It’s no secret that venture capitalists are pouring cash into greentech. But it turns out it’s been harder than expected to get a return in the industry.

At the CTSI conference in Boston last week, RockPort Capital Partners’ Wilber James told the audience that greentech is “taking more time and more money” than expected.

“We haven’t had robust exits in the cleantech space … not the robust exits people expect us to have,” he said (see Green Light post).

So RockPort set out to raise more money and last week announced that it had raised a $450 million fund, which is almost twice the size of its previous one.

That’s not surprising considering the growing trend of super-sized cleantech funds, which some claim could be leading to fewer early stage deals as venture capitalists turn to larger, later-stage investments to spend the money (see Filling Greentech’s Early-Stage Gap and this Cleantech Investing post).

Foundation Capital, Element Partners, Craton Equity Partners and Capricorn Venture Partners each have closed funds worth hundreds of millions of dollars in just the past couple of months (see Funding Roundup: SunEdison Snags $161M and Funding Roundup: Greentech Sees $988M in Q1).

RockPort plans to put the money into both early and late-stage companies and speed up product development and sales, as well as exits.

The company isn’t alone is hunting for new money. Vinod Khosla is reportedly angling for $640 million from the California Public Employees’ Retirement System (CalPERS). CalPERS would become Khosla Ventures’ only other limited partner if it puts up the money.

Khosla, famed Sun Microsystems co-founder and Khosla Ventures founder, , is fond of ethanol companies such as Range Fuels in Broomfield, Colo. and Mascoma in Boston. These are companies with capital-intensive projects, and that makes the $244 billion CalPERS a valuable partner for Khosla.

Still, while good greentech exits may be few and far between for now, some analysts and companies believe they are just around the corner (see Greentech Exits Ahead? and Funding Roundup: Solar, Biofuels Dominate Light Week).

One recent deal provides some hope. Robert Bosch, a car-parts supplier in Germany, plans to buysolarpanel maker Ersol Solar Energy for roughly €1.8 billion ($1.67 billion), a deal that surpassed previous merger and acquisition deals in the solar sector (see Is Ersol Solar Worth $1.67B?).

Check out other money deals from last week:

Solar:

  • Xtreme Energetics is raising a first round of $5 million to develop solar panels incorporating Hewlett-Packard’s flat-panel display technology. The startup, based in Livermore, Calif., announced a technology-licensing deal with HP last week. The HP technology goes into transistors that can bend and increase the amount of light collected by concentrating solar arrays. Xtreme Energetics said it will need $35 million more soon after its first infusion to help commercialize the new products.
  • Tigo Energy said it has raised $6 million to develop hardware and software for solar-panel installations. Matrix Partners and OVP Venture Partners co-led the first round for Tigo, based in Los Gatos, Calif.
  • FTL Solar said it has raised an undisclosed amount of money on the way to a $50 million round, which it expects to close in the fourth quarter. The company is developing a flexible, lightweight thin-film solar structure for prefabricated solar projects that it claims can easily be relocated. The startup, based in New York City, also has received a $200,000 matching grant from the New York State Energy Research Development Authority.

Biofuels:

  • Hadley, Mass.-based SunEthanol, which got a new CEO last week, wants to raise $20 million in venture funding. Investors in the cellulosic-ethanol company already include VeraSun Energy, Battery Ventures, Long River Ventures and Camros Capital.

Fuel Cells:

  • United Kingdom-based chip startup Evince Technology, which is developing devices it claims can improve the performance of wind turbines and fuel cells, raised $1 million. Investors included Imperial Innovations, North Star Equity Investors and the Low Carbon Seed Fund.

Other:

  • Green Vision Systems has raised €3.5 million ($5.4 million) in a first round of funding from the Gabriel Lippman Institute of Luxembourg. The Israeli company, which has spent 10 years on research and patents, plans to use the money to commercialize sensors for detecting contaminants in water, air and on land. Green Vision said its sensors could be used for anti-terrorism efforts and environmental-resource management.
  • Intel’s venture investment arm put an undisclosed amount into Grid Net, a San Francisco company that makes software to help consumers and utilities manage their energy use. The metering software provides real-time information about a power grid’s performance, so that businesses and consumers can manage their electricity use accordingly over the Web.