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NREL Solar Cells to Lighten a Soldier's Load

May 23, 2008

Photo close up of the hand of a young man.  The hand is holding up a transparent red solar cell mounted on a glass slide; the man's face is in the background.

NREL post-doctoral scientist Myles Steiner shows a prototype very high efficiency solar cell being developed for military use.

The scene is a familiar one from the nightly news: A U.S. soldier on patrol in a remote locale, outfitted in the latest high-tech gadgetry — radios, night vision goggles, navigation gear — devices that enhance mission capabilities and help keep the infantry safe.

While such electronic wizardry has become indispensible to the modern military, it also requires an ever growing amount of power to keep it all running.

What that usually has meant is more and more batteries. At some point, however, lugging around heavy batteries becomes a logistical nightmare, and ultimately, it's self defeating, for it contradicts the "light and portable" premise on which the technology is based.

How Will the Army of the Future Keep the Charge Light on Green?

The National Renewable Energy Laboratory and the Defense Advanced Research Projects Agency are teaming with a consortium of universities and private companies to perfect an advanced solar cell designed to be smaller and far more efficient than existing cells.

Such a solar photovoltaic (or PV) panel would be tiny enough to be built into differing types of portable electronic equipment, yet powerful enough to deliver a sufficient current for charging.

To achieve this ambitious goal, scientists are bringing together several of the most revolutionary concepts yet developed for PV cells. The cell they envision would have different layers of PV materials, each producing the optimum amount of electricity from varied portions of the light spectrum. It additionally would be topped by a lens that would concentrate the amount of sunlight directed on the PV materials.

"By drawing upon several of the most important innovations in PV design and combining them into an entirely new concept for cell design, we believe we can leapfrog over the limitations that had long been assumed for efficiency, size, cost and other critical factors," said Dr. Mark Wanlass, principal scientist at NREL.

"The new device we are looking to develop could not only solve many of the limitations our soldiers today encounter with electronics in the battlefield," Wanlass added, "it may spur other new solutions for solar power in space, and eventually, for our homes and businesses here at home."

Supplying Electricity, While Taking the Load Off

There are many reasons the military finds it advantageous to use solar cells to charge batteries. By being able to reliably charge batteries, it reduces the number of spare batteries needed. From a logistical standpoint, that means fewer trucks, helicopters and planes are required to ferry stocks of batteries into the field.

For individual soldiers, it can mean as much as a 20-pound decrease in the field supplies they must carry — a lighter load that can enhance their agility and stamina.

The end result is an armed force that is more efficient, as well as more environmentally sustainable.

Other Applications for the New Class of Solar Cells

In a related project, Wanlass says the research team is also putting a lot of focus on what is being called the "inverted metamorphic multi-junction," or IMM, solar cell, which he says "has clear advantages in performance, engineering design, operation, and cost."

It employs an entirely new way of constructing cells, with layers being grown, or deposited, from top to bottom, a notion that turns the well established method of putting layers one atop another, literally on its head. The IMM cell is particularly well suited to power space vehicles, thereby supporting the soldier who relies on satellites for communications and reconnaissance.

Wanlass believes research should continue as well on other approaches to higher efficiency solar cells, such as different cell structures and even more novel materials. In the short run, however, he believes the IMM cells hold the most promise for breaking the boundaries of efficiency with a new class of solar photovoltaic device.

For more information, visit NREL Photovoltaics Research.