While I'll be interested to see how the blockchain gets exploited for new tech, there are a couple of problems with your statement. First, right now there is a problem with how we generate energy, and a centralized banking system should be a lot more efficient in that regard, for all its other flaws - Bitcoin relies on the calculations being difficult and therefore compute/energy intensive, after all. Second, even if we had perfectly clean energy generation, there is a limit to how much we can use unless we get into really crazy future tech like exhausting energy into space via refrigerant/laser system: see http://physics.ucsd.edu/do-the-math/2012/04/economist-meets-.... (also the `Sundiver' sci-fi!).