Massive cranes on “tippy-toes:” Tricky sites might herald peak hub height for wind farms

Contractors are almost finished hauling all the parts of the 28 massive wind turbines up the steep hills surrounding the new Kaban wind farm, but it’s not the concrete pour that will excite engineers from this particular installation.

These turbines might just be the limit of what is achievable in Australia, experts say, not because of the 150m hub height of the Vestas EnVentusTM V162-5.6 MW but because of the sheer scale of the earthworks required for the cranes needed to build them on site. 

“It [earthworks] is the most challenging part of the project now, balancing program with safety and footprint, and by footprint I mean impact on the environment,” says Nick Canto, principal consultant at icubed consulting.

“The loads and components are getting bigger and bigger. The six-times platforms of 150m or 160m hub height, more than-200 tonne vehicle configurations, having to navigate some fairly steep terrain to try and get the projects built. It’s hard.

“All the easy sites are built now, we’ve got to go build on the hard ones.”

In the good old days of lower hub heights, small crawler cranes could be sent out to erect a turbine then crawl over to the next site even in hilly terrain. 

But today’s ultra high turbines require bigger cranes, which also have to be assembled on site and are driving ever higher civil works costs, pushing the cost per megawatt up past $2.8 million to $3.2 million

One source spoken to by RenewEconomy said the Leibherr LG1750 crane, favoured for most turbine installations these days, needs a 30-40m by 200m patch of cleared land next to the turbine site so it can also be built. 

The LG1750 has to stand on its “tippy toes” to install the biggest turbines, Canto says. 

“I think there’s actually a natural constraint on hub heights now and there’s a couple of things driving that,” he says.

“You’ve got overhead height restrictions from port to site. Road and pedestrian overpasses for example. You can only get loads of a certain diameter from port to site now because there are many overhead obstructions.

“The crane of choice in Australia at the moment is a Leibherr LG1750. Its lifting capacity is maxed out at about 166m hub height, so we’re reaching the point now where you can’t go much taller because of other things.”

Challenging logistics

The 28 turbines for Neoen’s 157 megawatt (MW) Kaban wind, near Ravenshoe in the Atherton Tablelands, arrived in the Port of Cairns 18 months ago, and have a ‘tip’ height of 225m.

The Vestas turbines are the first of their kind to be installed in Australia but the 79m blades themselves aren’t unique – similar sized ones are being installed around the country. 

It’s the Kaban site that is the first example of really big turbines being erected in relatively difficult terrain.

Contractor Mammoet said it used high traction “block trucks” to provide extra power to get the equipment up the steep hills, a 700 tonne Terex Demag AC700 crane for the pre-installation work and Scheuerle SPMT and Goldhofer THP multi-axle trailers to move the 400t of superlift counterweight all at once in order to install the LG1750 crane.

The company said it not only reduced the carbon footprint from reducing truck movements on site, but also saved money. 

However, it is the civil works cost that is already changing how wind farms are laid out. 

Mammoet supplied the K1650L tower crane for the Rye Park wind farm, which was used on about a third of the turbines installed. 

Tower cranes only need a small pad to sit on and in hilly areas, where batters are needed to shore up hillsides, dramatically reduced the earthworks footprint. 

While the tower crane is significantly more expensive – some say double that of a LG 1750 due to the extra time and labour needed to set up up – and there are only a handful in Australia, it can also be a cost saver less earthworks means a faster installation a smaller footprint in places like New South Wales (NSW) saves on expensive biodiversity offset costs.

“I really want tower cranes to work. I’m very enthusiastic about tower cranes because they reduce the amount of earthwork you need to do,” Canto says.

“We’re working on a project now where we halve the amount of earthworks from 2 million m3 to 1 million m3.”

Installation set to get more expensive

With the windiest sites mostly already built on, there are a few options available for developers. 

The bigger turbines mean many sites, such as Windy Hill, also near Ravenshoe, and Starfish Hill near Cape Jervis, are unlikely to be repowered, Canto says, because the larger turbines won’t comply with current planning rules – or, as with the latter, the local community simply won’t have it. 

New sites, such as hilly Kaban or those in NSW where biodiversity offsets make earthworks extremely expensive particularly on difficult sites, might force developers to simply walk away, or test out some new ideas. 

Canto says concrete hybrid towers, which are being seen in Europe and Asia in small numbers, are one avenue for developers wanting to install turbines with the highest hub heights, Canto says. 

But these are expensive and he “struggles to see the economics of it in our market”. 

Cranes that crawl up a tower as it builds are possibilities for the future, but with OEMs not making any money right now, no one is keen to put cash into testing out interesting and future-proofing ideas like this which could see hub heights continue their march upwards.