Geothermics 34 (2005) 286–296
CO2 emissions from geothermal power plants and natural geothermal activity in Iceland ∗, Thr´ ´ Halld´or Armannsson ainn Fridriksson, Bjarni Reyr Kristj´ansson ISOR, Iceland GeoSurvey, Grens´asvegur 9, IS-108 Reykjav´ık, Iceland Received 17 May 2004; accepted 16 November 2004 Available online 5 February 2005
Abstract The ratio of CO2 emissions from power plants to natural emissions is a measure of the environmental impact associated with geothermal power production. Emissions from Icelandic geothermal power plants amounted to 1.6 × 108 kg year−1 in 2002. Two independent estimates of natural CO2 emissions range between 1 × 108 and 2 × 109 kg year−1 . Thus, power plant emissions are significant compared to estimated total emissions (i.e., not less than 8–16%). However, direct CO2 flux measurements from four of the approximately 40 geothermal/volcanic systems in the country amounted to 3 × 108 kg year−1 , indicating that these estimates of the total natural flux may be too low. © 2004 CNR. Published by Elsevier Ltd. All rights reserved. Keywords: Carbon dioxide; Geothermal power plants; Natural geothermal activity; Volcanic systems; Greenhouse gases; Iceland
1. Introduction Geothermal energy is generally considered a relatively benign energy source as regards environmental impact. Release of the greenhouse gas CO2 to the atmosphere is commonly considered to be one of the negative environmental effects of geothermal power production, even though it has been shown to be considerably less than from fossil fuel power plants (Fig. 1). Recent studies of CO2 emissions from geothermal/volcanic systems ∗
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[email protected] (H. Armannsson).
0375-6505/$30.00 © 2004 CNR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.geothermics.2004.11.005
´ H. Armannsson et al. / Geothermics 34 (2005) 286–296
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Fig. 1. CO2 emissions from various types of power plants (based on Hunt, 2000).
have demonstrated that vast quantities of CO2 are released naturally and that, in many cases, natural emissions far exceed emissions from geothermal power production (e.g., Seaward and Kerrick, 1996; Delgado et al., 1998; Bertani and Thain, 2002). Consequently, doubts have recently been raised as to the validity of considering CO2 emissions as a negative environmental impact of geothermal power production in systems in which anthropogenic emissions are negligible in comparison to natural emissions (Bertani and Thain, 2002). In this paper we evaluate the relative magnitudes of CO2 emissions from geothermal power production and natural CO2 emissions from geothermal systems in Iceland. We present the emission data for Icelandic power plants and review the data available on natural CO2 emissions from geothermal/volcanic systems in this country. We also present previous estimates of the total CO2 emissions from all Icelandic geothermal systems; finally, we use geological observations to constrain the upper limit for long-term average CO2 output from Icelandic geothermal systems.
2. Background Bertani and Thain (2002) described the results of a survey of CO2 emissions from geothermal power plants with the purpose of demonstrating the environmental advantage of using geothermal energy to mitigate rising atmospheric CO2 levels. The results are presented in Table 1 in terms of emitted CO2 per electric energy output (g kWh−1 ). The emissions from geothermal plants range between 4 and 740 g kWh−1 , with a weighted average of 122 g kWh−1 . The authors suggested that the natural pre-development emission rate be subtracted from that released by the geothermal operation, citing the Larderello (Italy) geothermal project as an example of a recorded decrease in the natural release of CO2 ; they suggest that this decrease is a result of field development. Geothermal systems are often located in volcanic terrains or other areas characterized by high CO2 fluxes of magmatic origin or derived from metamorphism of carbonate rocks at depth. Large CO2 fluxes through shallow-depth layers are often observed; some of the
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Table 1 CO2 emissions and total running capacity of geothermal power plants divided into nine emission categories (Bertani and Thain, 2002) Emission category (g CO2 kWh−1 )a
Running capacity (MWe )b
Weighted average (g CO2 kWh−1 )
>500 400–499 300–399 250–299 200–249 150–199 100–149 50–99
