Chemical Energy Storage | Hydrogen, Ammonia, Methanol, LOHC & Hydrogen-to-Power EPC

Chemical Energy Storage

Electricity turned into molecules you can keep for months.

Chemical storage converts electricity into a fuel — hydrogen, ammonia, methanol or synthetic gas — that can be kept in tanks or underground caverns, shipped across oceans and turned back into power, heat or industrial feedstock. It is the main route to storing energy for weeks and seasons, not just hours. BARREL develops, engineers and builds the full chain: electrolyser, compression, storage, conversion to carriers and back-to-power, through OEM partners and its own engineering teams.

Sector hub · 24 sections

Section 01

Chemical Storage — Overview

Chemical storage keeps energy in chemical bonds. Electricity splits water into hydrogen and oxygen; the hydrogen can be stored as it is, or combined with nitrogen (to make ammonia) or with carbon dioxide (to make methanol, methane or liquid e-fuels) into carriers that are easier to store and move.

Its round-trip efficiency is lower than a battery's, but the stored energy costs very little to keep, does not leak away over the months and can also be sold outside the power sector — as fertiliser, shipping fuel or refinery feedstock. That is why it is the leading option for seasonal storage and for moving renewable energy between countries.

This page is the storage view: how the energy goes in, how it is held and how it comes back. The production, offtake and export side of green hydrogen and its derivatives is covered in depth on the Green Hydrogen hub at /sectors/green-h2.

1.1Energy carriers compared

Energy carriers compared
Carrier	How it is stored	Energy (LHV)	Main uses
Hydrogen (compressed)	30–700 bar steel or composite vessels, tube trailers	33.3 kWh/kg	Power, mobility, industry
Hydrogen (liquid)	−253 °C vacuum-insulated tanks	33.3 kWh/kg	Long-distance transport, aerospace
Hydrogen (salt cavern)	Underground cavern, roughly 60–180 bar	33.3 kWh/kg	Seasonal and strategic storage
Ammonia (NH₃)	−33 °C refrigerated or ~10 bar pressurised tanks	5.2 kWh/kg	Fertiliser, shipping fuel, H₂ carrier, co-firing
Methanol (CH₃OH)	Ordinary atmospheric liquid tanks	5.5 kWh/kg	Chemicals, shipping fuel, blending
Synthetic methane (CH₄)	Gas grid, cavern or LNG tanks	13.9 kWh/kg	Gas grid, power, heat
LOHC (e.g. dibenzyltoluene)	Diesel-like liquid at ambient conditions	≈2 kWh per kg of carrier	Transport and storage of H₂

1.2Why chemical storage

Very long duration

Holds energy for weeks or months with almost no standing loss — batteries cannot do this economically.

Cheap to scale energy

Adding a bigger tank or cavern is far cheaper per MWh than adding more battery cells.

Moves across oceans

Ammonia and methanol ship in existing tankers, so renewable energy can be exported.

Many buyers

The same molecule can be sold to power, fertiliser, steel, refining or shipping.

1.3Strengths and limits in plain words

Strengths

Seasonal storage at low cost per stored MWh
Power and energy sized separately
Uses existing gas, chemical and shipping know-how
Decarbonises sectors electricity cannot reach directly

Limits

Power-to-power efficiency of roughly 30–40 %
High capital cost of electrolysers today
Needs careful safety design and licences
Supply chains in India are still being built up

Energy values are standard lower-heating-value (LHV) figures. Efficiencies and pressures are typical ranges from public literature and depend on technology, size and operating pattern.

Section 02

How Chemical Storage Works

Every chemical store has three stages: charge (electricity makes a fuel), hold (the fuel is kept) and discharge (the fuel makes electricity, heat or a product). Unlike a battery, the three stages are separate machines, so each can be sized on its own.

The electrolyser sets the charging power (MW), the tank or cavern sets the stored energy (MWh or tonnes) and the fuel cell or turbine sets the discharge power. A plant can charge slowly for months and discharge quickly for days.

2.1The power-to-power chain

Surplus solar / wind
Electrolyser (H₂O → H₂ + ½O₂)
Compression or conversion
Tank, cavern or carrier
Fuel cell / turbine / engine
Electricity back to grid

2.2Key reactions

Key reactions
Step	Reaction	Typical conditions
Water electrolysis	2H₂O → 2H₂ + O₂	60–90 °C (AWE/PEM), 700–850 °C (SOEC)
Ammonia synthesis (Haber-Bosch)	N₂ + 3H₂ → 2NH₃	150–300 bar, 400–500 °C, iron catalyst
Methanol synthesis	CO₂ + 3H₂ → CH₃OH + H₂O	50–100 bar, 200–300 °C, copper-zinc catalyst
Methanation (Sabatier)	CO₂ + 4H₂ → CH₄ + 2H₂O	300–450 °C, nickel catalyst
Ammonia cracking	2NH₃ → N₂ + 3H₂	Roughly 500–900 °C with catalyst
Fuel cell	2H₂ + O₂ → 2H₂O + electricity + heat	60–80 °C (PEM) to 600–800 °C (SOFC)

2.3Three things sized separately

MW in

Charge power

Electrolyser MW — chosen from the surplus renewable profile and how many hours a day it can run.

MWh held

Stored energy

Tonnes of hydrogen or carrier — chosen from how many days or weeks of supply are needed.

MW out

Discharge power

Fuel cell, turbine or engine MW — chosen from the load or grid commitment during deficit periods.

2.4Where the energy goes

Electrolysis: about 30–40 % lost as heat (can be recovered)
Compression to 200–500 bar: roughly 2–4 % of the hydrogen energy
Liquefaction: roughly 25–35 % of the hydrogen energy today
Carrier synthesis (ammonia, methanol): a further 10–20 %
Cracking or dehydrogenation: heat equal to roughly 15–30 % of the energy
Conversion to power: 40–60 % efficient, rest as heat

Section 03

Charging the Store — Electrolysers

The first machine of every chemical store is an electrolyser powered by renewable or surplus electricity. Four families exist; alkaline and PEM are the ones bought at scale today.

For storage duty the key questions are how well the electrolyser follows variable solar and wind, how fast it starts, how low it can turn down and how quickly its stack wears under cycling.

