We decided to test thermal energy harvesting usability in reality. As we mentioned in other articles Peltier element cannot generate high power, but we can store this power in some time interval and then use it. We already described functionality of Peltier element (aka. Thermo electric cooler - TEC) and ECT 310 boost converter and here we will measure their performance.
We will measure time needed to charge different capacitors using single low cost Peltier element and ECT310 by using just body heat. Capacitors used are 10uF, 1000uF and massive supercapacitor with capacity of 1F!
Depending on the specific application, energy stored in these capacitors would be enough for some routine to be executed in short time that would be repeated periodically.
Manufacturer claims that ECT 310 operation starts at typically 20 mV relating to a 2 Kelvin temperature difference at a standard low-cost Peltier element. We made little bit larger temperature difference since one side is at room temperature and my best guess is that it is 23°C. When both sides of TEC are at room temperature no energy is being fed into capacitor. Moment we touch TEC with finger we make temperature difference between its sides which causes voltage to be generated. Temperature difference is about 10°C. It is not at the edge of ECT 310 possibility, but these are conditions that could be expected if this type of power supply is used for powering up wearable electronic devices.
On videos below you can see results of these tests.
Capacitor used is 10uF
Here is video of 10uF capacitor charging by just using human hand thermal energy:
As you can see capacitor is charged to 4V almost instantly, but energy stored is enough just for short blink of a LED.
Video showing discharging 10uF capacitor with LED:
Capacitor used is 4700uF
Here is video of 4700uF capacitor charging by just using human hand thermal energy:
Capacitor is charged in few minutes, and there is actually enough energy to do something useful with it. We didn’t do anything useful :) but LED stayed on for about ten seconds.
Video showing discharging 4700uF capacitor with LED:
Capacitor used is 1F!!
First we tried to charge it by just using human body thermal energy. It was charging, but we would have to hold hand on Peltier element for very long time, so to speed things up a little bit, we put plastic glass fuilled with hot watter on it. It was charging faster, but still it needed long time, so we left it on table until it was fully charged:
Charging of this capacitor might take a while, but then you have a lot of energy stored in it - enough even to put some actuator in motion. You can see that LED stays on for long long time when connected to fully charged supercapacitor:
These were results of the test so as you can see it all depends on how much energy you want to collect before you use it. If you want to make low power sensor nodes that will make measurement once in every five minutes, thermoelectric energy harvesting could be right choice. Especially if other power sources cannot be used, as described in our previous article.
Alternate energy sources are definitely our future, and they must be considered when designing new electronic device.
If you would like to try to integrate it in your design, here are links where you can buy it:
We especially want to thank our dear friend Francesca and Newark Electronics/ Element 14 for their contribution on making this article possible.