General information on the SM
The simplified models
(https://www.geoenvi.eu/wp-content/uploads/2021/02/D3.4-Simplified-parameterized-models.pdf) were
developed as one of the outcomes of the European project GEOENVI [Grant agreement n°818242 --
2018-2021]. These simplified models estimate the environmental impacts of four different categories
of geothermal installations, namely:
(1) enhanced geothermal systems (EGS) for heat generation with very low direct emissions
(2) geothermal flash power plant producing electricity and a limited amount of heat from a
geothermal source with moderate to high content of NCGs, composed mostly of CO2
(3) combined Heat and Power (CHP) geothermal plant with low direct emissions
(4) a heat production plant including a demonstration ORC producing electricity for self-consumption
with very low emissions.
The simplified models are based on equations with a small number of variable parameters and provide
first environmental assessments of geothermal installations belonging to any of the four categories
described, whenever the resources are lacking to conduct full life cycle assessments (LCAs). The
generation of the simplified models for each of the four categories of geothermal installations
relied on a five-step protocol
(https://www.geoenvi.eu/publications/elaboration-of-a-general-protocol-to-generate-simplified-models-for-geothermal-installations/)
including:
(i) the definition of the scope of the study
(ii) the modelling and validation of the reference LCA model
(iii) the statistical process to identify the key input variable parameters for each impact category
(iv) the generation and validation of the simplified models, and (v) the description of the models’
applicability domain.
The reference LCA model was developed based on one representative geothermal installation per
category and followed whenever possible the LCA guidelines developed within GEOENVI
(https://www.geoenvi.eu/publications/lca-guidelines-for-geothermal-installations/). Adaptations were
necessary to ensure that the developed reference LCA model was not too specific for the
representative installation and thus general enough to represent all possible installations within
that category. Seven simplified models per category of geothermal installation were developed,
describing impacts on climate change, minerals and metals resource depletion, fossil resource
depletion, human carcinogenic effects, human non-carcinogenic effects, freshwater ecotoxicity, and
freshwater and terrestrial acidification. Each model relied on two to six variable parameters
specific to the geothermal installation and explaining around 75% or more of the variance observed
per impact category. In addition, the simplified models for the EGS for heat generation includes
electricity shares as inputs to consider different types of electricity mix used to power the pumps
during the plant’s operation phase. It appears that the influencing variable parameters vary
depending on the impact category and the geothermal installation category. Only the most influencing
variable parameters were kept per simplified model, as explained in more details in the description
of the protocol.
The simplified models presented here are first estimates of the environmental impacts of a
geothermal installation and do not replace a full Life Cycle Assessment. While a simplified model is
a good representation of a specific type of geothermal installation, its accuracy in estimating the
environmental impacts does not fully match the one of a full LCA. Furthermore, the use of the
simplified models is strictly limited to the defined applicability domain. Carefully choosing among
the different types of installations available is therefore essential to ensure the relevance of the
estimated impacts. Whenever an installation falls partly within the defined parameter ranges and/or
the specified applicability domain, the user might want to apply all simplified models and compare
their outcomes. We suggest that if the results per impact category for each installation type vary
by less than 10%, the estimated values might be considered an acceptable first rough estimate of the
environmental impacts of the considered installation. Otherwise, we advise against the use of the
simplified models and recommend the development of a new simplified model for the specific
installation type. Overall, we advise against applying a simplified model to an installation whose
characteristics do not match the defined parameter ranges or the specified applicability domain at
all.
For further information on the GEOENVI LCA tools, please visit:
https://www.geoenvi.eu/lca-for-geothermal/
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