Techno-economic analysis of long-duration energy storage and flexible power generation technologies to support high-variable renewable energy grids

Abstract

•Lifetime cost for 14 energy storage or flexible power generation technologies•Pumped hydro, compressed air, and batteries are best for 12-h discharge•Hydrogen and NG-CC with CCS have the lowest cost for 120-h discharge applications•Heavy-duty vehicle fuel cells reduce LCOE by 13%–20% relative to stationary fuel cells Dramatic reductions in the costs of wind, solar, and batteries are accelerating renewables penetration in electricity grids. However, the least-cost approach to achieving a high penetration of variable renewable electricity remains unclear. Capacity expansion and dispatch optimization models are instrumental in identifying which technologies have the greatest potential. This study provides a rigorous characterization of the cost and performance of leading flexible, low-carbon power generation and long-duration energy storage technologies that can be included in electricity grid planning models. To ensure that state-of-the-art data are used, the data have been reviewed and developed with subject matter experts across the US Department of Energy and the US national laboratories. These data can and will be used in future capacity expansion and grid dispatch optimization models; here, we provide a techno-economic comparison of technologies based on the levelized cost of energy. As variable renewable energy penetration increases beyond 80%, clean power systems will require long-duration energy storage or flexible, low-carbon generation. Here, we provide a detailed techno-economic evaluation and uncertainty analysis of applicable technologies and identify challenges and opportunities to support electric grid planning. We show that for a 120-h storage duration rating, hydrogen systems with geologic storage and natural gas with carbon capture are the least-cost low-carbon technologies for both current and future capital costs. These results are robust to uncertainty for the future capital cost scenario, but adiabatic compressed air and pumped thermal storage could be the least-cost technologies in the current capital cost scenario under uncertainty. Finally, we present a new storage system using heavy-duty vehicle fuel cells that could reduce the levelized cost of energy by 13%–20% compared with the best previously considered storage technology and, thus, could help enable very high (>80%) renewable energy grids. As variable renewable energy penetration increases beyond 80%, clean power systems will require long-duration energy storage or flexible, low-carbon generation. Here, we provide a detailed techno-economic evaluation and uncertainty analysis of applicable technologies and identify challenges and opportunities to support electric grid planning. We show that for a 120-h storage duration rating, hydrogen systems with geologic storage and natural gas with carbon capture are the least-cost low-carbon technologies for both current and future capital costs. These results are robust to uncertainty for the future capital cost scenario, but adiabatic compressed air and pumped thermal storage could be the least-cost technologies in the current capital cost scenario under uncertainty. Finally, we present a new storage system using heavy-duty vehicle fuel cells that could reduce the levelized cost of energy by 13%–20% compared with the best previously considered storage technology and, thus, could help enable very high (>80%) renewable energy grids. Solar and wind energy are quickly becoming the cheapest and most deployed electricity generation technologies across the world.1IRENARenewable Capacity Statistics 2020. International Renewable Energy Agency (IRENA), 2020https://irena.org/-/media/Files/IRENA/Agency/Publication/2020/Mar/IRENA_RE_Capacity_Statistics_2020.pdfGoogle Scholar,2Lazard Lazard’s levelized cost of energy analysis - version 140.https://www.lazard.com/media/451419/lazards-levelized-cost-of-energy-version-140.pdfDate: 2020Google Scholar Additionally, electric utilities will need to accelerate their portfolio decarbonization with renewables and other low-carbon technologies to avoid carbon lock-in and asset-stranding in a decarbonizing grid;3Alova G. A global analysis of the progress and failure of electric utilities to adapt their portfolios of power-generation assets to the energy transition.Nat. Energy. 