The making of West Wind

Where else but windy Wellington as a site for the world’s most efficient wind farm? HUGH DE LACY visits Meridian’s West Wind project as the foundations were laid.

It’s not just legend, nor even parochialism: the Wellington region is the best place in the country to build a wind farm because of the funnelling effect created by the norwesterly and southerly winds barrelling through Cook Strait from the Southern Ocean.

Accordingly, state-owned Meridian Energy, which prides itself on being a 100 percent renewables electricity generator, chose the Makara Hills west of the capital for the third and largest of its major wind farms. Called West Wind, its capcity is 140 megawatts when it comes on-stream at the end of next year, and follows on the completion of Meridian’s 90MW Te Apiti windfarm in the Manawatu in 2004 and 58MW White Hill in Southland last year.

West Wind, on which the Higgins Group began construction as principal contractor in  November 2007 following a tortuous resource consent process, will feature 62 turbines spread across a precipitous 52 square kilometre site that will see the highest turbine at an altitude of 432 metres. The site not only required 1.5 million cubic metres of earthmoving and the construction of 45 kilometres of seven metre wide internal access roads, but access issues through Wellington’s narrow streets that a special temporary wharf was built to get the Siemens-made tower modules, 2.3MW turbines and 40 metre long blades to the site.

Typical of New Zealand’s very efficient wind sites (above the world average), West Wind is expected to generate electricity 92 percent of the time and be at full capacity for over 48 percent of the time (more than double the international average) in wind speeds ranging from 15 to 90 kilometres per hour, generating enough power to supply most homes in Wellington city.

The massive blades only need a wind speed of two to three metres per second to generate, and are expected to be running at an average speed of 10.5 MPS. In extreme conditions where the wind hits 25 MPS, the turbines will automtaically shut down to prevent damage. Providing up to 142MW capacity of renewable electricity into the national grid, the wind farm will feature a substation on Terawhiti Station where the on-farm 33kV network will be increased to 110kV before it connects to Transpower’s double-circuit 110kV line from Wilton to Central Park.

Touch and go decisions

When Meridian first announced the project in 2005, it was met with a storm of resistance from the scattered residents of the Makara Valley, who feared the sight and sound of the turbines would ruin their rural lifestyles. In its original form the project envisaged a capcpity of 210MW from seventy 125 metre high turbines, which the objectors cited as being too many, too close and too big for the community.

The consent process was inundated with over 4000 submissions, some of them opposing the project. The Environment Court cut the number of turbines to 66. Meridian itself subsequently reduced the final number of turbines to 62 because of turbulence issues at four of the remaining sites.

Even so it was touch-and-go whether the project would be built at all. In announcing the decision to go ahead in August last year, Meridian chief executive Keith Turner said it had been saved only by the high value of the New Zealand dollar: “We have been incredibly lucky: the exchange rate peaked about the time the board gave me the [final] decision.”

Had the dollar been any lower, the cost of buying the turbines from manufacturer Siemens Wind Power, and shipping them out from Denmark, might have canned the project.

But if West Wind at first struggled to get off the ground, it has taken flight since. The lower half of the North Island enjoyed one of the best summer construction seasons in years in 2007-08, allowing no less than 1.2 million cubic metres of dirt to be shifted in 16 weeks. By spring, all the bulk earthworks had been completed and 40 of the 62 concrete turbine foundations had been poured.

Massive construction

The wind farm is being built by a small army of men and machines braving the ridge top elements through 12-hour days and five-and-a-half day weeks. The wind can be so strong on the exposed site that a worker can hardly stand up. On other days, such as on Energy NZ’s visit, the sun shines out of a blue sky with just a hint of a breeze, and the ocean views and isolation are simply majestic.

The actual construction of West Wind is in the hands of Higgins Projects and an exclusive group of site contractors who have worked with with the company on two previous windfarm projects – Meridian’s Te Apiti and Trustpower’s Tararua T3.

Projects division under manager David Rubery says Higgins’ contracts overall are worth over $50 million, and the on-site staff of up to 250, chewed through Meridian’s investment capital at the rate of $1 million to $1.5 million a week.

Higgins’ planning for the project was dominated from the start by the need to get aggregate and cement onto the site without clogging up the narrow winding roads that lead from Wellington through the suburb of Karori to Makara. The resource consent precluded the use of anything bigger than an HCV1 vehicle for most of the bulk materials, which ruled out conventional cement trucks. Instead cement for the 25,000 cubic metres of turbine foundations was carted to an on-site concrete batching plant aboard a specialist single-unit pod, and the aggregate in eight-wheeler trucks with no trailers.

To supply the metal for the internal roading, Higgins used two crushers working on site at Oteranga Bay where both the Cook Strait high-voltage electricity and Telecom fibre-optic cables come ashore from the South Island. The crushers also supplied the bedding sand with its thermal and non-conductivity properties that protect the 60 kilometres of underground cabling.

Oteranga Bay is also the site of the temporary wharf that was installed to bring the turbine components on-site. Planning for this and the quarry was constrained by the existence of Maori burial sites and Transpower’s HVDC cables.

International heavy-cargo handler Deugro will ship the turbine components to the deep-water Shakespeare Bay near Picton, where they will be loaded onto barges for the final trip across Cook Strait to Oteranga Bay, and then distributed round the site by specialist heavy-haulage equipment.

Assembly of the towers is due to begin in February 2009. The 15 and 16 metre diameter tower foundations are up to 1.6 metres deep and sit on a 75mm blinding layer of concrete that provides the steel-fixers with a perfectly flat surface on which to work.

Each foundation required between 330 and 375 cubic metres of concrete applied in a   single continuous pour over about six hours. Once set the concrete was covered in compacted earth with only the hold-down bolts for the towers visible above the surface.

Adjacent to each foundation a flat 40 by 20 metre pad was constructed to accommodate the 160 tonnes of pressure applied by the 400 tonne capacity crane used in the assembly of the towers. The heaviest component is the 87 tonne nacelle atop the 68 metre tower, containing the generator, gearbox and turbine controls.

As each string of turbines is completed, it will be hooked up via the on-site sub-station. The sub-station will connect to a new transmission line being built by Higgins and United group, and thence to Transpower’s Wilton-Central Park circuit. The first power from West Wind is expected to flow in the autumn of 2009, with the project fully operational from December.

Although West Wind will be one of the country’s most isloated wind farms, passengers flying into Wellington Airport in the future will have a birds-eye view of the site in fine weather, as it sits under one of the flight paths into the capital.