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The southernmost and coldest wind farm in the world was completed this year thanks to a collaborative effort between New Zealand and the US, and innovative designs by Kiwi engineers and construction teams.
Over past four-month Antarctic summers a dedicated team made up of Opus International Consultants, Meridian Energy, a number of subcontractors, and Antarctic New Zealand staff worked together to install and commission the three 333KW wind turbines to supply electricity for the Kiwi and America bases in Antarctica. The wind farm, located at Crater Hill on Ross Island, is part of the country’s contribution to the New Zealand/United States joint co-operation initiative, and was developed under an alliance between Meridian and Antarctica New Zealand, with logistical support from the US National Science Foundation (which operates McMurdo Station) and the United States Antarctic Program. Ross Island is attached to the Antarctic mainland by the Ross shelf and is about 40 percent larger than Stewart Island. The island features the world’s southernmost active volcano – Mt Erebus (3794 metres). Scott Base houses up to 100 people and is operated by the NZ Antarctic Institute (known as Antarctica NZ). The average load of the base is 50kW. New Zealand and the US have longed pooled resources in the region. McMurdo Station is just three kilometres from Scott Base and houses up to 1250 people and is operated by the National Science Foundation (NSF) using contractor Raytheon Polar Services. The average load at this base is 1.6MW. The wind farm is sited halfway between the two bases. The project was initiated in 2005 from a University of Canterbury energy review of Scott Base, when Meridian, on behalf of Antarctica NZ, carried out assessment of wind farm sites and erected a monitoring mast on Crater Hill. By mid 2006 there was enough wind data to proceed with feasibility studies. A year later a design proposal was presented to AntNZ/NSF outlining technical/commercial concept for wind to supply both Scott Base and McMurdo Station. The chosen site has volcanic scoria ice-free covering with permafrost at depth 200-450mm, and with good wind of an average wind speed 7.9 metres per second (28.4 kph) and gusts of 237kph. There were minimum environmental issues as the site had already been extensively altered and had existing road access. Involved in the design and construction of the project were: Opus International Consultants; Leighs Construction; Nelson’s Drill & Blast (foundations); Daniel Smith Industries (crane services); Powercorp – Australia (Electrical & Controls); Raytheon Polar Services Company – United States (transportation logistics and construction support; and Enercon GmbH – Germany (Turbines). The project had a core team of between six and 15, who were reliant on Antarctica NZ to house project staff at Scott Base (costing $1000 a night for each person) as every site project worker displaced a scientist, and on USAP to transport staff, plant and equipment.
On this project, a single day late with component delivery had ramifications for the whole project, and could translate into the whole project running an entire year behind. With only a single supply ship making the 3832 kilometre trip from New Zealand each year, the team had to plan the logistics extremely carefully to ensure every component that was needed on site (including a 65-tonne crane) was landed and ready a year ahead of construction. Typically, the team worked 10 hour days, six days a week. Simple tasks were complicated by the workers’ clothing and gloves. Tasks such as signing in and out of the base, changing into extreme cold weather clothing and waiting for vehicles to warm up made for long days. FoundationsTraditional concrete gravity pads for the hollow, 39 metre high towers were not possible due to chilly temperatures, a lack of a concrete batching plant, aggregate or fresh water.
