Plug Power's management touts its long-term potential, but some analysts are starting to worry. If you listen to Plug Power's (PLUG -4.54%) management team, there's a ton of long-term upside to the company's business. Trillions of dollars are being invested into renewable technologies right now, including hydrogen fuel cells, which Plug Power specializes in. There's a case to be made that the company is primed to ride a tidal wave of investor interest. Analysts at Goldman Sachs aren't so sure. In fact, acco ...