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A weed Civil War soldiers used to write letters home may hold the secret to cheaper and more efficient solar energy today.

Researchers at Wake Forest University’s Center for Nanotechnology and Molecular Materials in North Carolina have discovered that red dye from the pokeberry weed makes their low-cost, fiber-based solar cells even more energy efficient.

The center’s director David Carroll says the solar cells, which have been patented under the company FiberCell, Inc., can create twice the power existing solar flat cells produce. The cells have more surface area and can trap light at any angle, meaning they can take advantage of the sun from dawn to dusk.

Cue the berries.

When the dye is spread over these cells, it acts as a light absorber, boosting the technology’s efficiency by about 7 percent. The dye helps the cell’s fibers capture more sunlight to convert into power.

The pokeberry weed, a resilient purple-stemmed plant, can grow up to 14 feet high in infertile soil and areas with severe drought. They are native to North and South America, East Asia and New Zealand, and are found all over the world today. Poisonous to mammals but safe for birds, the berries have been used for a variety of activities including letter writing and garment dying. Now the berries are making their mark on solar technology.

Boosting efficiency is great, says David, but one of the goals is to boost local economies in developing nations with agricultural growth and provide them with sustainable energy.

“It’s a low-cost solar cell that can be made to work with local, low-cost agricultural crops like pokeberries and with a means of production that emerging economies can afford,” David says.

The idea is to distribute the solar cells to areas that have the ability to grow the crop and eventually sell it. “Instead of giving them a fish, we are teaching them how to fish,” he says.

FiberCell received a license to build up manufacturing processes for the new solar cells in the U.S. David says it would cost about $5 million to install a finishing plant for cells, compared to about $15 million for a flat cell plant.

David and his team are working on improving the yield of dye from the berry and several other varieties of “agra-solar” crops to be used and sold in the U.S. They would like to boost efficiency of the cells by 12 percent.

“This approach yields a home-sourced, renewable form of inks for solar panels,” he says.