A Guide to Humans and Thermoelectric Generators
Have you ever forgot your charger and thought to yourself “if only I could power my iPhone using my own body heat?” If so and you haven’t yet stuck some strange device to your forearm, today’s you lucky day! I’ll be going over how thermoelectric generators (TEGs) work and how they can be integrated with the human body. The term I’ll use to shorten down ‘human integrated thermoelectic generators’ is going to be ‘HInt TEGs’.
Strictly Science
To generate electricity TEGs, also called Seebeck generators, must be in contact with differences in temperature in order to use the Seebeck effect to generate electricity from a heat gradient. This happens due to particles moving from one side of the device to the other and causing an electric current as electrons move.
In technical terms, TEGs are solid-state heat engines and are made of two types of semiconductors, p- and n-types. P-type semiconductors are made to carry positive charged particles and n-types carry negatives. This charge difference is used by connecting the semiconductors against each others heat gradient in order to generate an electrical charge.
Building a basic TEG is very simple, thermoelectric plates made from those semiconductors can be bought for around 2–3 bucks a pop. These are all connected together to make on big plate, one side of this plate is heated, the other is cooled, you stick an output to it and you can charge something.
You can go even simpler, thanks, Wired, and with a paperclip, copper wire, and some cold water you can generate a small amount of electricity. Of course, using semiconductors is more efficient, but the basic design of using the movement of electrons created from a heat imbalance is what really matters.
Now that you know a little about how these things work we can talk about some of the research done in the area.
Refer to Researchers
In a paper titled Wearable Thermoelectric Generators for Human Body Heat Harvesting by M. Hyland et al. in 2016 states that they have built a device that is comfortable and functional on a human body. their design used alloys based on n- and p-type bismuth telluride sandwiched between aluminim oxide ceramic headers. A heat spreader was glued to the bottom and the whole device was surrounded by polysimethylsiloxane to reduce heat loss. However, they found that airflow was far more important to power generation than insulating in heat.
In their airflow testing they found that energy generation peaked at airflow of 0.85 m/s but did not dip down with greater speeds (note that human walking speed is roughly 1.2 m/s). In human testing the most power was generated when the TEG was placed on the inner upper arm of a person, but this time peak power was at 1.4 m/s, and did not increase or decrease with further increases in velocity.
A 2018 article out of Stanford states that impressive amounts of heat are given off as waste by the human body, at around 58.2 watter per meter squared (w/m2). Not all that can be harvested through TEGs as heat is lost through perspiration and exhalation, and not all of it even makes it to the surface of the skin. However, a user could still power low-energy devices even when they are immobile. Beyond human applications they noted that hundreds of watts could be harvested from the exhaust gases of cars.
M-K Kim et al. in 2014 created a study rather similar to M. Hyland et al. in title and content with Wearable Thermoelectric Generator for Harvesting Human Body Heat Energy. Their study came to many of the same conclusions that their peers would two years later, but they had a focus on integrating their TEG into fabric so it would be confortable whereas the 2016 study focused simply on reducing the size of the TEG. By sticking n- and p-type composites into a fabric substrate they were able to create a device that was less efficient than most other TEGs but far more wearable. As one could expect they had quite a fabrication process that spent a lot of time on making sure the device would still be flexible and able to produce electricity, and the end product looks (at least in my personal opinion) pretty good, I could see this on a Sportchek mannequin.
Over time the power generation was lower, but this seemed due to changes in the body’s temperature difference rather than any flaws in their device. They do state that it is a prototype and that in order for it to be usable they’d need to make changes such as increasing the thermocouple density in order for it to generate more power to any sort of device. A study from MIT points out that as the weight and power required for sensor devices decreases it will become far easier to power them with TEGs, as with decreases in size and power required fro devices one can also assume that the power generation capabilities and required weight of TEGs will likely decrease with research.
There are a lot of nice points about how we could reduce reliance on batteries, save lives of patients in power outages, and possible create a new major source of sustainable electrical power, but are there any companies making this stuff? Technically: yes, practically: no.
Tons of small groups, I don’t feel its honest to call them companies, exist that (at least claim) to make parts for TEGs, or things that they say are fully-fledged devices, however their sites are old and don’t look too legit.
This was a pretty disappointing point in the research, seeing that there are pretty much no companies worth looking into, or even that seem to be trying to sell their product well. At least I can tell you that there is space to start a company and if you have some way to get customers and move things forward you’ll be clearly ahead of the competition. If just one company was out there developing and seeling TEGs would be great, that would be enough to start more movement towards body heat power generation as an actual thing.