3.1Electrolyser technologies

Electrolyser technologies
Type	Maturity	System energy	Load following	Watch-out
Alkaline (AWE)	Commercial, largest plants	≈50–55 kWh/kg	Turn-down ≈15–20 %, slower response	Larger footprint, caustic electrolyte
PEM	Commercial	≈50–57 kWh/kg	Fast (seconds), wide range	Platinum-group metals, iridium supply
Solid oxide (SOEC)	Early commercial	≈40–45 kWh/kg + heat	Best at steady load	700–850 °C, stack degradation
Anion exchange (AEM)	Emerging	≈50–55 kWh/kg	Fast, small units	Membrane life still being proven

3.2Electricity per kilogram

Electrolyser output

H₂ (kg) = E (kWh) ÷ SEC

10 MW × 1 h = 10,000 kWh ÷ 52 kWh/kg ≈ 190 kg H₂

The theoretical minimum is about 39.4 kWh/kg (hydrogen's higher heating value). Real plants use about 50–55 kWh/kg at system level including rectifiers, pumps, cooling and purification; the figure rises slowly as stacks age.

Symbol	Meaning
E	Electricity supplied (kWh)
SEC	Specific energy consumption (kWh/kg)

3.3What sits around the stack

Electrical

Transformer and rectifier (AC to DC)
Harmonic filters
Auxiliary supply and UPS
Stack DC busbars

Process

Water treatment (RO, demineralisation)
Gas-liquid separators
Deoxo and dryer for purity
Lye or water circulation pumps

Utilities

Cooling (dry coolers or towers)
Nitrogen for purging
Instrument air
Oxygen venting or recovery

3.4Resources per kilogram of hydrogen

Electricity: about 50–55 kWh
Pure water: 9 kg by chemistry; about 10–15 litres of raw water after treatment losses
Cooling water: more if wet cooling towers are used
By-product oxygen: about 8 kg — can be sold to hospitals or industry

Energy and water figures are indicative ranges from IEA and IRENA publications and vary with technology, stack age, cooling method and water quality. Detailed production economics are on the Green Hydrogen hub (/sectors/green-h2).

Section 04

Storing Hydrogen above Ground — Compressed and Liquid

Hydrogen is the lightest gas: a cubic metre at normal conditions weighs only about 90 grams. To store useful amounts it must be squeezed to high pressure or cooled to a liquid at −253 °C.

For stores up to a few tens of tonnes, compressed-gas vessels are the usual answer. Liquid hydrogen is denser but costs a lot of energy to make and slowly boils off, so it suits transport and large hubs rather than long-term static storage.

4.1How much hydrogen fits in a cubic metre

How much hydrogen fits in a cubic metre
Form	Approx. density	Energy (LHV) per m³	Typical use
Gas at 1 bar, 15 °C	≈0.085 kg/m³	≈0.003 MWh	Pipelines (before compression)
Compressed, 30–50 bar	≈2.5–4 kg/m³	≈0.08–0.13 MWh	Buffer tanks after electrolyser
Compressed, 200 bar	≈15 kg/m³	≈0.5 MWh	Tube trailers, bulk stores
Compressed, 350 bar	≈24 kg/m³	≈0.8 MWh	Buses, trucks
Compressed, 700 bar	≈40 kg/m³	≈1.3 MWh	Cars, compact stores
Liquid, −253 °C	≈71 kg/m³	≈2.4 MWh	Large tanks, shipping, aerospace

4.2Pressure-vessel types

Type I and II

Type I: all-steel, cheapest, heaviest
Type II: steel liner with hoop-wound fibre
Used for stationary bulk banks
Watch steel grade for hydrogen embrittlement

Type III and IV

Type III: aluminium liner, full carbon-fibre wrap
Type IV: polymer liner, full carbon-fibre wrap
Light; used for vehicles and trailers
Higher cost per kg stored

4.3Liquid hydrogen in practice

Liquefaction energy

Today's plants use roughly 10–13 kWh per kg — about a third of the hydrogen's energy. Larger, newer plants aim for 6–8 kWh/kg.

Boil-off

Heat leaking in boils off roughly 0.1–1 % per day depending on tank size; large spheres lose the least.

Spherical tanks

Large vacuum-insulated spheres, such as those at space launch sites, hold several thousand cubic metres.

4.4Vessel volume for a given mass

Water volume needed

V (m³) = m (kg) ÷ (ρ(Pmax) − ρ(Pmin))

2,000 kg usable between 200 and 30 bar: 2,000 ÷ (15 − 2.5) ≈ 160 m³

Not all the gas can be taken out: the vessel must stay above the minimum pressure the compressor or fuel cell needs. Densities come from real-gas tables (hydrogen is about 10–15 % less dense than the ideal-gas law predicts at 200 bar).

Symbol	Meaning
m	Usable hydrogen (kg)
ρ	Hydrogen density at the stated pressure (kg/m³)

4.5Reference installations

Laboratory water electrolysis cell — Reference: water electrolysis, the first step of every chemical store

Densities are approximate real-gas values at about 15 °C; liquefaction and boil-off figures are typical published ranges and depend strongly on plant and tank size.

Section 05

Storing Hydrogen Underground

For seasonal storage of hundreds or thousands of tonnes, steel vessels become too expensive. The answer is geology: caverns leached out of thick salt layers have stored hydrogen safely for decades.

Salt caverns in Teesside, UK (operating since the 1970s) and on the US Gulf Coast (Clemens Dome since 1983, later Moss Bluff and Spindletop) store hydrogen for the chemical industry. Other geological options are being studied. The full geology, cavern design and a cavern calculator are on BARREL's Underground Storage page.

