'Twas the morning after Earth Day, and all through Wall Street, lots of fuel cell stocks were stirring this morning. As of 10:20 a.m. ET, shares of Plug Power (PLUG 10.00%) had risen 8.2%, Bloom Energy (BE 2.84%) was up by 9.3%, and FuelCell Energy (FCEL 7.29%) was doing best of all -- up 11.9%. Considering the calendar, investor interest in renewable energy stocks this week was probably to be expected.

But thanks to Plug Power, there's some good news to underlie the enthusiasm.

Plug sees pathway to profitable growth

Plug announced today it has "achieved nameplate capacity" (aka full production capacity) at its plants in Georgia and Tennessee. Plug's Louisiana plant is "on track" to report the same in the third quarter. Thus, Plug is producing about 25 tons per day (TPD) of liquid hydrogen fuel, and is on course to grow to 40 TPD over the next five months.

What does this mean for Plug? Like gasoline, hydrogen fuel prices change from day to day. Also, Plug says it's "recalibrating" its pricing to reflect "the value of Plug's services." Still, a recent quote from California suggests prices can range as high as $36 per kilogram. Running all three plants at max capacity, Plug Power might soon generate $1.4 million in daily hydrogen sales -- about $525 million per year.

Added to the $891 million in revenue Plug made from fuel cell sales last year, this means Plug should soon be a $1 billion-plus business, and Plug says it's now on a path "to achieve profitable growth."

Buy fuel cell stocks?

That sounds like good news for Plug, and investors seem to agree that what's good for Plug will be good news for FuelCell Energy and Bloom Energy, too.

But the converse is also true. Plug's revenue may rise, but despite steadily rising revenue, Plug Power has never earned a profit, after more than 25 years of trying. To the contrary, the more Plug sells, the more money it loses. Likewise for Bloom and FuelCell, each boasting 10-plus year histories of losing money.

I wouldn't buy any of them.