Eskom has only managed to meet peak demand with its own fleet on 49 of the 106 days between the most recent instance of load shedding on 23 March, and 7 July.

An analysis by Moneyweb of data published by the utility shows that for just more than half the time over the past three months, Eskom has not generated sufficient electricity to meet peak, night-time demand. This shortfall has ranged from just 30MW to 3.1GW, and was in excess of 1GW for 35 of the 57 days.

Generation performance deteriorated noticeably over the two weeks to Sunday (7 July), with Eskom’s own fleet only able to meet peak demand itself on two of the 14 days (29 and 30 June).

Peak demand has not exceeded 33GW yet this winter, with the highest demand (32.9GW) reported on 28 May. On that day, Eskom reported 35.3GWMW of available generation, its highest total in many months. It must be remembered that there were a number of public holidays over this period, including the Easter weekend, Workers’ Day and Election Day, which would have depressed demand.

In the joint briefing by the minister of public enterprises and Eskom executives at the beginning of April, it was clear that to avoid load shedding this winter, Eskom had to ensure that unplanned outages (plant breakdowns and trips) were kept below 9.5GW. With this headroom, Eskom said it planned to “execute proper maintenance” this winter, a departure from previous years where planned maintenance was cut to about 1GW. The utility has forecast planned maintenance of as much as 4GW at a time during the winter months.

Peaking plants

The extent to which it has been able to execute this maintenance is not known, but running a negative operating reserve margin seems to suggest it is comfortable it can take plant out of service for repairs because of capacity from other sources.

Chief among these, obviously, are the independent power producer (IPP) gas (diesel) peaking plants, Avon and Dedisa, which together provide just over 1GW. It is clear these are being used when Eskom is unable to meet demand.

Renewable energy from other IPPs is also available and being fed into the grid. Already, wind and solar photovoltaic (PV) and concentrated solar power (CSP) are consistently supplying just under 2GW of power through the day. But given that the evening peak is at around 6pm, only wind is able to provide a significant amount of capacity at that time. There is some supply from CSP, likely around 200MW.

We know that, together, wind and CSP are able to provide around 1GW of supply during the peak.

Eskom is also able to use its so-called “virtual power station” to manage demand. This allows it to effectively remove demand (load) from contracted customers. In the utility’s 2018 integrated report, it discloses that its “demand response programme achieved an average certified capacity of 1 296MW during the year”. It is unlikely this number is substantially higher currently. This means it can remove demand of over 1GW during peaks.

A shortfall in available generation capacity of around 1GW to 2GW is therefore comfortably made up by a mix of the above sources. The gap of 3.1GW on Wednesday, 26 June, would have been a big ask.

Each IPP project supplies Eskom at a contracted price, and the utility will buy a mix of supply at the cheapest possible rate when it is unable to meet demand. For instance, if its demand-side management agreements with large customers cost more than running the diesel peaking plants, it will favour the latter.

Eskom has given itself additional headroom to do maintenance on its coal fleet by synchronising a total of three units at its Medupi and Kusile power stations to the grid ahead of its revised schedule.

Unit 2 at Medupi was first synchronised to the grid on 7 October 2018, and reached full load on 12 November 2018. Kusile unit 3 was synchronised to the grid for the first time on 14 April, which it says is eight months ahead of schedule. Eskom has not yet announced that this unit has achieved full load, meaning that it is contributing less than this to the grid when it operates.

Eskom is able to use this capacity, typically up to 600MW from each unit, to supplement its supply.

Outlook

Medupi unit 3 fell into this category too, as it was first synchronised to the national grid on 8 April 2018, reached full load (796MW) on 16 May 2018, and has been ramping up over recent months. This unit, however, achieved commercial operation on 28 June, meaning that its additional 796MW is now formally part of the utility’s installed capacity.

While it plans to achieve commercial operation of Kusile unit 3 in November this year (much earlier than the scheduled August 2020 date), Medupi unit 1 is the only other unit from the new-build programme slated to achieve commercial operation next year.

The risk of load shedding remains, with Eskom noting this at the April briefing. The outlook, however, has improved significantly as it slowly catches up on its maintenance backlog, as plant performance improves, and as it brings new units at Medupi and Kusile online.