Storage · the complete global ecosystem
Store energy today. Power the world tomorrow.
Storage balances generation and demand, manages intermittency, steadies the grid and cuts peaks. BARREL covers it all — pumped hydro, batteries, thermal and molten salt, compressed and liquid air, hydrogen, gravity and the long-duration technologies to come — classified by how each one actually stores energy.
- Storage families
- 10
- Compared
- 17
- Lifecycle stages
- 17

Not everything is a battery. Some technologies store electricity electrochemically; others store it as water at height, pressure, motion, heat, cold or chemical fuel. Output, duration, efficiency and applications differ — so BARREL classifies storage by its actual mechanism.
Master taxonomy
Ten ways to store energy.
Groupings in line with EPRI, IEA and US DOE classifications.
- 01Pumped Hydro StorageOpen-loop, closed-loop, underground and seawater PSP
- 02Battery Storage (BESS)Lithium, sodium, lead, flow, zinc and metal-air
- 03Thermal StorageMolten salt, sand, concrete, PCM and thermochemical
- 04Mechanical StorageCompressed air, liquid air, flywheel, gravity, pumped heat
- 05Chemical StorageHydrogen, ammonia, methanol and synthetic fuels
- 06Electrical StorageSupercapacitors, ultracapacitors and SMES
- 07Cold StorageIce, chilled water and cryogenic
- 08Underground StorageSalt caverns, depleted reservoirs, aquifers, mines, boreholes
- 09Hybrid StorageBattery-hydro, battery-thermal, hydrogen-battery
- 10Emerging TechnologiesIron-air, liquid metal, metal fuels and advanced systems
Technology explorer
Every storage family, its system and its industry.
Storage · 01
Pumped Hydro Storage
Storing electricity through the power of water.
Pumped Storage Hydropower (PSP) pumps water from a lower to an upper reservoir and releases it through turbines when electricity is needed — mature, utility-scale and long-duration.
Viability depends on topography, geology, reservoir design, water availability, environment and transmission access.
Open-loop
- Existing hydro reservoirs
- River-connected upper or lower reservoir
- Integrated with conventional hydro
- Multipurpose dams
Closed-loop
- Two off-stream reservoirs
- Mountain-based
- Flat-terrain engineered
- Mine-pit and quarry conversions
Underground & seawater
- Underground lower reservoir
- Abandoned mine conversion
- Underground powerhouse
- Coastal seawater PSP
Configurations
- Pure and with natural inflow
- Reversible or separate pump and turbine
- Fixed and variable speed
- High-, medium- and low-head
- Single- and multi-stage
Civil
- Upper and lower reservoirs
- Concrete, earthfill and rockfill dams
- Intakes and outlets
- Headrace and tailrace tunnels
- Penstocks and pressure shafts
- Surge tanks
- Underground caverns
Electro-mechanical
- Reversible Francis pump-turbines
- Spherical and butterfly inlet valves
- Governors
- Motor-generators
- Static frequency converters
- Excitation and synchronisation
- HV switchgear
Applications
- Renewable time-shifting
- Peak management
- Frequency regulation
- Spinning reserves
- Black start
- Seasonal energy management
Lifecycle services
- Hydrological and geological studies
- Water balance and hydraulic modelling
- DPR and financial model
- Dam safety assessment
- Turbine and pump overhaul
- Uprating and modernisation
Storage · 02
Battery Storage (BESS)
Advanced electrochemical energy storage, from cell to container.
BESS store electricity through reversible electrochemical reactions, at utility, transmission, distribution, industrial, commercial, residential and off-grid levels.
BARREL works with an OEM / JV partner for batteries and covers minerals, chemicals, active materials, cells, modules, packs, BMS, PCS, containers, recycling and second life.
