While government officials and venture investors who supported Solyndra LLC are being put through the wringer by House Republicans, a powerful force on Wall Street that brought these players together has largely stayed out of the spotlight.

Goldman Sachs Group Inc. (NYS:GS) , which Solyndra hired in 2008, helped propel the solar panel maker from Silicon Valley start-up to White House showcase. It solicited investors for the company with rosy valuation projections and helped Solyndra win a $535 million Department of Energy loan guarantee. And it positioned itself to earn underwriting fees if the company held an initial public offering.

The banking giant's name has come up in the course of the Congressional investigation that has followed Solyndra's spectacular downfall, but it's not the focus. Even so, the extent of Goldman's role helps explain how Solyndra catapulted from unknown start-up to secure more than $1 billion in private capital. That private backing was "absolutely" a factor in the government's decision to make Solyndra the first beneficiary of a DOE loan-guarantee program, said department spokesman Damien LaVera.

(This story was also published in Dow Jones VentureWire, a daily publication that covers news about start-ups and venture capital.)

Whether or not the DOE plowed through warning signs in its decision to back Solyndra, it is clear the agency relied on the expertise of the company's investors. During Energy Secretary Steven Chu's five-hour testimony Nov. 17, he said his approval of the Solyndra loan and a subsequent decision to restructure it was based on the analysis of "highly professional investors." Those investors include Argonaut Private Equity and Madrone Capital--the investment vehicles for Oklahoma billionaire George Kaiser and the Walton family, respectively--as well as venture firms Rockport Capital, CMEA Capital, U.S. Venture Partners, Redpoint Ventures and Virgin Green Fund.

At the heart of those investments was Goldman, whose push for private capital spanned the arc of Solyndra's rise and fall. In 2008, Goldman even considered investing its own money in Solyndra, but decided against the move, according to a person familiar with the matter.

Goldman spokesman Michael Duvally declined to comment on most aspects of Goldman's work for Solyndra, as well as whether the company has been contacted as part of the federal investigation.

Investment banks often help promising young companies raise capital, deal with the government and prepare to go public. Goldman's role in Solyndra followed that standard script, but its client turned out to be anything but typical, as Solyndra's bankruptcy filing in September triggered a political tempest.

As recently as 2005, Solyndra was just a vision in the mind of founder Chris Gronet. The company had fewer than 10 employees and barely an idea of how to make the unique cylindrical solar panels that would become its selling point.

But with enthusiasm rising about solar power's prospects, the company won its first significant financing in 2006, when three venture-capital firms agreed to invest a total of $20 million. A second round in late 2006, for $79 million, brought in the investment vehicle of energy billionaire Kaiser's family foundation, which later became Solyndra's largest investor. By the time Goldman got involved in 2008, Solyndra had already raised at least $300 million in equity and $93.5 million in debt, according to regulatory filings and research firm Dow Jones VentureSource.

That summer, as oil prices were at a record high, fueling interest in renewable energy, Goldman began soliciting investors for another round. Other solar start-ups were getting billion-dollar valuations, and Solyndra was ahead of rivals because it had already built a factory. Goldman was vying for a major stake in the rising clean-technology market--it eventually co-led successful initial public offerings for battery maker A123 Systems Inc. and electric car company Tesla Motors Inc. (NAS:TSLA) .

A private-placement memorandum viewed by VentureWire, which was shopped around in July 2008 by Goldman to prospective investors, stated Solyndra had long-term sales contracts that "allow for approximately $1 billion of sales from 2008 to 2012."

Gronet, then Solyndra's chief executive, said in a July 2008 email to an investor that Goldman was projecting an IPO valuation of $4 billion to $6 billion, according to a person who read the email. Gronet wrote in the email that Goldman was targeting an initial public offering in the first or second quarter of 2010, this person said. Gronet couldn't be reached for comment on the email.

