What happened

While the S&P 500 inched higher to start today's trading session, hydrogen investors aren't particularly charged up about Plug Power (PLUG 0.40%). An analyst's uninspiring opinion on the stock is leading investors to unplug the fuel cell specialist from their portfolios.

As of 10:14 a.m. ET on Tuesday, shares of Plug Power are down 3.2%, having recovered slightly from their earlier decline of 4.2%.

So what

Espousing a less-bullish take on shares of Plug Power than her previous opinion, Sophie Karp, an analyst at KeyBanc Capital Markets, downgraded the stock to market perform from outperform, according to TheFly.com. Last June, Karp had expressed considerably more optimism, setting a price target of $40. At that time, the ambitious price target had implied upside of more than 110%.

It's not merely Karp's downgrade that's affecting investors today though. Rather, it's the appearance of a trend that's rattling Plug Power shareholders. Yesterday, Piper Sandler (PIPR 2.59%) analyst Kashy Harrison slashed the price target on Plug Power's stock to $12 from $17.

Over the past year, shares of Plug Power have plunged more than 64%.

Now what

Oftentimes, a single analyst's downgrade of a stock doesn't evoke a major reaction from the market. But the situation regarding Plug Power is a little different. There are lofty expectations that will play a pivotal role in helping facilitate the growth of the hydrogen economy. Similarly, investors presume that the company's financial situation will improve dramatically, reversing the trend of it consistently failing to report a profit.

But investors today seem to be coming to terms with the idea that Plug Power's growth isn't as certain as previously thought. Fortunately, for those bullish on the burgeoning hydrogen economy, there are other stocks to consider.