In its most recent presentations on the performance of its power stations, Eskom pointed to improvements in the energy availability factor (EAF) of its coal-fired power stations over the past few months as evidence of a solid operational turnaround.

Eskom shows, for example, that the EAF, which fell to 67.68% in April 2015, the start of its 2016 financial year, recovered to 74.6% 12 months later.

It has also reported further recoveries since the start of its 2017 financial year, stating that the EAF for the period April to the end of June has improved to 78.6%. Eskom adds that, since June, the EAF has pierced the 80% target level and has expressed optimism that the performance will be sustained for the remainder of the year.

This, at first glance, is impressive, adding over 3 700 MW of capacity during the first quarter of Eskom’s current financial year that was not available from the coal fleet in the same period last year. This, together with lower demand and the contribution from renewable-energy plants, has enabled Eskom to burn far less diesel than during the load- shedding-afflicted months of 2015. The monthly diesel bill has fallen to below R20-million from well over R700-million period-on-period.

Although Eskom has tended to dismiss the contribution of renewables to this stabilisation, research by the Council for Scientific and Industrial Research Energy Centre shows that solar and wind generation have indeed helped improve system stability and enabled South Africa to avoid load-shedding.

Between January and December 2015, there were 103 load-shedding days, or 858 hours of disruption. In the absence of solar and wind, the system would have exceeded 30 000 MW for 1 470 hours in 2015. In the event, the number of hours of running above 30 000 MW was reduced to 680 hours, which helped to materially reduce the load-shedding threat. This trend is likely to have continued into 2016, with even higher levels of production as new renewables plants have come into operation.

Another critical issue is that the EAF is seasonal, with the recovery reported by Eskom, to date, coinciding with the low-maintenance winter months, when the EAF is typically higher anyway.

In fact, public domain information suggests that the EAF of 78.6% for the period April to June is more or less in line with the EAF of the winter periods of 2013 and 2014. However, it is an improvement on 2015. The implication is that lower peak demand - estimated at around 3 000 MW less - is likely to have been as important a contributor to system stability as, if not a more important one than, the recovery in plant performance.

Eskom needs to demonstrate that the EAF recovery can be sustained throughout the year, including through the high-maintenance summer months, when plant vulnerabilities tend to present themselves not only during shutdowns but also when the units are returned to service.

South Africans will recall, no doubt, that the recovery in the EAF prior to and during the 2010 FIFA World Cup later turned out to be unsustainable. While the EAF recovered to above 85% in 2009 and 2010, it fell precipitously thereafter. By Eskom’s 2013 financial year, it had sunk below 80% for the first time, to 77.7%, and the slide continued to the low of 71% last year.

The recent recovery could be showing that the decline has been arrested but, without independent verification, it is simply too early to tell for sure.