The study, by New York research firm Lux Research, said about $US5.6 billion ($A6.8 billion) was spent on clean energy investments in 2006, up from $2.2 billion in 2005.
New floats of companies in this sector – most of which were either solar or biofuels – also rose to $4.1 billion from $1.6 billion.
Lux president Matthew Nordan said the investment was driven by fears of peak oil and the possibility of new measures to curb greenhouse gas emissions.
But he warned that the investment had happened too quickly.
“When you see venture capital more than double from one year to the next, and IPO values double from one year to the next, that’s the sign of a bubble in the making,” Nordan said.
“Driven by solar and biofuel deals, the energy segment looks overheated – there’s no way that more than a fraction of the 930 energy start-ups operating worldwide can possibly succeed.”
Lux also reported research and development in clean technology rose 9% from 2005 to $48 billion last year, with the Asia-Pacific region the leader. The region accounted for 38% of global R&D spending by governments and 34% by corporations.
