This story is from the category Computing Power
Date posted: 29/05/2014
Vast amounts of excess heat are generated by industrial processes and by electric power plants; researchers around the world have spent decades seeking ways to harness some of this wasted energy. Most such efforts have focused on thermoelectric devices, solid-state materials that can produce electricity from a temperature gradient, but the efficiency of such devices is limited by the availability of materials.
Now researchers at MIT and Stanford University have found a new alternative for low-temperature waste-heat conversion into electricity — that is, in cases where temperature differences are less than 100 degrees Celsius.
The new approach, based on a phenomenon called the thermogalvanic effect, is described in a paper published in the journal Nature Communications by postdoc Yuan Yang and professor Gang Chen at MIT, postdoc Seok Woo Lee and professor Yi Cui at Stanford, and three others.
Since the voltage of rechargeable batteries depends on temperature, the new system combines the charging-discharging cycles of these batteries with heating and cooling, so that the discharge voltage is higher than charge voltage. The system can efficiently harness even relatively small temperature differences, such as a 50 C difference
To begin, the uncharged battery is heated by the waste heat. Then, while at the higher temperature, the battery is charged; once fully charged, it is allowed to cool. Because the charging voltage is lower at high temperatures than at low temperatures, once it has cooled the battery can actually deliver more electricity than what was used to charge it. That extra energy, of course, doesn’t just appear from nowhere: It comes from the heat that was added to the system.
The system aims at harvesting heat of less than 100 C, which accounts for a large proportion of potentially harvestable waste heat. In a demonstration with waste heat of 60 C the new system has an estimated efficiency of 5.7 percent.
See the full Story via external site: newsoffice.mit.edu
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