There wasn’t much consensus about the most promising energy technologies, but everyone at a panel on the future of energy at the EmTech conference at MIT this morning seemed to agree that three energy-related technologies won’t make money, at least not in the current economic and regulatory environment.

Heading the list of losers is photosynthetic algae–technology that would use algae to convert sunlight into fuel. Jim Matheson, a general partner at Flagship Ventures, said “we just don’t believe the economics.” Although the venture capital firm invests heavily in bio-energy technology, “we just haven’t gotten very comfortable that algae is going to come down the cost curve.”

BP also doesn’t like photosynthetic algae. “We don’t think that [technology] will ever reach the kind of cost or supply that we think people are prepared to pay,” said David Eyton, the head of research and technology at BP. His statement was a direct challenge to a main BP competitor, Exxon-Mobil, which recently announced an investment of $600 million in photosynthetic algae.

Eyton noted that BP is investing in algae–just not the photosynthetic kind. Some companies are developing technology that use algae to convert sugar, instead of sunlight, into fuel and other products. That’s easier to scale up, since the algae can be far more concentrated.

Hydrogen, at least for vehicles, was also panned. That’s perhaps not surprising given Energy Secretary Steven Chu’s recent comments about hydrogen. Then again, the car companies have been clamoring for continued investment in it. Uma Chowdry, senior vice president and chief science and technology officer at DuPont said the company had killed its research on hydrogen storage “because it’s very far away.” Eyton said BP had also killed its investment in hydrogen for transportation.

And finally, technology for capturing and storing carbon dioxide doesn’t look promising. The technology could be key to reducing carbon emissions, but Chowdry said, “We can’t figure out how we’re going to make money at it.” Eyton noted that “it’s tough to make it work, when nobody’s putting a price on it.”