Venture capitalists have invested in the search for clean technologies -- from renewable energy to sustainable building materials -- for several years.

But renewable energy recently gained the attention of large Wall Street banks and private equity firms amid widespread concerns about soaring oil prices and global warming.

Last year, global investments in clean energy grew 41 percent to US$117 billion, according to research firm New Energy Finance.

In 2006, Riverstone, an energy-focused private equity firm, teamed up with the Carlyle Group to set up a US$685 million renewable energy fund. (Reporting by Anupreeta Das; Editing by Andre Grenon)