2020; 5: 920-927Crossref Scopus (22) Google Scholar however, variable renewable energy (VRE) deployments are already sometimes challenging grid operations.4Denholm P. Mai T. Timescales of energy storage needed for reducing renewable energy curtailment.Renew. Energy. 2019; 130: 388-399Crossref Scopus (84) Google Scholar,5Denholm P. O’Connell M. Brinkman G. Jorgenson J. Overgeneration from solar energy in California: a field guide to the duck chart. National Renewable Energy Lab, NREL/TP-6A20-65023.https://www.nrel.gov/docs/fy16osti/65023.pdfDate: 2015Google Scholar Current methods for handling the variable nature of these resources include load-following with conventional power plants, careful forecasting of wind and solar resources with appropriate scheduling of conventional plants, flexibly managing loads, and curtailing excess renewable energy, among others. Increasing VRE penetration levels could create situations where the ramp rates and fast dynamics required for balancing the grid are difficult to achieve with existing grid resources, resulting in an increase in renewable energy curtailment.5Denholm P. O’Connell M. Brinkman G. Jorgenson J. Overgeneration from solar energy in California: a field guide to the duck chart. National Renewable Energy Lab, NREL/TP-6A20-65023.https://www.nrel.gov/docs/fy16osti/65023.pdfDate: 2015Google Scholar VRE penetration levels are already exceeding 40% in places such as California6Canonica R. Micek K. Rapid renewables growth brings challenges for US states: Part 1 – California. S&P Global, 2020https://www.spglobal.com/en/research-insights/articles/rapid-renewables-growth-brings-challenges-for-us-states-part-i-california#:∼:text=California%20has%20long%20been%20a,wind%2C%20according%20to%20the%20ISOGoogle Scholar and Germany,7Rechsteiner R. German energy transition (Energiewende) and what politicians can learn for environmental and climate policy.Clean Technol. Environ. Policy. 2020; : 1-38PubMed Google Scholar and near-term levels up to 55% can likely be achieved with short-duration storage in the realm of 4 to 8 h.4Denholm P. Mai T. Timescales of energy storage needed for reducing renewable energy curtailment.Renew. Energy. 2019; 130: 388-399Crossref Scopus (84) Google Scholar,8Kloess M. Zach K. Bulk electricity storage technologies for load-leveling operation – an economic assessment for the Austrian and German power market.Int. J. Electr. Power Energy Syst. 2014; 59: 111-122Crossref Scopus (44) Google Scholar Battery costs for short-duration grid storage systems are already approaching the cost of natural gas peaking plants,9Lazard Lazard’s levelized cost of energy analysis - version 13.0.https://www.lazard.com/media/451086/lazards-levelized-cost-of-energy-version-130-vf.pdfDate: 2019Google Scholar,10Lazard Lazard’s levelized cost of storage - version 5.0.https://www.lazard.com/media/451087/lazards-levelized-cost-of-storage-version-50-vf.pdfDate: 2019Google Scholar and further battery storage cost reductions are expected in the near future;11Schmidt O. Melchior S. Hawkes A. Staffell I. Projecting the future levelized cost of electricity storage technologies.Joule. 2019; 3: 81-100Abstract Full Text Full Text PDF Scopus (265) Google Scholar,12Cole W. Will Frazier A. Cost projections for utility-scale battery storage. National Renewable Energy Lab NREL/TP-6A20-73222.https://www.nrel.gov/docs/fy19osti/73222.pdfDate: 2019Google Scholar however, studies predict that as renewable penetration levels approach 100%, improvements in transmission, long-duration or seasonal energy storage, and flexible, low-emission power generation will become the most affordable ways to meet demand.13Blanco 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: 1049-1086Crossref Scopus (319) Google Scholar, 14Weitemeyer S. Kleinhans D. Vogt T. Agert C. Integration of renewable energy sources in future power systems: the role of storage.Renew. Energy. 2015; 75: 14-20Crossref Scopus (296) Google Scholar, 15Child M. Bogdanov D. Breyer C. The role of storage technologies for the transition to a 100% renewable energy system in Europe.Energy Procedia. 