Abstract
Geothermal energy is a key renewable energy for Italy, with an annual electric production of 6.18 TWh. The future of geothermal energy is concerned with clarity over the CO2 emissions from power plants and geological contexts where CO2 is produced naturally. The Mt. Amiata volcanic–geothermal area (AVGA) is a formidable natural laboratory for investigating the relative roles of natural degassing of CO2 and CO2 emissions from geothermal power plants (GPPs). This research is based on measuring the soil gas flux in the AVGA and comparing the diffuse volcanic soil gas emissions with the emissions from geothermal fields in operation. The natural flux of soil gas is high, independently from the occurrence of GPPs in the area, and the budget for natural diffuse gas flux is high with respect to power plant gas emissions. Furthermore, the CO2 emitted from power plants seems to reduce the amount of natural emissions because of the gas flow operated by power plants. During the GPPs’ life cycle, CO2 emissions in the atmosphere are reduced further because of the reinjection of gas-free aqueous fluids in geothermal reservoirs. Therefore, the currently operating GPPs in the AVGA produce energy at a zero-emission level.
Highlights
IntroductionMt. Amiata is a Pleistocene silicic dome field volcano [1,2] located in southern Tuscany (Italy) in the peri-Tyrrhenian margin of the Apennine chain
The same value is obtained for the Piancastagnaio area. These data demonstrate that the Amiata volcanic–geothermal area (AVGA) is a good example of the replacement mechanism operated by the CO2 carried by deep wells from the reservoir to the surface
The strong reduction observed between 50% and 70% of natural soil gas flux compared to the emissions in greenfield areas is balanced by the gas emission of geothermal power plants (GPPs)
Summary
Mt. Amiata is a Pleistocene silicic dome field volcano [1,2] located in southern Tuscany (Italy) in the peri-Tyrrhenian margin of the Apennine chain. Geothermal area (AVGA) is characterized by a heavy thinning of the continental crust [3], intense crustal extension [4,5], pluton emplacement at shallow crustal levels [6,7,8], hydrothermal Hg ore deposits [9,10], and high heat-flow values 150–200 mW/m2 [11]. A high-enthalpy geothermal resource in the AVGA has been well known since the 1960s [12]. Geothermal energy is used for power generation in the geothermal fields of Bagnore and Piancastagnaio, located SW and SE of the volcanic massif, respectively, with a total installed capacity of 121 MW which represented 18% of the total geothermal electricity production in
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