What happened

Shares of hydrogen fuel cell stocks Plug Power (PLUG -3.11%) and FuelCell Energy (FCEL -8.02%) declined sharply in Tuesday morning trading, and alongside them fell shares of electric-car-charging company Blink Charging (BLNK 0.44%).

As of 11:20 a.m. EST, Plug stock is down a disheartening 7%, FuelCell has fallen 8.3%, and Blink is faring worst of all -- down 10.5%.

Three red arrows going down and crashing through the floor

Image source: Getty Images.

So what

Why are all of these stocks down today? There's no obvious answer to that question aside from "skittish investors." Fact is, the only news in evidence so far this week directly touching on any of these three stocks is the announcement yesterday afternoon from investment bank Roth Capital Partners that it raised its price target on Plug Power stock.

In a note covered today by TheFly.com, Roth doubled down on its buy rating on the fuel cell pioneer, arguing that Plug's just-announced partnership with French tractor-trailer maker Gaussin will begin adding revenue to Plug as early as next year, potentially becoming a material driver of the business over the long term.

Now what

Personally, I have my doubts about that. As I explained yesterday, Gaussin is really just a bit player in the global automotive market -- a small-cap stock bordering on micro-cap status, with just $11 million in annual sales, that will be unable to move the needle for Plug. Be that as it may, Roth said the deal makes Plug stock worth a cool $30 a share. You'd think that, no matter how tenuous the analyst's argument, Plug stock fans would be happy to hear that -- but in fact, investors are doing the opposite, and selling Plug stock.

Why is this happening, and will it continue? I suspect that the twin sell-offs of FuelCell Energy and Blink Charging shares may provide a clue to the answer. So far today at least, there's been no news -- good or bad -- about those two companies, and yet they're falling right alongside Plug. And what this tells me is that investors are still all shook up over yesterday's news that General Motors has scrapped its plans to invest $2 billion in electric-truck start-up Nikola ... and wondering if perhaps everybody's gotten just a bit too excited about the future of alternative energy stocks in transportation in general.

If I'm being honest, I kind of wonder the same thing myself.