February 04, 2011
Vertical Axis Wind Turbines For Offshore

An article in Technology Review takes a look at the use of vertical axis wind turbines to lower the center of gravity in order to enable a cost reduction by cutting the size of the flotation system.

French oil and gas engineering company Technip and wind-power startup Nenuphar recently announced Vertiwind, a two-megawatt wind turbine that they plan to float in Mediterranean waters by the end of 2013. The project employs a turbine with a main rotor shaft that is set vertically, like a spinning top, rather than horizontally, as in a conventional wind turbine. 

The benefit of the vertical-axis design is that it lowers the turbine's center of gravity. Vertiwind's design stands 100 meters tall, but places the generator, which weighs 50 tons, inside a sealed tube beneath the turbine's rotating blades, 20 meters above the sea. This makes the turbine less top-heavy, allowing for a significantly smaller flotation system, which would extend only nine meters below the surface of the ocean.

As the article points out, vertical-axis designs cost more than horizontal-axis designs on land. Offshore operation brings additional costs as well. So unless the wind quality is better offshore it is hard to see how offshore wind can compete with onshore wind - at least for regions that have high quality wind onshore. Wind farms in the US great plains will generate cheaper power than wind farms off of New England. But if assorted interest groups in the Midwest and New England block the construction of sufficient long distance power lines to bring the power from the great plains the offshore wind won't have to compete with cheaper onshore wind.

Every time I read about renewal energy technology advances my reaction is tempered by the thought that while renewables have at least the potential to be cleaner than fossil fuels so far they are substantially more expensive and less convenient. When I refer to potential to be cleaner my point is that you have to look at total lifecycle to measure total pollution. Fossil fuels get used to create capital equipment to generate new energy. Fossil fuel-driven capital equipment generation (e.g. extract and purify and transport minerals to use to make photovoltaics or to make magnets for wind turbines) itself generates pollution, as does the upkeep of that equipment). The more expensive that capital equipment the lower the odds that use of a form of renewable energy really cuts pollution.

I still see the renewable energy industries as worth having around because they do continuously innovate and they will eventually get their costs down. But the amount of money spent to subsidize renewable energy installations and the number of years the subsidies have been going on suggest a slow rate of innovation because the problems with making renewable energy viable are so difficult to solve.

Share |      Randall Parker, 2011 February 04 06:06 PM  Energy Wind

Fat Man said at February 7, 2011 8:29 AM:

How much are these things going to cost? Because they will be a great boon for oceanographers researching rouge waves. Just be sure your equipment is water tight and can float back to the surface.

Rob said at February 7, 2011 9:03 AM:

The problem is that many of the issues facing renewables are facts of nature, rather than limitations of engineering. A small solar installation I monitor in Colorado was, up until last week, putting out about 7 to 8 kilowatts during the day. Last week, however, they had bad weather. Lots of it. For the last 7 days, that installation was putting out less than 4 kilowatts and probably averaged about two. There's just no way to make that work. Batteries? To last seven days on a once-a-year event? No way that ever makes sense, no matter how cheap the solar power gets.

Chris T said at February 7, 2011 3:48 PM:

The focus on using centralized solar plants for grid power is especially wrong headed. Their best use is for off-grid applications with consistent power requirements. The more uncertain power requirements are, the worse solar is as an energy source.

Doug said at February 8, 2011 11:59 AM:

As a layman, not an engineer, I'm just curious about whether managing the torque effect on a (hopefully) rapidly spinning vertical shaft is a significant problem. Is the whole thing likely to just violently flip over? Do you need some sort of counter-rotating damper? Would that involve a significant loss of energy?

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