Capital is tight for clean tech, and it's not just because of the economy -- investors are also being asked to back some pretty long-term technologies, and not everyone wants to be first to assume the risk.
Consider Potter Drilling, which has the potential to solve a very big problem. With enough financial backing, it could supply enough clean energy to equal 2800 times the current consumption of the U.S. -- if it can drill enough 10-kilometer-deep holes to extract the heat that's trapped in the rocks below the surface of the earth. Every town could have its own hole, says CEO Jared Potter -- and it's own little power plant.
It's a tantalizing picture, but now, drilling a well that's only 30,000 feet (9.1 kilometers) deep costs over $200 million with today's technology. Asking investors to bet on a vision has been tough.