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#New battery turns wasted heat into energy Stanford university rightoriginal Studyposted by Dan Stober-Stanford on May 22 2014researchers have developed a new battery technology that captures low-temperature waste heat and converts it into electricity. Vast amounts of excess heat are generated by industrial processes and by electric power plants. Researchers have spent decades seeking ways to harness some of this wasted energy. Most such efforts have focused on thermoelectric devicesâ##solid-state materials that can produce electricity from a temperature gradientâ ##but the efficiency of such devices is limited by the availability of materials. Now researchers have found a new alternative for low-temperature waste-heat conversion into electricityâ##that is in cases where temperature differences are less than 100 degrees Celsius. The researchers describe the approach inâ Nature Communications. irtually all power plants and manufacturing processes like steelmaking and refining release tremendous amounts of low-grade heat to ambient temperaturessays Yi Cui an associate professor of materials science and engineering at Stanford university. ur new battery technology is designed to take advantage of this temperature gradient at the industrial scale. he new system is based on the principle known as the thermogalvanic effect which states that the voltage of a rechargeable battery is dependent on temperature. o harvest thermal energy we subject a battery to a four-step process: heating up charging cooling down and dischargingsays Seok Woo Lee a postdoctoral scholar at Stanford and co-lead author of the study. First an uncharged battery is heated by waste heat. Then while the battery is still warm a voltage is applied. Once fully charged the battery is allowed to cool. Because of the thermogalvanic effect the voltage increases as the temperature decreases. When the battery has cooled it actually delivers more electricity than was used to charge it. That extra energy doesn t appear from nowhere explains Cui. It comes from the heat that was added to the system. The system aims at harvesting heat at temperatures below 100 C which accounts for a major part of potentially harvestable waste heat. ne-third of all energy consumption in the United states ends up as low-grade heatsays co-lead author Yuan Yang a postdoc at the Massachusetts institute of technology (MIT. In the experiment a battery was heated to 60 C charged and cooled. The process resulted in an electricity-conversion efficiency of 5. 7 percent almost double the efficiency of conventional thermoelectric devices. This heating-charging-cooling approach was proposed first in the 1950s at temperatures of 500 C or more says Yang who notesâ that most heat recovery systems work best with higher temperature differences. key advance is using material that was not around at that timefor the battery electrodes as well as advances in engineering the system says co-author Gang Chen a professor of mechanical engineering at MIT. his technology has the additional advantage of using low-cost abundant materials and manufacturing processes that are used already widely in the battery industryadds Lee. While the new system has a significant advantage in energy conversion efficiency over conventional thermoelectric devices it has a much lower power densityâ##that is the amount of power that can be delivered for a given weight. The new technology also will require further research to assure long-term reliability and improve the speed of battery charging and discharging Chen adds. t will require a lot of work to take the next step. here is currently no good technology that can make effective use of the relatively low-temperature differences this system can harness Chen says. his has an efficiency we think is quite attractive. There is so much of this low-temperature waste heat if a technology can be created and deployed to use it. he results are very promising says Peidong Yang a professor of chemistry at the University of California Berkeley who was involved not in the study. y exploring the thermogalvanic effect the researchers were able to convert low-grade heat to electricity with decent efficiencyhe says. his is a clever idea and low-grade waste heat is everywhere. ther authors of the study are Hyun-Wook Lee of Stanford and Hadi Ghasemi and Daniel Kraemer of MIT. The US Department of energy (DOE) the SLAC National Accelerator Laboratory and the National Research Foundation of Korea helped support the study. The DOE in part through the Solid-state Solar-Thermal energy Conversion Center helped support the MIT research. Source: Stanford Universityyou are free to share this article under the Creative Commons Attribution-Noderivs 3. 0 Unported license r

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