Since making this video, I am thinking that the sun plays an indirect role. Its likely Atmospheric Electricity is mostly responsible for the charge, however Atmospheric Electricity was not a described phenomenon in Tesla's day.
I break with the theory that a liquid Nickel - Iron molten core is responsible for earth's magnetic field as there is no practical example of a metal in molten form being able to hold a electromagnetic potential. Rather the diamagnetic substances of the Earth such as Silicon (found in most of the granite and sedimentary rock) and Water create a Diamagnetic field in opposition to the magnetic field generated by the sun.
Patent: https://www.google.com/patents/US685957
"This phenomenon, I believe, is best explained as follows: The sun, as well as other sources of radiant energy, throws off minute particles of matterpositively electrified,which,impinging upon the plate P, communicate continuously an electrical charge to the same"
University of Michigan lecture by Steven Rand:
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