If you could harness low temperature waste heat as stored energy in a battery, would you? Though the technology that could one day capture and convert waste heat into stored energy is not yet commercial viable or available, the possibilities are intriguing.
The research, which was conducted by teams at Stanford University and the Massachusetts Institute of Technology, seeks to provide an alternative to thermoelectric devices for low temperature waste heat conversion into electricity. Specifically, the teams sought means that could recoup energy from low temperature waste heat where the temperature differences are less than 180°F (100°C). Though most waste heat recovery solutions target much higher temperature streams — with the goal of repurposing the energy elsewhere in the process as secondary heating, perhaps as makeup air or in lower temperature process equipment — the research looked at ways to use the lower temperature gradient because virtually all power plants and manufacturing process release a significant amount of low grade heat to ambient.
The Stanford-MIT approach seeks to exploit the fact that the voltage of a rechargeable battery is dependent on temperature — a principal known as the thermogalvanic effect. Through a four-stage process of heating the battery with waste heat, applying the charge and cooling the battery, when the battery reaches the fourth stage — discharging its stored energy — it delivers more energy than was used to charge it. That extra energy does not appear magically, says Yi Cui, a member of the Stanford research team. Heating the battery before charging it stores some of the heat as energy, thereby capturing low temperature waste heat.
According to a paper published about the research in Nature Communications (http://bit.ly/thermogalvanic), in one experiment, the process resulted in an electricity conversion efficiency of 5.7 percent.
Though the research teams concede that further research is required, the possibilities are enticing. For instance, I imagine processors could use the waste heat for temporary process equipment operations, auxiliary office energy for demand comfort heating and cooling, or perhaps even green energy projects such as electric vehicle charging.
Linda Becker, Associate Publisher and Editor,
P.S. If real-world technologies are more enticing to you than theoretical, waste heat recovery and energy conservation methods are the focus of “Heat Recovery for Conveyor Dryers.” In it, Frank Poandl of Bühler Aeroglide looks at adding energy reuse and conversion methods such as cascading makeup air, using flash steam coils to preheat makeup air and heat recovery via an air-to-air-heat exchanger for an energy-intensive process that depends on convection for proper product characteristics.