Lithium-ion batteries currently hold more than ninety-five percent of the deployed energy-storage market, but no single technology can satisfy every storage requirement. The full multi-dimensional set of demands—temporal scale, energy density, power density, cycle life, resource availability, safety, and cost—can only be met by a portfolio of complementary storage technologies. This chapter classifies next-generation storage into five branches and surveys the standardization status of each: (1) hydrogen storage (HYDROGEN_STORAGE), (2) compressed air energy storage (CAES, Compressed Air Energy Storage), (3) flywheels (FLYWHEEL), (4) thermal storage (THERMAL_STORAGE), and (5) advanced chemistries (solid-state, sodium-ion, and flow batteries). The manifest classifies these technologies through nine ENUM values: HYDROGEN_STORAGE, COMPRESSED_AIR, CAES, FLYWHEEL, THERMAL_STORAGE, MOLTEN_SALT, ICE_STORAGE, GREEN_HYDROGEN, and BLUE_HYDROGEN.1
The defining value of next-generation storage is temporal diversity. Lithium-ion is optimized for storage horizons of minutes to hours; it is markedly inefficient at horizons of days to weeks. Hydrogen, CAES, and thermal storage are well suited to the day-to-week scale and are the leading candidates for seasonal storage. Flywheels deliver second-to-minute response and are ideal for short-cycle ancillary services such as frequency regulation. WIA-ESS requires implementations to declare their temporal scale through the `temporal_scale` ENUM (SECONDS, MINUTES, HOURS, DAYS, WEEKS, SEASONAL).
Hydrogen is classified by production method using a color palette. Green hydrogen (GREEN_HYDROGEN) is produced by electrolyzing water with renewable electricity and is carbon-free at the point of production. Blue hydrogen (BLUE_HYDROGEN) is produced by reforming natural gas with simultaneous carbon capture and storage (CCS), and is therefore low-carbon. Gray hydrogen, produced by natural-gas reforming without CCS, dominates today's industrial hydrogen supply (approximately ninety-five percent of global production). The International Energy Agency's Hydrogen Outlook 20242 projects the levelized cost of green hydrogen to fall from approximately five dollars per kilogram in 2024 to approximately 2.5 dollars per kilogram by 2030.
Hydrogen storage divides into four primary methods: (1) high-pressure gaseous storage at 350 bar or 700 bar, (2) liquid hydrogen storage at minus 253 degrees Celsius, (3) metal-hydride storage, and (4) liquid organic hydrogen carrier (LOHC) storage. Industrial-scale, long-duration storage typically uses high-pressure gaseous storage in underground salt caverns or depleted gas fields. The salt caverns of Spindletop in Texas and Teesside in the United Kingdom offer storage capacities of tens to hundreds of gigawatt-hours. In Korea, Doosan Enerbility, POSCO, and Hanwha Solutions are developing liquefied-hydrogen storage infrastructure, with a fifty-tons-per-day liquefaction plant scheduled to commence operation in 2025 at the Ulsan and Changwon industrial complexes.
The Ministry of Trade, Industry and Energy's Hydrogen Economy Roadmap 2030 targets the production of one million tons of green hydrogen per year, the construction of 660 hydrogen refueling stations, and the deployment of 800,000 hydrogen-fueled vehicles by 2030. The Hydrogen Economy Promotion Act, enacted in 2020, provides the legal foundation; MOTIE, the Ministry of Environment, the Ministry of Land, Infrastructure and Transport, and the Ministry of Oceans and Fisheries jointly execute the policy. WIA-ESS manifests record alignment with this roadmap through the `hydrogen_strategy_alignment` field.
CAES uses surplus electricity to compress air into an underground reservoir; the air is later expanded through a gas turbine to generate electricity. Diabatic CAES rejects the heat of compression and adds natural-gas combustion during expansion, with round-trip efficiency near fifty to fifty-five percent. Adiabatic CAES (sometimes called isothermal CAES) stores the heat of compression in a separate thermal reservoir for reuse during expansion, raising round-trip efficiency to roughly sixty-five to seventy percent.
The principal commercial CAES installations operating today are: (1) Huntorf in Germany (290 megawatts, commissioned in 1978), (2) McIntosh in Alabama, United States (110 megawatts, commissioned in 1991), (3) Jintan in Jiangsu Province, China (60 megawatts, commissioned in 2022), and (4) Hydrostor in Goderich, Ontario, Canada (2.2 megawatts, commissioned in 2019). ApexCAES, scheduled for commissioning in Texas in 2025, will be a 317-megawatt single-site CAES marking the renaissance of large-scale CAES. WIA-ESS classifies CAES assets with the COMPRESSED_AIR ENUM and requires disclosure of reservoir type (salt cavern, porous rock, hard rock, surface vessel), rated power, rated energy, and round-trip efficiency.
