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Planning an on-site electrolyser means sizing the entire hydrogen-production system—not just the electrolyser stack—for its output, operating profile and delivery requirements. The practical answer to “how much space, water and power will it need?” is project-specific: obtain the selected supplier’s written balance-of-plant requirements, then verify them with utility studies, qualified engineers and the authority having jurisdiction.
A sound preliminary brief defines hydrogen output, pressure, purity, operating hours, storage autonomy and end use. It then accounts for rectifiers and transformers, water treatment, cooling, purification, compression, storage, vents, drainage, maintenance access and safety separations. The figures below help you create that brief and request comparable vendor proposals; they are not universal design values.
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Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →What should an on-site electrolyser plan include?
An electrolyser converts water and electricity into hydrogen and oxygen, but the stack is only one part of the installation. A construction plan normally needs space and interfaces for:
- Electrolyser modules, skids and their controls
- Incoming switchgear, transformers, rectifiers and power-quality equipment
- Feed-water storage, pretreatment, reverse osmosis, deionisation or polishing, dosing and monitoring
- Cooling equipment, pumps, heat exchangers, fans and heat-rejection systems
- Hydrogen purification, drying, metering and product-quality monitoring
- Compression, buffer vessels, storage tanks, loading or delivery equipment
- Oxygen handling or venting, hydrogen vents and safe discharge points
- Drainage, effluent tanks, spill control and wastewater pumps
- Gas detection, ventilation, fire protection, emergency-shutdown systems and control rooms
- Vehicle access, lifting routes, maintenance clearances and future expansion space
The U.S. Department of Energy’s Water Electrolyzer Installations – Summary Report and the Welsh Government’s Green Hydrogen planning guide both show why a stack-only footprint understates the site requirement.
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How do I define the design basis before requesting quotes?
Write a one-page design basis first. Every supplier should price and size against the same assumptions, otherwise apparent differences in power, water and footprint may simply reflect different system boundaries.
- Set the hydrogen duty. State the required mass or normal cubic metres per hour, product pressure, purity, delivery pressure, annual operating hours and allowable outage.
- Describe the operating profile. Say whether the plant follows variable renewable power, runs at a steady load, or switches frequently. Include minimum turndown, ramping, start-up frequency and seasonal operation.
- Define storage and delivery. Specify storage autonomy, maximum inventory, pressure, loading method, pipeline or trailer interface and whether compression is inside the electrolyser package.
- Set reliability requirements. Identify duty/standby pumps, redundant treatment trains, spare electrolyser capacity, backup controls and the consequence of a utility interruption.
- Fix the battery limits. Ask each bidder to mark what is included for electricity conversion, water treatment, cooling, purification, compression, storage, buildings, controls and civil works.
- Record site constraints. Provide available plot dimensions, ground conditions, flood risk, nearby occupied buildings, access roads, noise limits, drainage connection, incoming voltage and water-source information.
The Environment Agency’s guidance on hydrogen production by electrolysis notes that operating mode, power supply and user demand can change plant design. Put those conditions in the request for proposal rather than allowing each vendor to assume a different duty.
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How much electrical capacity does an electrolyser need?
Electrical capacity must cover the stack and every auxiliary load that can operate at the same time. The connection study should use the supplier’s rated and operating load, start-up demand, power factor, harmonic performance and ramp limits—not an electrolyser nameplate alone.
Loads to include
- Electrolyser stacks and their DC power supplies
- Transformers, rectifiers, inverters and switchgear
- Hydrogen purification, drying and compression
- Water pumps, treatment skids, deionisation and instrument air
- Cooling pumps, fans, chillers or heat-rejection equipment
- Ventilation, gas detection, controls, lighting and trace heating
- Storage, loading and site services
Request the following from the OEM:
- Continuous, peak and standby electrical demand at the defined production rate
- AC voltage, phase, frequency, short-circuit level and acceptable voltage variation
- Power factor, harmonics, flicker and any power-quality correction equipment
- Transformer and rectifier ratings, inrush current and energisation sequence
- Start-up load, ramp rate, minimum stable load and turndown limits
- Separate load schedules for the stack, auxiliaries, compression and storage
- Control voltage and uninterruptible-power requirements
For a project example, the IESO/York University Hydrogen Innovation Fund final report cites about 2.5 MWe for approximately 500 Nm³/h of hydrogen, with a described 480 VAC connection for cell stacks and auxiliaries and 24 VDC controls. Those are report-specific vendor-data examples, not default connection ratings.
