“Today, as South Africans, we stand tall and proud as we register further progress in our quest for energy security,” says President Jacob Zuma.
President Jacob Zuma officially inaugurated Unit 4 of the Ingula Pumped Storage Scheme (PSS), which on completion will be the largest PSS in Africa. The Ingula PSS consists of an upper dam in the Free State and a lower dam in KwaZulu-Natal, each capable of holding approximately 22 million cubic metres of water. The dams, 4,6km apart, are connected by underground waterways passing through a subterranean powerhouse with four 333 Megawatts (MW) generators.
Prior to the official inauguration at the Ingula Visitors Centre, Zuma toured the facility and met with the operators in the control room and posed for photos for the media.
Although only Unit 4 was officially inaugurated on 27 July, Units 1 and 2 were also delivering their rated 333 MW to the national grid during the visit as the recent cold snap had pushed up demand for power for heating.
To cope with the peak demand, Eskom uses pumped storage schemes such as Ingula and expensive to run Open Cycle Gas Turbines (OCGT). Pumped storage uses off-peak power to pump water to an upper dam and then releases this water to a lower dam to generate power during peak periods. OCGT use diesel to power turbines, but this is more than 20 times more expensive than coal-fired power.
The commitment to “keep the lights on” meant that instead of using OCGT only during peak periods, Eskom was using it during daylight periods. The result was that generating costs escalated sharply, which Eskom tried to recoup by asking for higher tariff increases.
In the case of Ingula, the only operational cost is the efficiency loss of electricity as the whole operational staff is only five people in a simple control room. This efficiency loss is only 20% as it takes 20 hours to fill the upper dam, which can provide 16 hours of power when the water is released to run the four generators each weighing 230 tons and rotating at 330 km/hour. The water that is released would fill eight Olympic-sized swimming pools every minute.
The main cost of Ingula is the capital cost as two dams have to be constructed, the tunnels have to be excavated, the turbine/pumps have to be installed and the high-voltage transmission lines have to be linked to the rest of the national grid. The total cost for Ingula is some R27bn.
As most of Ingula is located inside the mountain, little of the immensity of the scheme is visible from the outside. Even inside in the underground machine hall, the turbines are mostly submerged and only a low humming sound is evidence that they are running.
Eskom said investigation for the new pumped storage scheme began in 1985 when planners identified 90 potential sites across the country. By 2002 they had narrowed down the choice to just three sites and construction at Ingula began in 2005.
The upper Bedford Dam on Bedford stream, a tributary of the Wilge River, which then flows into the Vaal river and then empties into the Atlantic Ocean once it joins the Orange river, was completed in April 2011. It is a 39 meter tall concrete-face rock-fill dam. It has a 22.4 million cubic meters water storage capacity of which 19.2 million cubic meters can be used for power generation. The lower Braamhoek Dam on Braamhoek stream, a tributary of the Klip River, which then becomes part of the Tugela river and flows into the Indian Ocean, was completed in November 2011. It is a 41 meter tall roller-compacted concrete gravity dam. It has a 26.3 million cubic meters water storage capacity of which 21.9 million cubic meters can be pumped up to the upper reservoir.
Both dams are obliged to discharge water in the adjacent wetlands in terms of their environmental impact assessment as the Ingula wetlands are home to four of South Africa’s six critically endangered bird species. A 2 kilometer long headrace tunnel connects the upper reservoir to the underground power station, which then leads to a 2.5 kilometer long tailrace tunnel to the lower reservoir. The underground power station is a 150 meter long by 25 meter wide cavern adjacent to a 160 meter long by 15 meter wide transformer hall. A total of 3 million tons of rock was excavated using the conventional drill and blast method.