Lithium-ion
- LFP — utility, C&I, residential
- NMC — high energy density
- NCA — specialised
- LTO — high power, frequent cycling
- LMO — specialised and hybrid
Sodium-based
- Sodium-ion
- Sodium-sulphur (NaS)
- Sodium-nickel chloride
- Solid-state sodium
Lead-acid
- Flooded
- VRLA, AGM, gel
- Lead-carbon
- Bipolar
- Telecom, substation and UPS backup
Flow batteries
- Vanadium redox (VRFB)
- Zinc-bromine
- All-iron and iron-chromium
- Organic redox
- Hybrid flow
- Energy sized by tanks, power by stacks
Zinc & metal-air
- Zinc-air, zinc-ion, zinc-MnO₂
- Iron-air for multi-day storage
- Aluminium- and magnesium-air
- Lithium-air research
Other chemistries
- Solid-state
- Lithium-metal and lithium-sulphur
- Nickel-iron, NiCd, NiMH
- Liquid-metal
- Aluminium-, magnesium-, calcium-ion
- Organic and proton batteries
System components
- Cells, modules, racks, packs
- BMS
- Thermal management and liquid cooling
- Fire detection and suppression
- PCS and bidirectional inverters
- Transformers and switchgear
- EMS, SCADA, SoC and SoH monitoring
- Cybersecurity
Cell manufacturing
- Active materials
- Electrode coating, drying, calendering
- Cell assembly
- Electrolyte filling
- Formation and grading
- Module and pack assembly
Applications
- Solar- and wind-plus-storage
- Standalone grid storage
- Peak shaving and load shifting
- Frequency regulation
- Congestion management
- Data centres and EV charging
- Microgrids and off-grid
Recycling & services
- Second-life applications
- Dismantling and black mass
- Lithium, nickel, cobalt recovery
- Cell qualification and pack testing
- Thermal runaway testing
- Health assessment and O&M
Storage · 03
Thermal Storage
Storing heat and cold for electricity and industry.
Thermal storage captures heat or cold for later use — for power cycles, process heat, district heating and cooling.
Molten salt, sand, concrete and PCM store heat, not electricity: returning electricity needs a heat engine, so efficiency is judged on the whole electricity-to-heat-to-electricity system.
Molten salt
- Two-tank direct
- Two-tank indirect
- Single-tank thermocline
- Nitrate and chloride salts
- Salt pumps, valves, heaters
- Steam generators
- CSP and industrial heat
Sensible heat — liquid
- Hot and pressurised water
- Thermal oil
- Liquid metal
- Industrial thermal fluids
Sensible heat — solid
- Sand and gravel
- Crushed rock
- Concrete and ceramics
- Refractory brick
- Cast iron
Underground thermal
- Borehole (BTES)
- Aquifer (ATES)
- Pit (PTES)
- Cavern (CTES)
- Tank (TTES)
Latent heat (PCM)
- Paraffin and fatty acids
- Salt hydrates
- Metallic PCM
- Eutectics
- Encapsulated, panels, PCM tanks
Thermochemical
- Reversible reactions
- Adsorption and absorption
- Metal oxide redox
- Calcium looping
- Zeolites and silica gel
- Seasonal heat storage
Industrial high-temperature
- Electric thermal storage heaters
- Sand heat batteries
- Steel, cement and glass
- Chemicals and food processing
Engineering
- Thermal modelling and sizing
- Insulation engineering
- Tank structural design
- Corrosion assessment
- Heat exchanger design
- Thermal performance testing
Storage · 04
Mechanical Storage
Energy stored in pressure, motion and height.
Mechanical systems convert electricity into potential, kinetic or pressure energy and back — from seconds of flywheel response to days of compressed or liquid air.
Compressed air (CAES)
- Diabatic
- Adiabatic and advanced adiabatic
- Isothermal
- Salt and rock caverns
- Above-ground vessels
- Compression trains and expanders
Liquid air (LAES)
- Purification and compression
- Liquefaction
- Cryogenic tanks
- Evaporation and expansion
- Cold energy recovery
Flywheel
- Low- and high-speed
- Composite and steel rotors
- Magnetic bearings
- Vacuum enclosures
- Frequency and power quality
- Railway regenerative braking
Gravity
- Tower and stacked blocks
- Mine-shaft weights
- Rail-based and inclined
- Crane-based lifting
- Winches, motors and generators
Pumped heat (PTES)
- Reversible heat pump / heat engine
- Hot and cold reservoirs
- Packed-bed storage
- Grid-scale long duration
Other concepts
- Hydraulic accumulators
- Subsea compressed gas
- Underwater storage
- Advanced kinetic storage
Storage · 05
Chemical Storage
Converting electricity into storable chemical energy.