What should the utility connection study cover?
Ask the electricity distributor about available capacity at the proposed connection voltage, fault level, protection coordination, metering, export restrictions, reinforcement work and lead time. Confirm whether the project may import rapidly changing loads or export electricity from on-site generation. Establish who supplies the transformer, switchgear, protection relays, harmonic filters and communications gateway.
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Model at least these operating cases:
| Case | Why it matters |
|---|---|
| Normal full production | Sets continuous feeder, transformer and cooling duty. |
| Start-up and restart | Captures inrush, simultaneous motor starts and rectifier energisation. |
| Minimum load or turndown | Checks control stability, power quality and minimum-flow requirements. |
| Compression and loading coincident with production | Prevents under-sizing when downstream equipment operates together. |
| Utility outage and recovery | Defines safe shutdown, ride-through, black-start and backup-control needs. |
How much water does an electrolyser consume?
The process minimum is 9 kg of pure water for each kilogram of hydrogen. The Environment Agency states: “Water is consumed in the process to make hydrogen in a minimum ratio of 9kg of pure water per 1kg of hydrogen gas produced.” That is a stoichiometric minimum, not the gross intake your site must draw from a mains, well or other source.
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Use a source-to-drain water balance
- Characterise the source. Record whether water comes from a municipal supply, well, reservoir or another source. Obtain dependable flow, pressure, seasonal variation, temperature and laboratory impurity data.
- Confirm the feed specification. Obtain the electrolyser supplier’s limits for conductivity or resistivity, silica, sodium, chloride, total organic carbon, hardness, dissolved gases and other contaminants.
- Define treatment stages. Identify filtration, softening, reverse osmosis, electrodeionisation, mixed-bed polishing, ultraviolet treatment, storage and online monitoring. Ask which stages are supplied by the OEM.
- Calculate recovery and rejects. Quantify reverse-osmosis concentrate, regeneration chemicals, backwash, purge and off-specification discharge. Include maximum as well as average flow.
- Provide treated-water storage. Size tanks for treatment interruptions, maintenance and short-term fluctuations in production. Include level control, overflow, bunding and freeze protection where needed.
- Design the drain route. Confirm discharge chemistry, temperature, permitted flow, sampling points and whether a trade-effluent consent or treatment system is required.
The IESO/York report gives a project-context example of approximately 9 L of treated water and approximately 19 L of potable input per kilogram of hydrogen. Treat those values as examples, not guarantees for another technology, water source or recovery rate.
What do published water-quality figures mean?
The same IESO/York report includes example limits of maximum conductivity 0.056 µS/cm at 25 °C, minimum resistivity 18.2 MΩ-cm, maximum total organic carbon 10 µg/L, sodium 1 µg/L, silica 3 µg/L and chlorine 1 µg/L. Confirm the selected electrolyser’s current specification before designing treatment around these numbers.
A conductivity meter measures conductivity over its specified range and accuracy; it does not certify silica, sodium, organic carbon, chlorine or microbiological quality. Use the supplier’s required laboratory tests and online instruments, with calibration and alarm setpoints defined in the control philosophy.
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How should I estimate the site footprint?
Start with an equipment arrangement, not a single area allowance. Obtain dimensioned general-arrangement drawings, operating weights, maintenance envelopes, lifting requirements, noise data, heat rejection and environmental limits for every package.
Allocate space for the whole system
- Electrolyser skids and module replacement routes
- Rectifiers, transformers, switchgear and control panels
- Water-treatment equipment, chemical storage and treated-water tanks
- Cooling towers, dry coolers, chillers, pumps and heat exchangers
- Gas purification, dryers, compressors and buffer vessels
- Hydrogen storage, loading bays, tube trailers or pipeline metering
- Oxygen vents or use equipment, hydrogen vents and dispersion zones
- Firewater, detection, emergency-shutdown and access-control equipment
- Effluent tanks, drains, sampling points and spill containment
- Roads, crane pads, laydown areas and emergency-vehicle access
Include clearances for opening doors, removing membranes or stacks, replacing filters, lifting motors and connecting temporary equipment. Show the route for the heaviest component from the delivery gate to its final position. A compact arrangement that cannot be serviced is not an adequate design.
