Renewables queueing to connect to a grid with no capacity

Wind turbines. The problem that poor planning has created is a bottleneck in the transmission grid, says the author. Picture Henk Kruger/African News Agency (ANA)

Wind turbines. The problem that poor planning has created is a bottleneck in the transmission grid, says the author. Picture Henk Kruger/African News Agency (ANA)

Published Oct 18, 2023


By Dominic Preuss

As South Africa’s economic growth struggles to trend upwards, with the weight of load shedding suppressing the optimism in its industries and while we wait for solutions to magic themselves out of thin air, it seems the planners of the country have let us down in their foresight to plan adequately and implement infrastructure that will solve the load shedding fiasco.

President Cyril Ramaphosa was first appointed to the energy action task group in 2014, when he was deputy president. If anything, the problem has worsened under his oversight and planning.

The problem that poor planning has created is a bottleneck in the transmission grid. There are many renewable projects that want to connect but they in a queue, waiting for the transmission grid’s capacity to be expanded. This is very much the case in the Cape region where there is no more capacity in the Eastern, Western Cape and Northern Cape.

In the Northern Cape, which has some of the best incidences of solar radiation in the world, a few international companies are interested in investing in PV plants.

However, the northern corridor has up to 150% over supply of renewables versus the demand, creating what is known in the industry as a weak grid.

The constraints in the transmission grid fall into three categories. The first is the thermal constraint, which is the limiting factor on how much energy can move across the transmission line before the lines start to heat up like an element.

The second is the voltage stability limit which refers to the ability of the system to maintain stable voltages at all buses (nodes) under various operating conditions, including changes in load demand and generation. When the voltage in a power system falls outside a certain range, it can lead to voltage instability, which may cause equipment damage and power outages.

The third is steady state stability limit. This refers to the ability of the system to maintain synchronism following a small disturbance, such as a sudden change in load or a flux in a renewable plant’s electricity generation.

All the factors determine the amount of electrons that can be put on to the grid, bottlenecking the commissioning of many planned renewable power plants, particularly in the wind industry, With wind power plants not receiving referential transmission access in the latest IPP bid window.

The grid and its sub-stations are starting to become oversubscribed.

However, the good news is that there is an appetite for up take in development.

“The installed amount of renewables and that under development is at present in 2023 at levels forecast for 2027/9,” says Ronald Marais, Eskom’s strategic grid planning senior manager, at the Windaba conference this past week in Cape Town.

“So far it’s up to 26 gigawatts of renewables that have been installed,” Marisa says.

“Our own IRP plans seems (sic) to underestimate the growth in renewables,” said Steve Nicholls of the Presidential Climate Commission.

Naniki Nzuza, a senior grid manager at Mulilo Energy Holdings, also presenting at Windaba, said: “Renewables have changed the dynamics of the grid for what it was originally designed.”

The backbone of the grid infrastructure was developed with Gauteng and Mpumalanga as coal power generation hubs that exported the electricity to the rest of the country. For example, now the Northern Cape grid, originally a receiver of coal electrons, is the biggest exporter of solar electrons today.

“The mismatch between grid capacity and renewable generation supply leads us to look at operational short-term fix,” said Nzuza. “It means wind needs curtailment and PV need batteries.”

“We must ensure that the race to connect does not create imbalance and grid stability,” said Chris Bellingham, the head of project development at Juwi Renewable Energies.

The process of building new transmission lines is complex, with environmental approvals needed and the expropriation of land. It’s also reliant on the availability of the raw materials – aluminium, copper and steel – in the country. Line construction requires transformer manufactures to build expensive equipment that take time to manufacture.

While the National Transmission Company now has a licence approved by the National Energy Regulator of SA, to operate the national power grid as it unbundles from Eskom, it has a long way to go before it can become a functional competent transmission operator independent from Eskom.

It needs a mandate to move procurement to a time-based signal, which prioritises the power profile matching demand, quantifying the time of day that electrons are delivered.

Dominic Preuss is an engineering technologist at Amore Hydro.