Two Quirky Turbines, Combined At Sea

Darrieus and Savonius turbines have been combined before – but never with one of them under water, grabbing the energy of the tides.

That’s the plan with a Japanese marine energy device [PDF] from Mitsui Ocean Development & Engineering Co. (MODEC), a company that has a history dating back to 1968 of building a wide range of floating production systems.

image via MODEC

image via MODEC

The company says the Savonius Keel & Wind Turbine Darrieus is the “world’s first wind & current hybrid power generation” system, and according to a report from CBS News, the plan is to deploy it before the end of this year off the west coast of Japan.

Earlier reports said the company was planning to deploy a 500-kilowatt device in its test this year.

A vaguely similar hybrid marine-energy device is being pursued by an Australian company, Marine Power Technologies, but that one uses a horizontal-axis wind turbine and oscillating water column wave generators – each a common technology, although combined in a unique way.

The SKWID device is a curiosity for both what’s above and below the water. First, Darrieus wind turbines, after getting a fair bit of attention in the 1970s and 1980s, are pretty out of fashion these days – although the Sandia lab down in New Mexico thinks they could work for super-big offshore applications, like between 10 and 20 megawatts.

MODEC makes the case for the Darrieus thusly:

The omnidirectional Darrieus turbine rotates regardless of the wind direction. Due to the location of the generator, the system has excellent stability with a low center of gravity, as well as excellent maintainability with easy access. The Darrieus’ rectangular swept area catches twice as much wind when compared to the circular swept area of typical onshore wind turbines of the same diameter and is therefore capable of delivering twice as much power from a single installation – far more power from the same wind farm area.

The Savonius keel for generating tidal power is pretty wild, too; these stocky turbines have been around a long time in wind applications, but while reliable they aren’t very efficient, which has limited their use. Here’s what MODEC says about that part of the device, beyond its capability of acting as ballast:

The split-cylinder-shaped buckets of the Savonius current turbine can harness any weak current and will rotate in one direction regardless of current direction. This turbine is insensitive to marine growth on the buckets and is harmless to the marine ecosystem, as it rotates slowly at the speed of the current.

Pete Danko is a writer and editor based in Portland, Oregon. His work has appeared in Breaking Energy, National Geographic's Energy Blog, The New York Times, San Francisco Chronicle and elsewhere.