Resource World Magazine

A LT ER NATI V E EN ER G Y R E VI E W Developments in Alternative Energy by Jane Bratun SCIENTISTS DEVELOP BATTERIES MADE FROM WOOD Researchers at the University of Maryland at College Park have taken a sliver of wood coated with tin and made a tiny, longlasting, efficient, and environmentally friendly battery. The new battery is among the most long-lasting of all sodium-ion, nanobatteries. Because of the low cost of materials, the researchers think that batteries based on this new technology would be best suited for large-scale energy storage, such as storing the excess energy produced by some renewable energy installations. The components in the battery are a thousand times thinner than a piece of paper, yet the wood fibers help nanoscale batteries keep their structure. Using sodium instead of lithium, as many rechargeable batteries do, makes the battery environmentally benign. Sodium doesn't store energy as efficiently as lithium, so this battery isn't for mobile phone use. Instead, it is ideal for storing huge amounts of energy at once, such as solar energy at a power plant. Batteries are often created on stiff bases, which are too brittle to withstand the swelling and shrinking that happens as electrons are stored in and used up from the battery. The team found that wood fibers are supple enough to let their sodium-ion battery last more than 400 charging cycles, which puts it among the longest lasting nanobatteries. "The inspiration behind the idea comes from the trees," said Hongli Hu, assistant professor of materials science. "Wood fibers, that make up a tree, once held mineral-rich water, and so, are ideal for storing liquid electrolytes, making them not only the base but an active part of the battery." Zhu and other team members noticed that 50 www.resourceworld.com after charging and discharging the battery hundreds of times, the wood ended up wrinkled but intact. Computer models showed that that the wrinkles effectively relax the stress in the battery during charging and recharging, so that the battery can survive many cycles. "Pushing sodium ions through tin anodes often weaken the tin's connection to its base material," said Li, an associate professor of mechanical engineering. "But the wood fibers are soft enough to serve as a mechanical buffer, and thus can accommodate tin's changes. This is the key to our long-lasting sodium-ion batteries." The team's research was supported by the University of Maryland and the US National Science Foundation. SOLAR POWER SAVES SOLDIERS' LIVES A new US Army solar project integrates solar power with the army's new Firefly sniper detection system, which has been exposing soldiers to enemy fire when they have to install fresh batteries to power the equipment. That risk has now been practically eliminated, thanks to solar power. As described by Edric Thompson of the army's Communications-Electronics Research Development and Engineering Center (CERDEC), Firefly refers to the new Hostile Fire Detection Sensor, a portable surveillance system that can be carried in a backpack or mounted at forward operating bases. The problem, according to Thompson, is deploying 21st century technology while relying on 20th century energy. Firefly is dependent on batteries, and soldiers had to get above perimeter wall line to change these batteries. To solve this problem, CERDEC has developed a renewable energy microgrid system called Reusing Existing Natural Energy, Wind and Solar system (RENEWS). It includes solar panels, a wind turbine, and a rechargeable battery unit featuring advanced, lightweight BB-2590 batteries developed by CERDEC. The system can produce about 300 watts of power and it is silent and self-sustaining, meaning that it is free of two key operational drawbacks suffered by conventional diesel generators: noise and refueling. The result is a silent, refueling-free power system with practically no routine maintenance issues that would pile on risks for soldiers. With no need to change the batteries, the solar panels can easily be located below the wall line where they can be cleaned regularly without exposing soldiers to enemy fire. Along with reducing risks on site, the RENEWS and Firefly combination also eliminates the need to use diesel generators for recharging batteries, which helps to reduce risks related to fuel convoys. GATHERING LIMITLESS CLEAN ENERGY FROM SPACE India and the US-based National Space Society (NSS) have announced a spacebased solar power initiative that plans to market the idea of a viable, space-based, solar power infrastructure to governSEPTEMBER 2013

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