2018; 155: 44-60Crossref Scopus (60) Google Scholar, 16Mouli-Castillo J. Wilkinson M. Mignard D. McDermott C. Haszeldine R.S. Shipton Z.K. Inter-seasonal compressed-air energy storage using saline aquifers.Nat. Energy. 2019; 4: 131-139Crossref Scopus (62) Google Scholar, 17Pfenninger S. Keirstead J. Renewables, nuclear, or fossil fuels? Scenarios for Great Britain’s power system considering costs, emissions and energy security.Appl. Energy. 2015; 152: 83-93Crossref Scopus (145) Google Scholar At these high VRE penetration levels, seasonal variation in wind and solar potential will incentivize flexible power generation and/or the ability to shift large quantities of grid electricity for durations longer than a few hours. Long-duration or seasonal energy storage and flexible generation will also be necessary to provide electricity during long summer doldrums, natural disasters, and extreme weather events, such as polar vortexes,[18]North America Power & RenewablesPerformance Review: Nuclear, Fossil Fuels, and Renewables During the 2019 Polar Vortex. Wood Mackenzie Power & Renewables, 2019Google Scholar and can be used for multiyear storage.19Dowling J.A. Rinaldi K.Z. Ruggles T.H. Davis S.J. Yuan Mengyao Tong F. Lewis N.S. Caldeira K. Role of long-duration energy storage in variable renewable electricity systems.Joule. 2020; 4: 1907-1928Abstract Full Text Full Text PDF Scopus (77) Google Scholar Most analyses of long-duration or seasonal energy storage consider a limited set of technologies or neglect low-emission flexible power generation systems altogether.11Schmidt O. Melchior S. Hawkes A. Staffell I. Projecting the future levelized cost of electricity storage technologies.Joule. 2019; 3: 81-100Abstract Full Text Full Text PDF Scopus (265) Google Scholar,19Dowling J.A. Rinaldi K.Z. Ruggles T.H. Davis S.J. Yuan Mengyao Tong F. Lewis N.S. Caldeira K. Role of long-duration energy storage in variable renewable electricity systems.Joule. 2020; 4: 1907-1928Abstract Full Text Full Text PDF Scopus (77) Google Scholar,20Albertus P. Manser J.S. Litzelman S. Long-duration electricity storage applications, economics, and technologies.Joule. 2020; 4: 21-32Abstract Full Text Full Text PDF Scopus (90) Google Scholar Investigations that focus on flexible power generation technologies to balance renewables often overlook seasonal energy storage.21Sepulveda N.A. Jenkins J.D. de Sisternes F.J. Lester R.K. The role of firm low-carbon electricity resources in deep decarbonization of power generation.Joule. 2018; 2: 2403-2420Abstract Full Text Full Text PDF Scopus (165) Google Scholar Studies that consider both flexible power generation and energy storage systems usually focus on a limited suite of technologies or limit the storage duration to less than 12 h.22Brouwer A.S. van den Broek M. Zappa W. Turkenburg W.C. Faaij A. Least-cost options for integrating intermittent renewables in low-carbon power systems.Appl. Energy. 2016; 161: 48-74Crossref Scopus (186) Google Scholar Several other studies focus on a subset of either long-duration energy storage (LDES) or flexible power generation technologies, but the costs used in these studies vary widely, making it difficult to compare technologies across studies. Further, the effects of uncertainty in future cost are often either not captured or not clearly communicated. A comprehensive, detailed, systematic assessment of all applicable technologies using up-to-date cost estimates for both current and future technologies, in the context of uncertainty, is needed to identify key technology cost drivers and opportunities to support high VRE electric grid planning. Here, we present a comprehensive techno-economic comparison of LDES and flexible power generation technologies in a US Western Interconnection with 85% renewables. We employ state-of-the-art cost, performance, and learning rate data to estimate the current and future levelized cost of energy (LCOE) of each technology. Cost and performance data obtained from the literature have been reviewed and, if data are limited, developed with subject matter experts across the US Department of Energy (DOE) and the US national laboratories. We also introduce a hydrogen energy storage system using heavy-duty