It is well known that green technologies present a double externality problem. Both innovation and environmentally friendly goods have significant positive spillovers (and thus will be undersupplied absent government intervention), and the problem is magnified for environmentally friendly innovations. The standard policy solution is to correct each externality, such as through carbon taxes (or cap and trade) and innovation subsidies (e.g., patents, grants, and R&D tax incentives).
Liscow and Karpilow argue that this approach misses the dynamics of cumulative innovation. We know that innovators stand on the shoulders of giants, but Innovation Snowballing describes recent research on how innovators "prefer to stand on the tallest shoulders in order to get the quickest, largest financial returns." Specific "clean" technologies (like solar) thus need a big push to snowball past "dirty" technologies (like fossil fuels):