Investments in “green” or environmentally friendly firms in the “cleantech” sector present a wide range of challenges to venture capital firms, according to a new study.

Topline Strategy Group, a consulting firm in Boston, says in its reports that cleantech companies have “significantly different business models” than the high-tech and life science firms VCs have focused on in the past.

As a result, some VC firms who specialize in energy and other cleantech industries are making deals, most firms remain cautious, the group said.

The study is titled “Cleantech and Venture Capital: A Whirlwind Romance or Just Dating?”

“Cleantech companies have significantly different business models than high technology and life sciences companies,” said Jonathan Klein, founder and general partner of Topline Strategy Group. “These fundamental differences require venture investors to evaluate opportunities differently and require different capabilities. Mainstream venture capital investors are interested, but they are moving cautiously as they begin to understand the unique needs of the space.”

Some $1.36 billion was invested in 121 deals between April of last year and March of this year – a miniscule portion of the $25 billion in 3,200 deals made overall, the report said.

Cleantech firms tend to operate at low margins and rely on what the study called “heavy” government subsidies.