Why the lights went out last night

Eskom is battling a “constrained and vulnerable” generation fleet, with “plant performing at very low levels of reliability”.

In the 28 days since emergency overnight load shedding was implemented on November 7/8, so-called “unplanned breakdowns” were above the 9 500 megawatts (MW) level on practically half of them.

An analysis by Moneyweb, using public data provided by Eskom, shows that these breakdowns were only below the 9 000MW level on three of the last 28 days. Importantly, the data published by Eskom provides only daily snapshots of breakdowns across the system at a point in time, generally between 6am and 8am.

This number is not static as some plants will return to service, while others may break down or experience partial load losses.

On Thursday morning, Eskom advised that unplanned breakdowns were at a worryingly high 12 300MW. By mid-afternoon, it experienced a “loss of additional generation” resulting in Stage 2 load shedding from 4pm. Stage 2 requires 2 000MW of load to be reduced, which means that breakdowns likely neared the 14 000MW level.

Eskom’s plan to avoid load shedding during summer requires unplanned breakdowns to be kept below the 9 500MW level. On top of that, it maintains a 2 200MW reserve margin to protect the grid in the case of additional breakdowns, trips or load losses.

When breakdowns exceed the 9 500MW level – Eskom actually forecasts using a “planned risk level” of 11 700MW of breakdowns – it has to rely on emergency generation resources, including pumped storage schemes and open cycle gas turbines, to ensure than an adequate operating margin is preserved. When that runs out of headroom (or if these emergency generation resources are unavailable), it has to resort to load shedding.

On November 7/8, given the high levels of breakdowns, it had to implement overnight load shedding so that it could replenish its pumped storage schemes.

The utility is increasingly using these schemes, which are net consumers of power (they require more power to operate than each unit of power they produce), to generate baseload power. Traditionally, pumped storage schemes are meant to operate as peaking plants only.

Along with this, Eskom is using as much as 3 500MW of power from renewable energy plants to supplement its own generation.

And it is relying on units at the Medupi and Kusile power stations that are not yet in commercial operation to provide anywhere from 900MW to 1 600MW of power daily. Medupi Unit 1, the only unit at that plant yet to be commercialised, is feeding an average of 400MW to the grid.

On November 7, with 10 500MW of unplanned breakdowns across the coal fleet, you can see the problem.

The total installed capacity of this fleet is around 40 000MW. Energy availability in this fleet is around 57%, far below the (still very low) 66.18% Eskom energy availability factor reported by the utility in that week. It needs the overall number to get above 70%, and ideally to 75%.

The longer-term problem for Eskom is that it continues to defer and “adjust down” the levels of planned maintenance to ensure that it has sufficient generation capacity.

It did, however, manage a level of 8.58% planned maintenance in the second quarter this year, versus a target of 7.5%. The summer plan calls for an average of 5 000MW of maintenance to be done across the seven months.

For now, things seem to be vaguely on track. But longer-term, not having the headroom to do enough maintenance translates into more unreliable plants and more breakdowns. It’s a vicious circle.

As at last week, Eskom’s planned outage factor was 9.85% in the year to date, versus 10.4% last year. This is a significant regression. Unplanned outages are at 21.01% in the year to date, versus 15.87% in 2018. This means that, on average, over 9 990MW of generation capacity has been unavailable due to breakdowns this year (versus an average of around 7 500 last year).

What Eskom really requires is the time and space to do proper maintenance to improve levels of plant reliability. Politically, this is unpalatable, so the utility is forced to battle on, trying to repair ageing plants while maintaining enough generation capacity.

By winter next year, we’ll have some indication of whether Eskom has managed to do sufficient maintenance – it is too late now to change the course materially.

If not enough has been done, new CEO Andre De Ruyter’s first few months are likely to be quite the baptism by fire.

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