Recovery and harvest of heat is the conservationist’s best route to reduce energy consumption. The amounts of energy that escape use via heat is a stunning number and the heat available from solar and geothermal are huge resources. When a new technology shows up, even if it’s at the first bright idea stage, we want to know more.
Professor Andrew Jordan of the University of Rochester is proposing a new type of nanoscale engine that would use quantum dots to generate electricity from waste heat, potentially making microcircuits as an example, more efficient.
Jordan said, “The system is really a simple one, which exploits certain properties of quantum dots to harvest heat. Despite this simplicity, the power it could generate is still larger than any other nanoengine that has been considered until now.”
The engines would be microscopic in size, and have no moving parts. Each would only produce a tiny amount of power – a millionth or less of what a light bulb uses. But by combining millions of the engines in a layered structure, Jordan says a device that was a square inch in area could produce about a watt of power for every one-degree’s difference in temperature. Enough of them could make a notable difference in the energy consumption of the computer example.
Do the math on that and the good professor has a much better idea than he’s thinking. Your standard sheet of paper could have the energy to drive a 75-watt bulb. Maybe its too good to be true . . .
A paper describing the new work has being published in Physical Review B by Jordan, a theoretical physics professor, and his collaborators, Björn Sothmann and Markus Buttiker from the University of Geneva, and Rafael Sánchez from the Material Sciences Institute in Madrid.
Jordan explained that each of the proposed nanoengines is based on two adjacent quantum dots, with current flowing through one and then the other. Quantum dots are manufactured systems that due to their small size act as quantum mechanical objects, or artificial atoms.
The path the electrons have to take across both quantum dots can be adjusted to have an uphill slope. To make it up this (electrical) hill, electrons need energy. They take the energy from the middle of the region, which is kept hot, and use this energy to come out the other side, higher up the hill. This removes heat from where it is being generated and converts it into electrical power with a high efficiency.
To do this, the system makes use of a quantum mechanical effect called resonant tunneling, which means the quantum dots act as perfect energy filters. When the system is in the resonant tunneling mode, electrons can only pass through the quantum dots when they have a specific energy that can be adjusted. All other electrons that do not have this energy are blocked.
Quantum dots can be grown in a self-assembling way out of semiconductor materials. This allows for a practical way to produce many of these tiny engines as part of a larger array, and in multiple layers, which the authors refer to as the Swiss Cheese Sandwich configuration (see image above).
How much electrical power is produced depends on the temperature difference across the energy harvester – the higher the temperature difference, the higher the power that will be generated. This requires good insulation between the hot and cold regions, Jordan says.
The idea proposes great numbers. One would wonder how the performance would change as temperature differences get larger and other salient inputs and design impacts apply. Your humble writer for one is very hopeful the funding appears to pursue this idea.