5.1Underground options for hydrogen

Underground options for hydrogen
Option	Status for hydrogen	Size	Notes
Salt cavern	Proven (UK, USA)	Hundreds to several thousand tonnes per cavern	Salt is gas-tight and does not react; fast cycling possible
Lined rock cavern	Demonstration	Tens to hundreds of tonnes	Steel-lined cavern in hard rock; useful where no salt exists
Depleted gas field	Research and pilots	Very large	Risk of mixing, microbial reactions and gas loss
Aquifer	Research	Very large	Least understood; cushion gas needs high

5.2A cavern storage cycle

Electrolyser output
Compressor to cavern pressure
Injection through wellhead
Storage (months)
Withdrawal
Drying and purification
Pressure reduction to user

5.3Words you will hear

Working gas — the hydrogen you can take out and use
Cushion gas — gas left in to keep the cavern stable (often 25–35 % of the total)
Pressure window — the safe minimum and maximum set by depth and rock strength
Leaching — dissolving salt with water to form the cavern; brine must be disposed of

India's known thick salt deposits are limited (studies have looked at Rajasthan), so most Indian projects will rely on above-ground vessels, carriers such as ammonia, or lined rock caverns. For cavern sizing use the estimator on the Underground Storage page (/energy-storage/underground-storage).

Section 06

Green Ammonia — Hydrogen in a Liquid That Ships

Ammonia (NH₃) is made from hydrogen and nitrogen taken from the air. It turns into a liquid at −33 °C or at about 8–10 bar at room temperature — far easier than liquid hydrogen. The world already makes and ships about 180–190 million tonnes a year, mostly for fertiliser, so tanks, ships and safety rules exist.

As a store it holds about 1.5 times more hydrogen per cubic metre than liquid hydrogen. It can be burned directly in engines, turbines and boilers, or cracked back into hydrogen.

6.1Green ammonia chain

Renewable power
Electrolyser (H₂)
Air separation (N₂)
Hydrogen buffer
Haber-Bosch loop
Refrigerated tank (−33 °C)
Ship, fertiliser, fuel or cracker

6.2Ammonia key figures

Ammonia key figures
Property	Typical value
Hydrogen content	17.6 % by weight
Energy (LHV)	≈5.2 kWh/kg (18.6 MJ/kg)
Liquid density at −33 °C	≈680 kg/m³
Hydrogen per m³ of liquid	≈120 kg (vs ≈71 kg for liquid H₂)
Hydrogen per tonne of NH₃	≈0.18 t
Electricity per tonne (green)	≈9.5–11 MWh incl. electrolysis, air separation, synthesis
Large refrigerated tanks	10,000–50,000 t each

6.3Ways ammonia returns energy

Co-firing

Blended into coal boilers; a 20 % co-firing trial ran on a 1 GW Japanese coal unit in 2024.

Gas turbines

Small and medium turbines burning ammonia are being developed; NOx control is the main task.

Engines

Marine two-stroke and power-plant engines for ammonia are entering service.

Cracking

Heated with a catalyst to release hydrogen for fuel cells — costs about 15–25 % of the energy.

6.4What needs care

Toxic: leaks must be detected early; emergency planning off-site
Corrodes copper and zinc alloys — material selection matters
Burns slowly and makes NOx — combustion design and SCR
Haber-Bosch prefers steady load — hydrogen buffer needed with solar and wind

Figures are indicative from public literature (IEA Ammonia Technology Roadmap, IRENA). Electricity per tonne depends on electrolyser efficiency and plant design.

Section 07

Methanol, Synthetic Methane and Liquid e-Fuels

Combining green hydrogen with captured or biogenic CO₂ gives carbon-based fuels that behave exactly like today's fuels. Methanol is a liquid at room temperature and is stored in ordinary tanks; synthetic methane can go straight into the gas grid; e-kerosene and e-diesel suit aviation and heavy transport.

The catch is the CO₂: it must come from a sustainable source (biogas, biomass, unavoidable industrial emissions or, later, direct air capture) for the fuel to count as low-carbon.

7.1e-Methanol chain

Green hydrogen
CO₂ capture and clean-up
Compression to 50–100 bar
Synthesis reactor
Distillation
Atmospheric tank
Fuel, chemicals or back-to-power

7.2Carbon-based e-fuels compared

Carbon-based e-fuels compared
Fuel	Inputs per tonne (approx.)	Energy (LHV)	Storage
e-Methanol	≈0.19 t H₂ + ≈1.4 t CO₂	≈5.5 kWh/kg	Ambient liquid tanks, like petrol
e-Methane (SNG)	≈0.5 t H₂ + ≈2.75 t CO₂	≈13.9 kWh/kg	Gas grid, caverns, LNG
e-Kerosene / e-diesel (Fischer-Tropsch)	≈0.4–0.5 t H₂ + ≈3–3.5 t CO₂	≈12 kWh/kg	Ordinary fuel tanks

7.3Where the CO₂ comes from

Biogenic

Compressed biogas upgrading
Ethanol fermentation
Biomass boilers

Best for low-carbon rating

Industrial

Cement kilns
Steel and refinery off-gas
Fertiliser plants

Rules on counting vary by market

Direct air capture

Fans and sorbents
Very energy-hungry today
Long-term option

Early stage, high cost

7.4Why methanol is easy to store

Liquid from −97 °C to 65 °C — no pressure or refrigeration
Uses standard tank farms, pipelines and road tankers
Can be reformed back to hydrogen at about 250–300 °C
Care: toxic, flash point about 11 °C and a near-invisible flame

Input ratios follow from the chemistry and are rounded; real plants need slightly more hydrogen and CO₂ to cover purge and side reactions.

Section 08

LOHC, Metal Hydrides and Metal Fuels

Some carriers hold hydrogen without turning it into a new fuel. Liquid organic hydrogen carriers (LOHC) are oils that soak up hydrogen in one reactor and give it back in another; metal hydrides absorb hydrogen like a sponge; and metals such as iron can be burned for heat and then regenerated with hydrogen.

These are less mature than ammonia and methanol, but they avoid high pressure, very low temperature or toxicity, which makes them interesting for safe storage near people.

8.1Carrier options compared

Carrier options compared
Carrier	H₂ by weight	Release conditions	Maturity
Dibenzyltoluene (LOHC)	≈6.2 %	250–320 °C, catalyst, heat ≈ 25–35 % of the H₂ energy	Demonstration
Toluene / methylcyclohexane (LOHC)	≈6.1 %	≈300–350 °C, catalyst	Shipped in a 2020 Brunei–Japan demonstration
Room-temperature metal hydrides (e.g. LaNi₅, TiFe)	≈1–2 %	Near ambient, low pressure	Commercial in niches (submarines, backup)
Magnesium hydride	≈7.6 %	≈300 °C	Research and pilots
Iron powder (metal fuel)	Not a H₂ store — burned for heat	Iron oxide regenerated with H₂	Industrial pilots in Europe

8.2LOHC loop

Green H₂
Hydrogenation reactor (releases heat)
Loaded oil stored in ordinary tanks
Truck / ship / pipeline
Dehydrogenation (needs heat)
Pure H₂ to user
Unloaded oil returns

8.3Where they fit

LOHC

Long-distance transport and storage with existing fuel logistics; best where waste heat is available to release the hydrogen.

