This article on space solar power (collecting energy from sunlight using one or more satellites in geostationary orbit, then beaming it down to Earth using microwaves) contains some interesting information on American military logistics in Iraq:
The armed forces are Americaâ€™s single greatest consumer of oil. The Department of Defence delivers 1.6m gallons (7.3m litres) of fuel a dayâ€”accounting for 70% by weight of all supplies deliveredâ€”to its forces in Iraq alone, at a delivered cost per gallon of $5-20. It also spends over $1 per kWh on electric power (ten times the domestic civilian price) in battle zones, because electricity must often be provided using generators that run on fossil fuels.
This helps explain why militaries have such a keen interest in new energy generation and efficiency technologies.
The information on space solar power is also quite interesting. It actually seems to be a bit less infeasible than I thought, though the launching costs remain a very significant barrier.