High-Temperature Geothermal Utilization in the Context of European Energy Policy—Implications and Limitations

Publisher's version (útgefin grein)The European Union (EU) has made climate change mitigation a high priority though a policy framework called "Clean Energy for all Europeans ". The concept of primary energy for energy resources plays a critical role in how different energy technologies appear in the context of this policy. This study shows how the calculation methodologies of primary energy content and primary energy factors pose a possible negative implication on the future development of geothermal energy when comparing against EU's key energy policy targets for 2030. Following the current definitions of primary energy, geothermal utilization becomes the most inefficient resource in terms of primary energy use, thus contradicting key targets of increased energy efficiency in buildings and in the overall energy use of member states. We use a case study of Hellisheidi, an existing geothermal power plant in Iceland, to demonstrate how the standard primary energy factor for geothermal in EU energy policy is highly overestimated for efficient geothermal power plants. Moreover, we combine life cycle assessment and the commonly utilized combined heat and power production allocation methods to extract the non-renewable primary energy factor for geothermal and show how it is only a minimal fraction of the total primary energy factor for geothermal. The findings of the study apply to other geothermal plants within the coverage of the European Union's energy policy, whether from high- or low-temperature geothermal resources. Geothermal has substantial potential to aid in achieving the key energy and climate targets. Still, with the current definition of the primary energy of geothermal resources, it may not reach the potential.This work is a part of the Primary Energy Efficiency (PEE) project that was funded by Nordic EnergyResearch, grant number 16X753.02, and co-financed by the National Energy Fund (Orkusjóður), grant number 12-2007, owned by the Government of Iceland. Also partially funded by the Landsvirkjun Energy Research fund,grant number FMV 04-2013.Peer Reviewe

Utilization of Geothermal Brine for Electrical Power Production

The objective of the study is to compare methods that increase power generation from conventional single flash power plants by utilizing waste heat contained in brine from steam separators. Three different utilization methods are investigated by constructing thermodynamic models of different power cycles and optimizing the specific net power output for each cycle using conditions of hypothetical geothermal areas. The cycles investigated include a conventional double flash cycle, an organic Rankine bottoming cycle in parallel with a single flash cycle using isopentane as a working fluid and a modification of the double flash cycle involving an added recuperator between the geothermal brine and the steam at the high pressure turbine outlet. Also, a model of a single flash power plant is constructed for comparison. The specific net power outputs of the different cycles are compared along with the overall efficiency of the cycles. Finally, an economical analysis is performed to further compare the feasibility of the different cycles using conventional economical analysis to estimate the cost of the final product. The results of the study can be used to compare the different conventional methods of utilizing geothermal energy for electrical power production with respect to the energy content, or the enthalpy, of the geothermal fluid produced from production wells. Also, a new method of utilizing geothermal brine by modifying the double flash cycle is introduced and compared to the conventional cycles. The new method could provide useful results for increased power production compared to the other cycles and also, as a future study, provide a method of better controlling the double flash cycle in case of changes in the fluid characteristics from production wells, which is expected in future operation time of geothermal power plants.Markmið þessa verkefnis er að bera saman aðferðir til þess að auka rafmagnsframleiðslu hefðbundinna eins þrepa hvellsuðuorkuvera (e. Single Flash Power Plants) með því að nýta betur varma í skiljuvatninu frá gufuskiljunum. Þrjár mismunandi vinnsluaðferðir voru greindar með því að útbúa varmafræðileg líkön af vinnslurásum fyrir hverja gerð orkuvers og raforkuframleiðslan bestuð á hverja massaeiningu úr vinnsluholum. Skilgreint er fræðilegt jarðhitasvæði með ákveðnum skorðum sem tekið er tillit til við bestun vinnuhringjanna. Vinnuhringirnir sem rannsakaðir voru eru sem hér segir; tveggja þrepa hvellsuðuorkuver (e. Double Flash Power Plant), hvellsuðuorkuver með tvívökva organic Rankine rás (e. Hybrid Single Flash - ORC Power Plant) sem nýtir skiljuvatnið til þess að hita og sjóða isopentan vinnuvökva og breytt tveggja þrepa hvellsuðuorkuver (e. Modified Double Flash Power Plant) með endurhitara sem yfirhitar gufuna úr háþrýstihverflinum. Einnig var byggt líkan af hefðbundnu eins þrepa hvellsuðuorkuveri til samanburðar. Bestuð raforkuframleiðsla hvers hrings er borin saman ásamt nýtni orkuveranna. Að lokum er gert kostnaðarmat á framleiðslukostnaði fyrir hverja virkjun með aðferðum hagverkfræðinnar. Niðurstöður verkefnisins geta nýst í að bera saman hefðbundna nýtingarmöguleika skiljuvatnsins frá eins þrepa hvellsuðuorkuverum miðað við vermi jarðhitavökvans sem um ræðir. Einnig er kynnt til sögunnar ný aðferð við að nýta skiljuvatnið með því að bæta við endurhitara í hina hefðbundnu uppsetningu á tveggja þrepa hvellsuðuorkuveri og sá hringur borinn saman við hina hefðbundnu hringi. Hin nýja aðferð gæti gefið áhugaverðar niðurstöður fyrir aukna raforkuframleiðslu og einnig, sem framhaldsverkefni, boðið upp á stýrimöguleika fyrir hinn hefðbundna tveggja þrepa hvellsuðuhring ef komi til verulegra breytinga á eiginleikum háhitasvæðisins eftir að vinnsla hefst úr því sem gjarnan gerist við nýtingu jarðvarma á jarðhitasvæðum.Umhverfis- og orkuskjóður Orkuveitu Reykjavíku