Despite a speed up of electrification which is bad news for thermoelectric based waste heat recovery in internal combustion engines, not all has been bad for this energy harvesting technology... The newest developments come to us from South Korea and represent good news for the proponents of the use of energy harvesting technology for consumer electronics, wearables in specific. Wearable thermoelectric generators (TEGs) using the temperature difference between the body heat and ambient air have received significant attention in recent years, as research groups try to identify ways to extend battery life of portable electronic devices. However, one of the main drawbacks of wearable TEGs techniques driven by body heat was that such temperature difference is only 1 ~ 4 degrees, resulting in low power output and this has hindered further commercialization.
A research team at UNIST in Korea solved this low temperature difference faced by conventional wearable TEGs by introducing a local solar absorber on a PI substrate. The solar absorber is a five-period Ti/MgF2 superlattice, in which the structure and thickness of each layer was designed for optimal absorption of sunlight. This has increased the temperature difference which has now reached 20.9 °C, which is the highest value of all wearable TEGs reported to date.
Photograph of the thermoelectric ink printed in various shapes. Credit: UNIST
Recent developments have seen flexible stretchable generators developed at KAUST, and thermoelectric paint, which could harvest energy from the temperature difference between ambient air and the wall surface, also developed at UNIST. But, these are still academic research projects which probably means, probably still aways from commercial products; what's being commercialized today?
As luck would have it, the Matrix technologies PowerWatch should be in the process of being made available to its supporters as this article is being typed (it was crowdfunded by an Indiegogo campaign).
The Matrix PowerWatch
For wearable TEGs, a power level of 10-30 μW/cm² can be produced for a typical person indoors. These values have been practically obtained in different prototypes of wearable self-powered wireless sensor nodes but have been limiting to date. Advances in device optimization like those at UNIST and ultra low power electronics like the ones described by Matrix indicate there's a possibility of improvement. It is important to manage the expectations of what these improvements might be: we should expect to see additional functionalities in wearables and an expansion into more applications as improved devices are demonstrated. Any other type of device, like high end smart watches, smartphones or tablets, are still out of reach due to their high power consumption requirements.
Matrix technologies is presenting its PowerWatch at the IDTechEx Show in Santa Clara, Nov 15-16. To attend and for more information on the event, please visit: www.EnergyHarvestingUSA.com