vehicle (HDV) proton exchange membrane (PEM) fuel cells in stationary service, which reduces power production capital costs relative to conventional stationary PEM fuel cells without introducing the need for frequent fuel cell stack replacements throughout the project life due to the low power generation capacity factor for LDES. This work offers a detailed characterization of the cost and performance of leading technology systems to support high VRE grids and could be used in electric grid capacity expansion and dispatch optimization models. We show that for 12-h storage duration, pumped hydro has the lowest LCOE with current costs, and vanadium flow batteries become competitive if future costs are achieved. For 120-h storage duration, hydrogen systems with geologic storage and natural gas with carbon capture and sequestration (CCS) achieve the lowest LCOE in both current and future capital cost scenarios. In particular, the configuration of HDV-PEM fuel cells with hydrogen storage in geologic formations could reduce the LCOE by 14%–21% compared with stationary fuel cell systems typically evaluated, which thus might help enable very high renewable energy electric power grids. Pumped thermal energy storage (TES) and hydrogen stored in underground pipes (long tanks) are the least-cost options for 120-h storage that do not require some form of geologic storage. Results also illustrate that coproducing and selling hydrogen to other markets could reduce the LCOE of hydrogen systems by up to 39% compared with scenarios without coproduction. Last, sensitivity analysis and Monte Carlo analysis illustrate that the general trends seen in this study are valid for a wide range of capacity factors and future cost scenarios. Technology selection for this work is based on the technology’s ability to flexibly support high VRE grids, compensate for seasonal variations in power supply and demand, and fill long-term supply disruptions. Additionally, technology systems are limited to those for which sufficient cost, performance, and learning curve data have been derived to enable reliable techno-economic modeling. Thus, this technology set provides a benchmark for novel systems that do not yet have sufficient, rigorous cost and performance data. Electrical energy storage systems are reviewed first, followed by flexible power generation technologies and other grid flexibility mechanisms. Common electrical energy storage technologies considered in the literature and for actual grid applications include pumped hydropower storage (PHS), compressed air energy storage (CAES), flywheels, supercapacitors, and various types of batteries.23Akhil A.A. Huff G. Currier A.B. Kaun B.C. Rastler D.M. Chen S.B. Cotter A.L. Bradshaw D.T. Gauntlett W.D. DOE/EPRI Electricity Storage Handbook in Collaboration with NRECA. Sandia National Laboratories, 2015https://www.sandia.gov/ess-ssl/publications/SAND2015-1002.pdfCrossref Google Scholar,24Mongird K. Fotedar V. Viswanathan V. Koritarov V. Balducci P. Hadjerioua B. Alam J. Energy storage technology and cost characterization report. Pacific Press Northwest National Laboratory, PNNL-28866.https://energystorage.pnnl.gov/pdf/PNNL-28866.pdfDate: 2019Google Scholar TES for concentrating solar power and heat pump energy storage systems are also being considered by researchers and industry to store energy for durations longer than a few hours.25Mehos M. Turchi C. Vidal J. Wagner M. Ma Z. Ho C. Kolb W. Andraka C. Kruizenga A. Concentrating solar power Gen3 demonstration roadmap. National Renewable Energy Laboratory, NREL/TP-5500-67464.https://www.nrel.gov/docs/fy17osti/67464.pdfDate: 2017Google Scholar, 26Laughlin R.B. Pumped thermal grid storage with heat exchange.J. Renew. Sustain. Energy. 2017; 9: 044103Crossref Scopus (80) Google Scholar, 27Smallbone A. Jülch V. Wardle R. Roskilly A.P. Levelised cost of storage for pumped heat energy storage in comparison with other energy storage technologies.Energy Convers. Manag. 2017; 152: 221-228Crossref Scopus (110) Google Scholar LDES requires large energy capacities so that a typical rate of charging or discharging can be sustained for days, weeks, or even longer. Recent studies have shown that developing seasonal storage with conventional battery chemistries may be prohibitively expensive11Schmidt O. Melchior S. Hawkes A. Staffell I. Projecting the future levelized cost of electricity storage technologies.Joule. 