Lights Out, South Africa

As a nation, South Africans know blackouts well. Except we don’t, at least not long-term ones. Losing power for two-to-four hours due to load shedding is an inconvenience; losing power for two weeks is a catastrophe.

And yet it is this scenario that South Africa potentially faces should our electricity grid collapse. That’s total collapse: when all power plants and distribution units nationwide fail. It’s a frightening scenario.

In fact, were it not for the conscientious work of the Eskom National Control Centre (NCC) in Germiston, the grid would already have collapsed, says Prof Thinus Booysen, of Stellenbosch University’s Faculty of Engineering.

“Eskom has a supply and demand problem,” explains Booysen. “On the one side is generation, which continuously generates energy regardless of how much is consumed. On the other side is demand, which changes throughout the day, peaking in the evening, with a slightly lesser peak in the morning, and remaining flat for the rest of the day. The balance hinges on the NCC.”

The NCC continually monitors the difference between supply and demand, notes Booysen. “If the margin between these becomes too small, the risk increases. Should a whole city switch on their geysers with ripple control, that will create a huge surge in demand, which could exceed supply.” The NCC’s job is to keep the margin sufficient that should this occur, or should a generator fail, the whole house of cards doesn’t come tumbling down.

What is grid collapse?

To understand why this is so important, let’s take a quick look at what a power grid actually is. Booysen explains that the grid comprises generation (power stations), transmission (high-voltage power lines between major centres) and distribution (lower-voltage lines that transport electricity to businesses and homes). All these elements, including the power plant turbines, solar and wind farms, and the plugs and devices in our homes, are synchronised to an alternating current frequency of 50Hz.

“When supply is too low and the NCC doesn’t reduce demand [for example through load shedding], then say the weakest generation unit needs to generate more than it safely can,” says Booysen. “In this instance, the frequency of the turbines in that unit will drop so low that it will fall out of synch with the rest of the grid. When that happens, the unit switches off automatically.”

The real problem is that if you’re already in a scenario where units need to produce more power than they can, if one shuts off, then the next one will shut off, and so on. “It produces a cascading effect across the entire grid,” says Booysen. “This would take anything from 30 seconds to two minutes.”

The grid can shut down really quickly, but bringing it back online could take two weeks or more, explains Booysen. “When they start the grid back up, they need to synchronise all these units. They’ll start up one unit for the others to synchronise to, then the next, and the next. Every time this is done, there’s a chance that the synchronisation will be unsuccessful, which means restarting the latest or even already synched units.”

The availability factor

It’s a dire scenario indeed. But at least it is an unlikely one. That’s the view of the National Energy Regulator of South Africa (NERSA), according to full-time regulator for electricity Nhlanhla Gumede. “The NCC does a great job of managing the risk and ensuring we don’t experience widespread blackouts. As long as they keep doing their job, all that will happen is more load shedding and the price of electricity will continue to rise.”

What isn’t rising is Eskom’s energy availability factor (EAF), which is how much power its generators can actually supply. This is due to maintenance issues and plants being run poorly, says Gumede. “From 2011, there was an increase in renewables alongside new Eskom capacity coming online. Despite that, the EAF dropped from 86 per cent in 2008 to 67 per cent now, because the plant availability dropped.”

Peak condition

The other issue is that demand for electricity has evolved, shifting from industrial towards residential. “It used to be that 56 per cent of Eskom’s power went to industry, followed by 13-18 per cent to residential, 8-10 per cent to commerce, then agriculture and other,” explains Gumede. “Nowadays, only 40 per cent goes to industry, while residential demand has increased to 31 per cent.”

The problem with residential demand is that it operates in morning and evening peaks, which require a certain type of plant to meet it. “You may get a situation where you have plant capacity,” says Gumede, “but it’s inappropriate capacity.”

To meet this demand, Eskom has been using base-load plants, which aren’t designed to change their power output quickly. “In terms of engineering and thermodynamics, the last thing you want to do is treat your boiler tubes in this way,” says Gumede. “Ramping them up and down will cause them to fail eventually.” Which would obviously further reduce EAF.

To this end, the power utility also uses open-cycle gas turbines to address peak demand. These are flexible, fast-starting plants that burn diesel, which is expensive. “If you compare solar during the day, it’s 43 cents per kilowatt hour (kWh),” says Gumede. “Open-cycle gas turbine costs R4/kWh. Solar is cheap, but the sun rises and sets. You can deal with the peaks using energy storage, but that by its nature is very costly: around R18/kWh.”

The price must be right

Gumede says it’s essential to set the price of energy in a way that reflects the new reality of electricity consumption patterns. “Most people don’t understand the pricing approach we’re trying to create, which represents an unbundling of services. If you clearly identify this peak power consumption as a service and price it accordingly, then people know it will be supplied either by batteries, diesel, or gas turbines. That needs a specific dispensation – a recognition that it’s a separate service from the electricity that you consume the rest of the day.”

Differential pricing can send a signal to people to make better decisions about how they use energy and consider whether or not they could do the energy-consuming things at night earlier in the day, when cheap solar energy is available.

Gumede says NERSA is also advocating for differential pricing in order to avoid driving the price of electricity up across the board, so as not to increase the burden on industry or agriculture, and to avoid overcharging people who use less peak power.

South Africa’s not in the dark just yet, but it’s clearly not a sustainable situation. Booysen says the crux of the matter is that recognised by Eskom CEO Andre de Ruyter: adding renewables as quickly as possible. “If you look at the bigger picture, we simply need more generation. Given that South Africa has abundant sunshine and wind, we need to invest in renewables, but they can’t be the whole picture. I think we’ll be stuck with load shedding for a while, but if we focus on maintenance, then we can get through this.”