Far more green technology companies cashed out by being sold to a corporate buyer than via entry to the public markets last year. That’s the gist of Cleantech Group’s preliminary 2011 green technology investment figures, which showed that corporations spent $41.2 billion on greentech M&A last year, up 153 percent from 2010.

That doesn’t count a lot of undisclosed transactions, such as Siemens’ purchase of eMeter, which could significantly boost that tally, Cleantech Group CEO Sheeraz Haji said in a Thursday conference call. According to conversations he’s having with corporate execs today, that trend is going to continue in 2012, he said.

That’s a good thing, because the IPO window has been “effectively shut for most venture-backed cleantech companies,” Haji said. All told, 51 IPOs were priced in 2011, with a value of $9.6 billion, down 42 percent from 2010, Cleantech found. Most of those were Chinese companies -- perhaps you’ve heard of Sinohydro, Rentech Nitrogen Partners, Kingsun or Technovator?

Meanwhile, the list of U.S. startups that have filed S-1s but have yet to go public include Silver Spring Networks, BrightSource Energy, Enphase Energy, Elevance Renewable Sciences, Smith Electric Vehicles, Coskata, Mascoma, Fulcrum Energy and BioAmber.

Still, Haji foresaw “some real rock-star IPOs in 2012” that stood the chance of opening up the markets to other startups in their respective sector. Here’s what he had to say about some IPO candidates:

- Smart grid networking upstart Silver Spring Networks is likely to have a very successful IPO, “but they’ve had to do some insider financing” to shore up their growth plans, raising $24 million from EMC last month.

- Solar thermal developer BrightSource “needs to raise money -- we think it’s going to happen, but it needs to be watched closely.”

- Solar microinverter leader Enphase “is growing very quickly -- we’re keeping an eye on it, but the market has to cooperate.”

Haji stressed market conditions, which aren’t good. The Cleantech Group’s index of publicly traded green technology companies lost roughly 20 percent of its value over the course of 2011, compared to a flat S&P 500.

In the meantime, venture capital investment rose to $9 billion, with North America growing to $6.8 billion and Europe/Israel shrinking to $1.3 billion -- a reflection of Silicon Valley’s influence and Europe’s economic malaise. But late-stage investments continued to take an increasing share of VC totals, a reflection of the fact that close-to-IPO portfolio companies are going back for more private cash.