The enormous boilers at Medupi and Kusile will have to be modified to add 12.5m to their already substantial height, in an attempt to try to reduce exhaust steam temperatures.

The boilers are now 130m tall, but the temperature of the exhaust steam is 128°C.

“That’s too hot and it’s damaging the exhaust equipment. That’s why we can’t operate the units to their full capacity,” said André de Ruyter, the chief executive officer of Eskom.

Eventually, every one of the 12 boilers will be higher than the head offices of Standard Bank and Absa in the Johannesburg CBD, both of which measure 140m high.

De Ruyters’ announcement of further modifications at Kusile and Medupi means that each one of the 12 generation units, which now contribute 600MW of electricity to the national grid, will have to be turned off for 75 days to effect the repairs.

We’re not just lengthening the boilers, we’re also fixing faults with the coal mills and the equipment used to handle coal. Eskom CEO André de Ruyter

The first of those, unit three at Medupi, was taken offline on January 25 to make the modifications and will begin running again only after April 9.

This was according to a repair schedule that De Ruyter presented to Parliament on Tuesday.

The last unit of Medupi was meant to be completed in April to enable the power station to start delivering 4 700MW of electricity. However, it is now scheduled to be completed only in July next year.

According to De Ruyter’s timeline, Kusile will be completed only in August 2022.

“We’re not just lengthening the boilers, we’re also fixing faults with the coal mills and the equipment used to handle coal,” De Ruyter told Parliament’s standing committee on public accounts.

The total cost of Medupi was originally put at R80 billion, but it will now cost R145 billion to complete construction. Independent analysts, however, estimated that its cost could rise to R234 billion.

Kusile’s initial cost was put at R100 billion, but it will now cost R161.4 billion.

Last year the conveyor belt that is meant to transport coal from the Grootegeluk Mine to Medupi broke down, leaving the power station without coal and plunging the country into stage six load shedding.

“I inspected the entire conveyer belt myself and made sure that we have sufficient alternatives to ensure something like that never happens again,” De Ruyter told the committee.

There clearly isn’t enough room for sufficient ventilation.

Energy expert Mike Rossouw, who completed a comprehensive audit of the state of Eskom’s coal-fired power stations, said not nearly enough engineering work was done when the two power stations – the biggest in Africa – were designed.

He pointed out that Medupi and Kusile were both air-cooled power stations, which was why the boilers had to be bigger than those at other power stations.

“The vertical and horizontal spacing of various components is critically important in the power stations. There clearly isn’t enough room for sufficient ventilation,” Rossouw said.

He was also sceptical about Eskom’s estimation that it would take between 18 months and two years to catch up with the maintenance backlog at Eskom’s older, coal-fired power stations.

The work, which will mostly involve major maintenance that should have been completed at the midpoint of a power station’s 50-year lifespan, had been neglected in the past 10 to 15 years.

De Ruyter and Jan Oberholzer, operational head of Eskom, said that planned load shedding would have to take place during the maintanence period. De Ruyter is expected to present a plan regarding load shedding to Eskom’s directors early in March.

After the maintanence period, the country’s electricity should be stable again.

Rossouw, however, believed Eskom was being overoptimistic.

“I think it could take as long as five years before we have a stable electricity network again,” said Rossouw, who conducted comprehensive inspections at all coal power stations in 2015. After the audit, he predicted that the backlog in maintenance would lead to the load shedding now being experienced.