2019; 3: 81-100Abstract Full Text Full Text PDF Scopus (265) Google Scholar,19Dowling J.A. Rinaldi K.Z. Ruggles T.H. Davis S.J. Yuan Mengyao Tong F. Lewis N.S. Caldeira K. Role of long-duration energy storage in variable renewable electricity systems.Joule. 2020; 4: 1907-1928Abstract Full Text Full Text PDF Scopus (77) Google Scholar, 20Albertus P. Manser J.S. Litzelman S. Long-duration electricity storage applications, economics, and technologies.Joule. 2020; 4: 21-32Abstract Full Text Full Text PDF Scopus (90) Google Scholar, 21Sepulveda N.A. Jenkins J.D. de Sisternes F.J. Lester R.K. The role of firm low-carbon electricity resources in deep decarbonization of power generation.Joule. 2018; 2: 2403-2420Abstract Full Text Full Text PDF Scopus (165) Google Scholar,28Wärtsilä Path to 100% renewables for California. Wärtsilä White Paper.https://www.pathto100.org/wp-content/uploads/2020/03/path-to-100-renewables-for-california.pdfDate: 2020Google Scholar but do indicate that lithium-ion battery costs are declining rapidly and are potentially pushing into the storage durations up to or beyond 12 h.11Schmidt O. Melchior S. Hawkes A. Staffell I. Projecting the future levelized cost of electricity storage technologies.Joule. 2019; 3: 81-100Abstract Full Text Full Text PDF Scopus (265) Google Scholar,29Mongird K. Viswanathan V. Alam J. Vartanian C. Sprenkle V. Baxter R. 2020 grid energy storage technology cost and performance assessment. U.S. Depaartment of Energy, DOE/PA-0204.https://www.pnnl.gov/sites/default/files/media/file/Final%20-%20ESGC%20Cost%20Performance%20Report%2012-11-2020.pdfDate: 2020Google Scholar Thus, we include conventional Li-ion batteries in this analysis. Innovations in battery chemistry could further reduce energy costs; however, these technologies have not yet been demonstrated nor do they have sufficient data to be included in the current analysis.30Turcheniuk, K., Bondarev, D., Amatucci, G.G., and Yushin, G. Battery materials for low-cost electric transportation. Mater. Today 42, 57–72.Google Scholar Sodium-sulfur batteries are one of the most common grid energy storage technologies currently deployed but have very high costs relative to other storage technologies considered here such as PHS, vanadium redox flow batteries (VRBs), CAES, and Li-ion batteries11Schmidt O. Melchior S. Hawkes A. Staffell I. Projecting the future levelized cost of electricity storage technologies.Joule. 2019; 3: 81-100Abstract Full Text Full Text PDF Scopus (265) Google Scholar,23Akhil A.A. Huff G. Currier A.B. Kaun B.C. Rastler D.M. Chen S.B. Cotter A.L. Bradshaw D.T. Gauntlett W.D. DOE/EPRI Electricity Storage Handbook in Collaboration with NRECA. Sandia National Laboratories, 2015https://www.sandia.gov/ess-ssl/publications/SAND2015-1002.pdfCrossref Google Scholar,24Mongird K. Fotedar V. Viswanathan V. Koritarov V. Balducci P. Hadjerioua B. Alam J. Energy storage technology and cost characterization report. Pacific Press Northwest National Laboratory, PNNL-28866.https://energystorage.pnnl.gov/pdf/PNNL-28866.pdfDate: 2019Google Scholar,31Zakeri B. Syri Sanna. Electrical energy storage systems: a comparative life cycle cost analysis.Renew. Sustain. Energy Rev. 2015; 42: 569-596Crossref Scopus (986) Google Scholar, and for this reason, we exclude them from this analysis. Flywheels and supercapacitors are best suited to applications with low energy-to-power ratios, such as frequency regulation,24Mongird K. Fotedar V. Viswanathan V. Koritarov V. Balducci P. Hadjerioua B. Alam J. Energy storage technology and cost characterization report. Pacific Press Northwest National Laboratory, PNNL-28866.https://energystorage.pnnl.gov/pdf/PNNL-28866.pdfDate: 2019Google Scholar and are, therefore, excluded from this analysis. This limits the previously mentioned list of electrical energy storage technologies to be included in this study to PHS, CAES, TES, Li-ion batteries, and flow batteries. Hydrogen has also been considered for electrical energy storage.11Schmidt O. Melchior S. Hawkes A. Staffell I. Projecting the future levelized cost of electricity storage technologies.Joule. 