Could have something like a ecology balance ...
Use generators as coal generators, furnaces of iron and normal, will generate damage to the ecological balance,as several nuclear accidents and excessive use of geothermal generators.
With bad ecology balance,the color of biome change, was more dead ... the color of water also could change, less field of view, less passive and more hostile mobs,where trees and seeds do not grow, and where neither the life of Steve will be welcome.
With that the players would use more resources to generate clean energy, such as solar panels ...Improve water mill for large hydroelectric system ,but we must leave these clean energy more expensive.
Players must choose between two paths
The clean, but slower, means of generating energy
The fast, but non-technological and polluting, means of generating energy.
(sorry for the bad english, I'm using Google Translate)