Establishing, maintaining and funding State Green Banks are an integral part of any efforts to combat climate change here in the US (and of course in other countries), the purpose of these banks is to lower the cost and increase the amount of private financing for clean energy technologies. Actually there are already a couple of these, New York has one, albeit on a relatively small scale. In July 2015 the Bank received an infusion of $150 Million. The basic characteristics of these institutions would to cover all upfront costs, attract private investment to help leverage public funds investment funds, provide scale, increase lending efficiency and recycle capital. The three different models that are already in use are in New York, Connecticut and Hawaii.
Hallie Kennan wrote and excellent Working Paper on State Green Banks that is well worth reading for those who have a more detailed interest, in particular how the Connecticut program works and has worked.