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Geothermal energy resources in Ethiopia: Status review and insights from hydrochemistry of surface and groundwaters

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Abstract Ethiopia has an estimated >10,000 MW of geothermal energy potential, more than double its current power generating capacity (4,400 MW). Electricity access stands at 44% of the total population, with 31% in rural areas, so effective development of this low‐carbon resource could make a significant impact to equitable delivery of electricity. However, geothermal energy exploitation must be done responsibly to protect valuable water resources under stress from climate‐change driven drought conditions and competing uses across agricultural, domestic, and industrial sectors. Our review provides progress updates on geothermal developments—which soon aim to deliver more than 1,000 MW of electricity—and performs a high‐level assessment of hydrochemical data for ground and surface waters across Ethiopia. A water quality database was built using publicly available information and three quality control criteria: well‐defined sample location, cation‐anion balance (CAB) of ±10%, and clear fluid type definition. Ethiopia hosts two major geothermal water types, sodium‐alkalinity dominated in the Main Ethiopian Rift and sodium‐chloride dominated in the Afar Depression, separated by sodium‐mixed waters between Dofan‐Fantale and Meteka. H and O stable isotopes suggest a largely meteoric source for geothermal waters, with δ18O enrichment adding to evidence of a high enthalpy resource at Tendaho. Hydrochemical investigations provide critical information for successful delivery of sustainable geothermal energy developments. However, the current lack of data available for Ethiopia poses a significant challenge for completion of predevelopment baselines and ongoing environmental impact assessment. We encourage the release of unpublished findings from private companies and government agencies to build upon our database and demonstrate social and environmental responsibility in the development of Ethiopian geothermal resources. This article is categorized under: Engineering Water > Methods
The eastern and western branches of the East African Rift System. Digital Elevation Model (DEM) published in 1996 by the U.S. Geological Survey's Centre for Earth Resources Observation and Science (EROS) and available at https://databasin.org; water bodies published in 2015 by the Regional Centre for Mapping of Resources for Development (RCMRD) and available at https://energydata.info/; and active volcanoes as identified by Wadge et al. (2016)
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δ2H and δ18O isotope data as a function of fluid source for the following geothermal areas: (a) Aluto‐Langano; (b) Tendaho; (c) Corbetti; (d) Abaya; (e) Dofan, Fantale and Meteka; (f) Abhe and Dobi Graben; (g) Remaining Rift Valley; (h) Outside Rift Valley (Highlands). GMWL: Global Meteoric Water Line as defined by Craig (1961); LMWL: Local Meteoric Water Line; LEL: Local Evaporation Line; and SWEL: Surface Water Evaporation Line (based on compiled data). The LMWL and LEL for Ethiopia were calculated using available data in the Global Network of Isotopes in Precipitation (GNIP) database (IAEA/WMO, 2019)
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Distribution of δ2H and δ18O isotope data as a function of fluid source. The bracketed values indicate the total number of measurements for each source. These totals include both single locality measurements and features that were sampled multiple times
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Distribution and concentration of fluoride for each water type. Background elements as per Figure 2
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Trilinear diagram of water‐rock chemical equilibration conditions for Na–K–Mg with geothermal fluids from (a) geothermal wells and (b) hot springs. The axes show relative concentrations (similar to the anion trilinear plot). For clarity, only the 245 and 210°C isotherms are shown respectively in (a) and (b) as examples. Isotherms are calculated from the equations of equilibrium water–mineral interactions for K+ and Na+ (Na/K isotherm) and for K+ and Mg+ (Mg/K isotherm), according to Giggenbach (1988). The intersection of the two isotherms represents equilibrium conditions at this temperature. Samples plotting on the “K/100” axis have magnesium concentrations below detection limit (which vary from <0.1 to <1 mg/kg where reported). For other abbreviations, see Figure 4
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Status of main geothermal prospects in Ethiopia (as of 2019). Base DEM sourced from the Consultative Group for International Agricultural Research‐Consortium for Spatial Analysis (CGIAR‐CSI) website (http://srtm.csi.cgiar.org). All other background map elements from OpenStreetMap (http://download.geofabrik.de)
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Trilinear diagram Cl‐SO4‐∑CO3 for the classification of geothermal waters according to Giggenbach (1988) with geothermal fluids from (a) geothermal wells and (b) hot springs. CTG and LA‐TGW represent temperature gradient wells. Plot axes represent the relative concentrations (in mg/L) of major anions (chloride: Cl, sulfate: SO42−, and carbonates species: HCO3, CO32−, or ΣCO3). MER samples plot as “peripheral waters,” typically indicative of CO2‐rich soda springs or local heating of groundwater by steam and other volcanic gases. Afar Depression samples plot closely to “mature waters,” corresponding to highly concentrated chloride brines representative of thoroughly‐equilibrated fluids from major up‐flow zones. The chemistry of steam‐heated and volcanic waters are typically related to gas absorption and oxidation processes (Giggenbach, 1988; Haizlip, 2016; Younger, 2014)
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Distribution of water type and calculated Total Dissolved Solids (TDS) in Ethiopia: (a) Geothermal fluids from geothermal wells and temperature gradient wells; (b) Geothermal fluids from hot springs and fumarole condensates; (c) Groundwater from boreholes, cold springs, and dug wells; and (d) Surface water from lakes and rivers
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