Venture capital investors put solar on top as the sector that received the most dollars globally in 2011, but a lack of stellar initial public offerings means investors have to pump in more money while waiting for their companies to exit, said Sheeraj Haji, CEO of Cleantech Group, on Thursday.

Investments in solar totaled $1.81 billion in 111 deals in 2011, followed by energy efficiency with $1.46 billion in 150 deals and transportation with $1.12 billion in 61 deals, according to preliminary numbers from the Cleantech Group.  Money that solar companies received accounted for about 20 percent of the overall venture capital raised worldwide in 2011, Haji said during a press conference to discuss venture capital investments for 2011. 

Two themes have remained true for solar and overall venture capital investments throughout 2011:  more money for later-stage deals and fewer attempts to go public.

The top three solar deals of the year went to BrightSource, which raised $201 million, Stion with $130 million, and MiaSole with $106 million. All three California companies already had raised multiple rounds before lining up more funding last year, and BrightSource is waiting to go public.

Solar inverter maker, Enphase Energy, also filed to go public last year but began raising a private round in late 2011.

The focus on late-stage investments means “big investors like Kleiners and Khosla have big companies that require capital that are still private and haven’t tapped into the public market,” Haji said.

The IPO window narrowed and then was essentially closed in the second half of the year as Europe faced sovereign debt crisis and the U.S. grappled with a weak economy. Many public solar companies saw the values of their shares dive last year. First Solar, the industry bellwether, saw its shares plummet more than 70 percent. Investors aren’t likely to feel bullish about any solar IPOs if they don’t see the public companies regain their footings, Haji said.

The fact that two of the top three deals involved thin film technology developers also continues what is now a familiar waiting game to see when thin films will gain broader market acceptance and produce hopefully good returns for their investors. Both Stion and MiaSole, along with several other companies working on copper-indium-gallium-selenide thin films, are pushing to either enter mass production or scale up manufacturing significantly. They are using this method in order to compete with companies, particularly those making silicon solar cells and panels, that run factories with hundreds of megawatts of capacities (or gigawatts for the top 10 players).

CIGS companies are pushing the efficiencies of their thin films to rival the silicon variety. But until they do so, they will have to sell their wares at lower prices to entice buyers. Paula Mints at Navigant Consulting has said thin films have to cost on average 12 percent lower than the lowest-cost crystalline silicon panels in order to be competitive.

Corporate investors have played a key part in helping these startups stay in business. Korea companies, in particular, have taken a keen interest in a few American CIGS companies. Part of the $130 million round for Stion came from AVACO, a factory equipment maker. SK Group injected $50 million into HelioVolt. Stion also received $50 million from contract chip maker, Taiwan Semiconductor Manufacturing Co., in 2010.

Overall, cleantech companies raised $8.99 billion worldwide in 2011, a 13 percent bump from 2010, according to the Cleantech Group. The number of deals fell seven percent, however. China was the place to be for IPOs: 28 of the 51 took place in China last year. Sinohydro, Sinovel Wind Group and Huaneng Renewable Energy were among the big exits.