Eskom has confirmed that it will release a curtailment addendum to its recently published Generation Connection Capacity Assessment (GCCA) that will unlock 4 GW of connection capacity immediately in the grid-constrained Eastern and Western Cape provinces.

Published at the end of October, the GCCA indicated the grid capacity in the two wind-rich regions had been fully absorbed, along with that in the Northern Cape and Eskom’s Hydra Central grid area, which borders the Cape provinces and the Free State.

The document indicated that there was 19.9 GW of grid capacity elsewhere in the country and stated that curtailment studies were being undertaken to provide “developers with an alternative option if they are still keen to connect in these constrained areas”.

The results, Eskom added, would be shared either in the next release of the GCCA or in an addendum, but only after approval from the regulator.

The lack of a framework came to the fore last year when none of the 23 wind projects that bid for a 3.2 GW public-procurement allocation was selected to proceed on the basis of grid “depletion”.

In addition, the Independent Power Producer Office (IPPO) confirmed to Engineering News & Mining Weekly recently that the ensuing Bid Window Seven, which was initially expected to be launched in the middle of 2023, had been delayed partly because of ongoing uncertainty regarding Eskom’s approach to curtailment.

However, Eskom Transmission MD Segomoco Scheppers confirmed last month that a renewable-energy curtailment framework would indeed be implemented.

In an address on the implementation of the Transmission Development Plan (TDP), Scheppers said the framework would “ensure that new grid integration capacity, especially for wind, can be unlocked in the quickest possible time at the least cost to the economy”.

Strategic grid planning senior manager Ronald Marais also used the platform to confirm that the curtailment framework would be published in the form of an addendum to the GCCA, rather than in the next edition of the document.

Marais also stressed that curtailment was the optimal way to expand the network at least cost and would, thus, remain a feature, albeit at variable rates, even as new grid capacity was added in future.

This was confirmed in a recent assessment by Eskom and two European transmission system operators – 50Hertz of Germany and Elia of Belgium – which showed that curtailment of up to 10% offered more economic value than new grid investments.

Technical operation senior manager Comfort Masike underlined this point at the TDP forum by stating that transmission companies globally used curtailment not only to manage system frequency but because it was also the most cost-effective way to manage grid capacity.

Curtailment involves the active reduction of output from wind and solar plants in response to system security needs or temporary transmission capacity constraints and has been widely used by system operators to facilitate the introduction of renewable generators in a context of grid constraint.

A cost comparison between allowing 4 GW of additional wind generation in the Western Cape with 10% curtailment against adding the two 765 kV and one 400 kV powerlines that would otherwise be required had yielded positive results.

The model pointed to yearly curtailment costs of R650-million, which were significantly lower than the R2.6-billion annual project costs associated with the additional grid infrastructure.

Masike said curtailment, thus, met the least-cost criterion embedded in the country’s Grid Code.

The South African framework, he added, would stipulate that no single plant be curtailed by more than 10% in a year and that curtailment be governed by operational guidelines that stipulated both fairness and that the measure be used only when necessary to alleviate congestion.

Eskom was also proposing that compensation for curtailment be a contractual matter between buyers and sellers. In the case where Eskom was the designated buyer, the “deemed energy”, or electricity that could not be consumed as a result of system congestion, be payable under the power purchase agreement.

No timeline was provided for the publication of the addendum, but Masike confirmed that the framework had been approved by Eskom’s regulatory, policy and economic committee and shared with both the IPPO and the National Energy Regulator of South Africa.