Ultra-long-duration energy storage anywhere: Methanol with carbon cycling

Abstract

Tom Brown leads a group of energy system modelers at the Technische Universität Berlin, where he holds the professorship for digital transformation in energy systems. His group researches future pathways for the energy system, with a particular focus on revealing the trade-offs between energy resources, network expansion, flexibility, and public acceptance of new infrastructure. He is a strong supporter of openness and transparency in research and is one of the lead developers of the widely used open-source software Python for Power System Analysis (PyPSA).Graphical AbstractView Large Image Figure ViewerDownload Hi-res image Download (PPT)Johannes Hampp is a researcher at the Potsdam Institute for Climate Impact Research and is finishing a doctorate at the University of Gieβen in energy system modeling. His research focuses on the production of hydrogen and hydrogen derivatives and on the effects of regional differences in renewable endowments around the world on energy and feedstock supply chains. Tom Brown leads a group of energy system modelers at the Technische Universität Berlin, where he holds the professorship for digital transformation in energy systems. His group researches future pathways for the energy system, with a particular focus on revealing the trade-offs between energy resources, network expansion, flexibility, and public acceptance of new infrastructure. He is a strong supporter of openness and transparency in research and is one of the lead developers of the widely used open-source software Python for Power System Analysis (PyPSA). Johannes Hampp is a researcher at the Potsdam Institute for Climate Impact Research and is finishing a doctorate at the University of Gieβen in energy system modeling. His research focuses on the production of hydrogen and hydrogen derivatives and on the effects of regional differences in renewable endowments around the world on energy and feedstock supply chains. Wind and solar generation are rapidly expanding around the globe as their costs come down and societal pressure to reduce greenhouse gas emissions rises. To supply a high fraction of electricity demand with variable sources, different types of storage are needed to balance daily, weekly, seasonal, and interannual weather fluctuations. Battery storage can bridge several hours of low solar and wind feed-in. However, if wind and solar penetration rises to cover all demand in the absence of other generation technologies, longer duration energy storage becomes necessary to supply multiple days or weeks of dark wind lulls and seasonal variations in supply and demand, as well as to bridge years of low renewable production. While the term long-duration energy storage (LDES) is often used for storage technologies with a power-to-energy ratio between 10 and 100 h,1Denholm P. Cole W. Frazier A.W. Podkaminer K. Blair N. The challenge of defining long-duration energy storage. NREL, 2021https://www.nrel.gov/docs/fy22osti/80583.pdfCrossref Google Scholar we introduce the term ultra-long-duration energy storage (ULDES) for storage that can cover durations longer than 100 h (4 days) and thus act like a firm resource. Battery storage with current energy capacity investment costs of 100–200 €/kWh would be too costly for these long periods. Simulations show that for renewable systems to be competitive with dispatchable low-carbon technologies, ULDES would need to cost at most around 10 €/kWh.2Sepulveda N.A. Jenkins J.D. Edington A. Mallapragada D.S. Lester R.K. The design space for long-duration energy storage in decarbonized power systems.Nat. Energy. 2021; 6: 506-516https://doi.org/10.1038/s41560-021-00796-8Crossref Scopus (208) Google Scholar (Note that all costs are given in 2020 euros, while all fuel energy units and efficiencies refer to the lower heating value.) Hydrogen storage is a promising candidate for ULDES, whereby hydrogen is produced by electrolysis of water, stored and then used to generated electricity in a gas turbine or fuel cell.3Blanco H. Faaij A. A review at the role of storage in energy systems with a focus on power to gas and long-term storage.Renew. Sustain. Energy Rev. 2018; 81: 1049-1086https://doi.org/10.1016/j.rser.2017.07.062Crossref Scopus (428) Google Scholar,4Dowling J.A. Rinaldi K.Z. Ruggles T.H. Davis S.J. Yuan M. Tong F. Lewis N.S. Caldeira K. Role of long-duration energy storage in variable renewable electricity systems.Joule. 