In a difficult year for solar, venture capital investors continue to invest in the sector -- although the activity has shifted away from early stage to the late stage follow-up rounds seen below. Here are the six heftiest rounds in solar in 2011.

BrightSource Energy (Oakland, Calif.) raised a $201 million Round E for its concentrated solar power (CSP) technology in March, bringing its total funding to more than $530 million in private equity. That funding is in addition to a federal loan guarantee of $1.3 billion. The investors include Alstom, a French power plant player, as well as the usual suspects: Vantage Point Venture Partners, Alstom, CalSTRS, DFJ, DBL Investors, Chevron Technology Ventures, and BP Technology Ventures, with assistance from Advanced Equities. The company has had an S-1 filed with the SEC in registration for an IPO since April 2011 and recently added thermal energy storage to several of its projects. The BrightSource deal looks like it narrowly beat battery-swapping startup Better Place's $200 million as the largest greentech VC funding deal of 2011.


In the largest photovoltaic funding round of 2011, San Jose, California-based Stion, a manufacturer of CIGS-based thin-film modules, raised $130 million in private equity in December led by AVACO and Korean private equity funds. The firm's existing investors -- Khosla Ventures, Taiwan Semiconductor, Lightspeed Venture Partners, Braemar Energy Ventures and General Catalyst Partners -- also participated in the funding round, the company said. The firm is expanding manufacturing in its Hattiesburg, Mississippi facility, as well as opening a Korean manufacturing subsidiary. Lead investor in this round, AVACO, is a supplier of thin-film processing equipment. Stion's module are monolithically produced on glass, and the firm has achieved 14 percent efficiencies in early production. The firm has a tandem design in the works and has licensed its technology to Taiwanese foundry TSMC.

Suniva raised $115M in a Round D, closed after suspending its request for a DOE loan guarantee. The VC funding for Suniva's high-efficiency crystalline silicon solar cells came from Advanced Equities, Goldman Sachs, HIG Ventures, New Enterprise Associates, and Warburg Pincus. Suniva is "suspending" its efforts to close on a loan guarantee because of the company's displeasure with the DOE's terms and conditions. Suniva uses a number of different cell structures and processes to build a high-efficiency crystalline silicon solar cell. 

MiaSolé (Santa Clara, Calif.) raised $106 million of a $125 million round for its CIGS thin-film solar panels. The firm has raised in the neighborhood of $500 million in VC funding since its founding in 2004. MiaSolé raised most of a $125 million round F in February at a pre-money valuation of $550 million. New investors included Voyageur Mutual Funds III, joining existing investors Kleiner Perkins, Firelake Capital, and VantagePoint Venture Partners. Board members include KP's John Doerr, Firelake's Marty Lagod, VantagePoint's Stephan Dolezalek, and Rob Chandra of Bessemer. The new CEO was quoted as saying, "A lot of companies are interested in this space, and if we could find the right partner, [one] that could help make MiaSolé a more long-term enduring company [and] that's good for our shareholders and our employees, then I would support that strategy," according to a Reuters piece.


Heliovolt (Austin, Texas), a manufacturer of CIGS solar panels, won $50 million from SK Innovation, South Korea's biggest refiner and a company that accounts for 10 percent of South Korea's gross domestic output, as part of an $85M round which included New Enterprise Associates, et al. The firm's monolithic-construction panels have the same form factor as First Solar with what HelioVolt claims is a comparable efficiency of 11.7 percent. Like First Solar, these are frameless panels with an edge treatment and power output in the 75-watt to 80-watt range. The firm will be expanding operations in Austin, and the purpose of this financing is "to test manufacturing scalability and take the next step," according to BJ Stanbery, the firm's founder.

Alta Devices, a Santa Clara, California-based developer of high efficiency solar photovoltaics, raised $72 million. The firm's technology is based on thin-film gallium arsenide (GaAs), with investments from August Capital, Kleiner Perkins Caufield and Byers, Crosslink Capital, DAG Ventures, NEA, Presidio Ventures, Technology Partners, Dow Chemical, AIMCo, Good Energies, Energy Technology Ventures, and Constellation Energy. The CEO of the firm said that the single-crystalline, direct-bandgap structure of GaAs, "a perfect crystal," distinguishes its technology from the CIGS players.