Cavern a powerhouse for electricity

By Keith Ross
A huge cavern has been excavated deep within the Drakensberg Mountains, in KwaZulu-Natal, and is destined to play a vital role in solving some of South Africa’s most pressing power-shortage problems.

The cavern will be the powerhouse of the Ingula Pumped Storage Scheme and will eventually contain four generators, each capable of producing 333 megawatts of electricity.

The generators can be brought into operation at short notice when, for example, there is an unusually high demand on Eskom’s national grid and power cuts are looming.

They can, therefore, help Eskom solve an acute problem: there is no simple way to store electricity, so surplus power tends to go to waste during times of low demand and extra sources have to be found to meet the country’s needs when demand peaks.

This is where a pumped storage scheme comes in. It uses surplus electricity in times of low demand to pump water up to a dam situated at high altitude – as can be built in places such as the Drakensberg – where it is stored to meet power needs during peak periods.

When the need arises, water is released from the dam through tunnels in the mountain to drive generators in a cavern below.

“They can start producing electricity within three minutes,” said Fifi Meyer, who runs the Ingula Visitors’ Centre.

Meyer said the power used by big industrial users, such as the metal smelters, was regulated and predictable, but the demands of domestic users often posed problems.

She said domestic demand peaked in winter when temperatures dropped and heaters were turned on in millions of homes. “With every one degree drop in temperature, Eskom has to push out an extra 600MW.”

Eskom has long been aware of the need for pumped storage schemes and started looking at suitable sites in the 1980s. In all, Eskom looked at 90 possible sites and Ingula was eventually chosen for development because of its “ideal” geography.

Ingula is in the Little Drakensberg, north-east of Van Reenen’s Pass. It straddles the boundary of KwaZulu-Natal and the Free State, on the watershed of both the Vaal and Tugela rivers.

On the Free State side, on the edge of the escarpment, Eskom has built the Bedford Dam, the upper storage facility, which holds about 22 million metres3 of water. It is linked by tunnels that take the water down 441m in altitude, past the generators to the Bramhoek Dam, 4.6km away on the KwaZulu-Natal border.

The Ingula Scheme will be able to generate electricity for up to 16 hours. It will then take 22 hours to replenish the system fully. In the process, the scheme suffers a loss of power because of the need to pump the water back to the upper storage dam.

The scheme is being built at a cost of R27 billion and is scheduled to come into operation in 2014. It is the third one of its kind in South Africa, the others being the Drakensberg Pumped Storage Scheme, near Bergville, with a capacity of 1 000MW, and the Palmiet scheme in the Western Cape, with a capacity of 400MW.

With its 1 332MW capacity, Ingula will be the largest scheme of its kind in Africa and the 19th largest in the world. At the moment – during construction – there are 4 500 people working on site. This number will drop to 150 when it becomes fully operational. – Sunday Tribune

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