Yamaha was the only legitimate company that I found while looking into this, but you could probably build a half-decent TEG out of some parts from a hardware store or off Amazon.
My advice to one who has decided to create a business selling things you want to people to stick to themselves to generate electricity would be to take an approach similar to M-K Kim et al. Build a device that looks and feels like clothing, and focus on low-power applications and situation where it would be more socially acceptable to wear a strange wetsuit-like outfit (think patients that require medical devices, emergency situation in remote areas).
Speculation on the Future
If anything comes out of this tech in the near future I’m willing to bet it’ll be small-scale TEGs used to power optional pieces of personal technology like smartwatches. To my knowledge no one has tested a large number of TEGs together on a human yet, and given the cost in time and resources to do such an experiment it’s not happening until there is a market or research goal with it.
A few groups have spitballed the idea of using them in ICE vehicles to harvest waste heat so they don’t need to create as much power for their electronics, however given that all major manufacturers have pledged to working towards solely making EBs they have no reason to put R&D into improving a product they tend to kill off. Unfortunately, this is another example of a cool technology that doesn’t have a lot of real-world uses.
Ethical Discussion
I do see some ways in which integrating TEGs into human bodies could be problematic if enough care is not put into it. Cooling is an issue at the moment for a lot of concepts, and if there are issues with how heat is distributed or dealt with on the device this can lead to physical harm. I don’t see any cyborg stuff happening anytime soon with this, so burning people’s skin off is unlikely.
As I said earlier I think the most likely medium for this device will be in under-armour type clothing that is worn just like normal clothes. In this case any burning caused by a device can be stopped quickly and simply by removing the garment, and any company that is going into this area is likely going to be wary of how difficult it will be to make such a product mainstream and as such will make safety a priority to avoid scaring off customers who don’t want to quite literally get burned by a purchase.
Other than the few safety issues that could come up I believe that if htis is able to become a usable technology it could be very beneficial to the healthcare sector in particular, and having a patient generating electricity to work the devices keeping them alive seems fine. But there is the issue of low power generation and that it lacks proof of efficacy. The solution to these two things is to use TEGs as one of a few possible power sources, or as the backup in case of a loss of power.
It is already possible for attackers to gain access to a lot of stuff simply through low-power bluetooth connections that are commonly found in IoT devices. This could create a serious problem depending on the chosen connection between a medical device and its power source or information display source. Say a medical device manufacturer decides to make a futuristic heart monitor that can communicate its power needs to to the source via Bluetooth. I like the premise of a medical device that is slightly less invasive as wires and batteries are not needed to power it.
But it could be possible based on current vulnerabilities to able to dictate how much power is sent to the heart monitor, possibly causing the device to fail. Its also possible to track the position of the user, which is problematic. Alas many security features are being added to make Bluetooth more secure, but as always there is the chance of someone you don’t want finding a hole, finding one.
As with anything there is the wrong people get their hands on it, or use it in a way that is not so humanitarian. In the case of a device like this, if a large company created it in a way that was hell-bent on squeezing every advertising dollar out of you there could be privacy concerns if it tracks where you’ve been, how much exercise you get, what devices you charge with it, etc.
These are all issues we already have with other devices like smartphones and there is an ongoing fight against them, and if a more extreme example in a HInt device comes up I’m sure many will see more reason to fight, or just not buy the thing.
So long as the device is safe and relatively easy to use I don’t imagine there being reason for much concern of it developing into an unreasonable device on the consumer end. I’m sure there’s worse things people could think to do with them, but I’m in a mood to think humanity is better than that.
Conclusion
To sum up all I’ve said about HInt TEGs, they are a futuristic piece of technology that still requires further development and is a long ways away form being adopted in any way. There is ongoing research into these devices but not a lot of work on the consumer front. If it ever does develop into a usable technology there are a few ways in which it could go horribly wrong unless all due diligence is done, but there is absolutely no guarantee that it goes anywhere in the first place.
References
TechXplore: Wearable Body Battery
Forbes: Nanotech Body Heat Breakthrough
Science Daily: Recovering Waste Energy
Stanford: Human Body as a Portable Power Source
M-K Kim et al.: Wearable TEG for harvesting Human Body Heat Energy
M. Hyland et al.: Wearable TEGs for Human Body Heat Harvesting