2020; 4: 1907-1928https://doi.org/10.1016/j.joule.2020.07.007Abstract Full Text Full Text PDF Scopus (195) Google Scholar,5Llewellyn-Smith C. Large-scale Electricity Storage. The Royal Society, 2023https://royalsociety.org/electricity-storageGoogle Scholar While aboveground pressure vessels can cost 10–40 €/kWh, depending on their rated pressure, storing hydrogen underground in solution-mined salt caverns has much lower costs in the range 0.1–0.5 €/kWh. Several salt caverns with sizes up to 274 GWh are already used for storing hydrogen at petrochemical facilities in the United Kingdom and in Texas in the United States. Despite the attractive cost, hydrogen salt caverns face several challenges. Many regions do not have salt deposits, such as large parts of Africa, southeast Europe and southeast Asia.3Blanco H. Faaij A. A review at the role of storage in energy systems with a focus on power to gas and long-term storage.Renew. Sustain. Energy Rev. 2018; 81: 1049-1086https://doi.org/10.1016/j.rser.2017.07.062Crossref Scopus (428) Google Scholar In those countries that do have suitable salt deposits for caverns, they are often highly localized: in the northeast of the island of Ireland, centrally in Great Britain, and in the north of the Netherlands and Germany, to name a few examples.3Blanco H. Faaij A. A review at the role of storage in energy systems with a focus on power to gas and long-term storage.Renew. Sustain. Energy Rev. 2018; 81: 1049-1086https://doi.org/10.1016/j.rser.2017.07.062Crossref Scopus (428) Google Scholar The distance of cavern sites from hydrogen supply and demand presents a transportation challenge: bringing electricity to electrolyzers at storage sites would mean a significant expansion of power transmission lines, while placing electrolyzers close to renewables sites and transporting the hydrogen would require a hydrogen pipeline network.6Neumann F. Zeyen E. Victoria M. Brown T. The potential role of a hydrogen network in Europe.Joule. 2023; 7: 1793-1817https://doi.org/10.1016/j.joule.2023.06.016Abstract Full Text Full Text PDF Scopus (1) Google Scholar Small-diameter hydrogen pipelines have been in service for decades, and existing fossil gas pipelines could be repurposed for hydrogen, but open challenges remain such as the embrittlement of pipeline steel and the global warming potential of hydrogen leaks.7Sand M. Skeie R.B. Sandstad M. Krishnan S. Myhre G. Bryant H. Derwent R. Hauglustaine D. Paulot F. Prather M. Stevenson D. A multi-model assessment of the global warming potential of hydrogen.Commun. Earth Environ. 2023; 4: 203https://doi.org/10.1038/s43247-023-00857-8Crossref Scopus (12) Google Scholar There may be delays when building new transmission lines or hydrogen networks or problems during the simultaneous scale up of hydrogen supply, transport, and storage. Proposals for new salt cavern storage have encountered public opposition, with concerns that range from ground shifting above caverns and the impacts of saline discharge from solution mining on marine wildlife to general concerns about hydrogen safety. On the generation side, the high combustion temperature of hydrogen leads to high nitrogen oxide emissions from gas turbines, which must be managed with strategies such as water injection. Methanol as ULDES could offer an alternative to hydrogen storage. A concept for methanol storage with carbon cycling from Baak et al.8Baak J. Pozarlik A. Arentsen M. Brem G. Techno-economic study of a zero-emission methanol based energy storage system.Energy Convers. Manag. 2019; 182: 530-545https://doi.org/10.1016/j.enconman.2018.12.015Crossref Scopus (39) Google Scholar is sketched in Figure 1 with all inputs and outputs. Methanol can be synthesized from electrolytic hydrogen and carbon oxides (so called “e-methanol”). E-methanol is already produced today at a scale of thousands of tons per year in Iceland, and a similar process is used for methanol at megaton scale using gasified coal in China, where the methanol is used in the chemical industry.9Bertau M. Offermanns H. Plass L. Schmidt F. Wernicke H.-J. Methanol: The Basic Chemical and Energy Feedstock of the Future: Asinger’s Vision Today. Springer, 2014https://doi.org/10.1007/978-3-642-39709-7Crossref Scopus (244) Google Scholar Methanol is liquid at ambient temperature and pressure, and can thus be stored in large aboveground tanks, just as oil products are today, at costs of around 0.01–0.05 €/kWh. A single 200,000 m3 cylindrical tank with diameter 80 m and height 40 m can store 880 GWh of methanol. When combusted with pure oxygen in a transcritical Allam cycle turbine using carbon dioxide as the working fluid, up to 98% of the carbon dioxide from combustion can be captured with minimal effort, producing power at efficiencies of up to 66%.10Mitchell P. Avagyan V. Chalmers H. Lucquiaud M. An initial assessment of the value of Allam Cycle power plants with liquid oxygen storage in future GB electricity system.Br. J. Neurosurg. 2019; 33: 1-2https://doi.org/10.1016/j.ijggc.2019.04.020Crossref PubMed Scopus (30) Google Scholar The oxygen for the turbine can be taken from the water electrolysis and stored cryogenically as a liquid in aboveground steel tanks or separated from the air. A 50 MWth plant using the Allam cycle is already operating in Texas11Martin S. Forrest B. Rafati N. Lu X. Fetvedt J. McGroddy M. Brown B. Allam R. Beauchamp D. Freed D. Progress Update on the Allam Cycle: Commercialization of Net Power and the Net Power Demonstration Facility.in: 14th Greenhouse Gas Control Technologies Conference Melbourne 21-26 October 2018 (GHGT-14). 