What happened

Alternative-energy stocks performed well for investors this week, with shares of FuelCell Energy (NASDAQ:FCEL) ending Thursday trading up 9.7% from Friday's close, uranium-miner Denison Mines (NYSEMKT:DNN) gaining 13.9%, and lithium-battery maker Enovix Corporation (NASDAQ:ENVX) doing best of all -- up 15.4%. Enovix investors will be happy to hear that their stock was the only one of the three to also be "in the green" for Thursday, in particular, tacking on 1.6%.

So what

Such a varied group of companies, however -- albeit all operating broadly in the green-energy industry -- owed their gains to different catalysts.

In the case of FuelCell, the fuel-cell industry's eponymous star owed its gains primarily to bullish pronouncements from one of its rivals, Plug Power, which announced last week that hydrogen fuel cells are getting so popular that it expects to record as much as $850 million in sales next year -- and more than triple that number by 2025. Investors are betting that what's good news for Plug will be good news for FuelCell, as well, which, at $3.1 billion in market capitalization, is far smaller than Plug and therefore has more room to grow.

Three colorful arrows racing straight up on a black background.

Image source: Getty Images.

Denison Mines, in contrast, is riding the coattails of a different -- but just as popular -- fuel source: uranium. According to data from TradingEconomics.com, the price of uranium is up $10 a pound over the past two weeks alone -- a 27% spike -- and Denison Mines, which mines the stuff, can be expected to profit as its stock in trade gets more valuable. 

Last but not least, Enovix Corp, which only last month crossed the milestone of producing its first battery cells in the U.S., exploded higher on Wednesday -- the same day that Tesla announced that Q3 earnings were up 73%, confirming that buyer interest in battery-powered electric cars in the U.S. is growing even faster than analysts had forecast.

Now what

All that being said, let's not lose sight of the "forest" despite all these fast-growing green energy stock price "trees." While the rapid rise in the share prices of FuelCell, Denison, and Enovix this week has certainly been fun for investors, it's important to remember that none of these three stocks is currently profitable.

Over the past 12 months, Denison Mines has lost $16 million, Enovix nearly $62 million, and FuelCell stock has racked up losses of $125 million. While positive price gains are great, in the long run, I suspect investors in these three stocks would be better served if their companies could produce a bit of positive earnings, as well.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.