CO2 emissions from geothermal power plants and natural geothermal activity in Iceland
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 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.
Section snippets
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
CO2 emissions from geothermal plants in Iceland
Three major geothermal power plants are in operation in Iceland, at Krafla, Svartsengi, and Nesjavellir. The Svartsengi and Nesjavellir plants produce both electricity and hot water for space-heating, whereas the Krafla plant generates electricity only. The total installed capacity of these three power plants is 195 MW and they produce about 17% of the total electricity used in the country. The CO2 emissions from Icelandic geothermal plants have been recorded since the early 1980s when it was
Natural CO2 emissions from Icelandic geothermal and volcanic systems
Geothermal systems can be considered as geochemical reservoirs of CO2. Carbon isotope ratios of CO2 in Icelandic geothermal fluids indicate that degassing of mantle-derived magma is the sole source of CO2 in these systems (Ármannsson, 1998; Fig. 3); elsewhere metamorphic decarbonation of marine limestone and decomposition of organic sediments are also important sources of CO2 in some geothermal systems. CO2 sinks in geothermal systems include calcite precipitation, CO2 discharge to the
Discussion
Worldwide geothermal power (i.e., electricity generation and direct applications) is a small sector of the energy industry, and CO2 emissions related to the utilization of geothermal resources are consequently negligible. In some countries, however, geothermal energy production contributes significantly to their energy budget, so that any discussion of the importance of CO2 emissions from geothermal power plants is extremely relevant. In one such country, Italy, the Larderello geothermal field
Acknowledgements
Funding for this study was provided by Hitaveita Sudurnesja, Landsvirkjun, Icelandic Research Center (Rannís), the National Energy Authority, and Iceland GeoSurvey.
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