Life Cycle Assessment of a Geothermal Power Plant in the Southern German Molasse Basin (Germany)
Florian HEBERLE, Thorsten KOEPP, Peter BAYER, Dieter BRÜGGEMANN
[University of Bayreuth, Germany]
In this work, a life cycle assessment (LCA) is conducted for a geothermal power plant in the Southern German Molasse Basin. The considered power plant is a two-stage Organic Rankine Cycle (ORC) power system with a nominal electrical power output of 5.5 MW. By considering the environmental impacts resulting from the construction, operation and decommissioning of the geothermal power plant, CO2-emissions, cumulated energy demand (CED), acidification and eutrophication have been determined as the four main impact indicators. For a comprehensive analysis, available data sets like borehole depth, casing material or material demand of the power plant are evaluated. In the first step, no leakage of the ORC working fluid and a self-supply regarding the auxiliary requirements of the power plant are assumed. Compared to common, rather theoretical LCA of geothermal applications, the conducted analysis for a specific binary power plant shows significant lower values for the selected impact indicators. In particular, a CO2-equivalent of 11.8 g/kWhel and a CED of 164.6 kJ/kWhel are quantified. In context of CO2-emissions, the effect of the subsurface construction dominates with 82 % and is mainly due to the operation of the drilling rig and the consumption of steel for the casing of the wells. The constructions at the surface contribute by 15 % and the operation of the power plant yields 3 %. Based on the described LCA, further scenario calculations are performed. In scenario I, a leakage rate of 1 %/a of the filling quantity of the ORC working fluid R245fa is considered. In scenario II the leakage rate is increased to 2 %/a. For scenario I, a CO2-equivalent of 29.3 g/kWhel is obtained and in case of scenario II a value of 46.8 g/kWhel results. Furthermore, a replacement of the ORC working fluid R245fa by R1233zd(E) with a low impact on climate is evaluated. This leads to a CO2-equivalent of 13.6 g/kWhel at a conservative leakage rate (2 %/a). The present LCA of a specific binary power plant shows that in general, mainly theoretical analyses tend to overestimate the environmental impact of a geothermal power plant and thus create a negative image compared to other renewable power sources. In particular, using ORC working fluids with low GWP, the environmental impact of a geothermal power plant is shown to be in the same range as for wind turbines. Under consideration of moderate leakage rates of the fluorinated ORC working fluid R245fa the environmental impact is still lower than for photovoltaic systems.
|        Topic: Sustainability and Climate Change||Paper Number: 05007|