COLUMN-Unknown cost of offshore wind a concern:Gerard Wynn

Mon Apr 23, 2012 12:16pm EDT

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By Gerard Wynn

LONDON, April 23 (Reuters) - As countries go offshore to generate more consistent wind power and avoid blight to their landscapes caused by onshore turbines, they will be increasingly limited to unproven, floating turbine designs, adding to doubts over cost.

The problems underline the fraught issues behind a modern energy strategy, balancing carbon emissions, security of supply and affordability.

The state of technology development in offshore wind shows how wide open the field is between low-carbon technologies including nuclear, wind, solar and carbon capture and storage.

As far newer technologies, offshore wind and CCS have most to prove, but doubts over nuclear (cost and safety) and solar (cost, according to latitude, and space) make CCS and offshore wind demonstration programmes worthwhile.

FOUR-FOLD

The deepest commercial turbines so far deployed anywhere are around 30 metres deep. In theory they can go as deep as 60 metres.

These are turbines attached to the sea bed directly, either with a single steel post hammered into the rock, or (in a more innovative approach) at greater depths using a "jacket" of three or four legs joined together in a latticework frame of crisscrossing steel, also driven into the sea bed.

World offshore wind leader Britain has now leased most of the wind resource accessible to these standard, fixed turbines, according to a study published two years ago by the "Offshore Valuation Group", a government-industry collaboration.

That leasing programme has so far licensed a potential 47 gigawatts, more than half the country's entire generating capacity using all technologies now.

Only a fraction has been constructed, however, at 1.9 GW.

By tapping deeper waters, floating platforms would increase potential wind power generation even more, by four times, the Offshore Valuation Group estimated.

That's because Britain's windier coastline is on the more steeply shelving western seaboard, with shallower waters on a more sheltered, eastern shore.

DESIGNS

Off northwest Europe higher average wind speeds are found almost exclusively in deeper waters, motivating interest in floating designs.

Norway's Hywind project is leading early-stage innovation.

The Statoil project tests a floating turbine with a deep keel (called a spar buoy), which is a single steel post plunging 100 metres below the turbine to keep it upright, and additionally moored to the sea bed.

Two alternative approaches to remaining upright are: first, using the wide surface area of a half-submerged platform, moored to the sea floor using anchors; or, second, a system of cables tethered to piles driven into the sea bed (called a submerged tension leg).

A version of the first approach is presently being tested off the coast of Portugal.

Britain will decide by early next year which of these latter two to support in a 25 million pound ($40 million)demonstration programme.

The United States Department of Energy recently announced $180 million for advanced projects in offshore wind.

Britain and the United States announced on Monday an intention to coordinate research and development.

COST

Onshore wind is less predictable and potent than offshore, but has the advantage of cheaper servicing and grid connection.

The upfront capital cost and ongoing servicing and running costs of energy technologies can be combined in a measure called the levelised cost of energy (LCOE).

At present, onshore wind generation costs in Britain are approximately 0.09 pounds ($0.15) per kilowatt, according to various consultancy estimates, and will hardly fall through 2020.

That compares with a gas-fired power plant LCOE started in Britain today of about 0.08 pounds per KWh.

Offshore wind generation costs, using fixed turbines, are presently around 0.17 pounds ($0.27) per KWh, projected to fall to as little as 0.10 pounds by 2020.

The UK-based Energy Technologies Institute is involved in Britain's present floating turbine demonstration programme, and estimates these can generate electricity at around 0.09 pounds per KWh, "post 2020".

That's an estimate for a well-understood but nevertheless unproven technology. As ETI Strategy Director Andrew Haslett states, the cost range "could be a lot more (than 9 pence), it's not likely to be a lot less."

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