Plug Power (PLUG 25.75%) stock, maker of everything hydrogen, from fuel cells to the hydrogen gas that fuels them, soared more than 19% in morning trading on the Nasdaq Tuesday -- before giving back almost all its gains by early afternoon.

As of 12:30 p.m. ET, Plug stock has gone essentially full circle -- back at only a 1% gain.

Tanker truck labeled Hydrogen drives along a road under a blue sky with clouds.

Image source: Getty Images.

Plug throws a party

But why did Plug Power stock explode higher today in the first place? Well, the most obvious catalyst appears to be the company's announcement this morning that today it is hosting "an investor tour" of its new green hydrogen production plant in Georgia.

In addition to ginning up institutional investor interest in its stock, the tour will celebrate the fact that Plug's Georgia facility just had its best month ever, producing 324 metric tons of green hydrogen fuel in August.

Is Plug stock a buy?

How good is this news, though, really? Assume Plug can sell its green hydrogen at the going rate, anywhere from $4 to $12 per kilogram -- so call it $8 at the midpoint. 324 metric tons of the stuff would therefore be worth about $2.6 million in monthly revenue for Plug.

Annualize that, and the Georgia plant looks like perhaps a $31.2 million-a-year business for Plug -- better than nothing, but adding less than 5% to Plug's $673 million in annual revenue currently. That sounds to me like a poor reason for investors to have bid up Plug stock by 19% this morning, the more so seeing as Plug's revenues still aren't earning the company any actual profits.

With a $3 billion market capitalization and annual losses of nearly $2 billion, Plug stock still looks like a sell to me.