Korea's predominantly mountainous geography limits the availability of underground salt caverns. The Korea Institute of Energy Research (KIER) has therefore pursued small-scale surface-reservoir CAES research since 2023, with a five-megawatt pilot scheduled for 2027. The Korea Institute of Geoscience and Mineral Resources (KIGAM) is separately assessing the suitability of abandoned mine shafts along the east coast as CAES reservoirs.
A flywheel (FLYWHEEL) stores electricity as rotational kinetic energy. A motor-generator accelerates a rotor (typically at 16,000 to 50,000 revolutions per minute) during charging and operates as a generator during discharging. The rotor is generally constructed from carbon-fiber composite, suspended on magnetic bearings, and enclosed in a vacuum chamber to minimize friction losses. Round-trip efficiency is high (85 to 90 percent), and the response time of four to five milliseconds is the shortest among all storage technologies. The drawback is a high self-discharge rate of approximately twenty percent per hour, which makes flywheels unsuitable for long-duration storage.
Flywheels are most useful for frequency regulation, voltage support, and uninterruptible power supply (UPS) applications. The reference installations are Beacon Power's 20-megawatt Stephentown plant in Massachusetts (commissioned in 2011), Temporal Power's 2-megawatt installation in Quebec (commissioned in 2014), and Amber Kinetics' 8-kilowatt-hour modular flywheel commercialized in 2019. WIA-ESS classifies flywheel assets with the FLYWHEEL ENUM and requires disclosure of rotational speed, rotor material, self-discharge rate, and round-trip efficiency.
Thermal storage divides into three branches: (1) sensible heat storage, (2) latent heat storage, and (3) thermochemical storage. Sensible heat uses temperature change—molten salt (MOLTEN_SALT), water, and concrete are the representative media. Latent heat exploits the fusion or solidification enthalpy of phase change materials (PCM). Thermochemical storage uses the bond energy of reversible chemical reactions and achieves the highest energy density but also the most demanding system integration. IRENA's Innovation Outlook: Thermal Energy Storage (2020) reported cumulative global thermal storage capacity at approximately 234 gigawatt-hours.
Molten salt thermal storage is the most commercially mature thermal technology, coupled almost exclusively with concentrated solar power (CSP). A 60:40 mixture of sodium nitrate and potassium nitrate is heated to 565 degrees Celsius in the receiver, stored in an insulated tank, and used to generate steam through a heat exchanger during dispatch. The principal installations are Andasol in Spain (150 megawatts, 7.5 hours storage), Crescent Dunes in the United States (110 megawatts, 10 hours), Noor Ouarzazate in Morocco (580 megawatts, 7 hours), and Delingha in China (135 megawatts, 7 hours).
Ice storage (ICE_STORAGE) freezes water with inexpensive nighttime electricity and uses the stored cooling for daytime air-conditioning loads. Large Korean commercial buildings (Lotte World Tower, COEX, the Grand InterContinental Seoul) have deployed ice storage systems, supported by Ministry of Environment Energy-Conservation Facility Financing subsidies. WIA-ESS classifies ice storage assets with the ICE_STORAGE ENUM.
Solid-state batteries replace liquid electrolytes with solid electrolytes, simultaneously improving energy density and safety. Samsung SDI is developing an oxide-based solid-state cell targeting mass production in 2027; LG Energy Solution is developing a sulfide-based solid-state cell targeting mass production in 2028. SK On is conducting joint R&D with the U.S. firm Solid Power. The projected energy density of solid-state cells is 400 to 500 watt-hours per kilogram—approximately twice that of current lithium-ion—and the elimination of liquid electrolytes fundamentally reduces fire risk.
Sodium-ion batteries substitute sodium for lithium, achieving decisive advantages in resource availability and cost. China's CATL began mass production in 2023. Energy density is approximately 160 watt-hours per kilogram (about seventy percent of LFP), but cost is roughly thirty percent lower than LFP. In Korea, LG Energy Solution is in R&D as of 2024, and SK On is at the prototype stage planned for 2025. WIA-ESS does not allocate a dedicated ENUM for sodium-ion; instead, implementations report `cell_chemistry = "Na-ion"`.
