Royal Dutch Shell took a lot of flak when it pulled out of the huge "London Array" offshore wind farm in the U.K. last week. The prevailing explanation for the withdrawal? Higher oil prices make old-fashioned energy a more attractive investment than still-immature renewable energy.

Perhaps there's a less-conspiratorial explanation. Maybe offshore wind power just isn't up to snuff yet. Denmark's Vestas, the world's biggest wind-turbine maker, today said Europe should curb its enthusiasm for massive offshore wind farms, and focus on regular onshore wind power. Vestas isn't hiding vested interests-it's one of the leading makers of offshore equipment, too. Dow Jones' Clean Tech Investor reports:

"If you look at offshore wind capacity there's basically only Vestas and Siemens AG who can do it and we can only do one to two major projects a year, so for all these offshore projects I wonder who's going to build them - we can't do it," [Vestas CEO Ditlev] Engel said [...] "We're expanding Vestas' offshore business and we have good growth expectations, but we're afraid that the political ambitions are impossible to meet," Engel said.

Offshore wind power has long been a holy grail of renewable energy. Stronger winds and bigger turbines, the reasoning goes, should mean cheaper electricity. Turbines way off the coast should alleviate NIMBY concerns. But offshore wind can't get up to speed. Shortages in turbine supplies, as well as in gear needed for offshore installation, like rigs, ships, and steel supports, have increased costs and pushed back projects.

Vestas isn't alone in its call for a return to more-economical, tried-and-true onshore wind. Last month, German utilities called their country's ambitious offshore wind plans-15 gigawatts by 2020-"absolutely unrealistic." British utilities are wondering how their country can meet their stated targets of 30 gigawatts of offshore wind power by 2020. Worldwide today, just over 1 gigawatt (think one big coal plant) of offshore wind is installed. Onshore wind counted about 93 gigawatts at the end of last year.

Of course, a return to onshore wind would suit Vestas just fine, in any event. The company's first-quarter profit, announced today, doubled even as sales fell. Relentless demand for hard-to-source turbines means Vestas is charging more for each machine. And that situation won't ease anytime soon, Mr. Engel said.