Believe it or not, energy efficiency is big business, and it's only getting bigger. HSBC estimates that the market could grow from $87 billion today to $245 billion per year by 2020. Numbers like that are hard to ignore, especially given that investors are by and large ignoring the energy efficiency opportunity right now.

One thing is for sure, though: Wall Street stalwarts such as Bank of America and Goldman Sachs are not. In this video, contributor Aimee Duffy looks at the recent energy investments at these banks, and what investors should take away from their specific initiatives.