Lightning Power? What is the power source of a lightning? It doesn't consume fuel, nor an atomic fission/fusion, but it discharges a large amount of energy. Is it feasible to create an artificial lightning using the same method of the natural lightning? If it is, can we create a power plant from the same source?
 A: 
The first process in the generation of lightning is the forcible separation of positive and negative charge carriers within a cloud or air. The mechanism by which this happens is still the subject of research, but one widely accepted theory is the polarization mechanism. This mechanism has two components: the first is that falling droplets of ice and rain become electrically polarized as they fall through the atmosphere's natural electric field, and the second is that colliding ice particles become charged by electrostatic induction. Once charged, by whatever mechanism, work is performed as the opposite charges are driven apart and energy is stored in the electric fields between them. The positively charged crystals tend to rise to the top, causing the cloud top to build up a positive charge, and the negatively charged crystals and hailstones drop to the middle and bottom layers of the cloud, building up a negative charge. Cloud-to-cloud lightning can appear at this point. Cloud-to-ground lightning is less common. Cumulonimbus clouds that do not produce enough ice crystals usually fail to produce enough charge separation to cause lightning.

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A: Ultimately, the power source can be traced back to the sun.  This supplies the heat energy to cause the atmospheric movements which give rise to the charge separation in Jack's answer.
I don't think it's feasible to do it artificially the same way (charge separation on water  droplets/ice crystals).  You would need an environmental chamber of size of the order of a sizeable portion of the atmosphere !  Charge separation and sparking is of course achieved in the Van de Graaff generator, but on a much smaller scale.
A: Like almost everything that is not nuclear on earth the energy comes from the Sun. 
Its possible some tiny amount of unused chemical energy still exists from the formation of the earth. Its hard to know since everything gets renewed from the Sun.
Either way, all our weather is powered by the Sun. Without it we would be a deep frozen planet with no weather.