2019; 3: 81-100Abstract Full Text Full Text PDF Scopus (265) Google Scholar,31Zakeri B. Syri Sanna. Electrical energy storage systems: a comparative life cycle cost analysis.Renew. Sustain. Energy Rev. 2015; 42: 569-596Crossref Scopus (986) Google Scholar,32Hydrogen Council Path to hydrogen competitiveness: a cost perspective.https://hydrogencouncil.com/wp-content/uploads/2020/01/Path-to-Hydrogen-Competitiveness_Full-Study-1.pdfDate: 2020Google Scholar Conceptual renewable-powered hydrogen storage systems generally consist of an electrolyzer; storage in tanks, pipes, or underground caverns;33Ahluwalia, R.K., Papadias, D.D., Peng, J.-K., and Roh, H.S. (2019). System Level Analysis of Hydrogen Storage Options. In U.S. Department of Energy 2019 Annual Merit Review and Peer Evaluation Meeting, https://www.hydrogen.energy.gov/pdfs/review19/st001_ahluwalia_2019_o.pdf.Google Scholar,34Lord A.S. Kobos P.H. Borns D.J. Geologic storage of hydrogen: scaling up to meet city transportation demands.Int. J. Hydrog. Energy. 2014; 39: 15570-15582Crossref Scopus (97) Google Scholar and re-electrification via fuel cells or combustion turbines, which are available commercially.35Lindstrand N. This Swedish scientist works towards fulfilling Siemens Energy’s 2030 hydrogen pledge. Siemens energy.https://www.siemens-energy.com/global/en/news/magazine/2019/hydrogen-capable-gas-turbine.htmlDate: 2020Google Scholar,36Goldmeer J. Gas turbines: hydrogen capability and experience. GE Gas Power, 2020https://www.hydrogen.energy.gov/pdfs/06-Goldmeer-Hydrogen%20Gas%20Turbines.pdfGoogle Scholar Historically, hydrogen has not been deployed for grid energy storage because of high capital costs and low round-trip efficiencies;31Zakeri B. Syri Sanna. Electrical energy storage systems: a comparative life cycle cost analysis.Renew. Sustain. Energy Rev. 2015; 42: 569-596Crossref Scopus (986) Google Scholar,37Schmidt O. Hawkes A. Gambhir A. Staffell I. The future cost of electrical energy storage based on experience rates.Nat. Energy. 2017; 2: 17110Crossref Google Scholar however, recent studies have suggested that PEM electrolysis and fuel cell costs could be substantially reduced with research and development (R&D), economies of scale, and learning.38Strategic Analysis NRELH2A 2020 electrolysis production case studies.https://www.nrel.gov/hydrogen/h2a-production-models.htmlDate: 2020Google Scholar, 39James B.D. Huya-Kouadio J.M. Houchins C. DeSantis D.A. Mass production cost estimation of direct H2 PEM fuel cell systems for transportation applications: 2017 update. (Strategic Analysis).https://www.energy.gov/sites/prod/files/2019/12/f70/fcto-sa-2018-transportation-fuel-cell-cost-analysis.pdfDate: 2017Google Scholar, 40Battelle Memorial InstituteManufacturing cost analysis of 100 KW and 250 KW fuel cell systems for primary power and combined heat and power applications.https://www.energy.gov/sites/prod/files/2016/07/f33/fcto_battelle_mfg_cost_analysis_pp_chp_fc_systems.pdfDate: 2016Google Scholar Further, PEM fuel cells designed for HDVs provide a lower capital cost power generation option than stationary fuel cells, which are designed for continuous operation. PEM fuel cells designed for HDVs are not typically considered for stationary power applications due to the different performance and durability requirements between stationary and transport duty-cycles. However, seasonal energy storage systems may only be discharged 5%–10% of the time,41Zhang Jiazi Guerra Fernandez O.J. Eichman J. Pellow M. Benefit analysis of long-duration energy storage in power systems with high renewable energy shares.Front. Energy Res. 2020; 8: 313Crossref Scopus (6) Google Scholar equivalent to 13,000–26,000 h over a 30-year lifetime and similar to the demonstrated fuel cell lifetimes of more than 20,000 h achieved in transit buses.42Eudy L. Technology acceleration: fuel cell bus evaluations. In U.S. Department of Energy 2019 Annual Merit Review and Peer Evaluation Meeting, 2019.https://www.nrel.gov/docs/fy19osti/73407.pdfDate: 2019Google Scholar Thus, we consider PEM electrolysis with hydrogen stored in underground pipes or geologic caverns, with electrification via combined cycle or stationary PEM or HDV-PEM fuel cells. We assume geologic storage in