Metal hydrides

Compact, low-pressure stores for backup power, buildings, forklifts and sites where high pressure is not allowed.

Metal fuels

High-temperature heat for industry (boilers, kilns) with a recyclable fuel.

Weight percentages are theoretical carrier capacities; practical system values are lower once tanks, reactors and heat exchangers are counted.

Section 09

Turning Stored Fuel Back into Power

Stored chemical energy returns to the grid through fuel cells, hydrogen-capable gas turbines, reciprocating engines or co-firing in existing plants. The choice depends on size, running hours and whether the waste heat can be used.

Gas turbines and engines are cheapest per MW for rare, short peaks. Fuel cells are more efficient, quiet and modular, and suit sites that run often or need clean, local power.

9.1Conversion routes

Conversion routes
Route	Size range	Electric efficiency (LHV)	Fuel	Notes
PEM fuel cell	kW – tens of MW	≈45–60 %	Pure H₂	Fast start, needs high purity
Solid oxide fuel cell (SOFC)	kW – MW	≈50–65 %	H₂, methane, ammonia (some designs)	High temperature, useful heat
Phosphoric acid fuel cell	100 kW – MW	≈40–45 %	H₂	Long track record in CHP
Gas turbine, open cycle	5 – 400 MW	≈30–40 %	H₂ blends; 100 % in development	Fast peaking
Gas turbine, combined cycle	50 – 600+ MW	≈55–60 %	H₂ blends	Best for long runs
Reciprocating engine	1 – 20 MW per unit	≈40–45 %	H₂, ammonia blends	Modular captive and peaking

9.2Power-to-power efficiency

Round trip

η = η(electrolyser) × η(storage) × η(conversion)

0.64 × 0.95 × 0.55 ≈ 33 %

An electrolyser at 52 kWh/kg turns 64 % of the electricity into hydrogen energy (33.3 ÷ 52). Compression and storage lose a few per cent; a fuel cell or combined-cycle turbine returns about half. Using the waste heat raises the useful total to 60–80 %.

Symbol	Meaning
η(electrolyser)	33.3 ÷ SEC, on an LHV basis
η(storage)	Compression, boil-off, cushion and other losses
η(conversion)	Fuel cell, turbine or engine efficiency

9.3Hydrogen in gas turbines

What changes

Faster, hotter flame — risk of flashback
Higher NOx without new burners
Fuel skid, valves and sensors for hydrogen
Larger fuel volume per MW

Where it stands

Many turbines accept 30–50 % H₂ by volume
Several OEMs offer 100 % H₂ on smaller frames
Hydrogen-ready new plants are being ordered
Retrofits of existing units are possible

Using the heat as well

Electrolyser heat for buildings
Fuel cell CHP
Turbine exhaust steam
Oxygen sale
Absorption cooling

Efficiencies are typical published ranges at rated load; part-load efficiency of turbines is lower. Hydrogen capability depends on the exact turbine model and must be confirmed with the OEM.

Section 10

Plant Types and Configurations

Chemical storage is not one product. The same building blocks are put together in different ways depending on whether the aim is firm power, seasonal balancing, industrial supply or export.

10.1Common configurations

Seasonal

Power-to-power (P2P)

Electrolyser + compressed or cavern store + fuel cell or turbine. Firms up renewables over days to seasons.

Critical sites

Hydrogen backup

Stored hydrogen cylinders or hydrides + fuel cells for telecom towers, data centres and hospitals in place of diesel.

Off-grid

Island / microgrid

Solar + battery for daily cycling + hydrogen for multi-day cloudy or monsoon periods.

Export

Power-to-ammonia hub

Large renewables + electrolysers + ammonia plant and tank farm, near a port for export or fertiliser.

Gas grid

Power-to-gas

Hydrogen blended into the gas grid, or methanated to synthetic methane and stored in the grid.

Feedstock

Industrial buffer

Electrolyser + storage feeding a refinery, steel (DRI) or chemical plant that needs steady hydrogen while power varies.

10.2Choosing a storage form

Choosing a storage form
Need	Usual choice	Why
Hours to a day, small site	Compressed H₂ vessels	Simple, quick to build
Days to weeks, large site	Many vessel banks or lined rock cavern	Scales without geology
Seasonal, hundreds of tonnes	Salt cavern (if available) or ammonia	Lowest cost per tonne
Export over oceans	Ammonia or methanol	Existing ships and terminals
Near homes and offices	Metal hydrides or LOHC	Low pressure, non-toxic

10.3Pairing with batteries

Batteries handle daily cycles and fast grid services
Hydrogen handles long gaps and seasons
Together they cut total cost of firm round-the-clock power
See the Hybrid Storage page for battery-plus-long-duration splits

Section 11

Technical Architecture, Civil and Mechanical Works

A chemical storage plant looks like a small chemical works: process units in a fenced plot, separated by safety distances, with utilities, a control building and an electrical yard.

11.1Main process units

Production

Electrolyser halls or containers
Rectifier and transformer bays
Water treatment plant
Gas purification and drying

Storage & conversion

Compressors (piston, diaphragm, ionic)
Vessel banks or cavern wellhead
Ammonia / methanol synthesis loop
Refrigerated or pressurised tanks

Return & export

Fuel cells or turbine island
Ammonia cracker or reformer
Loading bays, jetty or pipeline
Flare and vent stacks

11.2Civil and structural scope

Civil and structural scope
Item	What it involves
Site grading and drainage	Flood level, storm water, oil and chemical separation
Foundations	Compressor blocks (vibration), tank ring walls, pipe racks
Bunds and dykes	Containment around ammonia and methanol tanks
Buildings	Electrolyser hall, control room, MCC, lab, stores
Blast and fire walls	Between compressors, vessels and occupied buildings
Roads and access	Fire tender routes, heavy-lift access, loading bays

11.3Mechanical points special to hydrogen

Hydrogen-compatible steels (low hardness, austenitic stainless)
Welded joints preferred over threaded fittings
Pipe design to ASME B31.12
Compressors with low leakage seals and purge systems
Vents routed high and away from ignition sources
Cryogenic piping and vacuum jackets for liquid hydrogen

Layout is driven by safety distances from a quantitative risk assessment and the applicable PESO and fire rules; footprint per MW varies widely with storage form.

