South Africa's geothermal energy hotspots inferred from subsurface temperature and geology

Abstract

ARTICLE INCLUDES: Supplementary material × Data set FUNDING:None South Africa intends to mitigate its carbon emissions by developing renewable energy from solar, wind and hydro, and investigating alternative energy sources such as natural gas and nuclear. Low-enthalpy geothermal energy is becoming increasingly popular around the world, largely as a result of technological advances that have enabled energy to be harnessed from relatively low temperature sources. However, geothermal energy does not form part of South Africa's future renewable energy scenario. This omission may be related to insufficient regional analysis of potentially viable geothermal zones across the country. We considered existing subsurface temperature and heat flow measurements and performed solutebased hydrochemical geothermometry to determine potentially anomalous geothermal gradients that could signify underlying low-enthalpy geothermal energy resources. We correlated these findings against hydro/geological and tectonic controls to find prospective target regions for investigating geothermal energy development. Our results show a significant link between tectonic features, including those oncraton, and the development of geothermal potential regions. In addition, potential regions in South Africa share similarities with other locations that have successfully harnessed low-enthalpy geothermal energy. South Africa may therefore have a realistic chance of developing geothermal energy, but will still need additional research and development, including new temperature measurements, and structural, hydrogeological and economic investigations. Significance:• The regional low-enthalpy geothermal energy potential of South Africa should be further researched for consideration of low-enthalpy geothermal energy as a renewable energy option. IntroductionSouth Africa is the leading carbon emitter in Africa and has one of the highest rates of emissions of nations in the world. 1 This status can be linked to South Africa's vast coal resources, which are an important contributor to the local mining sector and also account for more than 80% of South Africa's energy generation.1 South Africa intends to reduce its carbon emissions by producing about 40% of the country's total energy through renewable sources by 2030.1 This goal will be achieved mostly through solar-, wind-and hydro-generated forms of energy and largely accelerated by a Renewable Energy Independent Power Producer Procurement Programme, which has attracted considerable private-sector investment. 1 Renewable energy alone will not meet South Africa's growing energy demands and therefore the country will also consider additional large-scale coal-fired energy, nuclear energy and energy produced from shale gas. 1 Low-enthalpy geothermal energy is becoming increasingly popular around the world.2 This popularity is largely because it requires geothermal gradients as low as ca 40 °C/km, which may be found in many global settings. South Africa does not have any active or recent volcanism and is situat...

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“…Alternatively, the organic rankine cycle (ORC) technology could be implemented and used to generate high-pressure steam from very low-quality heat (using low temperature geothermal sources). 3,4 Dhansay et al 2 investigated South Africa's geothermal energy hotspots inferred from subsurface temperature and geology. The study identified five promising regions in South Africa where lowenthalpy geothermal energy can be explored and developed ( Figure 1).…”

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