Evergreen Solar director Gerald Wilson resigned from the board Friday, according to a U.S. Securities and Exchange Commission filing Monday that indicates he expressed frustration with CEO Rick Feldt to outside lead director Edward Grady (see Boston Business Journal).

The resignation is one of a series ofsolardepartures in recent months. Evergreen CFO Donald Muir left in December "to pursue other opportunities," Conergy CEO Hans-Martin R Rüter resigned Nov. 15 and Miasolé CEO Dave Pearce was replaced in September and left the company entirely in December, to name a few examples.

Then there are the Chinese solar chief financial officers. Trina Solar CFO Sean Shao said Thursday he would resign as of March 31 "to pursue other interests" and Solarfun Power Holdings CFO Kevin Wei, along with two other executives, left in November. China Sunergy CFO James Shaofeng Qi also resigned for personal reasons in August and, on Friday, the company announced its vice president of financing and investor relations, Fischer Xiaodong Chen, had left.

The trend has also become noticeable in over-the-counter Chinese companies (see this Seeking Alpha post).

Still, expressing frustration in an SEC filing stands out, said Travis Bradford, president of the Prometheus Institute, a research firm and Greentech Media partner.

"You've got to be pretty frustrated to overcome the natural desire not to air that kind of stuff in public," he said. "I don't know if there were any legal requirements. But it did seem pretty extreme."

Bradford said he doesn't see a pattern in the departures in the overall industry so far.

"The problem at Conergy was performance-related, the one at Miasolé wasn't bad performance, I don't think, but probably was just a chance to improve the technical capacity of the company," he said. "I wouldn't say that there's a clear pattern as to why."

"Clearly, all these companies – other than Conergy – are increasing their sales and earnings, so it's certainly not [poor performance]. Evergreen just made its first-ever quarterly profit, so it sounds to me like a random set of isolated events."

But the Chinese CFO departures are interesting, he said.

"It may be that people are taking a closer look at this and, in the wake of LDK, finding out their financial talent isn't good enough, which is both bad news and good news," Bradford said. "It also depends on whether they were fired or chose to leave, and often you can't tell even with the press releases."

Evergreen officials could not be reached late Monday.