Sweeping changes

The world’s longest wind turbine blade, made from a lightweight composite, promises cost savings with no risk to performance. Christopher Sell reports.

The world’s largest rotor blade has been developed in Denmark using a composite technology to combine light weight with efficiency. The LM 61.5P blade, measuring 61.5m – 6.4m longer than any blade now in use – is the brainchild of LM Glasfiber.

Utilising FutureBlade technology, a composite of glass fibre and carbon fibre, the blade was launched at Hamburg’s WindEnergy 2004 trade fair last month.

When fitted to a wind turbine with two others, the three blades will have a diameter of 126m swept area (the zone outlined by the tips of a turbine’s turning rotor blades, indicating how much wind is being harvested). This area will be capable of producing 5MW – the annual power consumption of 5,000 households.

FutureBlade is a concept that LM Glasfiber has developed over the last five years. Steen Broust Nielsen, group marketing manager said: ‘We could see that rotor blades were growing and we needed the technology that could produce longer ones. Instead of applying manufacturing processes and materials used in aerospace to satisfy demand for bigger blade capabilities in terms of fatigue and length, we developed FutureBlade. This enables us to use standard grade materials and reduces cost with no risk to performance.’

The blade combines glass fibre reinforced epoxy, with glass and carbon fibre in its most stressed areas. As a result LM Glasfiber has reduced the need for high-cost carbon fibres, so the blade weighs 17.74 tonnes, when far shorter ones are over 20.

The constant challenge, according to Nielsen, is the reduction of price per kilowatt hour of energy produced by wind power. While reducing the weight goes some way to lowering costs, a lighter blade is beneficial in a number of ways.

First, better structural designs and improved fabrication means less stress on hub components and the overall tower structure, which in turn sees a reduction in capital and operating expenses. Wind turbine owners will see benefits through enhanced reliability and consequently greater output.

Second, operating and maintenance costs are lower because of preventative care and organised service procedures. Blades only account for 10 per cent of the overall expense for a wind turbine, therefore blade innovation is a relatively small consideration in energy production costs.

The blade is also equipped with LM Glasfiber’s conditioning monitoring system – another world first – which will constantly monitor critical conditions such as load, temperature and damage.

Nielsen envisages a huge and growing demand for such systems, for example, in off-shore wind farms, which can be up to 12 nautical miles from the coast, and inaccessible in bad weather. The blade also has potential on land as it could improve or reduce a turbine’s service and maintenance costs by pre-empting a failure with a planned service and maintenance schedule based on a signal from the system.

The blade has completed its static test, having been stressed to 110 per cent static load, and will soon be undergoing the dynamic test. this takes between six to eight months and will test the equivalent to a fatigue load of 20 years of operation.

While this blade is pushing design and technology to its limits, Nielsen is confident that the future will see even longer blades. ‘We believe that blade sizes of maybe 80-100m are possible and will be commercially attractive within the next 10 years.’

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