What happened

Easy come, easy go. Yesterday, clean energy investors were heartened by the rising prices of fuel cell stocks, inflated by the twin tailwinds of a generally ebullient stock market and rebounding oil prices.

Today, most of those gains are going away, as shares of Ballard Power (BLDP 3.00%) decline 9.4%, Bloom Energy (BE 3.56%) sinks 11.3%, and FuelCell Energy (FCEL 2.89%) brings up the rear with an 11.5% loss, all as of 1:45 p.m. EDT.

Hand holding cartoon car emitting H2 bubbles

Image source: Getty Images.

So what

Who's to blame for the sell-off this time? I guess you could blame the oil market. WTI futures are down 2.9% as of this writing, and Brent Crude is selling 2.8% cheaper, priced at $36 and change a barrel.

But honestly, I think the companies themselves are still the greater culprits.

Oil prices rise, and oil prices fall, after all, but as my fellow Fool Travis Hoium pointed out yesterday, the real attraction of alternative energy sources is always going to be the fact that they contribute less to global warming -- not just that they're cheaper than oil. A few dollars' change in the price of black gold shouldn't deter an investor who has an honest and firm faith that the future of energy on this Earth is going to be companies that produce BTUs without emitting too much CO2.

Now what

But that's the real problem with investing in Bloom Energy, Ballard Power, and FuelCell Energy, too, isn't it?

In order to have a firm future, these companies simply must eventually figure out a way to earn a profit from the business of saving the planet. So far, none of them have been able to do that on any kind of a consistent basis, and all three of these companies remain deeply unprofitable today.

Until they find a way to change that, I expect to see more sell-offs than rallies in the fuel cell industry.