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United Kingdom

Connecting offshore plant

The cost of connecting large UK offshore wind projects into the mainland grid ranges from £117,000 to £254,000 per megawatt installed, according to a study by network consultants Econnect. The assessment of costs to connect the second round of offshore wind farms was commissioned by the Department of Trade and Industry (DTI).

The study looked at the cost of connecting each of the 15 "round two" projects individually and at the potential for sharing connections. It found that shared connections are cost effective for about 50% of the projects. The average cost for the best mix of individual and shared connections is £167,000/MW. This figure is considerably lower than a previous estimate of £250,000/MW, published by the DTI in 2002.

Econnect points out the potential for costs per megawatt to be brought down even further. Wind farm capacity could be either reduced slightly to avoid having to install one of the array-to-shore cables, it says, or increased to utilise fully the ratings of the installed connection assets.

The Econnect report shows there to be no economies of scale; larger projects are not cheaper to connect per megawatt than smaller projects. This is due to the likely connection of offshore wind plant in several modules and the high costs of array cables and losses when gathering output into a central location. The advantage, however, of building wind farms in modules is that it allows developers to phase the construction of larger projects so that they do not need to invest in the full costs of the final grid connection up front.

For most round two wind farms, connections using 132 kV subsea cables are the cheapest option, with high voltage direct current links becoming cost effective only where large amounts of power are to be transferred a long distance from connection.

The report will feed into the decision making of the DTI and the regulator, Ofgem, on the future offshore transmission infrastructure -- including the vexed question of how the costs of offshore grids will be recovered. The industry is hoping soon to see a consultation from Ofgem and DTI on how new offshore grids will be licensed.

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