Solar energy has been the victim of its own success, growing at an annual rate of 254% between 2004 and 2008 according to NEF, creating a mini bubble that was bound to burst.

CNN: The smart money's on green

The result is, there is now a vociferous group of shale-gas (and oil) enthusiasts who have created a mini-bubble in shale.

FORBES: Shale Oil And Gas: The Contrarian View

The solar stocks "mini-bubble", the meteoric rise of the clean energy sector in 2007 and the backing from Silicon Valley venture capitalists have led some to compare the clean energy sector to the dot com bubble of the late 1990s, but Nasdeo is quick to point out the differences.

CNN: The smart money's on green