Abstract
With the increased integration of renewable energy sources (RES) in the energy system, energy storage (ES) technologies will play a significant role in managing intermittent renewable power in future electricity systems. This research focuses on developing a Power-to-Gas (PtG/P2G) framework that simulates the production of renewable hydrogen and methane, evaluating its economic and environmental performance for possible application in the transport sector in South Africa. The study is important to understand how PtG can provide opportunities for sector coupling and contribute towards the decarbonization of different sectors. Two main research vehicles were used to deliver the research project: an in-depth review of the literature and the collection and analysis of empirical data.
A case study was conducted to model future hydrogen and methane production from South Africa’s 2019 ex-ante baseline data and evaluated the P2G technology’s eco-efficiency by analysing economic and environmental impacts. The economic evaluation was performed using specific cost metrics, and the environmental impact was assessed through a life cycle assessment (LCA). The results of this study offer substantiating evidence that South Africa’s electricity expansion plan for 2030 (i.e., IRP 2019) has a potential of approximately 13.1 TWh of surplus electricity, while a negative residual load of 117 TWh can be obtained from the renewable energy development zones (REDZs). A 3.68 GW country-wide distributed electrolyzer system can be installed to produce 195 kton of hydrogen or 398 kton of methane under the IRP 2019 framework, while a 37 GW electrolyzer capacity with a production capacity of 1.8 Mton of hydrogen or 3.8 Mton of methane can be realized for the base case.
There is evidence for the possibility of constructing 356 standard-size hydrogen fuelling stations in 2030 and 1268 in 2045, with the potential to cover 100% of Fuel Cell Vehicles (FCVs) energy demand plus 344 kton of methane to support CNGVs in 2030. Power-to-hydrogen (P2H) can decarbonize 4.51 MtCO2 emissions from SMR processes while displacing approximately 7% of the petrol used in 2019. When a P2G system operates for 1,962 hours in a year, the average cost of producing hydrogen is $0.17 per kWh ($5.72 per kg), while the cost of producing methane is $0.34 per kWh. Electricity and capital charges are the main factors driving these costs. Therefore, improving the efficiency of P2G units can mitigate the impact of high electricity costs on production prices.
From an environmental perspective, the global warming potential (GWP) of producing 1 MJ of hydrogen averages 5.1 gCO2eq when electrolyzers are powered by solar PV and 1.2 gCO2eq when powered by wind. Conversely, producing 1 MJ of methane from plant-derived CO2 results in a GWP
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of 6.5 gCO2eq when using electricity from solar PV and 1.5 gCO2eq when using wind power. For sustainable P2G hydrogen and methane production from grid electricity, the GWP of electricity employed should not surpass 183 gCO2/kWh and 16 gCO2/kWh, respectively. Additionally, South Africa’s baseline electricity supply mixes (i.e., for 2020) require a minimum of 76 % and 98% wind generation to achieve the break-even points for the SMR and natural gas extraction counterpart processes.
This research argues for a government to establish policies and regulatory frameworks that offer incentives, encourage investments, and establish an equitable environment for renewable energy and energy storage systems (ESS) projects to promote the uptake of RES into the grid and achieve a rapid scale-up of PtG systems.