Just how bad were clean-tech investments?

FORTUNE — Conventional wisdom is that venture capitalists have taken a bath on clean-tech, thanks to high-profile flops like Solyndra and Fisker Automotive. But new data suggests that such examples are exceptions rather than the rule.

Cambridge Associates today published its first-ever set of performance statistics statistics on investment into private cleantech companies, based on a data set of over 1,200 deals for 644 companies since 2000. The deals represented over $21 billion in capital from 302 venture capital funds and 106 private equity funds, with nearly three-quarters of the dollars disbursed to U.S. companies.

CA found that these deals produced a gross internal rate of return (IRR) of 6.6% through the end of Q3 2012, and a gross total value to paid in capital multiple of 1.2x. That’s several miles below spectacular — particularly since the net IRR to limited partners is closer to 2.2% — but it’s not the black hole that many have made clean-tech out to be.

Moreover, U.S. clean-tech companies outperformed foreign clean-tech companies, generating a gross company-level IRR of 7%.

CA also broke down clean-tech into four sectors, finding the strongest gross IRR performance in renewable power development (11.4%) and the weakest in resource resolutions (1.4%):

In its commentary, CA cautions that cleantech investment is still relatively young — with 89% of the investments coming since 2005. It adds that many investors have dropped out of the sector lately, which should reduce future investment volume but improve remaining returns.

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