Private investment firm Najafi Companies said Monday it has launched a new company, Energy Capital Investments, and armed it with $100 million to invest in green-energy projects.

The new fund is Najafi's first foray into green technology. The Phoenix-based firm has its roots in real-estate investments and has backed traditional IT companies like Network Solutions.

The move is part of a growing trend of investment firms raising millions to stake their claims in the greentech sector.

Among others, Chrysalix Energy Venture Capital and Robeco announced a joint venture fund with €50 million (about $72 million) in startup capital earlier this month, Expansion Capital Partners closed a $103 million fund in September, Climate Change Capital closed a €200 million fund for green investments the same month and Technology Partners closed a $300 million fund for cleantech and biotech in July (see Expansion Closes $103M Fund and Chrysalix Announces New €50M Fund).

The fund raisings are helping to fuel growing VC investment in greentech. Numbers vary widely, but Thompson Financial puts U.S. greentech venture-capital investments for the first three quarters of the year at $2.6 billion, up 46 percent from the $1.78 billion invested in all four quarters last year (see Greentech VC Hits $2.6B in U.S., Global Greentech VC Hits $1.1B and Wal-Mart Asks for Help to Achieve Green Goals).

But some industry watchers have questioned whether enough good investments are available to justify all the capital swirling around. A study earlier this year by New Energy Finance found that VCs were able to invest just 73 percent of the funds they had raised and had not been able to spend $2 billion of the money they had available.