Cleantech investments in the U.S. reached a record high of $1.6 billion in the third quarter of 2008, according to a report from the advisory group Ernst & Young. That’s a 55 percent increase over investments during the third quarter of last year.

Solar energy projects are attracting the bulk of investors’ cash, with seven of the top 10 deals focused on the solar industry. They include such developments as SolarReserve Inc.’s plan for solar thermal power plants, which attracted $140 million in second-round funding this past quarter.

Despite the faltering global economy, cleantech projects continue to attract growing piles of cash: a total of $3.2 billion in the U.S. so far this year, compared to $2.7 billion for all of 2007.

Incredibly, you can give a little credit for cleantech’s relatively smooth sailing in hard economic times to Washington’s $700 billion-plus bailout program, which has otherwise enjoyed questionable success. The bailout included support for renewable energy in the form of extended tax credits for solar, wind, geothermal and biomass projects (an eight-year extension for solar, one year for the rest).

The cleantech steamroller isn’t speeding along only in the U.S., though: the Cleantech Group reported today that seven new or expanded funds have injected some $1.9 billion into global clean-energy efforts this week alone. That’s one clean and mighty steamroller.

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