Biomass encompasses a wide variety of fuel sources from wood, vegetation, sewage, algae, etc. which gives a lot of promise to the Stirling Engine as the price of fossil fuels increase.  Having a power and heat source that is capable of utilizing multiple sources of fuel could allow for cheaper, cleaner, and more efficient use of our local resources.

In areas where sunlight is in abundance, there is a lot of promise using Stirling Engines on mirrored dishes that focus the solar energy onto the hot side of the engine to create the driving force.

Using a Stirling Engine with geothermal energy sources has a lot of promise to utilize the energy source more efficiently.  Some heat engines are designed to operate on very low temperature differentials, so as desinges are improved lower temperature thermal resources' may become viable for energy production.

NASA is developing a Stirling Engine using nuclear power for powering satellites and other deep space missions.