There has been a major shake-up in the solar-related stocks we cover during the two-week period to September 30. Short interest rose in four of the five companies, share prices fell in all four, and one has filed for bankruptcy protection.

First Solar Inc. (NASDAQ: FSLR) saw short interest fall by 3.3% to 8.21 million shares, which represents 11.2% of the company’s float. The days to cover rose to five. In the two-week short interest period to September 30, shares fell about 9.6% and are down about 1.7% year-to-date through Thursday’s close at $56.49. The stock’s 52-week range is $42.29 to $74.84.

SunEdison Inc. (NYSE: SUNE) showed an increase of 1.6% in short interest to 65.14 million shares. About 24.4% of the company’s stock is now short, and days to cover fell to five. In the latest two-week short interest period, shares fell 10%, but they are up about 22% year-to-date through Thursday’s close. The stock closed at $16.95 Thursday, in a 52-week range of $8.67 to $24.35.

SunPower Corp. (NASDAQ: SPWR) short interest remained essentially flat at 10.54 million shares, or 20.3% of the company’s float. In the two-week short interest period, shares fell about 11% and they are down about 9% year-to-date after closing at $29.34 on Thursday. The stock’s 52-week range is $25.38 to $42.07. Days to cover fell to six.

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SolarCity Corp. (NASDAQ: SCTY) saw a short interest rise of 19.3% to 13.8 million shares, or 26.2% of the company’s total float. Days to cover fell to three. In the two-week short interest period, shares slipped nearly 20%. They are down about 9% year-to-date, and the stock’s 52-week range is $41.85 to $88.35. Shares closed at $54.28 Thursday.

GT Advanced Technologies Inc. (NASDAQ: GTAT) surprised just about everyone when it filed for bankruptcy protection on Monday. The company on Thursday shut down its sapphire production and it has asked the bankruptcy court to keep confidential certain documents related to the filing. Details are scarce, but the company said in filings earlier this week that it has assets of $1.5 billion and liabilities of $1.3 billion.

As of September 30, however, the company was still operating as usual. In the prior two weeks, short interest in GT rose by 10% to 61.17 million shares, about 45% of the company’s float. Shares closed trading on Thursday at $1.29, down about 90% from their closing price on last Friday. The stock’s 52-week range is $0.75 to $20.54. Shares were trading down more than 23% in Friday’s premarket at $1.00.

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