Wind Turbines Keep Getting Bigger.

In recent years the manufacture of blades for wind turbines has undergone a revolution, as it were.

Two decades ago lengths of 40 metres or so were an achievement. Thanks largely to lighter and stronger carbon-fibre composites, the state of the art is now triple that.

As turbine output is proportional to the square of blade length, this has also increased how much power can be produced. The biggest turbines in 2004 could generate about two megawatts. Today’s giants can exceed 15.

But there’s a hitch. Today’s longest blades have become too big to be delivered to inland wind farms. They can be taken only by ship to offshore sites, where building costs are far higher.

Logistics specialists have consequently been raising their game. Lorries with “blade-lifter” hydraulics can rotate their cargo to reduce lateral displacement on turns, a useful trick in hilly terrain without overhead obstacles. The past decade has also seen the development of highly accurate "swept path analysis" software. Fed with a digital model of a transport corridor, tree branches included, the software reveals—to within a few centimetres—if a blade could get through.

For all that, problems still arise. During the many months it can take to secure transport permits, trees grow and new obstacles are often erected. Manufacturing the blades in segments that can then be assembled on site, as is done with the turbine towers themselves, has thus far proved impractical, says Zhao Feng of the Global Wind Energy Council, an industry body based in Lisbon.

In addition to introducing potential failure points, the joints are expensive and heavy. They also reduce wind-harnessing surface area by about 15%.

One idea is to 3D-print blades at wind farms. Orbital Composites, a Silicon Valley firm, has US$1.3 million in funding from America’s Department of Energy to print a prototype nine-metre blade later this year.

If all goes well, the company hopes to produce a 50-metre blade in late 2025. 3D-printed blades of 100 metres could follow by 2028. Amolak Badesha, Orbital’s boss, reckons on-site printing would cut developers’ total cost for blades by a quarter.

Wilder projects are getting off the ground. A handful of firms are designing helium airships to lift blades. One is Aeros, an airship-maker in Los Angeles whose customers include America’s Department of Defence. Within three years Aeros aims to operate a fleet of 169-metre-long airships able to carry 66 tonnes - enough for three 85-metre blades.

Successfully delivering the blade is only half the battle: engineers also need to stop airships from rapidly rising once the cargo is set down. The simplest solution, releasing helium, is prohibitively expensive: the gas can cost more than US$10 per cubic metre, and roughly 60000m3 would need to be released on each trip.

Aeros’s workaround involves compressing its on-board helium before filling the remaining hold space with compressed air sucked in from outside.

The increased mass would be enough to keep the airship stable. A French competitor, Flying Whales, plans to replace helium with water at journey’s end. Aeros’s founder, Igor Pasternak, is coy about the project’s costs, but he describes blade delivery as a "unique and lucrative market". Fees for moving a large blade can exceed US$370000, so airlift three, he says, and it’s "one day, US$1 million". Not everyone, however, believes giant dirigibles equipped with massive blades will be able to manoeuvre safely in windy areas.

That is one reason why Radia, a firm based in Colorado, has opted to build a monster aeroplane instead. Dubbed WindRunner, it is designed to carry a 105-metre blade in a cargo bay nearly 12 times larger than that of a Boeing 747. The WindRunner fleet would land at wind farms on a strip of packed earth 1800 metres long (shorter than most runways for commercial airliners) which Mark Lundstrom, Radia’s chief executive, describes as "essentially a higher-quality access road".

Radia says it is more than halfway through an eight-year process to get its beast built and certified. Like Aeros, Radia is keeping mum on its costs but spies an enormous opportunity. The windpower industry spends an astonishing 7% or so of its capital expenditures on moving blades, Mr Lundstrom says. Even expensive, long-shot bids to find a better way, then, could prove worth the effort.