Chemical carriers can be stored, transported and turned back into electricity, heat or industrial energy — the main route to seasonal storage and industrial decarbonisation.
Hydrogen production
- Alkaline electrolysis
- PEM
- SOEC
- Anion exchange membrane
Hydrogen storage
- Compressed vessels and cylinders
- Tube trailers
- Liquid hydrogen
- Salt caverns and reservoirs
- Metal and chemical hydrides
- Porous adsorbents
Back to power
- Fuel cells
- Hydrogen gas turbines
- Hydrogen engines
- Reversible fuel cells
- Hydrogen microgrids
Ammonia
- Air separation
- Haber-Bosch synthesis
- Refrigerated storage
- Transport
- Cracking or direct use
Power-to-gas & liquids
- Catalytic and biological methanation
- Synthetic natural gas
- E-methanol
- Synthetic diesel and SAF
- Power-to-liquids
Metal-based
- Iron-air
- Aluminium and magnesium carriers
- Metal hydrides
- Regenerative metal fuels
Engineering & safety
- Process design
- HAZOP and QRA
- Pressure vessel design
- Cryogenic engineering
- Explosion protection
- Materials compatibility
- Emergency response
Storage · 06
Electrical Storage
Energy held in electric and magnetic fields.
Very fast response and high power for power quality and grid stability — short-duration specialists, not substitutes for long-duration utility storage.
Supercapacitors
- EDLC
- Pseudocapacitors
- Hybrid supercapacitors
- Lithium-ion capacitors
- Graphene-based
SMES
- Superconducting coils
- Cryogenic refrigeration
- Vacuum insulation
- Power conditioning
- Magnetic shielding
Advanced capacitors
- High-voltage and pulse power
- Film and ceramic
- Hybrid capacitor-battery
- Advanced dielectrics
Applications
- Frequency regulation
- Voltage stabilisation
- Renewable smoothing
- Railway braking
- Industrial power quality
Storage · 07
Cold Storage
Storing cooling capacity for later use.
Cold storage shifts cooling load out of peak hours for buildings, district cooling, industry and cold chains.
Ice storage
- Ice-on-coil
- Encapsulated ice
- Ice harvesting
- Ice slurry
- Static and dynamic
Chilled water
- Stratified tanks
- Pressurised systems
- District cooling storage
- Industrial chilled water
Cryogenic
- Liquid air and nitrogen
- LNG regasification cold recovery
- Industrial cryogenic integration
Applications
- Malls, airports, hospitals
- Data centres
- District cooling
- Cold storage warehouses
- Process cooling
Storage · 08
Underground Storage
Subsurface space for large-scale, long-duration storage.
Geological formations and engineered underground structures hold hydrogen, compressed air, heat, cold and water at scales the surface cannot.
Formations
- Salt caverns — hydrogen and air
- Depleted reservoirs
- Aquifers — hot and cold water
- Abandoned mines — gravity, pumped hydro, air
- Boreholes — seasonal heat
Specialist services
- Geological and geophysical surveys
- Seismic investigation
- Reservoir characterisation
- Well drilling and cavern development
- Rock mechanics
- Pressure integrity and leak monitoring
Storage · 09
Hybrid Storage
Fast response from one technology, long duration from another.
A battery answers in milliseconds while pumped hydro, thermal or hydrogen carries the hours and days — one controlled system.
