(Reuters) - SunEdison Inc SUNE.N, once the fastest-growing U.S. renewable energy company, filed for Chapter 11 bankruptcy protection on Thursday after a short-lived but aggressive binge of debt-fueled acquisitions proved unsustainable.

The headquarters of SunEdison is shown in Belmont, California in this April 6, 2016 file photo. REUTERS/Noah Berger/Files

In its bankruptcy filing, the company said it had assets of $20.7 billion and liabilities of $16.1 billion as of Sept. 30.

SunEdison's two publicly traded subsidiaries, TerraForm Power Inc TERP.O and TerraForm Global Inc GLBL.O, are not part of the bankruptcy. In a statement, the companies, known as yieldcos, said they had sufficient liquidity to operate and that their assets are not available to satisfy the claims of SunEdison creditors.

The bankruptcy “will present challenges,” however, including with financing agreements for certain projects, the yieldcos said.

The Chapter 11 filing caps SunEdison Chief Executive Officer Ahmad Chatila’s seven-year quest to transform a struggling maker of silicon wafers into a renewable energy giant able to capitalize on burgeoning demand for solar and wind energy amid growing concerns about climate change.

Chatila was named CEO of what was then called MEMC Electronic Materials in 2009 and almost immediately bought fledgling solar project developer SunEdison. The company changed its name four years later and embarked on a rapid expansion that included entering new businesses like wind and energy storage and taking on projects worldwide. That growth racked up billions of dollars of debt.

Solar industry watchers said the bankruptcy was not a reflection of the sector, which is growing rapidly.

“SunEdison had a balance sheet that is way out of line with any other solar company,” said Shayle Kann, senior vice president and renewable energy research firm GTM Research. “The projects themselves are good. They just bought too much to quickly.”

The company said it secured up to $300 million in new financing from its first-lien and second-lien lenders, which is subject to court approval. The money will be used to support SunEdison’s operations during its bankruptcy.

“Our decision to initiate a court-supervised restructuring was a difficult but important step to address our immediate liquidity issues,” said Ahmad Chatila, SunEdison chief executive officer.

He said the company planned to use Chapter 11 to reduce debt, shed non-core operations and take steps to get the most value out of its technology and intellectual property.

SunEdison asked the bankruptcy court to appoint an independent examiner to review recent transactions. While it said it is not aware of any particular wrongdoing, it cited a subpoena from the U.S. Department of Justice related to financing activity, an investigation by the U.S. Securities and Exchange Commission and a lawsuit filed by TerraForm Global in its petition.

It asked that the investigation begin immediately and conclude within 60 days, a short timeframe compared to independent examinations in bankruptcies such as the operating unit of Caesars Entertainment Corp CZR.O, which lasted 12 months with costs topping $40 million.

SunEdison said the budget for the examiner should not exceed $1 million.

Shares of SunEdison were halted, and last traded at about 34 cents on the New York Stock Exchange. The company's stock traded as high as $33.44 in July 2015. Shares of First Solar Inc FSLR.O closed up slightly and shares of SolarCity Corp SCTY.O were up 3.7 percent in late trading. An index of solar shares .SUNIDX gained 0.7 percent.

Major SunEdison shareholders include OppenheimerFunds Inc with a 11.9 percent stake, BlackRock Inc BLK.N with a 6.5 percent stake, The Vanguard Group with a 6.4 percent stake and Adage Capital Partners GP LLC with a 5.4 percent stake, according to court documents.

Hedge fund Greenlight Capital, led by David Einhorn, earlier this week reported that it had sharply cut its stake in SunEdison. Greenlight, which won a board seat at the company earlier this year, declined to comment on the bankruptcy.

Investors began to lose confidence in SunEdison's supercharged expansion last summer, when the company announced a $2.2 billion deal to acquire rooftop solar installer Vivint Solar Inc VSLR.N. At the time, renewable energy stocks were under pressure, in part because falling oil prices sparked concerns about demand for alternative energy sources.

The Vivint deal touched off litigation involving SunEdison’s yieldcos, the listed subsidiaries that own and operate renewable energy assets, many of which were acquired from SunEdison.

Billionaire David Tepper’s Appaloosa Management sued to prevent TerraForm Power from buying some Vivint assets. Appaloosa is also seeking to overhaul TerraForm Power’s Conflicts Committee, claiming the company’s controlling shareholder, SunEdison, breached its fiduciary duties.

Tepper was not immediately available for comment.

In March, Vivint terminated the cash-and-stock deal after SunEdison failed to close on the planned acquisition. Vivint shares were up 4.9 percent on Thursday.

SunEdison is also being investigated by the U.S. Department of Justice and the U.S. Securities and Exchange Commission over the failed Vivint Solar deal and other issues.

SunEdison is also being sued by TerraForm Global, its other yieldco, for breach of contract, alleging SunEdison misappropriated $231 million of TerraForm’s cash.

The company has delayed filing its annual report twice after identifying material weaknesses in its financial reporting controls.

The case is in U.S. Bankruptcy Court, Southern District of New York, Case No: 16-10992