What happened

Alternative energy stocks are on the move for the second day in a row this week, but today, the water's getting a bit choppier. Shares of solar giant SunPower Corporation (NASDAQ:SPWR) drove 12% higher in early trading before retreating to about a 2.3% gain as of 11 a.m. EDT. Fuel cell stock Bloom Energy (NYSE:BE) gained 9% at first, then gave it all back, and has even gone negative to the tune of 4.2%.

And Plug Power (NASDAQ:PLUG), the company that's trying to capture the entire hydrogen supply chain, from production to transformation into usable electricity through fuel cells? Plug dropped early, and just keeps on dropping -- down 10% at last count.

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Image source: Getty Images.

So what

Why the early excitement, and why the sudden loss of enthusiasm? Plug's drop is the easiest to explain today, because, as TheFly.com reports this morning, Barclays just downgraded the stock. On one hand, Barclays revised its price target upward from $7 to $10 to account for the stock's recent gains. At the same time, however, Barclays worried that these gains have come too quickly -- and so the bank reduced its rating on Plug shares to "equal weight."

Bloom Energy, initially demonstrating strength today, may have gotten caught up in Plug's wake. In its note downgrading Plug, Barclays observed that other fuel cell companies (such as Bloom) have also enjoyed "smaller rallies" alongside Plug's surge. If Barclays is skeptical about Plug's gains, it stands to reason that it, and perhaps other investors, too, may rethink their enthusiasm for Bloom shares as well.

Given that Bloom stock is up 57% in just two weeks on essentially no news, this means Bloom's stock price, too, could be at risk.  

Now what

And what about SunPower? Here I think the picture looks a bit better. On the one hand, as we move closer to noonday trading, SunPower stock has already given up much of the gains it enjoyed earlier this morning. On the other hand, though, SunPower is the only one of these three stocks currently earning a profit ($110 million over the past year). SunPower also arguably received an endorsement from The Wall Street Journal earlier this week, when it noted how solar power -- but not fuel cell power -- is now "at least as cheap as fossil fuels" and offers investors "utility-like returns."

SunPower also could benefit from the catalyst of an upcoming spinoff of its solar panel manufacturing business, Maxeon, which is scheduled to take place later this quarter, allowing both halves of the business to focus on what they do best. Travis Hoium, The Motley Fool's resident solar specialist, thinks this is the deal that could position SunPower to become "the dominant player in both residential and commercial solar before long." 

With SunPower currently the only one of these three alternative energy movers still hanging onto gains today, it seems a lot of investors may agree with him about that.