Fear of the disintegration of the Euro resurfaced in May, sending all stocks downward. Clean energy stocks once again fell more than the market as a whole. Possible causes are that many clean energy sectors are exposed to further loss of European subsidies, and that clean energy stocks tend to be more volatile than the market as a whole, with both up and down moves being magnified. The Russell 2000 index (which I use as a broad market benchmark in this series) was down 7.1 percent in May, the Powershares Wilderhill Clean Energy ETF (PBW), was down more than twice as much, with a 14.6 percent decline.