Manufactured from great sheets of steel that
are curled into cylinders up to eight metres in diameter and seam welded at the factory, tower
sections arrive onside in sections to be stacked up. The tower is too big to be moved in one piece,
either for ships at sea or conventional trucks, so modular on-site assembly of prefabbed
elements is clearly the way to go. Craned into position and stacked one by
one, the tower elevates the turbine fan up above the aerodynamic sweet
spot of 30 metres above ground, where winds are usually less turbulent and
more desirable from an energy-harvesting standpoint. The tricky part here is aligning
the different tower sections as they rise, with huge components in windy locations up against
engineering tolerances of just a few millimetres. Atop the shaft sits the brains of the operation,
also known as the nacelle. Crammed with upwards of 1,500 bespoke components, the nacelle houses the
generator and drivetrain, inverters, sometimes a gearbox, as well as assorted monitoring,
communications and environmental maintenance gear. It’s affixed to the tower via a sophisticated
rotational ‘yaw’ system, which allows the nacelle, and by extension the turbine blades, to
turn and face the wind whenever it changes. The nacelle itself can be incredibly heavy, with one recent IEA offshore 15 MW
model weighing in at over 800 tonnes. How on earth is that installed? With
great difficulty. Mighty cranes, lift wires and supporting tugger lines are part
of the process. At sea, the impact of wind on the dangling nacelle is surprisingly less of an issue
than the oscillations of the tower itself, as it’s battered by waves and currents below. Careful
mathematical modelling is carried out before every installation, supported by clever civil
engineering gadgets called ‘tuned mass dampers’, which go some way to help align vibrations between
these two massive components before mating. Of course much of the nacelle is
prefabbed before being shipped to site. Construction bosses need to make tough
choices over what’s efficient to make onsite, against weight considerations, and even
simple limits on available deck space. Once in place, and covered up with
a weather-proof fibreglass gondola, the blades can now be attached to the hub. Engineers have come to favour a three-blade
turbine format. Even numbers of blades cause problems with resonance, which leads to
unseemly wobbles that in turn cause expensive and frustrating wear and tear. In theory
one blade works just fine, or 9 blades, although they suffer from exciting-sounding
‘vortex issues’. Fundamentally, engineers are pragmatists, and want an economical, scalable
solution. For now at least, that’s three blades. These blades – which nowadays
can stretch over 100metres long, and be four metres around at the
root – were once made of aluminium, but at current scales that’s far too
heavy so fibreglass is now in vogue. And in case you were thinking the
job of winching up a 100m long, 55 ton fibreglass blade – a blade
that’s literally designed to catch the wind – 150 metres in the air, at
sea, is easy. Well, it’s not easy. Each blade root is encircled by guide
pins that marry up with flange holes in the hub. How do engineers compensate
for the wobbly tower, and motion-prone blade? Those passive tuned mass dampers we
mentioned earlier play something of a role. But in recent years engineers have
dreamed up two new techniques, both of which sound a bit
like cheesy anime villains. ‘Blade Dragon’ is a lifting
yoke that attaches to the crane and holds the blade more firmly than
a regular hook. The advantage here is it can be affixed to the hub at
an assortment of inclined angles. ‘Boom Lock’ is a smart system that sets out
to eliminate, or at least compensate for, any lateral movement on the crane hook, so the
blade stays steadier. These techniques make great economic sense, as they work at relatively high
ambient windspeeds using fewer human operators, ultimately getting the installation
done quicker and therefore cheaper. Indeed, modern wind farms can erect the tower, install the nacelle and the blades in a
day, with just a little extra time for calibration of the blades pitch angle and
optimal yaw before connecting to the grid. As turbines get taller and more ambitious, construction obviously gets trickier. There’s
a limit to how tall a crane can usefully be, especially at sea, but some companies in the
field – like Mammoet – have developed bold new solutions; spin-off technologies, if you will.
Take this WTA, or ‘Wind Turbine Assembly’ crane. Instead of being rooted to the ground, or on a
jacked-up boat, the WTA 250 uses temporary guide rails attached to the turbine tower itself.
Capable of lifting a hefty 250 metric tonnes, it’s superior because it has no footprint, and can
theoretically rise as high as the tower itself. Minimising the role of humans in what
is often a perilous working environment is another priority as the turbine
construction field matures. Already, ultra-sophistical mathematical models
guide design and development of turbines and wind farms, and there’s an increasing
role for AI and software engineers to play in conceptualising the next generation
of taller, cheaper, more efficient turbines. So the rewards are massive for any young
nerds out there who wish to study the blade. What do you think? Are modern wind turbines
ugly blots on the natural landscape, or inspiring monuments to human ingenuity
and progress? Let us know in the comments, and don’t forget to subscribe for
more high rolling tech content.
