BuckminsterFuller suggested powering human activities simply by exploiting the potential in the different rotation rates of the ground and the magnetosphere. The earth has an iron core, you see, so Fuller envisioned looping wires around the planet to form a virtually inexhaustible generator of free energy for all human needs. 

'''Pros:'''

	* Much cheaper than any other form of generation.
	* Solves most of the planet's technical ills in a single swipe.
	* The amount of energy available is truly vast, and our usage would have no measurable effect on the Earth's rotation.

'''Cons:'''

	* You have to get all the governments of the world to agree to let you install this. Good luck.
	* You have to get some economic system going that would permit humans to cooperate in managing free resources. Good luck. 
		* ''Is it really free? There are tremendous infrastructure and maintenance costs.''
			* Those costs are immediately repaid by the value of the energy yielded. Everything after that is free.
	* You have to guarantee the idiots with guns (both inside and outside governments) won't shut the thing down over one or another schoolyard spat, plunging the planet into darkness. Good luck.
	* You have to ensure that a good hurricane/earthquake/hailstorm doesn't pull the thing down, plunging the planet into darkness.

See also: FloatingCities, SpaceElevator.

Some enterprising soul will run the numbers and see how many watts we could get. Hint, hint.