Leading black-owned contractor, Concor company recently completed hollow-cast of the last base at the San Kraal Wind Energy Facility in the Noupoort district, currently being developed by EDF Renewables and project partners H1 Holdings, Gibbs Crede and a local community trust.

San Kraal is one of the facilities making up the Koruson 1 Cluster, on the border of the Eastern and Northern Cape provinces. It comprises three wind farms, namely Phezukomoya, San Kraal and Coleskop, each with installed capacities of 140 MW. Once completed, the 78 wind turbines on the three wind farms will contribute 420 MW to the country’s energy grid.

Each turbine base constructed measures over 20 m in diameter and is around 3,3 m deep, requiring over 400 m3 of 45 MPa concrete – with an additional 18 m3 of 50 MPa concrete in the plinth.

A significant difference on the Koruson 1 Cluster of projects was the use of hollow cast foundations, which require considerably less concrete than a conventional foundation, reducing the overall carbon footprint of the project. While considerably more complex in design and execution, the hollow foundation allows for the inclusion of ducts and facilitates the post-tensioning of cables for the concrete tower. It also includes ducts for the power cables to the electrical reticulation network in the foundation.

At the same time, the construction of hollow foundations is more labour intensive, and requires more formwork and steel reinforcing. Each of the San Kraal wind turbine base foundations used a total of 64 tons of reinforcing steel, and Concor’s steel fixing teams had to work with high levels of precision to meet the stringent tolerances required.

The complexity of the hollow foundation design required each foundation to be surveyed in four stages, to ensure they were cast in strict accordance with the design – and to align the 40 post-tension duct cable sleeves for the tensioning cables within a tolerance of millimetres. With a full-time Concor surveyor on site to conduct all the setting out and verification survey work, a total of 168 setting out points were calculated for each base.

At the peak of construction, the project comprised about 400 employees, most of them from the local community of Noupoort. Concerted safety and technical training on site, as well as close supervision and guidance from Concor allowed the project to complete over 500,000 working hours without a lost-time injury. The contract to complete the turbine base foundations was completed in seven months.