Section 12

Power Conversion, Controls and Grid Integration

Electrolysers run on direct current and are among the largest single electrical loads in a grid. Fuel cells produce direct current; turbines produce AC through a generator. The electrical design links these to the renewable plant and the grid.

An energy management system (EMS) decides, minute by minute, when to make hydrogen, when to store it and when to turn it back into power.

12.1Electrical chain

Charging side

Grid or renewable connection (33–400 kV)
Step-down transformers
Thyristor or IGBT rectifiers
Harmonic and reactive-power compensation

Discharge side

Fuel cell DC/DC and inverters
Turbine generator and step-up transformer
Synchronising and protection
Black-start capability (optional)

Auxiliaries

Compressor drives (MV motors, VFDs)
Cooling and pumping loads
UPS for safety systems
Emergency lighting and ventilation

12.2EMS decision loop

Read solar, wind, grid price and load
Forecast next hours and days
Set electrolyser set-point
Manage storage pressure / level
Dispatch fuel cell or turbine
Report to grid operator

12.3Control and safety layers

Control and safety layers
Layer	Role
Plant DCS / PLC	Runs the process units, interlocks and sequences
Safety instrumented system (SIS)	Independent trips on gas leak, overpressure, fire
EMS	Optimises energy, storage and dispatch
SCADA / RTU	Links to state or regional load despatch centre
Gas and fire detection	H₂, NH₃ and flame detectors with alarms

12.4Grid integration in India

Connectivity under CERC (Connectivity and General Network Access) Regulations for ISTS projects
CEA Technical Standards for Connectivity to the Grid
Green Energy Open Access Rules, 2022 for sourcing renewable power
ISTS charge waiver for green hydrogen and ammonia plants commissioned by the notified date
Scheduling and forecasting under state and regional load despatch centres
Power-quality limits for large rectifier loads

Section 13

Sizing and Design Calculations

First-cut sizing needs only a few numbers: how much power you can spare, for how long, how long you need to store, and how efficiently you turn the fuel back into power. The formulas below show the method; the live estimator does the arithmetic for you.

13.1Live estimator

Enter the electrolyser size (MW), how many hours a day it runs, its specific energy (kWh per kg), how many days of production you want to store and the back-to-power efficiency (%). It returns hydrogen made per day (kg), the stored mass (tonnes), the stored energy on an LHV basis (MWh at 33.3 kWh/kg), the electricity you get back (MWh) and an estimate of the overall power-to-power efficiency.

Estimate

Hydrogen per day: 1,923 kg
Hydrogen to store: 13.5 t
Stored energy (LHV): 448 MWh
Electricity back: 224 MWh
Power-to-power efficiency: ≈ 32 %

Before compression, storage and auxiliary losses (typically a further 5–15 %). Energy uses hydrogen's lower heating value, 33.3 kWh/kg. Preliminary screening only; BARREL confirms any figure with a site study.

13.2Daily hydrogen production

Production

m(day) = P × t ÷ SEC

100 MW × 10 h × 1,000 ÷ 52 kWh/kg ≈ 19,200 kg/day

Running hours come from the solar or wind profile; a solar-only electrolyser often runs 7–9 equivalent hours a day, a solar-wind hybrid 12–18.

Symbol	Meaning
P	Electrolyser power (MW)
t	Equivalent full-load hours per day
SEC	Specific energy (kWh/kg)

13.3Stored mass and energy

Store

m(store) = m(day) × days ; E = m × 33.3 kWh/kg

19.2 t/day × 30 days ≈ 576 t ≈ 19,200 MWh (LHV)

This is the hydrogen to be held as working gas. Add the cushion or minimum-pressure inventory on top to size the vessels or cavern.

13.4Electricity back and discharge size

Return

E(back) = E × η(conv) ; P(out) = E(back) ÷ hours of discharge

19,200 MWh × 0.50 = 9,600 MWh; over 20 days × 24 h → 20 MW

The discharge plant can be much smaller than the electrolyser if the store fills over months and empties over weeks.

13.5Ammonia from hydrogen

Carrier

NH₃ (t) = H₂ (t) ÷ 0.178 ; tank V = NH₃ ÷ 0.68 t/m³

576 t H₂ ÷ 0.178 ≈ 3,240 t NH₃ ≈ 4,760 m³ of tank

The same hydrogen held as ammonia fits in a modest refrigerated tank instead of thousands of cubic metres of high-pressure vessels.

13.6Design checks after first sizing

Design checks after first sizing
Check	Why it matters
Hourly simulation (8,760 h)	Real renewable profile, not averages
Electrolyser turn-down and ramping	Can it follow cloud and wind gusts?
Stack degradation and replacement	SEC rises with age; stacks last ≈60,000–90,000 h
Compressor duty	Peak flow and number of starts
Storage pressure window	Usable vs total inventory
Water balance	Source, treatment and reject disposal

The estimator and worked examples give first-cut figures only. Compression, cushion gas, boil-off and auxiliary loads (typically a further 5–15 %) are not fully included; a feasibility study uses hourly simulation.

Section 14

Engineering Deliverables Register

A chemical storage project is engineered like a process plant. These are the main documents produced from study to handover; the client receives each one for review.