Combinations
- Battery + pumped hydro
- Battery + molten salt or sand
- Battery + chilled water
- Battery + electrolyser and fuel cell
- Wind + compressed air
- Renewables + pumped thermal
Industrial integration
- Battery + heat storage
- Battery + cold storage
- Waste heat + thermal
- Captive power + battery
- Industrial microgrids
Equipment
- Hybrid EMS
- Multi-source converters
- Grid-forming inverters
- Microgrid controllers
- Integrated SCADA
- Digital twins and forecasting
Storage · 10
Emerging Technologies
The next generation of long-duration storage.
Each is tracked with its stage — research, prototype, pilot, demonstration, early commercial or established.
Watch list
- Iron-air batteries
- Liquid metal batteries
- All-iron flow
- Organic flow
- Aluminium-based storage
- Metal fuels
- Pumped thermal electricity
- Thermophotovoltaic storage
- Sulphur thermal storage
- Subsea storage
- Geomechanical storage
- Reversible fuel cells
- Advanced solid-state
- Seasonal thermal
- Advanced gravity
Technology comparison
Seconds to seasons.
Qualitative classifications, not guaranteed specifications — real performance depends on design, operation and application.
| Technology | Typical role | Duration potential | Maturity |
|---|---|---|---|
| Pumped hydro | Bulk electricity | Hours – days | Established |
| Lithium-ion BESS | Grid and distributed | Seconds – hours | Established |
| Flow batteries | Stationary | Hours – long | Commercial |
| Sodium-ion | Stationary and distributed | Configuration-dependent | Developing |
| Sodium-sulphur | Stationary | Multi-hour | Established niche |
| Molten salt | High-temperature heat | Hours – longer | Established |
| Sand / concrete | Thermal | Hours – seasonal concepts | Developing |
| PCM | Heating and cooling | Hours – days | Commercial |
| CAES | Bulk electricity | Hours – days | Established niche |
| LAES | Bulk electricity | Hours – days | Developing |
| Flywheel | High power, short | Seconds – minutes | Established |
| Gravity | Bulk mechanical | Hours – days | Emerging |
| Hydrogen | Chemical and seasonal | Days – seasonal | Developing |
| Supercapacitors | Rapid power support | Seconds – minutes | Established |
| SMES | Rapid power support | Very short | Established niche |
| Ice / chilled water | Cooling | Hours – days | Established |
| Thermochemical | Heat | Potentially long | Developing |
Applications
The right storage for the job.
- Utility-scale grid
- PSP, BESS, CAES, LAES
- Renewable integration
- BESS, PSP, hydrogen, thermal
- Long duration
- PSP, CAES, flow batteries, thermal, hydrogen
- Seasonal
- Hydrogen, underground thermal, chemical
- Frequency regulation
- BESS, flywheel, supercapacitors, PSP
- Peak shaving
- BESS, PSP, chilled water, thermal
- Industrial heat
- Molten salt, sand, concrete, PCM
- Cooling
- Ice, chilled water, cryogenic
- Data centre backup
- BESS, flywheel, thermal
- EV charging
- BESS, supercapacitors, hybrid
- Remote and off-grid
- BESS, hydrogen, pumped hydro
- District heating / cooling
- Hot water, pits, boreholes · ice, chilled water
- Hydrogen economy
- Hydrogen, ammonia, synthetic fuels
- Emergency power
- Batteries, flywheels, fuel cells
Project value chain
Seventeen stages, from resource to recycling.
- 01
Resource assessment
Demand, resource and site
- 02
Technology assessment
Battery, hydro, thermal or other
- 03
Feasibility
Technical and economic
- 04
Engineering
Conceptual, basic and detailed
- 05
Project development
Land, permits, approvals, financing
- 06
Manufacturing
Cells, machinery, equipment
- 07
Procurement
Equipment and materials
- 08
Construction
Civil, structural, infrastructure
- 09
Installation
Mechanical, electrical, controls
- 10
Integration
Grid, renewable, industrial
- 11
Testing
FAT and SAT
- 12
Commissioning
Energisation and verification
- 13
Operation
Charge, discharge, energy management
- 14
Maintenance
Preventive and predictive
- 15
Modernisation
Upgrades and augmentation
- 16
Recycling
Material recovery and reuse
- 17
Decommissioning
Dismantling and restoration
Manufacturing ecosystem
Each technology, its own supply chain.
