This has been a volatile year so far for Plug Power (PLUG -0.45%) and its stock. The hydrogen production company and fuel cell maker soared in January after its CEO said it might not need to implement a previously announced $1 billion secondary stock sale. It also announced the start of production at two of its hydrogen facilities. Investors sent shares rocketing higher in the wake of those announcements. But Plug shares have lost a large portion of those gains. And as of Friday afternoon, they had dropped ...