I have started my energy harvesting trials to power up the carbon monoxide detector from the difference between ambient and wall temperature. Firstly, I checked these differences in some long periods of time in couple of rooms at home. I tested both the internal and home outline walls. And I must tell you, I was surprised. Despite of what I have read in the building construction companies fliers, my walls were always a little bit warmer than the air around them. Here is one data plot from the measurements.
All the measurements were taken with the ‘home made device‘ based on EFM32 and TMP006AIYZFTTMP006AIYZFT contactless thermometer chip. If you are interested in this device, let me know in the comments and I will try to prepare additional post about this device and include Eagle’s PCB designs and BOM.
I was a little bit confused with this experiment outcome, but I thought to myself: maybe I am doing something wrong? So, I have double checked everything and in TMP006AIYZFTTMP006AIYZFT docs I have found that this ambient temperature readings are in fact the die temperature. This is supposed to be the same with the ambient but I am measuring small differences and the error of this device measurements is +/- 1 deg. So I have decided to test the TEG from the kit I got.
I had put the TEG against the wall and checked the voltage. I was so happy with the results … for only a very short period of time. At first, I got over -40 mV from TEG. But it started to fall down. I realized that the readings were so optimistic because I had the radiator from TEG in my hands for a while and it accumulated my body heat. When it was dissipating, the voltage have been dropping.
I thought, do not worry, you will still have some voltage from difference you measured with thermometer. And I have watched the meter. It was dropping, and dropping, and dropping until the reading was zero.
Now I have waited for the positive readings. But the display was still indicating zero. I went to have tea, then something to eat and afterwards I went out with my friends. When I was back, on the LCD the zeros were still there. I have realized that the heat transfer between air and the wall via TEG is faster than the heat transfer inside the wall.
In retrospect I have to say that I was too optimistic to harvest energy from that little temperature difference. Maybe it would change something if I have used different radiator, but this is the big if. I believe I have to put on hold wall harvesting and find out other heat source for the carbon monoxide detector. I have checked the voltage when the TEG was put against the window. It got me 3,5 mV steady voltage (I suppose that this would vary due to inside and outside temperature), so I would need more than 6 Peltier modules (4x4 cm) to power up the harvester.
I have looked around the rooms I would like to install some green energy carbon monoxide detectors and I have to say that there aren’t many places with the large temperature differences. Nevertheless, in every bathrooms and kitchen there is a warm water source. But the warm water is not constantly running from a tap. I have to check how much energy I can store with one TEG during one shower, one bath or one washing the dishes. If enough energy can be stored in some supercap in order to power the device for the whole day, it would be great. And if the energy would be insufficient, I can always use hybrid power supply.
