1Make a metal anchor for your lamp.
A metal anchor in needed because metal is a great conductor of heat and metal can easy be driven into the ground.
2Acquire a thermoelectric device .
A thermoelectric device or TEG is a solid state device that converts heat differentials to electrical energy. They can be bought cheaply from eBay or various other online stores.
3Buy or make your own thermal paste.
Thermal paste is commonly used to bond CPUs to cooling devices in computers. I will try making some home made paste with three parts tooth paste and one part petroleum jelly.
4Drive the ground radiator into the earth.
I used a hammer to sink the metal radiator into the ground.
5Assemble the TEG stack.
The project should be assembled: ground radiator, thermal paste, TEG, thermal paste, heat sink.