14.1Main deliverables

Main deliverables
Document	Stage	Purpose
Basis of design	Concept	Agreed inputs: power, duration, purity, site data
Energy and mass balance	Concept / FEED	Flows of power, water, hydrogen, oxygen, heat
Hourly techno-economic model	Feasibility	Sizing, LCOH / LCOS, sensitivities
Process flow diagrams (PFD)	FEED	Main equipment and streams
P&IDs	FEED / detailed	Every pipe, valve, instrument and interlock
Plot plan and layout	FEED	Equipment positions and safety distances
Hazardous-area classification	FEED	Zones for electrical equipment selection
HAZID, HAZOP, SIL reports	FEED / detailed	Hazards, safeguards and safety-function ratings
Quantitative risk assessment	FEED	Off-site risk and licence application
Single-line diagrams	FEED / detailed	Electrical chain from grid to stacks
Equipment datasheets and specifications	Detailed	Basis for purchase
Civil and structural drawings	Detailed	Foundations, bunds, buildings
Commissioning procedures	Construction	Step-by-step start-up and tests
O&M manuals and as-built records	Handover	Operating the plant for its life

14.2Specialist studies often added

Dispersion and fire modelling
Noise study
Water availability study
Geotechnical survey
Grid impact study
Life-cycle carbon assessment
Environmental impact assessment

The exact list depends on the contract model and the authorities involved; licensing authorities such as PESO set their own drawing and document requirements.

Section 16

Turnkey EPC — From Study to Operation

BARREL can deliver chemical storage as one integrated plant — power supply, electrolysers, compression, storage, synthesis and back-to-power — or as separate packages under an owner's engineer.

16.1Project phases

1Pre-feasibility and site screening
2Feasibility, techno-economics and offtake study
3Technology selection and FEED
4Approvals and licences (PESO, pollution board, factory, fire, CEA)
5Detailed engineering
6Procurement of long-lead items (electrolysers, compressors, transformers, tanks)
7Civil, mechanical and electrical construction
8Pre-commissioning, commissioning and performance tests
9Handover, operator training and O&M

16.2Typical work packages

Typical work packages
Package	Contents
Electrical	Grid connection, transformers, rectifiers, MV/LV, earthing
Electrolyser island	Stacks, balance of plant, purification
Compression and storage	Compressors, vessels or cavern surface works
Synthesis (if any)	Ammonia or methanol loop, air separation, CO₂ capture
Back-to-power	Fuel cells, turbine or engine island
Utilities	Water treatment, cooling, nitrogen, instrument air, fire water
Civil and buildings	Foundations, bunds, roads, control building
Controls and safety	DCS, SIS, EMS, gas and fire detection, SCADA

16.3Delivery models

Full turnkey (LSTK)

One contract, one price, one point of responsibility for performance.

EPCM

BARREL engineers and manages; the owner buys equipment directly.

Split EPC

Separate supply and installation contracts, often for tax and duty reasons.

Build-own-operate

Developer finances and runs the plant and sells hydrogen or power.

Electrolysers and large compressors can have lead times of 12–24 months; early ordering is often the critical path. Lead times are indicative and vary with market conditions.

Section 17

Equipment, Supply Chain and Manufacturing in India

India is building a domestic supply chain for electrolysers and hydrogen equipment, helped by production-linked incentives under the National Green Hydrogen Mission. Some items are made locally today; others are still imported.

17.1Where key items come from

Where key items come from
Equipment	Indian manufacture	Notes
Alkaline electrolysers	Growing (incentive-backed)	Several Indian factories announced or under way
PEM electrolysers	Early	Membranes and catalysts largely imported
Transformers and rectifiers	Strong	Mature Indian industry
Pressure vessels and tanks	Strong	Built to ASME / IS 2825 codes
Hydrogen compressors	Partial	Many high-pressure units imported
Fuel cells	Early	Stacks mainly imported; system integration local
Ammonia and methanol plants	Strong process know-how	Licensed technology from global licensors
Instruments, valves, detectors	Mixed	Hydrogen-rated items often imported

17.2Support for manufacturing

SIGHT programme incentives for electrolyser manufacturing
SIGHT incentives for green hydrogen production
Approved List of Models and Manufacturers (ALMM) approach under discussion for electrolysers
Customs duty structure that favours local assembly

17.3Supply-chain risks to manage

Materials

Iridium and platinum for PEM
Nickel for alkaline electrodes
Carbon fibre for Type IV vessels

Delivery

Long lead times for large compressors
Factory capacity ramp-up
Warranty and spare-part support in India

The supply picture is changing quickly; status shown is a general indication, not a vendor assessment. BARREL sources equipment through OEM partners selected per project.

Section 18

Testing, Commissioning, Operations and Digital Monitoring

Hydrogen plants are commissioned carefully: every system is cleaned, leak-tested and purged with nitrogen before any hydrogen is introduced.

Running a chemical store then means managing a process plant: safety permits, gas detection, rotating machinery, water quality and electrolyser stacks that wear over time. Good O&M keeps efficiency high and stack life long.

18.1Commissioning sequence

1Factory acceptance tests (FAT) of stacks, rectifiers, compressors, control panels
2Mechanical completion and punch-list closure
3Pressure (hydrostatic or pneumatic) and leak tests
4Cleaning, drying and nitrogen purging
5Electrical tests: transformers, protection, earthing
6Loop checks and SIS function tests
7First hydrogen: low-pressure start-up
8Stepwise ramp-up to rated load
9Performance and reliability tests

18.2Performance tests

Performance tests
Test	What is proved
Specific energy consumption	kWh per kg at rated and part load
Hydrogen purity	Meets ISO 14687 grade or process need
Ramp rate and turn-down	Follows the renewable profile
Storage tightness	Pressure holds over the test period
Back-to-power output	Rated MW and efficiency
Reliability run	Continuous operation for the agreed period

18.3Main O&M tasks

Daily

Gas-detector and alarm checks
Water quality (conductivity)
Pressures and temperatures
Permit-to-work control

Periodic

Compressor valves and seals
Catalyst and dryer checks
Vessel inspections
Calibration of instruments

Long-term

Stack refurbishment or replacement
Fuel cell stack replacement
Pressure-vessel re-certification
Turbine hot-gas-path overhauls

18.4Digital and AI tools

Remote monitoring

Live dashboards of production, storage level, efficiency and alarms.

Digital twin

A model of the plant used to test dispatch plans and predict performance.

Predictive maintenance

Machine learning on vibration and stack voltage to plan work before failure.

Dispatch optimisation

Forecasts and prices decide when to make, store or sell hydrogen and power.

