Peter Tavner: Wind of change is picking up for green power

THE renewables industry has paid heed to people’s concerns over turbines, and they have been addressed, says Peter Tavner.

The announcement of the planning phase of the Moray Firth Round 3
Offshore Wind Power Station has got people in Scotland talking about wind power and offshore wind in particular.

Struan Stevenson, the Conservative MEP, is derisory about the project. Firstly, he says offshore turbine load factors are poor, with the real project output unlikely to meet the promised energy needs. Secondly, he states that, over their 20-year lifespan, turbines will require constant repair and maintenance due to the harsh conditions, meaning a reliance on constant base-load back-up from coal or gas-fired power stations.

This is an interesting point of view, reflecting concerns from many people. However, contrary to Mr Stevenson’s belief, they are not concerns disregarded by those developing offshore wind. It is exactly for this reason that its development in the UK has been approached carefully and cautiously, with offshore sites let in three licensing rounds over ten years, so that experience can be applied to reduce installation costs, run the wind plants as intensively as possible and extend their life beyond the initially planned 20 years.

The Round 1 sites, let in 2002, were limited in size to 30-60 machines, located in shallow water, producing 70-180MW. There was only one Round 1 site in Scotland, simply because Scottish offshore wind resources are stronger and further offshore in deeper waters than south of the Border, so Scottish sites were limited to curtail early risks.

Round 2 sites were let in 2003, with larger 184-300MW wind farms being installed further offshore. Developments have accelerated from this experience. Round 1 and 2 wind farms are now contributing a steady 1,000-3,000MW to the National Grid, as much as our largest coal-fired or nuclear power stations, and the cautious approach has yielded many installation and operational experience benefits.

In response to Mr Stevenson’s first objection regarding load factor – the wind farm’s output as a percentage of its rated capacity – it is important to note that all power stations are unavailable at some times and none has a 100 per cent load factor. Round 1 and 2 offshore wind farm experience shows load factors rising to 50-60 per cent in windy months, with annual averages in excess of 35-38 per cent, much higher than the 30 per cent suggested by Mr Stevenson.

The estimates for the Moray Firth site will have been based upon this positive experience from UK and European offshore wind farms, all placed in sites less favourable than the Moray Firth.

With regard to Mr Stevenson’s second point, it is fair to say one of the main challenges in offshore wind development is to ensure turbines operate in all feasible wind speeds, throughout their lifespan, which could be extended to 25-30 years.

Onshore wind farms achieve at least 98 per cent availability, but offshore farms to date are achieving 92-97 per cent. Rounds 1 and 2 show clear availability improvement in the first two years of their life, but subsequent availability can fall during periods of high resource, sometimes below 92 per cent, because of earlier faults that cannot be rectified due to rough sea conditions. This issue is now being addressed by better planning to ensure maintenance is done in fair weather; in bad weather, combined sea and helicopter activities are organised to rectify serious faults.

Mr Stevenson finally suggests the Moray Firth wind farm’s output will be highly variable, with the suggestion it needs investment in back-up generation in the event of low wind. This is simply not the case. The 1.5GW Moray Firth wind farm, constructed of turbines similar to those installed in the Moray Firth at the Beatrice project, will be connected directly to the National Grid, with an overall capacity of 78GW.

Again, experience from Rounds 1 and 2 is that wind resource is far from highly variable and can be forecast and planned into the overall generation mix, being balanced every half hour against nuclear, coal, gas and hydro resources, without the need for additional generation.

In Round 3, we are moving to much larger offshore wind power stations, where Scotland’s enormous offshore wind resources come into play and the Moray Firth, with more than 200 turbines, will be a substantial development providing clean energy and local jobs. The issues that need to be addressed are those set out above but with some additions because of the size of these new installations:

• Ensuring installation costs are restrained by efficient deployment and project management;

• Keeping turbines operational by well-planned operation and maintenance, hardly a burden considering the incoming fuel is free;

• Prolonging turbine life by monitoring performance and progressively enhancing the asset;

• Bringing the power ashore to large and convenient grid substations.

As a power station operations specialist with offshore wind experience, I believe all these issues will be more than adequately addressed, based upon the UK’s Round 1 and 2 experience, and that we are on the verge of a very important development to secure local energy from renewable sources on a scale that is no longer marginal, using skills at which Scotland and the UK excel.

• Peter Tavner is an Emeritus Professor of Durham University and president of the European Academy of Wind Energy. His new book, Offshore Wind Turbines: Reliability, Availability & Maintenance, is available at www.theiet.org/books-offshore