similar level of energy with the same or lower cost as existing technologies. May be a while yet, but it's an exciting time to teach your kids science as this is the kind of stuff that they'll probably see in mass later in life.

Source: http://en.wikipedia.org/wiki/Engine_efficiency