The South African electricity transmission system will need to change materially over the next 30 years if the country is to have any realistic hope of moving ahead with its current plan to diversify its generation mix away from coal to the integration of more renewable energy, imported hydropower and gas and, possibly, new nuclear capacity.
The existing network is premised on moving power, generated primarily in coal-rich Mpumalanga, to areas of demand in the rest of the country.
The network, which is operated by the transmission division within State-owned electricity utility Eskom, is, therefore, relatively stable and predictable. The demand centres are well defined, the generation is more or less concentrated in one geographical area and the electricity is dispatched to areas where the load resides.
But the future generation mix is meant to be dramatically different, with the Department of Energy’s Integrated Resource Plan (IRP) 2010–2030 anticipating the introduction of the 56 539 MW across various technologies and geographies over the 20-year period.
In fact, under the current version of the IRP, which is likely to be revised during 2013, coal’s contribution is expected to fall from more than 90% of the current mix to about 45.9% by 2030 – despite the fact that about 16 300 MW of additional coal-fired generation could be added, raising coal’s total installed base to 41 071 MW by 2030.
In addition, the centre of the coal-fired-plant universe is likely to shift from Mpumalanga, in the east of the country, where many of the plants have been operating for more than 30 years, to Limpopo, in the north-west, which contains most of the remaining unexploited coal resources.
Also envisaged (but subject to change once the IRP review is finalised) is the intro- duction of 9 200 MW of wind generation, 1 200 MW of concentrated solar power, 8 400 MW of solar photovoltaic production, 9 600 MW of new nuclear capacity, 4 930 MW of open-cycle gas-turbine peaking plant capacity, 2 370 MW of combined-cycle gas-turbine capacity, a 1 332 MW pumped-storage scheme, 2 659 MW of imported hydropower and 465 MW of mostly other renewables technology.
For the transmission network, these changes have material consequences, albeit at a pace that can be described as evolutionary, rather than disruptive.
Eskom Transmission strategic grid planning manager Ronald Marais says the utility is working with various configurations and scenarios, while using the current version of the IRP as the ‘base case’. The other scenarios include a ‘green scenario’, whereby renewables displace the proposed nuclear fleet and a scenario where South Africa doubles the amount of imported power from neighbouring countries as given in the IRP base case.
These scenarios are used to determine the likely impact on the design of the future transmission grid rather than a comparative assessment of competing generation scenarios.
However, amid all these circumstances, two key trends are apparent. Firstly, the role of Mpumalanga as the country’s power hub will diminish. Secondly, the greater Cape region, comprising the Western Cape, the Northern Cape and the Eastern Cape, will play a much bigger role in the production of electricity.
From a transmission planning perspective, this shift is material. In addition, the eventual mix will have a major impact on the relative contribution of each Cape province, which could vary significantly.
For instance, it is possible that the Northern Cape could transition from its current position of importing about 1 000 MW to exporting up to 13 000 MW by 2040, as considered in the ‘green scenario’.
But the variations are significant and they depend on the generation scenario adopted. For instance, the Northern Cape could export either 13 000 MW, or less than 1 000 MW, by 2040.
The variability for the Western Cape, meanwhile, ranges from importing 5 000 MW to exporting 5 000 MW by 2040. Similarly, the Eastern Cape could emerge as either an importer or an exporter. This variability is further compounded by the variable output of some of the renewable generation where the transmission corridors will have to be able to cater for both high and low generation output conditions under both peak load and low load conditions.
Another key risk factor pertains to demand and ensuring that the transmission infrastructure is aligned with the growth of existing load centres and possible future demand hubs.
Eskom’s models, which Marais says have been canvassed with municipalities, stakeholders and academics, show strong demand growth in several provinces, with Gauteng’s maximum demand expected to rise to 20 861 MW and KwaZulu-Natal’s to 12 459 MW. These two leading centres of demand are also unlikely to have much potential to produce electricity, with Gauteng’s deficit, by 2040, expected to be 19 461 MW and KwaZulu-Natal’s 7 879 MW.
Studies and Action Plans
To firm up on the options, Eskom Grid Planning has undertaken several studies to determine the available connection capacity for new generation at transmission sub- stations in the Cape area and elsewhere for the integration of renewable-energy generation.