The foundation sites were drilled and blasted and the loosened material removed by Cat 960 wheel loader and the base material removed with a Cat D9H bulldozer and Cat 330CL excavator. The foundation blocks were positioned and backfilled with compacted layers of screened material. Ross Island is one of the few Antarctic sites with out ice cover, allowing the foundation to be firmly anchored. Hamish Mackinven is a structural engineer with Opus. Based in Christchurch, he has been involved with various projects on the Antarctic continent for over 25 years and was actually involved in designing Scott Base while under contract to Antarctic New Zealand. Mackinven and Murray Mitchell, another Opus structural engineer with a lot of Antarctic experience and now nearing retirement, designed and oversaw the installation of the innovative ‘spider’ foundations that hold the three new turbines in place. The foundation design had to be within an accuracy of plus-or-minus 1mm over a 2.4 metre flange level. “The foundations were prefabricated in New Zealand, shipped to the Antarctic and assembled on site. We had to be absolutely bang-on with our measurements as there was no opportunity to check the foundations with the turbines prior to them being landed on the ice,” says Mitchell. “We also had to ensure the absolute accuracy of the foundation levels otherwise the turbine towers would be out of plumb, making them unstable and unworkable. Normally, turbine foundations are made from concrete poured on site, which means that there is some room for final adjustment when they are installed to ensure everything is level. “For this project, however, we needed to design and build foundations that sit above ground level. The spider shaped foundations, which comprise of eight radial legs around a central hub, are secured to individual 13-tonne pre-cast concrete anchor blocks. “These blocks are skewered onto vertical 12 metre Ishebeck ground anchors. ‘Antarctic grout,’ which is a mixture of hot water and sand, ‘sets’ [freezes] these permanently into place and provides adequate strength to support the turbines in the extreme and freezing wind gusts which can reach 240-250 kilometres per hour.” The ‘spider foundations’, designed by Opus, were pre-constructed by Leighs Construction in New Zealand and sit above the ground with eight legs radiating outwards. Each leg is secured to one of eight, 13-tonne pre-cast concrete blocks arranged in a circle in an excavated pit that was backfilled and frozen in so the tops of the blocks are flush with the ground. Each block is fitted with two 12-metre ground anchors bolts drilled and held in place with the ‘Antarctic grout’. The turbinesHamish Mackinven says that, despite the site being only about one kilometre from the sea, corrosion is not an issue with the new turbines.
“However, all the steelwork had to be tested to ensure it complied with the standards required to withstand the extremely low temperatures. “Components and tools also had to be designed in a manner that allowed construction workers to handle them while wearing thick insulated gloves. “Likewise, at metal edges had to be rounded to ensure the protective clothing worn by the construction team was not accidentally cut or torn.” The three Enercon E-33 turbines are direct drive (eliminating high maintenance gearbox and oil issues with freezing temperatures) and operate in combination with an annular generator. The system features flexible electronic energy conversion and control systems designed for wind diesel integration. This form of turbine was specifically chosen for this remote and frozen site as they require only minimal servicing and maintenance once a year. The Australian Antarctic base, Mawson, the longest continuously operating station south of the Antarctic Circle, has been running two, smaller 300KW Enercon wind turbines since 2003. The Kiwis learnt some valuable lesson from the Aussie project – the sealing brushes in the nacelles, for instance, were improved to keep out storm spindrift.
The Ross Island electricity network connecting Scott Base and McMurdo Station has the distinction of being the first electricity network in the world to serve towns belonging to two separate countries. The power transmission network operates through several frequency converters, as Scott Base operates at 50 hertz, while McMurdo operates at 60 hertz. A three-tonne, power-store flywheel system keeps the power output constant. “It will be more like the Antarctic prior to human occupation and will provide a cleaner and quieter form of power generation and a more natural means of supporting human life in this extreme climate at the bottom of the world,” says Mackinven. At an historic movement for wind power, the Scott base was connected to wind energy supply for the first time at 5pm on December 5, 2009 and the world’s most southern (and coldest) wind farm was in operation. Just one turbine producing at full capacity covered all of the base’s electrical demand. Scott Bennett, project manager with Meridian Energy, says this was just stage one. “We would like to investigate the potential for stage two, which we believe could offset power consumption on the island by 40 percent. But first we need to assess how stage one performs over the year.”
Contractor Vol.34 No.5 June 2010 |
A three turbine, 1MW capacity wind farm powering New Zealand’s Scott Base and the American McMurdo Station was completed earlier this year after two years of construction, and what must be the most challenging weather conditions for any project.
Construction started in November 2008 and equipment had to be planned and programmed down to the last nut and bolt, and it proved a challenging exercise. Apart from the difficulties of working in such a harsh environment, the team also had to work in a severely limited site access and a small construction window (November to February) when the temperatures can reach a ‘warm’ minus seven degrees Celsius, and the base is bathed in 24hr daylight. The average temperature at Scott Base is minus 20 degrees – the average household freezer is minus 15.
The solution was a pre-fabricated, transportable and anchored structural steel foundation that designed and built in Christchurch.
“This is because the sea is frozen and hence there is no salt spray. Consequently, the foundations only need minimal painting to protect them from the elements.
The three 333kW turbines on Ross Island will reduce the amount of diesel required for power generation of the two bases by about 463,000 litres and reduce the risks associated with transporting and storing liquid fuel at Scott Base.