The third quarter of 2009 saw the most-ever clean energy patent applications, according to the Clean Energy Patent Growth Index.
The big leader is in the fuel cell field, which saw nearly 160 patents applied for in the third quarter.
Patents for solar energy, specifically, have been up and down, however (see chart below).
With just over 30 solar patents applied for in Q3 2009, the rate has fallen dramatically since quarterly peaks in excess of 50 patents in 2002 and 2003, according to the index, which is compiled by the Cleantech Group and Heslin Rothenberg Farley & Mesiti PC.
While the number of cleantech patents may be on the rise, the sector has seen waning interest from investors.
Venture capital investments in green technology companies declined by 33 percent from $8.5 billion in 2008 to $5.6 billion in 2009.