I'd be extremely shocked if this kind of technology could compete with electrical energy storage given the advances in battery, etc., technology that we will probably see over the next couple decades. Sounds like another one of DARPA's "let's look at this just for fun" programs.

Also, what does it mean when it lists "solar" along with the hydrocarbon fuels that this thing could run on? You can't eat solar power. Do they mean that it would be equipped with photovoltaic cells along with the biomass-fueled power supply? Such a system would be entirely separate from, and unrelated to, the system that allowed it to extract energy from organic materials.