SKY SCRAPING

Twin towering wind farms – Loeriesfontein and Khobab – in the Northern Cape are a testiment to engineering mastery

SKY SCRAPING

The wind turbines, 122 of them, rise like giants from the hot, arid landscape of the Hantam Karoo, in the Northern Cape, SA’s most sparsely inhabited province. The turbines, each one nearly one and a half times the height of New York’s Statue of Liberty, populate 6 653 ha of semi-desert about 60 km from the tiny town of Loeriesfontein.

The ambitious renewable energy plan that’s been in the pipeline for some time has finally materialised. The Loeriesfontein wind farm and its sister, the Khobab wind farm, went live this past December and were initiated as part of the government’s Renewable Energy Independent Power Producer Procurement programme.

Owned by a consortium led by renewable power-generation company Lekela, which delivers utility-scale ventures that supply clean energy to communities across Africa, the project’s success is a key milestone, particularly for the company and its partners. They are the Thebe Investment Corporation, IDEAS Managed Fund, Future-growth Asset Management, Genesis Eco-Energy in partnership with Lereko Metier Sustainable Capital Fund, and the Khobab and Loeriesfontein community trusts.

‘Any occasion where you can switch on clean, renewable power to 240 000 homes is a moment to savour,’ says Lekela CEO Chris Antonopoulos. The energy generated by the wind farms will be sold to Eskom, in line with a 20-year power purchase agreement, adding more than 1 million megawatt hours of clean, renewable energy each year to the country’s national grid.

Chris Billingham, grid manager for Mainstream Renewable Power SA, which managed the construction and operations of the wind farms, says Loeriesfontein has a great deal of wind, which makes it an ideal site for a wind farm. ‘The flat terrain is conducive to a very steady flow with little turbulence,’ he says. ‘The site was chosen because of its proximity to Eskom’s Helios substation 7 km south of the site as well as its easy access to roads for transport of the turbines.’

While residents of Loeriesfontein and the surrounding towns of Niewoudtville and Calvinia have had to grow accustomed to the altered landscape, the project also provides job opportunities for locals. The wind farms are the future, and it’s a vital and progressive transition from fossil fuel overuse.

So, what is it like to walk underneath a turbine of such gargantuan proportions? ‘It’s awe-inspiring and actually very peaceful, considering the turbines are spaced 500m apart from each other,’ says Billingham. ‘You actually don’t realise how big the turbines are until you are up close.’

The project’s engineering is astounding. The turbine’s three blades are made from fibreglass-reinforced epoxy, and the towers are made from steel with a matt finish that reduces glare from reflected light. The turbines are connected to the rotor at ground level before being lifted to the top of the turbine tower. This is a complex exercise, in which one crane raises the assembled rotor while another smaller crane and taglines guide the rotor into the correct position. The heaviest component is the nacelle, which contains the generator and gearbox, weighing an astonishing 82.5 tons.

‘The process of constructing the turbines requires two cranes to work simultaneously and with great skill – it’s a really impressive manoeuvre to watch,’ says Billingham.

The four tower sections of each turbine are bolted together much like a giant Lego set. These were transported from Atlantis in the Western Cape to Loeriesfontein, in a five-day journey over 1 396 km. The imported components were moved on oversized trailers 1 158 km from Port Elizabeth. The project is the most expansive transport programme the industry has seen to date – it covered a total of 2.5 million km and moved 42 000 tons of turbine components.

If you’ve ever steadied an umbrella on a windy beach, you’ll appreciate that the foundations of these turbines are the hidden secret to the absolute success of the build. Concor Infrastructure, responsible for the foundations of the build, was highly commended for show-casing excellence in the SA Civil Engineering Contractors category in the 17th annual Construction World’s Best Projects competition.

‘Concrete works for both wind farms lasted 14 months with a total of 57 000 m³ of concrete poured on the project. Concor completed several critical processes in the project including the environ­mental search and rescue process, clearing of natural vegetation, excavating and blasting in preparation for the foundations for the bases of the wind turbines and casting the concrete,’ says Stephan Venter, Concor project manager. This included excavating and backfilling 70 km of cable trenches and constructing 122 hardstands as well as 50 km of internal access roads.

‘We were also responsible for upgrading and maintaining the 61.5 km auxiliary road to the site. We used a dust suppression product supplied by E-cat, which increased visibility and provided a seal on the road. The concrete mix design was optimised using a high slag content to counter brackish water from construction boreholes that reduced the production costs of concrete. The amount of cement used in the mix was more environmentally friendly.’ A steel-reinforced concrete base runs 3.5m deep and about 19m in diameter on each turbine.

Concor’s consortium partner, Consolidated Power Projects, built the two on-site substations as well as the 132 kV overhead power line connecting each substation to the Helios substation; installed the 122 external pad-mounted transformers; and laid the underground medium voltage cables connecting the transformers to the on-site substations.

The huge blades of a turbine have a curved shape like the wing of an aircraft, while the nacelle resembles a cockpit. When air moves across the wing of an aeroplane, it moves faster across the top than the bottom, creating a lifting force. Similarly, when the wind passes the rotor blade of a turbine, the pressure difference on either side of the blades causes them to turn.

When the wind speed reaches around 4m per second, the turbine blades will spin up to operating speed and start generating electricity. As the wind speed increases, the generator output increases. The blades rotate at between 15 and 20 revolutions per minute at constant speed. The generator output remains at its rated capacity until the wind reaches the turbine’s cut-out speed.

Strong winds are desirable but too much can be a problem so blade rotation has a maximum speed after which the turbine shuts down. The turbine can deploy its tip-brakes, then its disk brake, stopping the blades in a few revolutions.

The nacelle controllers change the pitch of the blades so that the straight edge faces the wind. This prevents the blades from catching the wind and rotating, like aeroplane propellers when the engine is shut down. The turbine will then rotate itself 90 degrees out of the wind and ‘park’ itself. When the wind speed drops to a level below the cut-out speed for a sufficient length of time, the turbine points itself back into the wind, releases its brake and resumes power production.

Each wind turbine is connected to a step-up transformer located at its base, boosting voltage output of the wind turbine generator from 690V to 33 000V. Power cables are routed underground connecting the turbines in grouped circuits bringing power from the step-up transformers to the substation, where the main transformer is located. The grouped circuit power cables meet at two conjoined substations and power is then directed through an 8 km overhead line to the Helios substation. This is distributed to the Eskom grid through separate overhead lines leading out of the substations. The town of Loeriesfontein is supplied by one of the overhead lines at 66 000V.

‘We’re working with governments in Senegal, Ghana and Egypt, developing wind farms so that they too can access cheap, renewable energy,’ says Antonopolous. ‘The more we share this kind of knowledge, the greater the impact renewable power can have in multiple locations across Africa.’

PROJECT LEAD
Lekela

www.lekela.com

FOUNDATIONS
Concor Infrastructure
www.concor.co.za

CONSTRUCTION AND
OPERATIONS MANAGER

Mainstream Renewable Power SA

www.mainstreamrp.com/south-africa

CONSTRUCTION
AND INSTALLATION
Consolidated Power Projects
www.concogrp.com

 

By Laura Jones
Images: Loeriesfontein Wind

Article written by