Geothermal Energy Harvesting Garden Lights

I have been doing voltage checks throughout the day. I have gotten just about half a volt during the hottest part of the day. I also insulated the exposed part of the ground radiator with earth.

So I tried the setup during day time with thermal paste. And I am making power! It's not much power though. It's defiantly in the energy harvesting range of power output.

This is a picture with my multimeter disconnected.

Here is a side view of the setup.

When the sun started to go down my voltage went down to 0.034 volts. I think this is due to a drop in ambient temp. I also checked the current and I was making about 1.5 miliamps short circuit. This means I'm making about 50 micro amps.  Another note, I flipped the TEG over to see if it preferred one side to be the hot side but it didn't matter.

I tried the setup with the ground radiator almost all the way into the ground. Then I placed the TEG on top of the ground radiator and then a PC CPU heat sink on top of the TEG. The test was done in the evening and I used a multimeter to measure voltage of the device. I did not produce any voltage.  I will try the test again in the day time so that the ambient air will be hotter.

Also of note is that I did not use any thermal paste on the device. I think thermal paste will be highly important to get decent performance from my setup.

I made a radiator out of scrap steel. This radiator will conduct heat into the ground to create a temperature differential for the thermoelectric device. The radiator is about 14 inches long and is make from two lengths of "angle iron".  A cross section of the radiator is 2 inches long.  At the top of the radiator is a flat square piece that the TEG will sit on. 

So when I first saw this year's Hackaday prize video, I was hyped! Then, I saw the energy harvesting category and thought "I can do this!". But no idea came to me unit months later when I was reading a blog post on here about energy harvesting. I tried to think of all the renewable forms of energy I knew of while I was walking though my house. Then, I looked out the window and into my back yard. I was thinking about  geothermal energy and how behind it was compared to wind and solar. That's when I got the idea. I was looking at the ground under a tree and thought how could I put a garden light under it.