The term "alternative" is nonsensical and really had no place in a technical discussion. What we're talking about is efficiency which can be a mission benefit if applied rationally. Historically the ability or inability to maintain the fuel supply chain has won and lost wars. Decreasing the requirements for fuel increases the chance it will be available when needed.

This is a no brainer! I would say that the military use alternative energy sources when it is feasable. However there may be times and place where it isn't appropriate.

Yes, but only if studies show definitively that it wont cost the taxpayer a great deal more in the total costs of planning, conversion, and operation, including labor and upkeep costs to support such systems.