Regarding the concept of Sterling engines being "low power", this company would beg to differ.
http://cyclonepower.com/whe.html
They apparently have models capable of running on temperatures as low as 500°F. Their aim is more toward industrial / military applications, but they do have a modest 10 kWh model.
I've never used, nor seen one in action myself, but considering the topic at hand, I thought this might be interesting food for thought.
