Environmental analysis of practical design options for enhanced geothermal systems (EGS) through life-cycle assessment

Abstract

International audienceThis study presents an analysis of the environmental performances of Enhanced Geothermal Systems (EGS) located in central Europe based on life cycle assessment (LCA) of ten significant design options. Each of those is identified with a set of several technical parameters including the risk of induced seismicity. Results show that EGS impacts are comparable to those of other renewable energy technologies and significantly lower than those of conventional power plants. A comparison of the ten scenarios enables us to formulate recommendations on the environmental suitability of their design. Moreover, it emerges from this study that the risk of induced seismicity is a key discriminating factor, as it increases proportionally to the environmental benefit. The model based on five impact categories presented in this paper provides a useful tool for obtaining an overview of the environmental constraints of EGS installations and can be replicated to evaluate possible analogous installations exploring other design options

A simplified model for the estimation of life-cycle greenhouse gas emissions of enhanced geothermal systems

“…Although in some cases the relation (2010) between the size of a plant's component and the amount of its materials is not linear, such scaling approach simplifies the process of compiling LCIs for a large sample of scenarios. The replacement rate of equipment follows the hypothesis of Lacirignola and Blanc (2013).…”

“…However, this study takes into account the possibility of drilling down to 6 km since this may become more economically viable in the near future thanks to the progress of the exploration and drilling techniques. Methodological characterization: the life cycle inventory (LCI), namely the compilation of all inputs and outputs (e.g., materials, emissions) from the processes occurring in the life cycle of an EGS plant, is based on the one proposed by Lacirignola and Blanc (2013). This paper is mainly based on technical data from the Soultz-sous-Forêts site.…”

“…The LCI of the wells, the ORC, and the pumps are obtained with a scaling approach from the EGS data regarding materials and processes published by Lacirignola and Blanc (2013) (e.g., for the ORC, we follow the assumption of a linear relation between the amount of material needed and the power installed, as in Frick et al 2010). Such data are represented by the black boxes in Figure 1.…”

“…The LCI of the ORC includes data regarding the electric generator, ORC turbine, circulation pump, air cooler, filters, pipes, and other surface elements as described in Lacirignola and Blanc (2013).…”

“…Number of wells Current EGS applications in Europe rely on a limited number of wells (two or three), because of the high construction costs. In addition, the seismicity risk related to the reinjection of high flow rates is emerging as a key factor for the design of the plant (Lacirignola and Blanc 2013), especially after the relevant seismic events in Basel and Landau (Schmidt et al 2010;Gross et al 2013). The correlation between the circulation strategy (number of wells used for the reinjection) and the seismicity risk is extensively discussed in Lacirignola and Blanc (2013).…”