18.5Key performance indicators

Key performance indicators
KPI	What it shows
kWh per kg (SEC)	Electrolyser efficiency and stack health
Availability (%)	Hours the plant could run
Stack voltage trend	Degradation rate
Storage losses	Leaks, boil-off, venting
Power-to-power efficiency	Overall plant performance
Safety events	Near-misses and incidents

Test durations and acceptance values are set in the contract and the OEM's guarantees. Stack life of roughly 60,000–90,000 operating hours is typical in OEM literature; actual life depends on cycling, water quality and operating temperature.

Section 19

Safety, Risk, Environment and Circularity

Hydrogen, ammonia and methanol are handled safely in industry every day. Each has its own hazard, and the plant is designed around it from the first drawing.

The environmental case matters as much: chemical storage is only as clean as the electricity and carbon that go into it, so it is checked with a life-cycle assessment, not assumed.

19.1Hazards by carrier

Hazards by carrier
Carrier	Main hazard	Key properties	Main safeguards
Hydrogen	Fire and explosion	Flammable 4–75 % in air; very low ignition energy; near-invisible flame; rises fast	Ventilation, leak and flame detection, zoning, vents high
Ammonia	Toxicity	Pungent; harmful at low concentration; flammable only 15–28 %	Leak detection, water curtains, shelters, emergency plan
Methanol	Toxicity and fire	Flash point ≈11 °C; poisonous if swallowed; pale flame	Bunding, foam systems, closed handling
Liquid hydrogen	Cold burns, pressure	−253 °C; can condense air on pipes	Vacuum jackets, relief valves, cold-resistant materials

19.2Safety studies and systems

Studies

HAZID and HAZOP
SIL determination and verification
Quantitative risk assessment (QRA)
Hazardous-area classification
Fire and explosion modelling
Emergency response plan

Systems

Safety instrumented system (SIS)
Gas detection (H₂, NH₃) and flame detection
Emergency shutdown and blowdown
Fire water, deluge and foam
Blast walls and safe separation distances
Materials tested for hydrogen embrittlement

19.3Project risks besides safety

Electrolyser performance below guarantee
Faster stack degradation under cycling
Delays in licences and approvals
Offtaker or tariff risk

Flammability limits and properties are standard published values (ISO/TR 15916 and safety data sheets). Site-specific risk is established only by the project's own QRA.

19.4Impacts to manage

Carbon

Grid electricity can make hydrogen dirtier than fossil hydrogen
Green standard: ≤2 kg CO₂e/kg H₂ in India
CO₂ source rules for e-fuels

Water

Freshwater use in dry areas
Brine from treatment or cavern leaching
Cooling water discharge

Air

Hydrogen leaks have an indirect warming effect
NOx from ammonia and hydrogen combustion
Ammonia slip control

19.5Circular practices

Recover and recycle platinum, iridium and nickel from stacks
Refurbish electrolyser stacks instead of replacing whole units
Reuse waste heat and sell oxygen
Treated wastewater or desalinated water instead of fresh water
Steel vessels and tanks are recyclable at end of life
Biogenic CO₂ for e-methanol closes the carbon loop

Life-cycle results depend on the power mix, equipment manufacturing and transport; ISO 14040/14044 and ISO 19870 give the accounting methods.

Section 20

Standards, Codes and Approvals

Chemical storage draws on hydrogen, gas, chemical and electrical codes. In India, licensing for gas and pressure-vessel storage sits mainly with PESO, alongside state pollution, factory and fire authorities.

20.1International standards

International standards
Standard	Covers
ISO 22734	Hydrogen generators using water electrolysis
ISO/TR 15916	Basic considerations for hydrogen safety
ISO 14687	Hydrogen fuel quality
ISO 19880 series	Hydrogen fuelling stations
ISO 16111	Transportable metal hydride storage
ISO 11114-4	Steel compatibility with hydrogen (embrittlement tests)
ISO 19870	Greenhouse-gas accounting for hydrogen production
IEC 62282 series	Fuel cell technologies
IEC 60079 series	Equipment for explosive atmospheres
IEC 61508 / 61511	Functional safety and safety instrumented systems
ASME B31.12	Hydrogen piping and pipelines
ASME BPVC Section VIII	Pressure vessels
NFPA 2 / NFPA 55	Hydrogen technologies code; compressed and cryogenic gases

20.2India — rules and approvals

India — rules and approvals
Rule / authority	Applies to
PESO — Gas Cylinders Rules, 2016	Hydrogen cylinders and cascades
PESO — Static and Mobile Pressure Vessels (Unfired) Rules, 2016	Bulk hydrogen and ammonia vessels
MSIHC Rules, 1989 (Environment Protection Act)	Hazardous chemicals such as ammonia and methanol above threshold quantities
Factories Act and state factory rules	Process plant licensing and worker safety
State Pollution Control Board	Consent to establish and to operate
CEA safety and connectivity regulations	Electrical installations and grid connection
IS 2825	Indian code for unfired pressure vessels
MNRE Green Hydrogen Standard (2023)	Definition of green hydrogen: ≤2 kg CO₂e per kg H₂

Edition years and the exact list change; the project's code list is fixed in the basis of design and checked against the current versions from ISO, IEC, BIS and PESO at that time.

Section 21

Commercial Models, Costs, Revenue and Investment

Chemical storage is capital-heavy and its economics hinge on cheap electricity, high running hours and a reliable buyer. Its advantage is cheap storage of energy: once the electrolyser and conversion plant are paid for, adding days of storage costs little.

21.1Indicative cost ranges

Indicative cost ranges
Item	Indicative range	Notes
Electrolyser system, installed	≈US$1,000–2,500 per kW	Lower for Chinese alkaline; higher for small PEM
Compressed-gas storage	≈US$500–1,500 per kg of H₂ capacity	Depends on pressure and vessel type
Salt cavern storage	Tens of US$ per kg of working gas	Where geology exists; excludes cushion gas
Ammonia tank storage	Low per kWh stored	Synthesis plant is the main cost
Fuel cell plant	≈US$1,500–3,000 per kW	Falling with scale
Hydrogen-capable gas turbine	≈US$700–1,200 per kW	Close to natural gas plant cost
Green hydrogen in India (LCOH)	≈US$4–5 per kg today	Mission aims to reduce this substantially

21.2Levelised cost of hydrogen

LCOH

LCOH = (CAPEX × CRF + fixed O&M) ÷ annual kg + SEC × power price

52 kWh/kg × ₹3/kWh ≈ ₹156/kg from electricity alone

Electricity is usually 60–70 % of the cost of green hydrogen, so cheap power and high running hours matter most.