2018https://doi.org/10.2139/ssrn.3366370Google Scholar and several commercial plants are planned in the United States and Europe in the 300 MW range. The captured carbon dioxide can then be stored as a liquid in aboveground pressure vessels to be used again for methanol synthesis, thus closing the carbon cycle. The Allam cycle is chosen for its high efficiency and high capture rates, which avoids having to source carbon dioxide from elsewhere. By combusting in pure oxygen rather than air, the system avoids both nitrogen oxide emissions and the thermodynamic cost of separating the carbon dioxide from the exhaust gases. Any carbon dioxide that leaks can be topped up either from biogenic sources or captured directly from the air. Ideas for a methanol economy, by which methanol could be used in transport, chemicals, power, and heat, go back at least to the 1980s, when Friedrich Asinger suggested using methanol as an alternative to imported hydrocarbons, first from coal gasification and later based on electrolysis using nuclear power.12Asinger F. Methanol — Chemie- und Energierohstoff. Springer, 1986https://doi.org/10.1007/978-3-642-70763-6Crossref Google Scholar More recently, methanol has been discussed using renewable power as the primary energy source.9Bertau M. Offermanns H. Plass L. Schmidt F. Wernicke H.-J. Methanol: The Basic Chemical and Energy Feedstock of the Future: Asinger’s Vision Today. Springer, 2014https://doi.org/10.1007/978-3-642-39709-7Crossref Scopus (244) Google Scholar,13Olah G.A. Goeppert A. Prakash G.K.S. Beyond Oil and Gas: The Methanol Economy.2nd Edition. Wiley, 2006Google Scholar,14Shih C.F. Zhang T. Li J. Bai C. Powering the future with liquid sunshine.Joule. 2018; 2: 1925-1949https://doi.org/10.1016/j.joule.2018.08.016Abstract Full Text Full Text PDF Scopus (456) Google Scholar While many studies see a role for methanol in industry as a precursor chemical for producing olefins and aromatics, for long-distance shipping, or as an intermediate for kerosene production for long-distance aviation, its potential role in long-duration storage is less explored. It has been favorably compared to methane for storage in terms of round-trip efficiency but without carbon cycling or economic analysis.15Räuchle K. Plass L. Wernicke H.-J. Bertau M. Methanol for renewable energy storage and utilization.Energy Tech. 2016; 4: 193-200https://doi.org/10.1002/ente.201500322Crossref Scopus (58) Google Scholar Cycling of carbon, oxygen, and hydrogen-derivatives has been suggested in the concept of “thermal hydrogen”16Moore J. Meeks N. Hourly modelling of Thermal Hydrogen electricity markets.Clean Energy. 2020; 4: 270-287https://doi.org/10.1093/ce/zkaa014Crossref Scopus (3) Google Scholar but not in the context of very high penetrations of renewable energy and inter-annual storage. Carbon cycling with Allam has been for methanol storage J. Pozarlik A. Arentsen M. Brem G. Techno-economic study of a zero-emission methanol based energy storage system.Energy Convers. Manag. 2019; 182: 530-545https://doi.org/10.1016/j.enconman.2018.12.015Crossref Scopus (39) Google Scholar but the focus on the cost of storage based on about capacity rather than a in with variable renewables and other storage like has been is a for high of wind and solar in a power system many weather which we in In production facilities using fossil methanol is with these high with hydrogen supply from variable electricity would require hydrogen storage to the hydrogen, which may not be as discussed While hydrogen can be in pressure vessels for several of low wind and solar generation would a challenge for is from large research as well as initial from plants be to methanol to large hydrogen storage. can be by to V. A. A. H. S. of or a Environ. 2020; Google T. K. methanol and with the Energy. Scopus Google S. A. D. or intermediate 2023; Google Scholar down V. A. A. H. S. of or a Environ. 2020; Google J. J. T.H. S. R. R. A for pathways to renewable energy for J. 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Manag. 2019; 182: 530-545https://doi.org/10.1016/j.enconman.2018.12.015Crossref Scopus (39) Google Scholar round-trip efficiency is at we a efficiency for the Allam turbine and for the methanol However, is in the range we the cost of electricity for the storage and Allam cycle has a lower capacity of compared to the capacity of in Baak et al.8Baak J. Pozarlik A. Arentsen M. Brem G. Techno-economic study of a zero-emission methanol based energy storage system.Energy Convers. Manag. 2019; 182: 530-545https://doi.org/10.1016/j.enconman.2018.12.015Crossref Scopus (39) Google Scholar cost of methanol in the Allam from to is carbon cycling and is cost rises to The range to which is than fossil methanol of but in with for methanol in J. M. 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