Diesel, the backbone of South Africa’s energy security, is no longer secure
5 min read
As the Hormuz disruption drags on, large energy users around the world and in South Africa have faced an unprecedented, sobering new reality: Diesel – always the last line of defence for power systems – cannot be relied upon in the case of grid outages or a power crisis.
The availability of diesel during a crisis has hardly been questioned until six weeks ago. When South Africa’s power goes out, diesel keeps the country running.
During stable system operations, like now, Eskom’s open cycle gas turbines (OCGTs) are used only at minimal levels to balance the system. But when Eskom’s system reserves are low, Eskom ramps up the usage of these diesel OCGT’s to reduce the need to loadshed as much as possible.
Once this fails and Eskom needs to loadshed, private users around the country burn diesel in backup, on-site gensets during loadshedding events.
During stable times, like now, Eskom only uses 3%–10% of South Africa’s total diesel demand. During times of crisis, such as the three severe loadshedding periods South Africa experienced during 2008–2009, 2014–2015 and 2022–2023, Eskom’s diesel consumption increased dramatically, to 20%–30% of the country’s consumption, to try keep the lights on and reduce loadshedding as much as possible.
During these loadshedding events, backup diesel generation spiked across the country when the grid was down.
Eskom is currently doing a remarkable job ensuring a stable grid with a troublesome and ageing fleet of assets. 17.7GW of Eskom’s coal assets are scheduled to be decommissioned by 2035 – about 40% of South Africa’s grid – with insufficient replacement generation planned.
In the immediate term, Eskom has ample reserve margin and a healthy system. Luckily for South Africans, the global fuel availability crisis from the Hormuz crisis has not coincided with a period of Eskom loadshedding. Over the long term, Cresco’s National Energy Balance Model forecasts that Eskom will return to periods of loadshedding from 2029 onward.
In any case, Cresco analysed what would need to happen for Eskom’s grid to return to a loadshedding risk in the immediate term, at the same time as the Hormuz crisis.
Eskom currently has 4.8GW of headroom prior to even reaching loadshedding risk levels. While this is quite an ample buffer, an unlikely but possible event of multiple unit trips at several Eskom power stations, coupled with minor issues such as boiler leaks that could delay the recovery time of these assets, could place South Africa at risk of loadshedding again within a matter of days.
If diesel supply is constrained, Eskom would be challenged to run the diesel OCGTs to avoid or reduce loadshedding as it does typically. The country therefore has a reduced safety buffer of diesel reliability in the face of a loadshedding risk event.
Multiple unit trips at Eskom’s ageing fleet of coal plants are not uncommon. As recently as February 2025, five units at Majuba power station tripped, which set off a trip at Medupi due to frequency issues. An unconnected event happened at Camden at the same time, where four units lost power due to hydraulic valve issues on the station’s cooling water pumps.
As a result, 10 units – more than 4GW – dropped off the grid almost instantly, plunging South Africa into stage 3 loadshedding at first, then stage 6 loadshedding. In that case, power was restored after only four days. Eskom had sufficient diesel supply to run the OCGTs, first to reduce the loadshedding, then to ramp up and support the fast restoration of the system.
Meanwhile, during these loadshedding events, private users such as hospitals, data centres, commercial, industrial, agricultural and residential end-users ran their diesel gensets on-site.
If such an issue had to occur during the Hormuz crisis, Eskom and private users may not be able to secure and burn enough diesel during such a crisis.
As the war and Hormuz crisis rage on, energy security experts are plagued with an unexpected new reality: that diesel is no longer the last line of defence in the case of a power outage.
On-site solar and batteries can provide a partial solution, or a layer of resilience – by reducing diesel fuel use as much as possible. Otherwise, over an extended crisis, for periods of time the power may simply run out.
Dominic Goncalves
Advisory Partner: Energy Strategy
Founder & Director
