Plug Power (NASDAQ: PLUG) stock price has been in a strong freefall since May as concerns about its business continue. It has retreated to below $2.50 and is nearing the important support at $2.22, its lowest swing in January and May this year. Concerns about Plug Power remainPlug Power is one of the most high-risk and high-reward companies in the United States. It is a pioneer in the hydrogen energy industry and has substantial potential if demand continues rising as some analysts expect. Plug Power has made costly progress in the past few years. It has already started selling hydrogen from i…