Energy And The Marines

Guns or butter?  The new version of the debate is - - "Bullets or Batteries?"  The Marine Corps is addressing this question and paradox.  In fact, the "Bullets or Batteries?" question is confronting all military planners.  Modern U.S. forces are more lethal and effective than any military organization in history.  But the Marines are just like the rest of us in terms of energy consumption; they gobble up huge amounts of energy (The N.S.A.'s Fort Meade 5,000 acre campus has an annual electric bill of $70 million - - computers that can download the equivalent of the Library of Congress every six hours aren't cheap).  From radios, to laptops, to GPS, to many other devices - - energy consumption is an enemy that lengthens vulnerable supply lines and overloads soldiers and Marines in the field.

A typical Marine carries about 100 pounds of gear into battle.  Batteries make up as much as 20% of the weight.  This same Marine infantryman uses four times as much fuel as his counterpart did in the early 1990s.  This is due to, among other things, laptops and other electronic gear that use electricity pumped out by portable generators.  Some 30% of all fuel trucked into Afghanistan goes to power those generators, at a time when roadside bombs remain the most dangerous weapon faced by our forces.  Given the "Bullets or Batteries?" question and strategic concerns, the Corps wants to cut per-Marine fuel use by 50% by 2025 (Note - - sometime write down all the things we as a country and global community need to get done by 2025.  From energy conservation, to climate change, to health care reform, to Social Security reform - - the Year 2025 is going to be a very busy year).

The Marines will be looking to sunlight and renewables to lighten their backpacks and shorten their convoys.  At the moment, there are two reliable ways to make electricity from sunlight.  You can use a panel of solar cells to create the current directly, by liberating electrons from semiconducting material such as silicon.  Or you can concentrate the sun's rays using mirrors, boil water with them, and employ the steam to drive a generator.  They work - - but both are expensive. 

A potential alternative is a process based on the thermoelectric effect.  Thermoelectric devices are not new.  They are used, for example, to capture waste heat from car engines.  They work because certain materials, such as bismuth telluride, generate an electrical potential difference within themselves if one part is hotter than another.  They can be used to drive a current through external circuit.  The reason thermoelectric materials have not, in the past, been applied successfully to the question of solar power is that to get worthwhile current you have to have significant temperature difference (something on the order of 200 degrees C).  This is easy in your car, but difficult on a hill in Afghanistan.

Researchers are working on three improvements to the efficiency of solar-thermoelectric materials - - (1) Making sure that most of the sunlight which falls on a device is absorbed rather than being reflected, (2) Choose a thermoelectric material which conducts heat badly (so that different parts remain at different temperatures) but electricity well, and (3) Be certain that the temperature gradient which that badly conducting material creates is not frittered away by poor design.

Consider the rooftop at a forward operating base (FOB) in the mountains of Afghanistan.  Modular solar panels adorn the roof.  If such heaters were covered with thermoelectric generators the sun's rays could be put to sequential use.  First, electric power would be extracted from them.  Then, the exhaust heat from the bottom plate of the thermoelectric device would be used in the traditional way to warm water up.  The Marines would get a two-for-one deal - - really a three-for-one deal.  Heat, power, and lighter backpacks.