It has found that the projects being procured under the Renewable Energy Independent Power Producer scheme should be able to be captured relatively easily into the system – a process aided partly by the fact that relatively, the projects are geographically, well spread.
But as more renewables projects emerge, some corridors and substations will have to be reconfigured to cater for the projects in a way that ensures “open access”.
A key concern is having sufficient transformation capacity along the length of the network and Eskom is, therefore, examining the potential of using the existing substations to create collector points for the renewables projects that could arise in future. Eskom is also concerned about the potential for congestion at certain collector points.
Therefore, the utility is finalising a new ‘Generation Connection Capacity Assessment for the 2016 Transmission Network’, which should be published during the first quarter of 2013.
The current focus of Eskom Transmission, though, is a significant investment plan designed to meet the immediate needs of the network and address the backlogs, while also starting to integrate some of the longer-term imperatives that will begin to emerge after 2030.
The division is planning to invest about R149-billion over the coming ten years in transmission projects designed to bolster network reliability and integrate new generation capacity into the power grid.
The investment forecast is outlined in the latest ‘Transmission Ten-Year Development Plan (TDP): 2013–2022’, which has been published in line with the South African Grid Code and is the fourth ten-year plan to be released by Eskom.
Transmission group executive Mongezi Ntsokolo says the investments aim to ensure that the network complies with the minimum reliability criteria and is ready to integrate new Eskom and independent power producer (IPP) generation capacity and connect new demand centres.
Grid Planning GM Mbulelo Kibido says the plan has been canvassed with Eskom Distribution, provincial authorities and the local metropolitan councils to “seek alignment of the TDP with the provinces’ security- of-supply aspirations”.
Kibido adds that efforts have also been made to integrate the imperatives outlined in documents such as the IRP with the regulatory stipulation that the network incorporates ‘N-1’ contingencies, which ensure seamless operability in instances where certain components fail.
About R121-billion has been set aside for projects designed to improve the reliability of the network, another R25-billion for programmes aimed at integrating new power generation projects, such as the Medupi, Kusile and renewable-energy projects, and about R3-billion for customer-related projects.
However, infrastructure investment planning manager Leslie Naidoo stresses that the outlined costs are described as high-level estimates that could change.
Naidoo currently expects that the trans-mission division will add about 12 700 km of new transmission lines, which would be almost equivalent to adding 50% to the existing 28 000 km network. It is expected that 8 631 km of new 400 kV capacity will be installed by 2022, with the balance being
3 700 km of 765 kV lines and 402 km of 275 kV lines.
Also planned is the introduction of an additional 83 500 MVA of transformer capacity, 2 600 megavolt-ampere reactive (MVAr) of capacitive support and 9 200 MVAr of reactors.
Refurbishments and repairs also feature prominently in the plan, with Eskom noting that the bulk of the transmission network and many of the existing 100 substations were constructed between 1960 and 1980. Asset investment planning manager Gavin Bruce says Eskom Transmission has to deal with substation plant, equipment and infrastructure that have been in service for more than 40 years.
Bruce says only some components can be refurbished, while substation batteries, the electronic components of protection and control systems and corroded conductors will simply have to be replaced. Other safety- critical equipment will have to be removed systematically from the network.
Deferring the replacement of “aged” equipment, Bruce warns, will increase maintenance requirements and lead to higher emergency repairs, which will result in even higher operating expenditure and unplanned maintenance costs.
Therefore, besides the R149-billion for the capacity expansion of the transmission division, financial planning and regulation senior manager Agnes Mlambo expects the division will spend R12.2-billion on refurbishment projects and R2.3-billion on capital spares over the period.
In addition, Mlambo reports that Eskom is budgeting a further R4.7-billion for the acquisition of servitudes and the completion of environmental-impact assessments, as well as a further R4.5-billion for production equipment and another R1.7-billion for strategic projects.
Ntsokolo says the most visible difference between the latest TDP and previous editions is the increase in the amount of transformation by about 11 000 MVA. This, he says, is mainly because of new substations being added in the latter part of the planning period.
The programme has also been rephrased to incorporate “more realistic completion dates”.
He is convinced, though, that the TDP projects will ensure that the overall network will not only become “Grid Code compliant”, but will also cater for increased load growth and the integration of new generation.