Plug Power Inc (NASDAQ:PLUG) stock has fallen more than 42% in the last three months. But bearish sentiment is far from abating. The stock was the target of a significant growth in short interest between Nov.14 and Nov.28, the latest date for which data is available. As of Nov.28, a total of 36.55 million shares of the company were held short, up 3.8% from 35.22 million on Nov.14.

Plug Power Inc Witnesses Significant Jump In Short Interest

21.9% of the float is held short

Based on the average daily trading volume of 4.96 million shares, it will take short sellers 7.4 days to cover their positions. Currently, 21.9% of the company’s total outstanding shares are held short. An increase in short interest is quite surprising, given there has been a lot of positive news about Plug Power in recent months. On Nov.4, it signed a hydrogen distribution deal with Praxair, Inc. (NYSE:PX) where Praxair agreed to supply hydrogen fuel to Plug Power’s customers across the United States.

Last month, Plug Power also installed its first ground support equipment (GSE) at the Memphis airport. Its system will power 15 trucks at the airport using Plug Power-made fuel cells. Last week, the Latham, New York-based company announced a $20 million multi-year deal with a leading U.S. telecom company. Plug Power will provide the undisclosed telecom carrier its GenFuel and ReliOn solutions.

Plug Power growing at a healthy rate

Plug Power’s revenue has been growing at a healthy rate. Wall Street forecasts the company’s revenue to jump 160% in FY2014, followed by an 80% increase in 2015. Plug Power CEO Andy Marsh projects 2014 revenue to come in at $75 million, almost triple the revenue in 2013. For the next year, the company is targeting $130 million revenue. Plug Power has won multiple deals with Volkswagen, Walmart, FedEx, BMW and others.

So, why are investors so bearish on the stock? Most likely because Plug Power remains unprofitable even 15 years after going public. Its cost of revenue over the last four quarters was 112.5%. That means the company spends $1.125 to earn $1 in revenue. Its gross profit margin is -12.5%.

Plug Power shares fell 6.25% to $2.75 at 11:26 AM EST on Monday.