Symbol	Meaning
CRF	Capital recovery factor (from interest rate and life)
SEC	Specific energy (kWh/kg)

21.3Where the money comes from

Firm power tariffs

Round-the-clock and FDRE (firm and dispatchable renewable energy) contracts reward long-duration storage.

Hydrogen and derivative sales

Supply to refineries, fertiliser, steel and shipping under long-term offtake.

Capacity and backup

Peaking capacity, backup for critical sites, diesel replacement.

Grid services

Flexible electrolyser demand and fast fuel-cell response.

By-products

Oxygen and heat sales.

Incentives

SIGHT incentives, ISTS waiver, carbon credits under the Indian Carbon Market.

21.4Investment risks and mitigations

Investment risks and mitigations
Risk	Mitigation
Technology performance	OEM guarantees, proven references, performance bonds
Offtake / demand	Long-term take-or-pay contracts, government tenders
Power cost	Long-term renewable PPAs, captive solar-wind
Policy change	Incentives locked at award; diversified buyers
Construction delays	Early long-lead orders, experienced EPC

All costs are indicative ranges from public sources (IEA, IRENA, BloombergNEF summaries) as of 2025–26 and move quickly. Project budgets require a site-specific estimate.

Section 22

India and Global Markets and Policy

India aims to be a major producer and exporter of green hydrogen and its derivatives. Long-duration and firm-power tenders are also creating a home market for storing renewable energy.

22.1India's policy framework

India's policy framework
Measure	What it does
National Green Hydrogen Mission (Jan 2023)	Target of 5 million tonnes a year of green hydrogen by 2030; outlay of ₹19,744 crore
SIGHT programme	Incentives for electrolyser manufacturing and green hydrogen / ammonia production
Green Hydrogen Standard (2023)	Defines green hydrogen at ≤2 kg CO₂e per kg H₂
ISTS charge waiver	Waiver of inter-state transmission charges for eligible green hydrogen plants
Green Energy Open Access Rules, 2022	Easier access to renewable power for large users
SECI tenders	Green hydrogen and green ammonia procurement, FDRE and RTC power tenders
Energy storage VGF scheme	Viability gap funding for battery storage; supports firm renewable supply

22.2Global picture

Europe

RFNBO rules for renewable fuels
Hydrogen Bank auctions
Hydrogen import corridors

East Asia

Japan contract-for-difference support (2024 act)
Korea clean hydrogen power auctions
Ammonia co-firing programmes

Americas & Middle East

US hydrogen hubs and tax credits
Large export projects in the Gulf
Salt-cavern storage in the US Gulf Coast

22.3What this means for storage

Export demand drives ammonia and methanol tank and terminal capacity
FDRE and RTC tenders reward plants that can store energy for days
Industrial clusters need hydrogen buffers between plants
Seasonal hydrogen storage becomes useful as renewable share rises

Policy details change; check the current MNRE, Ministry of Power and SECI notifications before relying on any figure. Production targets and markets are covered further on /sectors/green-h2.

Section 23

Frequently Asked Questions and References

Short answers to the questions owners, investors and engineers ask most about storing energy as hydrogen and other chemicals.

23.1Questions and answers

What is chemical energy storage?

Turning electricity into a fuel such as hydrogen, ammonia or methanol, keeping it, and later turning it back into electricity, heat or a product.

How is this page different from the Green Hydrogen hub?

This page is about storing and returning energy. The Green Hydrogen hub at /sectors/green-h2 covers production, offtake, industry use and export in depth.

How efficient is it?

Electricity to hydrogen and back to electricity is typically about 30–40 %. With the waste heat used, the useful total can be 60–80 %.

Why use it if batteries are more efficient?

Batteries are best for hours. For weeks or seasons, the cost of extra battery capacity is too high, while extra hydrogen or ammonia storage is cheap.

How long can hydrogen be stored?

Months or longer in vessels or caverns with very small losses. Liquid hydrogen slowly boils off, so it is used for shorter periods.

How much electricity does it take to make 1 kg of hydrogen?

About 50–55 kWh with today's commercial electrolysers, including auxiliaries.

How much energy is in 1 kg of hydrogen?

33.3 kWh on a lower-heating-value basis, about three times that of 1 kg of petrol, but it takes up much more space.

Is hydrogen dangerous?

It is flammable over a wide range and ignites easily, but it is light and disperses quickly. Industry handles it safely with ventilation, detection and proper codes.

Why convert hydrogen into ammonia?

Ammonia is a liquid at −33 °C or modest pressure, holds more hydrogen per cubic metre than liquid hydrogen and uses existing ships and tanks.

Can ammonia be used directly for power?

Yes — co-fired in coal or gas units, burned in adapted engines and turbines, or used in some solid oxide fuel cells.

Is methanol a good energy store?

Yes for long-term storage and shipping: it is a liquid at room temperature and uses ordinary tanks. It needs a sustainable CO₂ source.

Does India have salt caverns for hydrogen?

Thick salt deposits are limited; studies have looked at Rajasthan. Most Indian projects will use vessels, lined rock caverns or carriers.

How much water does it need?

About 9 kg of pure water per kg of hydrogen by chemistry, and roughly 10–15 litres of raw water after treatment, plus cooling.

Which licences are needed in India?

Typically PESO licences for gas and pressure-vessel storage, State Pollution Control Board consents, factory and fire approvals, and CEA rules for electrical works.

What does green hydrogen cost in India?

Indicatively about US$4–5 per kg today, mainly driven by electricity cost; the National Green Hydrogen Mission aims to bring it down.

Can existing gas turbines burn hydrogen?

Many can burn blends of roughly 30–50 % hydrogen by volume; higher shares need new burners. Check with the OEM for each model.

How long do electrolyser stacks last?

Typically around 60,000–90,000 operating hours before refurbishment, depending on technology and how the plant is run.

What does BARREL do in chemical storage?

BARREL can carry out feasibility, engineering, safety studies, equipment supply through OEM partners, turnkey EPC, O&M and project finance support.

23.2References

Answers give typical figures from public literature and are not project-specific advice.