The power consumption of banks isn't really comparable to the power consumption of Bitcoin unless you factor in the amount of transactions conducted with each service.  Considering that even in its current state Bitcoin takes up a pretty serious amount of power by all credible estimates, it would be a massive guzzler if it was more widely used.

It's not worth worrying about yet because there is value to Bitcoin's power consumption - it maintains the security of the system - and at some point renewable energy could become more commonplace, but let's not kid ourselves that it's really innocent compared to the big nasty banks.