Goldman's involvement in Solyndra, and its lofty valuation projections, lent credibility to the company and helped rouse investor interest. A big private-equity firm, brought in by Goldman, offered to put $300 million into Solyndra on the condition that it could get two board seats, said a person familiar with the matter. Argonaut Private Equity, the investment vehicle of Kaiser's foundation, won out with a counter-offer that would increase its Solyndra stake, which eventually reached 36%.

Goldman considered putting in its own money, but it decided to wait, because Solyndra had just completed its latest financing round, a person familiar with the matter said.

By early 2009, Goldman was Solyndra's exclusive financial adviser as it helped the company negotiate terms of its $535 million government loan guarantee. Emails from January 2009 show Goldman dealing directly with the Treasury Department unit that made the loan guaranteed by the Energy Department.

By that time, the market was already turning against Solyndra, because the price of a key material used by its Chinese competitors was falling sharply. That was clear to a Goldman Sachs research analyst, Michael Molnar, who in October 2008 warned clients that the risk of oversupply in the market would "soon become a reality" as subsidies shrink and financing tightens.

One of Solyndra's competitors, Nanosolar Inc., sent an email to an energy department official in February 2009, questioning "whether the DOE loan guarantee program is suitable as a 'bail-out' program for failing private manufacturers."

In the email, released to congressional investigators, Nanosolar's then-CEO cited the "rapidly deteriorating financial state" of Solyndra. Nanosolar declined to comment.

Goldman continued with plans to take Solyndra public. Following the closing of the federal loan in September 2009, Solyndra filed in December 2009 to go public and raise $300 million. Goldman and Morgan Stanley were the lead underwriters and stood to make millions of dollars in banking fees.

In March 2010, Solyndra's auditor raised doubts about the company's prospects. Two months later, Solyndra canceled its IPO, citing market conditions, and soon was in danger of defaulting on the DOE loan.

In an effort to keep Solyndra afloat, Goldman began canvassing for investors. In October 2010, Goldman representatives were scheduled to meet with the DOE to discuss the potential for bringing in more private capital from new investors, according to emails published last week as part of the Congressional investigation. It's not clear from the documents whether Goldman and the DOE actually met at that time, but an Oct. 30 email said the meeting "could potentially impact the DOE's decision to allow the November or December fundings," referring to a scheduled drawdown of capital under the loan agreement.

Around that time, Goldman was discussing with potential investors a sharply decreased valuation for Solyndra of around $200 million to $250 million, according to two people familiar with the matter. Even at that value, Solyndra was unable to find new backers. Potential investors participating in the discussions included General Electric Co. (NYS:GE) and Bosch Group, and private equity firms General Atlantic, Silver Lake and Warburg Pincus, according to emails.

By December 2010, Solyndra had run so short of cash that it violated terms of its loan agreement. A group of existing investors, including Argonaut, came to the rescue in February of this year by giving the company a $75 million loan, on the condition they be placed ahead of the U.S. government if Solyndra were to be liquidated. This August, Solyndra needed still more money. The government was in talks to restructure its loan but eventually declined.

With no options in sight, the company pulled the plug in September, filing for bankruptcy and laying off about 1,100 employees. Solyndra's $1 billion sales projection in the Goldman-advised 2008 memo proved to be overly optimistic. At least two Solyndra customers, Phoenix Solar AG and Solar Power Inc. , amended their long-term contracts with Solyndra in 2009, according to the companies. Solyndra didn't repeat the sales figure subsequently in its IPO filing. By the end of 2010, Solyndra had total sales of $246 million, with limited sales in 2011 before the bankruptcy.

All told, Solyndra raised $1.34 billion in private capital--including $632 million in equity and $300 million in debt with Goldman's help, according to filings and VentureSource data.

Solyndra is currently trying to unload its assets to the highest bidder in the wake of its bankruptcy filing. This time, it won't get any help from Goldman: Goldman's Duvally said the bank and Solyndra are no longer involved with each other.