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Short interest moves among solar and alternative energy stocks were mixed during the two-week reporting period that ended on April 30. Of the companies we watch, short interest fell on two of three solar stocks and fell on three of four alternative energy stocks.

On Wednesday, the California state regulators approved a measure that requires all new homes built in the state to have rooftop solar panels installed within two years. Solar stocks reacted positively to the news.

First Solar Inc. (NASDAQ: FSLR) saw short interest increase by 5.1% to 4.41 million shares, which represents about 6.1% of the company’s float. Days to cover fell from four to two. In the two-week short interest period, the stock’s share price dipped by about 1.6%. Its 52-week range is $33.27 to $81.72, and it closed at $69.43 on Wednesday, up about 3.2% for the day.

SunPower Corp. (NASDAQ: SPWR) short interest decreased by 6.7% to 14.81 million shares, or 24.4% of the company’s float. In the two weeks to April 30, the share price rose by 3.9%. The stock’s 52-week range is $6.46 to $11.70, and it closed at $9.01 on Wednesday, up about 6.4% for the day. Days to cover dipped from nine to five.

Canadian Solar Inc. (NASDAQ: CSIQ) saw a decrease of 16.6% in short interest during the two-week period. Some 3.3% of the total float, or 1.49 million shares, were short and days to cover remained unchanged at three. The company’s share price fell by about 5.4% over the two weeks, and shares closed Wednesday at $16.26, up about 3.4% for the day, in a 52-week range of $12.07 to $19.09.

FuelCell Energy Inc. (NASDAQ: FCEL) posted a decrease of 25.7% in short interest during the period. Some 5.86 million shares were short as of April 30. The stock closed at $1.93 on Wednesday, up about 1.6% for the day, in a 52-week range of $0.80 to $2.49. Shares traded down about 7.8% in the short interest period, and days to cover rose from six to eight.

Plug Power Inc. (NASDAQ: PLUG) saw short interest dip by 0.2% to 34.41 million shares. Days to cover remained unchanged at 10, and about 15.2% of the company’s shares were short. In the two weeks to April 30, the share price fell by about 3.2%. The stock’s 52-week range is $1.53 to $3.21, and shares closed Wednesday at $2.00, up about 8.7% for the day.

Clean Energy Fuels Corp. (NASDAQ: CLNE) saw a drop of about 6.3% in short interest to 4.2 million shares. About 3.1% of the company’s float was short, and days to cover rose from six to nine. The share price fell by 1.8% in the short interest period. The stock closed at $1.91 on Wednesday, up about 2.1% for the day, in a 52-week range of $1.31 to $3.05.

Pacific Ethanol Inc. (NASDAQ: PEIX) saw short interest rise by 4.5% in the two weeks to 2.27 million shares, about 5.3% of the company’s float. Days to cover remained at five. The stock price rose by about 1.2% in the period. Shares closed at $3.40 on Wednesday, up nearly 8% on the day, in a 52-week range of $2.75 to $7.50.