"But a lot of the new plants are replacing older ones, " says Brian Potskowski of BNEF.

CNN: Shale gas boom sparks EU coal revival

Defining clean energy companies can be tricky, and most industry observers such as BNEF use lists of technologies.

FORBES: Top Performing Clean Energy Funds in 2010

Gas-fired power plants supplied 31 percent of U.S. electricity in 2012, according to BNEF, up from 22 percent five years ago.

FORBES: U.S. Carbon Emissions Dip To 1994 Levels

In many cases, the answer is yes, according to a paper released last week by Bloomberg New Energy Finance (BNEF).

FORBES: Solar Power More Competitive Than Decision-Makers Or Consumers Realize