Rumors about Applied Materials’ (NSDQ: AMAT) mystery customer have been flying ever since the company reported a $1.9 billion sales agreement “with a privately held corporation based outside the United States” in March.

Some industry insiders thought the purchaser was Masdar, Abu Dhabi’s alternative-energy company, which later that month announced it would build $1.2 billion worth of concentrating solar projects in the south of Spain. Others guessed it was Moser Baer, which in February had said it would pump $1.5 billion into thin-film solar, and still others thought it was Chinese solar-wafer manufacturer LDK Solar (NYSE: LDK).

Now, the LDK Investor Group thinks it has solved the mystery.

In a report released Tuesday, Hakan Telenius, the group’s organizer, said the buyer is Best Solar, a new company set up by LDK CEO Xiaofeng Peng.

Best Solar is an independent company that is unrelated to LDK -- other than sharing a founder -- and that aims to become the world’s largest supplier of thin-film solar panels, according to the report.

“I’m sure this is correct,” said Telenius, who wouldn’t disclose his source but said it was “a direct source” and that the information was confirmed by “lots” of other unnamed sources. “I also knew the news was spreading – lots of people, including at least one analyst, were well aware of what was happening – and we felt we had to release the information to all shareholders.”

Jesse Pichel, an analyst at Piper Jaffray, said he believes the report is correct, based on his own information. The theory also fits in with LDK’s annual report, which states that Peng and his family members “are considering and may invest or otherwise participate in his personal capacity in several alternative-energy projects, including projects involving thin-film solar technology, solar-thermal, wind energy and biofuels.”

“If true, it means the CEO’s personal business is directly competing with LDK shareholders,” Pichel said. “It’s a competing technology – one’s thin-film and one’s polycrystalline. And given that Peng’s the driver of the company, his attention may be diluted now that he’s having to run a big private company. He’s ramping a 1.5-gigawatt poly plant, a 1.5-gigawatt wafer plant and a gigawatt of thin film all at the same time.”

Officials at LDK didn’t return a call and e-mails by press time, and Applied Materials spokesperson David Miller said he couldn’t confirm or deny the information. “Applied continues to have no comment beyond our earlier filing,” he said.

LDK earlier this month said it was raising $400 million to build a 15,000-ton polysilicon plant and to expand its wafer production (see LDK to Raise $400M, LDK Wants $300M and LDK Seeks Big-Time Capital).

Telenius also mentioned the possibility of competition.

“If you’re selling solar panels through regular technology and thin-film technology, you’re kind of competing,” he said. “I wish we knew the strategy behind it all. And there may not be a strategy.”

He said he hopes Peng is considering a merger that would integrate LDK and Best Solar, diversifying its technology. But client relationships might prevent that if LDK has agreed not to get into the solar-panel business, he said.

In the report, Telenius wrote that distraction is a concern, but also found some silver lining: Peng “is reinforcing the impression we have of his ability to strike bold deals and launch large companies – a true entrepreneur – and that he is committed to building a strong solar industry in China.”

On the phone, he said the news confirmed Peng’s reputation as a deal maker and a company builder.

“I’m not sure he’s that good at executing later, but he’s a bold entrepreneur. He’s going to do this again and again,” Telenius said. “To those who sort of doubt what’s going to come of LDK, this is one thing to keep in mind: He may well do lots of things that hopefully create value for shareholders.”

While the deal with Applied Materials is a big one, several analysts said they are waiting to see what materializes before chalking it up as a win for Best Solar.

After all, Applied Materials’ technology is still a risky proposition, said Brian Yerger, a research analyst with Jesup & Lamont.

“There’s a lot of promise and a lot of hype and market capacity built into their solar division, and they’re going to be spending a lot of money and [capital] to ramp it up, but in reality they don’t have any modules that generate power yet,” he said. “It’s unusual for someone so large with such a long history spending so much to take a large shot at solar. There’s always some risk that a startup could come up and find a game-changing technology that could make Applied Materials obsolete.”

Still, betting on Applied Materials, with its size, history and credibility, is less risky than investing in a startup, he said.