solution-mined salt dome caverns because of their low technological risk, but other geologic storage options—such as hard rock caverns—are also feasible. Use of porous rock formations and aquifers were not considered for this analysis because of the uncertainty of storage tightness, gas recovery purity, and potential reactivity of hydrogen with the storage media. Buried pipes can be a lower-cost storage option than above-ground tanks while still allowing more location flexibility than geologic storage. We assume API 5L Grade X52 tubes with polyethylene coating would be used for underground pipe storage.33Ahluwalia, R.K., Papadias, D.D., Peng, J.-K., and Roh, H.S. (2019). System Level Analysis of Hydrogen Storage Options. In U.S. Department of Energy 2019 Annual Merit Review and Peer Evaluation Meeting, https://www.hydrogen.energy.gov/pdfs/review19/st001_ahluwalia_2019_o.pdf.Google Scholar Note that 1,600 miles of existing steel hydrogen pipeline currently connect large industrial hydrogen producers and suppliers. Such pipelines are subject to American Society of Mechanical Engineers (ASME) code B31.12, which prescribes design and material choice to allow safe operation with 100% hydrogen.43USDRIVEHydrogen delivery techincal team roadmap.https://www.energy.gov/sites/prod/files/2017/08/f36/hdtt_roadmap_July2017.pdfDate: 2017Google Scholar For combustion-based power generation with hydrogen, we consider combined cycles instead of open cycles (combustion turbines without a steam cycle) because of their greater efficiencies. Flexible power generators can also support high VRE grids. Power generation technologies include coal, nuclear, natural gas, conventional hydropower, and bioenergy. Commercial coal and nuclear power plants are not considered flexible generators because they rely on steam Rankine cycles and light-water reactors, which cannot be rapidly cycled on and off.44IRENAFlexibility in conventional power plants. Innovation Landscape Brief. International Renewable Energy Agency, 2019https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2019/Sep/IRENA_Flexibility_in_CPPs_2019.pdf?la=en&hash=AF60106EA083E492638D8FA9ADF7FD099259F5A1Google Scholar Scalable, flexible nuclear plants, such as small modular reactors, are currently in the R&D stages and might be deployed in the future, but assessing the costs of such technologies is outside the scope of this study. Natural gas combined-cycle (NG-CC) power plant flexibility is limited by the heat recovery steam generator and steam turbines;44IRENAFlexibility in conventional power plants. Innovation Landscape Brief. International Renewable Energy Agency, 2019https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2019/Sep/IRENA_Flexibility_in_CPPs_2019.pdf?la=en&hash=AF60106EA083E492638D8FA9ADF7FD099259F5A1Google Scholar,45Eddington M. Osmundsen M. Jaswal I. Rowell J. Reinhart B. Improving the flexibility and efficiency of gas turbine-based distributed power plant. The Future of Gas Turbine Technology 8 th International Gas Turbine Conference.https://etn.global/wp-content/uploads/2018/09/Improving-the-flexibility-and-efficiency-of-gas-turbine-based-distrivuted-power-plant.pdfDate: 2017Google Scholar however, flexibility can be improved through several techniques,45Eddington M. Osmundsen M. Jaswal I. Rowell J. Reinhart B. Improving the flexibility and efficiency of gas turbine-based distributed power plant. The Future of Gas Turbine Technology 8 th International Gas Turbine Conference.https://etn.global/wp-content/uploads/2018/09/Improving-the-flexibility-and-efficiency-of-gas-turbine-based-distrivuted-power-plant.pdfDate: 2017Google Scholar, 46Moelling D. Jackson P. Malloy J. Protecting steam cycle components during low-load operation of combined cycle gas turbine plants.Power Mag. 2015; https://www.powermag.com/protecting-steam-cycle-components-during-low-load-operation-of-combined-cycle-gas-turbine-plants/Google Scholar, 47Welch M. Pym A. Improving the flexibility and efficiency of gas turbine-based distributed power plants.Power Engineering. 2015; https://www.power-eng.com/2015/09/14/improving-the-flexibility-and-efficiency-of-gas-turbine-based-distributed-power-plants/#grefGoogle Scholar and fast-start NG-CCs have been deployed commercially for several yea