@Alex - Although coal and other hydrocarbon products are used to generate electricity worldwide because it is cheap than any renewable source of energy, but one day, it will finish and that day will come soon.
So, I think, concentration in other forms of energy could be a better idea than making such a giant machinery for coal mine digging.

Burning of coal is a vital source of emitting green house gases in our environment. Why don't germen try to find solution of generating electricity with some renewable sources of energy. Making such a huge machines is no doubt, a master piece of engineering, but still, we want to save our planet from coal burning gases.