Flow batteries store electrolytes in external tanks and pump them through an electrochemical reaction cell during charge and discharge. Because energy capacity (tank volume) and power capacity (cell area) scale independently, flow batteries are particularly cost-effective for long-duration storage of four hours and beyond. The Vanadium Redox Flow Battery (VRFB) is the most commercialized variant; Iron-Chromium, Zinc-Bromine, and Hydrogen-Bromine variants are in R&D. In Korea, KIER commissioned a 100-kilowatt VRFB pilot in 2024, and Korea East-West Power and Lotte Chemical have announced commercial entry into the flow-battery market.
Standardization for next-generation storage technologies lags behind lithium-ion, but several standards have recently been published or are nearing publication:
WIA-ESS is designed to extend its manifest schema as each of these standards is published; Annex N (next-generation storage technologies) is updated semi-annually in June and December.
LCOS varies substantially with temporal scale across next-generation storage technologies. Combining Lazard's 2024 Levelized Cost of Storage Analysis with NREL's 2024 Annual Technology Baseline yields the following four-hour comparison: lithium-ion LFP 134 dollars per megawatt-hour, VRFB flow battery 220, CAES 180, molten-salt thermal storage 168, and flywheel 380 (competitive only at short scales). Extending to a 100-hour scale (long duration) reverses the ranking: lithium-ion LCOS rises sharply to approximately 380 dollars per megawatt-hour, while hydrogen storage falls to roughly 95, CAES to 78, and molten salt to 65. This scale-dependent inversion is the commercial driving force for next-generation storage.
The Korean Hydrogen Economy Roadmap 2030, first issued in January 2019 and revised in June 2024, targets one million tons of green hydrogen per year, 660 refueling stations, and 800,000 hydrogen vehicles by 2030, committing approximately eleven trillion won of public R&D spending to hydrogen over six years. The Hydrogen Economy Promotion Act of 2020 provides the legal framework, governed by the MOTIE Hydrogen Economy Committee with industry input channeled through the Korea Hydrogen Industry Association.
The Korea Atomic Energy Research Institute (KAERI) is developing the SMART small modular reactor, with an electrical output of 100 megawatts or a thermal output of 270 megawatts, designed as a multipurpose facility supplying both electricity and waste heat for high-temperature electrolysis and district heating; pilot operation is scheduled for 2025. Doosan Enerbility operates a 200-megawatt-per-year PEMFC fuel cell factory in Changwon, commissioned in 2024; POSCO has committed to producing one million tons of green hydrogen per year for its hydrogen-based iron-making transition by 2030; Hanwha Solutions operates approximately 38 hydrogen refueling stations nationwide under the H2 Mobility brand and plans to commission a 20-megawatt hydrogen fuel-cell power plant in 2025.
KOGAS, the Korean state gas utility, is converting the Pyeongtaek and Samcheok LNG facilities into liquefied hydrogen bases between 2025 and 2028, with a total investment of approximately 2.8 trillion won. Korea East-West Power plans a 200-megawatt hydrogen gas-turbine plant adjacent to Ulsan Thermal Power, scheduled for 2027; Korea Southern Power plans a 100-megawatt hydrogen-cofiring plant at Hadong Thermal Power, scheduled for 2026. The Ministry of Environment piloted the Green Hydrogen Certification scheme in July 2024, with the Korea Energy Agency conducting certification; certified green hydrogen earns additional credit under the EU Carbon Border Adjustment Mechanism.
The next-generation storage conformance hierarchy comprises three tiers. Surface implementations self-declare the storage medium, rated power, rated energy, and round-trip efficiency. Verified implementations attach test reports under the applicable international standards (IEC 62933, IEC 62282, IEC 62893, and ISO/TC 197). Anchored implementations stream continuous operating data into the manifest's `realized_performance{}` block and anchor it to Sigstore Rekor.
Each next-generation storage technology carries a distinctive environmental footprint. Hydrogen storage hinges on the carbon intensity of production; green hydrogen is essentially carbon-free, whereas gray hydrogen emits approximately ten kilograms of carbon dioxide per kilogram of hydrogen produced. Diabatic CAES requires supplemental natural-gas combustion and emits accordingly; adiabatic CAES is essentially emission-free in operation. Flywheels emit negligibly during operation but carry a significant manufacturing footprint from the carbon-fiber composite rotor. Thermal storage impacts vary by medium: molten salt poses leakage risk from nitrate salts, while ice storage poses refrigerant leakage risk. WIA-ESS requires the environmental impact assessment, conducted under IEC 62933-4-1:2017 life-cycle assessment methodology, to be linked from the `environmental_impact{}` block.
