Waste Heat a Source of Energy

July 21, 2014

Low-grade heat can generate electricity.

What if excess heat generated by industrial processes and electric power plants could be harnessed to make electricity?

Researchers at MIT and Stanford University have discovered a way to capture this wasted energy with rechargeable batteries.

The low-temperature waste-heat conversion aims at harvesting heat of less than 200 degrees F., which accounts for a large proportion of potentially harvestable waste heat. In a demonstration with waste heat of 60 C. (or 140 F.), the new system has an estimated efficiency of 5.7%.

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 the charge voltage.

The system can efficiently harness even relatively small temperature differences, such as 120 F.

This potential is particularly attractive as almost 30% of energy consumption in the U.S. ends up as low-grade heat, MIT notes. The process to recover this energy is described in the journal Nature Communications.

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