Eskom reckons there’s 4 400MW of rooftop solar installed in SA

Eskom has for the first time published data on the amount of rooftop photovoltaic (PV) solar it believes is installed in South Africa.

By June, the maximum capacity of this generation totalled 4 411.5MWp (megawatt peak), a 95% increase on the 2 264.5MWp installed in July last year. This itself is a doubling of the just under 1 000MWp installed at the end of the first quarter.

Read: How much Eskom wants to charge normal households, and those with solar

An interesting comparison can be made between the 4.4GWp of rooftop solar installed by households and commercial properties and the 2.2GWp installed to date under government’s Renewable Energy Independent Power Producer Procurement Programme (Reipppp).

Today, there is double the amount of rooftop solar in place than solar farm capacity that has been procured under four bid windows.

It is believed the data for private installations is being produced by Eskom’s transmission division, based on the difference between forecast and actual demand (there is no central database of installed solar, nor is there likely to ever be). These estimates would typically factor in weather information.

Put simply, if the utility expects demand of 30 000MW at midday midweek, and there is only demand of 28 000MW (with the sun shining in most of the country), it would then be able to reliably attribute this to the impact of rooftop solar.

Similarly, if demand at a particular feeder substation was X at the midday peak last year but only X less 10% now, it can attribute this to PV. Plus, it has a very good idea of what the supply curve for solar looks like and would be able to make inferences based on this (the reduction in demand at that sub would likely match the supply from PV).

Eskom’s transmission unit would have incredibly granular data (right down to city level), which would smooth out any distortions and is why these estimates can be this specific.

The first mention of this 4 000MW number ironically came in an interview with former Eskom COO Jan Oberholzer published earlier this month.

Eskom’s data also seems to line up – roughly – with solar PV import data. This shows that panels with approximately 1 500MWp of generation capacity were imported last year, with a further 1 000MWp in the first quarter of 2023. (There is also similar import data for inverters and batteries.)

The so-called ‘hot takes’ on Twitter – or X as we’ll soon be calling it – suggest somewhat shallowly that somehow this nearly 4.5GWp of capacity has reduced the severity of load shedding by four stages.

Everyone with a home solar system installed knows this is not possible. There is a steady build from sunrise to peak generation at midday, following which output steadily reduces to sunset. Cloud cover and the sun’s relative position in winter will also impact generation.

Between sunrise and sunset, the amount of this rooftop solar capacity that is ‘deliverable’ is likely, on average, to be a maximum of 50%. (More strictly, the capacity factor of solar PV is, at best, 30%; this takes into account the full 24 hours of the day and the impact of cloudy/rainy weather.)

Theoretically, then, this 4.4GWp of rooftop solar likely reduces demand during the day by an average of 2 000MW (perhaps peaking at a higher number at midday?).

Remember the 2.2GWp of installed solar projects under the Reipppp?

In the week to 24 July, these projects only generated more than 1 000MW for 37 of the 77 daylight hours (and only more than 1 500MW in three of the hours).

Yes, yes … winter, cold fronts (not to mention the fact that these solar farms are almost entirely all in the Northern and Western Cape).

Excess?

Also, the vast majority of excess generation from rooftop solar is not being fed back into the grid. The process for metros to correctly bill (credit) this is only just beginning, with a limited amount of generation likely to be coming on stream in the final quarter of this year (primarily, at this stage, in Cape Town).

Read/listen: Cape Town to pay cash for residents’ excess power

At this point, the impact from rooftop PV is simply from a reduction in demand on Eskom.

Read: Think carefully before selling excess solar to Joburg’s City Power

It must be borne in mind, that while weather patterns are predictable in the near term, this solar power is not dispatchable. On a rainy day in Gauteng, a household/shopping mall/factory cannot ‘switch on’ the supply from their rooftop solar. A backup needs to be in place, and with limited battery capacity (if any), that backup is the grid – ultimately Eskom.

Read: Think carefully before selling excess solar to Joburg’s City Power

As more and more rooftop solar gets installed, the ability for Eskom to be the supplier of last resort becomes more and more complex (and pricey).

A story for another day …