Integrating life cycle assessment and emergy synthesis for the evaluation of a dry steam geothermal power plant in Italy

Abstract

Greenhouse gas emissions, climate change and the rising energy demand are currently seen as most crucial environmental concerns. With the exploration of renewable energy sources to meet the challenges of energy security and climate change, geothermal energy is expected to play an important role.In this study a LCA (Life Cycle Assessment) and an EMA (Emergy Assessment) of a 20 MW dry steam geothermal power plant located in the Tuscany Region (Italy) are performed and discussed. The plant is able to produce electricity by utilizing locally available renewable resources together with a moderate support by non-renewable resources. This makes the geothermal source eligible to produce renewable electricity. However, the direct utilization of the geothermal fluid generates the release into the atmosphere of carbon dioxide, hydrogen sulfide, mercury, arsenic and other chemicals that highly contribute to climate change, acidification potential, eutrophication potential, human toxicity and photochemical oxidation.The study aims to understand to what extent the geothermal power plant is environmentally sound, in spite of claims by local populations, and if there are steps and/or components that require further attention. The application of the Emergy Synthesis method provides a complementary perspective to LCA, by highlighting the direct and indirect contribution in terms of natural capital and ecosystem services to the power plant construction and operation.The environmental impacts of the geothermal power plant are also compared to those of renewable and fossil-based power plants. The release of CO2-eq calculated for the investigated geothermal plant (248 g kWh−1) is lower than fossil fuel based power plants but still higher than renewable technologies like solar photovoltaic and hydropower plant. Moreover, the SO2-eq release associated to the geothermal power plant (3.37 g kWh−1) is comparable with fossil fuel based power plants.Results suggest the need for further investigation of other geothermal options (e.g. binary systems) in order to reduce the environmental impacts while taking the maximum advantage of the geothermal resource.