A Comparison of Different Approaches for Assessing Energy Outputs of Combined Heat and Power Geothermal Plants

• Published in: Sustainability
• Main Authors: Daniele Fiaschi, Giampaolo Manfrida, Barbara Mendecka, Lorenzo Tosti, Maria Laura Parisi
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2021
• Subjects: allocation; combined heat and power (CHP); geothermal energy; exergy; life cycle assessment (LCA); primary energy savings (PESs); envir; geo; Iceland
• Online Access: https://doi.org/10.3390/su13084527; https://doaj.org/article/f5be41040dca4553ab2bad12b28fdcb0

In this paper, we assess using two alternative allocation schemes, namely exergy and primary energy saving (PES) to compare products generated in different combined heat and power (CHP) geothermal systems. In particular, the adequacy and feasibility of the schemes recommended for allocation are demonstrated by their application to three relevant and significantly different case studies of geothermal CHPs, i.e., (1) Chiusdino in Italy, (2) Altheim in Austria, and (3) Hellisheidi in Iceland. The results showed that, given the generally low temperature level of the cogenerated heat (80–100 °C, usually exploited in district heating), the use of exergy allocation largely marginalizes the importance of the heat byproduct, thus, becoming almost equivalent to electricity for the Chiusdino and Hellisheidi power plants. Therefore, the PES scheme is found to be the more appropriate allocation scheme. Additionally, the exergy scheme is mandatory for allocating power plants’ environmental impacts at a component level in CHP systems. The main drawback of the PES scheme is its country dependency due to the different fuels used, but reasonable and representative values can be achieved based on average EU heat and power generation efficiencies.