That represents another big jump, after clean tech went from $836 million in the first quarter to $1.2 billion of second quarter.
"There is a lot of momentum and there are a lot of deals in the pipeline," said Eric Wesoff, who wrote the report. "People are energized by the A123 Systems Inc IPO. I'd say it's reasonable to look for moderate growth in the fourth quarter."
Shares of battery maker A123 soared more than 50 percent, marking it as the most attractive of that week's public offerings.
Wesoff said venture capitalists will take note of that, but that their pockets are not deep enough to support continued growth at the rate of the past two quarters.
More than half the clean tech investment in the third quarter went into two areas — solar and a combined category of biofuels, gasification and cleaner coal.
Solar accounted for $575 million in 29 deals, and biofuels, gasification and coal for $513 million in 17 deals.
One company alone, high-efficiency solar electric panel maker Solyndra, accounted for a $198 million, in a round led by Argonaut Private Equity.
Exxon Mobile Corp made a multi-year commitment to invest $300 million in Synthetic Genomics for the development of algae-based fuels.
Smart grid and associated technologies accounted for $160 million in 14 deals, and auto and transport in five deals for $158 million.
Green buildings at $105 million and green materials at $100 million were the other two major areas.
Still the deals failed to hit the record highs of 2008, when the third quarter saw $2.9 billion and the entire year $7.6 billion. Wesoff said the year — and the quarter — were driven by unusual capital investment to build out solar manufacturing plants.