Contact: Jerry Whitaker -- Chief, Public Affairs Office
(508) 233-5340
Jerry.Whitaker@natick.army.mil

Date: November 29, 2004
No: 04-46

Photovoltaics shine into new territory

NATICK, Mass. -- Sunlight is the bright filling station above that never asks for money or runs out of fuel for photovoltaic products, and some scientists believe that "the sky is the limit" for a new generation of photovoltaic technologies in development at the U.S. Army Soldier Systems Center here.

A promising technology that's existed for decades, photovoltaic (PV) solar cells convert light energy into electricity without noise, moving parts, fuel consumption or pollutant emissions. A breakthrough arrived in the past five years when PV technology transformed from the traditional large, heavy, rigid, reflective and expensive glass panels into lightweight, conformal and inexpensive devices that now can be directly integrated into textiles and warfighter systems, according to Lynne Samuelson, a research chemist in the Science and Technology Directorate.

"There's a lot of room to grow on how power is harvested according to the ambient light," Samuelson said. "Already it's at a usable level."

It's seen as boon to the military for a variety of reasons. Warfighters could cut their battery load weight in half when PV cells are used in combination with rechargeable batteries to power individual items such as night vision goggles, according to Steven Tucker, an electrical engineer in the Collective Protection Directorate.

"On 72-hour and longer missions, it makes a lot more sense to carry rechargeable batteries," Tucker said. "You get rid of that logistics tail by minimizing re-supply with disposable batteries. The benefit/weight payback for a photovoltaic charger and rechargeable battery combination is incredibly quick, and out past 72 hours it just keeps getting better."

Less weight means better mobility, and the ability to recharge batteries on-the-move can increase sustainability, extend mission times and distance from tactical operations centers, and reduce logistics support requirements.

Replacing or decreasing the number of liquid-fuel-powered generators further reduces logistics, and lowers the heat and sound signature in the field for improved stealth.

It's also a potential lifesaver as an emergency back-up power in case generators fail, say, in a field hospital.

These benefits are possible because of new lightweight and flexible solar cells made with two complementary PV technologies, amorphous silicon and dye-sensitized nanocomposites.

Of the two, the mature amorphous silicon is the "workhorse" of photovoltaic technology, Samuelson said. "Basically, wherever there's a surface, you can lay it out and generate electricity. These things are so versatile, you can make them to do whatever you want."

Iowa Thin Film Technologies in Ames, Iowa, advanced this technology through a quality award-winning Phase II Small Business Innovative Research (SBIR) effort by manufacturing a PV cell .005 inch thick, rollable to 3 inches diameter and less than 1.7 ounce per 250 mm by 300 mm frame.

Furthermore, the company developed a high-speed manufacturing process for the film and a unique process that allows finished PV product to be roll-laminated directly onto large swaths of shelter fabric.

"This gets away from the heavy glass of prior PV technologies," Tucker said. "PV made from amorphous silicon is mobile and deployable. It can take abuse. I've seen it cut and punctured and still be usable. What degrades over time is the protective covering, not really the PV cell itself."

Three prototype power-generating solar units were manufactured using the speedy process. A "Power Shade" that fits over two kinds of Army tents has PV material laminated into a mesh fabric that reduces solar load by 80-90 percent while generating up to 1 kilowatt of power for shelter electronics or battery recharging. The smaller TEMPER tent fly generates up to 750 watts, and at one-fourth the size of the fly, the "Quadrant" was designed to be placed wherever convenient and can be adjusted for better exposure to the sun. Its maximum power output is about 190 watts.

On a larger scale, PV cells on shelters for aircraft or field hospitals that cover thousands of square feet could generate 40-60 kilowatts of energy in peak sunlight.

"These shelters are out there in the sun baking away, so why not try to take advantage of it?" Tucker said. "This is not just a one-pronged approach. We're approaching the issue of getting power to the warfighter from all sides."

A spin-off from the SBIR is a roll-up module that charges AA batteries. Tucker said the software algorithm that controls the charger was designed to deliver more current to the battery.

"This is a big one. There's nothing out there like this that we're aware of," said Samuelson. "This is the one (Special Operations Command) is excited about and is willing to try."

A "colorful" approach to PV technology is seen in dye-sensitized nanocomposites, which brings a new wave of possibilities without any sacrifice in power output to amorphous silicon.

Out of an Army Science and Technology Objective, Konarka Technologies in Lowell, Mass., formed to develop PV cells based on light-harvesting dyes that are adsorbed onto titanium dioxide nanoparticles.

Reliable, flexible power for warfighters can be manufactured from a PV layer less than .0005 inch thick that is manufactured onto plastic and into textiles, according to Samuelson. It's made possible because of lower manufacturing temperatures that won't melt the plastic.

"The molecules give it color. We're looking at different color dyes and want to mimic the pattern used in the military," she said.

Demonstration of a photovoltaic fiber is a unique breakthrough for dye-sensitized nanocomposites, according to Samuelson, which could be woven into novel fabric-based PV devices that could be used where traditional PV devices were never thought possible, such as a detachable patch worn to prevent friendly fire or alert to chemical or biological agent contamination.

Konarka's reel-to-reel processing advantage is that it's inexpensive and widely available in foreign countries, and it may fulfill a dream of the late company founder as a way to produce inexpensive electricity in underdeveloped countries, said Samuelson.

"The applications will evolve with the technology," said Tucker. "It could be applied to toys so they don't need batteries or be a way to recharge cell phones or (personal digital assistants)."

Eventually, direct integration into soldier-borne systems may create electronically-active textiles to minimize cables and connections, and provide a more streamlined and multi-functional warfighter system, according to Samuelson.

A new Science and Technology Objective, beginning this year and continuing through 2008, looks to branch out the self-powered electrotextiles theme to achieve PV power generation from virtually any surface.

For more information about the Soldier Systems Center, please visit our website at: www.natick.army.mil.