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 IMPROVING BATTERY ENERGY STORAGE WITH SODIUM-AIR BATTERIES In pursuit of a better power source for hybrid locomotives, GE Global Research [GE-NYSE] identified sodium nickel chloride batteries as the most versatile and effective solution. The technology harnesses the chemistry of sodium and nickel. During the charging of GE's Durathon battery, chloride ions are released from sodium chloride and combined with nickel to form nickel chloride. These sodium ions then migrate from the cathode reservoir through a beta alumina separator into the anode reservoir. During discharge, the reverse chemical reaction occurs and sodium ions migrate from the anode reservoir through the beta alumina separator into the cathode reservoir. There is no selfdischarge because sodium ions can move easily across the beta alumina, while electrons cannot. Each cell is sealed within its own metal case, and is strung together with other cells in a thermally insulated battery module, which ensures that the battery's external surfaces remain within 10°C to 15°C of the surrounding ambient temperature. All Durathon Batteries are managed by the Durathon Battery Management System, which controls and protects the battery and relays information for monitoring the battery's condition. The GE Durathon Battery is the basis 50 www.resourceworld.com for energy storage systems for a variety of stationary and motive applications, such as telecommunications, power generation, grid operation and energy management. The company claims that the Durathon Battery's sodium nickel technology will change the way the world sees battery energy storage. GE has invested $100 million into a world-class Durathon Battery manufacturing facility in Schenectady, New York. Officially opened in July 2012, production started in September 2011 using advanced powder processing, ceramics and welding technologies. HARVESTING MORE OF SOLAR POWER'S HEAT According to Stanford University's online newsletter, Stanford engineers have determined how to simultaneously use the light and heat of the sun to generate electricity in a way that could make solar power production more than twice as efficient as existing methods and potentially cheap enough to compete with oil. Unlike the photovoltaic technology used in solar panels – which becomes less efficient as the temperature rises – the new process excels at higher temperatures. Called photon enhanced thermionic emission, (PETE), the process promises to surpass the efficiency of existing photovoltaic and thermal conversion technologies. "This is really a conceptual breakthrough, a new energy conversion process, not just a new material or a slightly different tweak," said Nick Melosh, an assistant professor of materials science and engineering, who led the research group. "It is actually something fundamentally different about how you can harvest energy." And the materials needed to build a device to make the process work are cheap and easily available; meaning the power that comes from it will be affordable. "Just demonstrating that the process worked was a big deal," Melosh said. "And we showed this physical mechanism does exist; it works as advertised." Most photovoltaic cells, such as those used in rooftop solar panels, use the semiconducting material silicon to convert the energy from photons of light to electricity. But the cells can only use a portion of the light spectrum, with the rest just generating heat. This heat from unused sunlight and inefficiencies in the cells themselves account for a loss of more than 50% of the initial solar energy reaching the cell. If this wasted heat energy could somehow be harvested, solar cells could be much more efficient. The problem has been that high temperatures are necessary to power heatbased conversion systems, yet solar cell efficiency rapidly decreases at higher temperatures. Until now, no one had come up with a way to wed thermal and solar cell conversion technologies. While most silicon solar cells have been rendered inert by the time the temperature reaches 100°C, the PETE device doesn't hit peak efficiency until it is well over 200°C. Because PETE performs best at temperatures well in excess of what a rooftop solar panel would reach, the devices will work best in solar concentrators such as parabolic dishes, which can get as hot as 800°C. "The light would come in and hit our PETE device first, where we would take advantage of both the incident light and the heat that it produces, and then we would dump the waste heat to their existing thermal conversion systems," Melosh said. "So the PETE process has two really big benefits in energy production over M AY 2 0 1 3

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