Doctoral Degrees (Mechanical and Mechatronic Engineering)

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Browsing Doctoral Degrees (Mechanical and Mechatronic Engineering) by Author "Clark, Stephen Richard"

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    The use of natural gas to facilitate the transition to renewable electric power generation in South Africa.
    (Stellenbosch : Stellenbosch University, 2020-12) Clark, Stephen Richard; Van Niekerk, J. L.; Petrie, J.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    Research Question: The proposed study aims to address the appropriate role for natural gas in meeting the requirement for dispatchable energy in the South African electricity grid to support the transition to a renewable energy based generation system. As a path for achieving its international commitments on climate change, South Africa intends to develop a renewable energy based electricity generation system to meet its greenhouse gas emission reduction targets. One of the necessary conditions for large scale renewable energy implementation is the corresponding use of dispatchable power to mitigate the variable nature of the renewable sources. This study intends to answer the question of whether natural gas dispatchable power is the best way to meet this need. This involves the determination of timing and amount of dispatchable gas power that will be required, as well as the sourcing of the gas and the economics of this particular use. The analysis covers the time period between 2020 and 2050, but as per the Integrated Resource Plan (IRP) process concentrates on the period up to 2030. This research establishes the economic case for natural gas based dispatchable power. The analysis has been based on system modelling on referenced renewable energy plans using performance data from installed wind and solar generation sources. While there has been much discussion within the South Africa Integrated Resource Plan (IRP) process about the benefit of the transition to renewable generation backed up with dispatchable gas generation, there have always been questions about the source for this gas in the IRPs. This research compares the potential use of shale gas, imported LNG and pipeline gas to meet this need. Review of the IRP scenarios shows there is a large range in the potential requirement for dispatchable power depending on growth in the amount of power required as well as the performance and decommissioning of the existing base load generation system. While there has been general realisation within the IRP process of the benefit of natural gas fuelled dispatchable power, the sourcing for that gas has been left undefined. This analysis shows thatsmall total volumes of gas on an annualised basis are needed for dispatchable generation for any likely scenario. There are several reasonable sources that can be utilised. Previously not discussed in any forum, storing the gas to provide for dispatchable use – large rates for short periods - presents the major challenge for whatever source is utilised. Solutions to store the gas have been reviewed and a conceptual option for storage utilising abandoned mine shafts is proposed. The analysis indicated that the dispatchable energy requirement from the system in 2030 could vary from 5 to 15 GW, with an expected capacity factor between 2 % and 5 %. This corresponds to an fuel requirement of 9 to 78 PJ per year, with an expected value of 27 PJ/a, compared to the current importation of gas into the country of 200 PJ/a. Storage of 140 million cubic meters of gas would likely be required to meet the forecasted demand profile. This work fills in this missing piece that currently exists in the IRP planning for the transition to renewable power generation, The results of this study, explaining the requirementfor gas storage to make gas generation viably dispatchable, can assist policy makers and planners in setting up long term plans for development programmes for renewable generation backed up with dispatchable gas generation.