Panel 4 compares the performance and cost curves of the nine technologies covered in this chapter (hydrogen, compressed air, flywheel, thermal, molten salt, ice, solid-state, sodium-ion, and flow). Users adjust temporal scale (minutes to seasonal), rated capacity (megawatts and megawatt-hours), round-trip efficiency, self-discharge rate, and cycle life, and the simulator automatically evaluates the suitability of each technology. A side panel shows the Korean policy-alignment score against the Hydrogen Economy Roadmap 2030 and the Energy Storage Industry Development Strategy 2024.
The rise of next-generation storage is not merely the arrival of better storage devices. Extending the temporal scale from days to seasons enables seasonal smoothing of renewable intermittency, which in turn enables the complete elimination of fossil-fuel backup. The standardization of next-generation storage is, therefore, the removal of the final technical barrier on the path to a one-hundred-percent clean grid.
Hydrogen storage carries a doubly significant role for Korea. First, it serves as a long-duration medium that bridges the intermittency of renewable resources. Second, as a clean industrial reductant, heat source, and fuel, it enables decarbonization of steel, refining, and chemicals. POSCO's hydrogen-based iron-making transition, the green hydrogen plans of SK Energy and GS Caltex, and Doosan Enerbility's hydrogen gas-turbine business are concrete instances of this multi-purpose role.
Furthermore, the diversity of next-generation storage technologies underpins improvements in energy self-sufficiency. Korea's energy self-sufficiency stood at approximately seventeen percent in 2024, the lowest among OECD members. Domestic deployment of hydrogen, CAES, and thermal storage reduces dependence on imported fossil fuels and directly advances the objectives of MOTIE's Energy Security Enhancement Plan. The mandatory disclosure regime of WIA-ESS manifests provides an objective basis for tracking these self-sufficiency outcomes.
An integrated review of the policies of KIER, MOTIE, and the Ministry of Environment yields five inflection points for next-generation storage over the next five years. In 2025, formal launch of the Green Hydrogen Certification scheme clarifies the market premium for green hydrogen. In 2026, operating data from the KIER 100-kilowatt VRFB pilot enable the first one-megawatt commercial flow-battery facility. In 2027, the hydrogen gas-turbine plants in Ulsan and Hadong enter full operation, with hydrogen accounting for one percent of total electricity. In 2028, the KOGAS liquefied hydrogen bases in Pyeongtaek and Samcheok commence operation, completing the import infrastructure. By 2030, the targets of the Hydrogen Economy Roadmap 2030—one million tons of green hydrogen production, 660 refueling stations, and 100 multi-technology portfolio sites—are achieved.
The manifest classifies next-generation storage technologies through nine ENUM values: (1) HYDROGEN_STORAGE for generic hydrogen storage; (2) COMPRESSED_AIR and CAES as aliases for compressed air energy storage; (3) FLYWHEEL for flywheels; (4) THERMAL_STORAGE for generic thermal storage; (5) MOLTEN_SALT as a sub-form of molten-salt thermal storage; (6) ICE_STORAGE as a sub-form of ice storage; and (7) GREEN_HYDROGEN and BLUE_HYDROGEN as production-method sub-forms of hydrogen. This taxonomy aligns with the IEC 62933 series and the work of ISO/TC 197.
The International Energy Agency's Hydrogen Outlook 2024 is the annual report analyzing global hydrogen production, storage, and utilization. It projects green hydrogen LCOH at 5 USD/kg in 2024, 2.5 USD/kg in 2030, and 1.5 USD/kg in 2050, with global hydrogen demand at approximately 150 Mt in 2030 and 530 Mt in 2050. Korea's Hydrogen Economy Roadmap 2030 adopts the IEA projection as its policy baseline; the Roadmap aligns with the Hydrogen Economy Promotion Act and the Korea Hydrogen Industry Association policy recommendations.
All code examples, simulator panels, and manifest schemas in this chapter are maintained as a single source of truth in the GitHub public repository github.com/WIA-Official/wia-standards-public/tree/main/energy-storage. Examples in the printed edition, EPUB, and PDF are snapshots; readers should consult the repository's CHANGELOG and release notes for the latest revisions. Every manifest example carries a Sigstore DSSE signature; the corresponding Rekor transparency log index enables post-hoc verification.
弘益人間 (Hongik Ingan) — Benefit All Humanity