Battery
- Mineral and chemical processing
- Cathode and anode materials
- Cylindrical, prismatic, pouch cells
- Modules, packs, racks
- BMS and PCS
- Cooling plates and HVAC
- Containers and cabinets
- Recycling
Pumped hydro
- Pump-turbines
- Motors and generators
- Penstocks
- Pressure valves
- Governors
- Transformers and switchgear
- Tunnel gates
- Heavy steel
Thermal
- Molten salt and oil tanks
- Sand and concrete storage
- Ceramic modules
- PCM and thermochemical materials
- Heat exchangers
- Electric boilers
- Insulation
- High-temperature pumps and valves
Mechanical
- Compressors and expanders
- Turbines
- Pressure vessels
- Cryogenic tanks
- Flywheel rotors
- Magnetic bearings
- Hoists and gearboxes
Hydrogen & chemical
- Electrolysers
- Fuel cell stacks
- Compressors
- Hydrogen and ammonia tanks
- Reactors
- Catalysts and membranes
- Gas detection
BARREL manufactures through OEM partners and works with an OEM / JV partner for batteries.
Raw materials, minerals & chemicals
What storage is made of
- Battery minerals
- Lithium, nickel, cobalt, manganese
- Anode materials
- Natural and synthetic graphite, silicon
- Cathode materials
- Iron phosphate, nickel, manganese, cobalt
- Sodium batteries
- Sodium compounds, aluminium, carbon
- Flow batteries
- Vanadium, bromine, zinc, iron
- Metal-air
- Iron, zinc, aluminium, magnesium
- Electrical
- Copper, aluminium, electrical steel
- Thermal storage
- Nitrate and chloride salts, sand, ceramics
- PCM
- Paraffin, fatty acids, salt hydrates
- Hydrogen systems
- Platinum, iridium, nickel, zirconium-based
- Mechanical
- Steel, cast iron, concrete, alloys
- Insulation and cryogenic
- Mineral wool, ceramic fibre, stainless steel, aluminium
Business ecosystem
One battery maker, many markets.
The same storage manufacturer may supply a solar farm, a substation, a factory, a data centre and an EV charging station — so every company and product is recorded once and linked to each application.
- ManufacturingCells, batteries, containers, PCS, tanks, compressors, turbines, thermal equipment, controls.
- Materials & miningLithium, sodium, graphite, nickel, cobalt, vanadium, zinc, salts, electrolytes.
- Trade & distributionStorage products, components, chemicals, spares and complete systems.
- Engineering & projectsFeasibility, technology selection, system design, EPC, integration, asset management.
- Investment & partnershipsStorage projects, manufacturing JVs, technology partnerships and tenders.
Shared directories
The same masters serve Generation and Storage. Live ones open on BARREL's platforms today.
- Technology directory
- Power plant directory · planned
- Project directory
- Manufacturer directory
- Product directory
- Material directory · planned
- Fuel directory · planned
- Supplier directory
- Service provider directory
- Contractor directory
- Consultant directory · planned
- Tender directory
- Investment directory
- Mining directory · planned
- Technology provider directory · planned
- Standards directory · planned
- Research & innovation directory · planned
Read the numbers right
Megawatts are not megawatt-hours.
- Power ratingMW
- How fast the system can charge or discharge.
- Energy capacityMWh
- How much it can hold. 100 MW / 400 MWh is a four-hour system.
- Discharge durationh
- Energy divided by power — seconds for flywheels, days for hydrogen.
- Round-trip efficiency%
- Energy out against energy in, over a full charge-discharge cycle.
- Cycle life & DoDcycles · %
- How many cycles at what depth of discharge before capacity fades.
- SoC & SoH%
- State of charge now; state of health against the new battery.
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