Exergo-economic and exergo-environmental assessment of two large CHP geothermal power plants

An Exergo-Economic and Exergo-Environmental Analysis is presented for two large geothermal power plants located in Iceland - Hellisheidi and Nesjavellir. The latest configuration of the power plants -including for Hellisheidi acid gas removal and Carbon capture -is analyzed. Cost and LCA data available within the EU H2020 GECO project were processed with an exergy approach, with the purpose to identify the major points of cost build-up or environmental impact along the energy conversion process. A considerable relevance of the cost and impact due to the activity of wells drilling was confirmed for geothermal energy systems; within the operation of the plant, the major effects of exergy destruction are found at the turbines and condensers. The inefficiencies and the buildup of cost and environmental impact along the energy conversion chain are highlighted and the out-comes are discussed with a comparison between the two plants. These are confirmed as performing very well both from the economics and sustainability points of view: recent and foreseen improvements for emissions and carbon capture will not change substantially the economics and will be very effective from the point of view of environmental performance.