Why storage can dominate land use
The DOE summary describes one large-scale example with about 10,000 kg of above-ground hydrogen storage at 30 bar and a total system footprint of roughly one acre, with most of that area occupied by storage tanks. It is an example, not a universal footprint benchmark. Storage pressure, vessel type, required autonomy, setbacks, delivery pattern and local code can produce a very different result.
Decide storage inventory and delivery assumptions before fixing the site boundary. Reducing storage may shrink the plot but increase compressor duty, delivery frequency or exposure to production interruptions. Increasing storage may improve resilience while creating larger separation, access and fire-protection requirements.
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Safety distances, building classifications and ventilation requirements depend on the applicable code, hydrogen inventory and pressure, equipment arrangement, site conditions and the authority having jurisdiction. Published distances are screening inputs only; a project-specific hazardous-area assessment, fire strategy and risk assessment are still required.
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Resolve these questions during concept design:
- Can the electrolyser, compression and storage be outdoors, or is an enclosure unavoidable?
- Where will hydrogen and oxygen vents discharge, and how will dispersion be demonstrated?
- What ventilation rate, airflow direction and low-point or high-point extraction are required?
- Where are gas detectors located, and what alarms, trips and emergency-shutdown actions follow?
- Which electrical equipment lies in classified or hazardous areas?
- How are occupied buildings, property boundaries, public roads and ignition sources separated?
- How are pressure vessels, relief devices, piping and isolation valves inspected and maintained?
- What firewater, extinguishing media, emergency access and incident-control provisions are required?
- How are oxygen releases, wastewater, chemicals and contaminated runoff managed?
The OECD’s section on leakage in water-electrolysis installations discusses outdoor siting where feasible, ventilation, detectors, shutdowns and storage minimisation. The DOE report also explains that codes and setbacks depend on the project and its components. Use the current requirements adopted in your jurisdiction rather than copying a distance from another country.
For an early risk-information package, the Aviva Risk Solutions electrolyser checklist is useful for organising information on water, ventilation, detection, electrical systems and layout. It does not replace statutory design review or insurer-specific requirements.
How do I compare electrolyser proposals on a like-for-like basis?
Issue the same design basis and require each bidder to identify guaranteed values, calculated estimates, exclusions and site assumptions. Compare the complete system boundary rather than the stack efficiency or headline footprint alone.
| Comparison axis | Questions to put in the proposal schedule |
|---|---|
| Hydrogen duty | What output, purity, pressure and availability are guaranteed, and at what temperature and operating profile? |
| Electrical interface | What are continuous, peak and start-up loads, AC voltage, phase, power factor, harmonics, transformer and rectifier requirements? |
| Water | What feed quality is required? What treatment, storage, recovery, reject and gross fresh-water flow are included? |
| Cooling | What heat load, cooling medium, supply temperature, flow, seasonal derating and make-up water are required? |
| Purification and compression | Are dryers, oxygen removal, product analysis, compressors, buffer vessels and controls inside the battery limit? |
| Footprint and access | What are equipment dimensions, weights, maintenance clearances, lifting points, noise levels and environmental limits? |
| Safety | What detection, ventilation, relief, shutdown, venting and separation assumptions underpin the arrangement? |
| Reliability | What redundancy, turndown, ramping, start-up time, planned maintenance and spare-parts strategy are provided? |
| Interfaces and exclusions | Who supplies buildings, foundations, cables, transformers, water connections, drains, fire systems, storage and permits? |
Require a marked-up plot plan and single-line diagram with every proposal. Ask vendors to state whether figures are per module, per train or for the complete plant, and whether they represent normal, maximum or design-case operation.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What should a construction team put in the preliminary brief?
Before land, foundations or utility applications are fixed, assemble a brief containing:
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- Hydrogen production rate, purity, pressure and delivery schedule
- Operating hours, turndown, ramping, start-up and outage assumptions
- Storage inventory, pressure, autonomy and loading arrangement
- Electrical load schedule, connection voltage, protection and power-quality requirements
- Water-source analysis, treatment train, gross intake, recovery, storage and effluent route
- Cooling duty, heat-rejection method, seasonal performance and make-up requirements
- Dimensioned equipment list with weights, clearances, access and lifting routes
- Preliminary plot plan showing vents, hazardous areas, occupied buildings, roads and drainage
- Applicable planning, environmental, pressure, electrical, fire and hazardous-area approvals
- Responsibilities matrix showing OEM, EPC, utility, civil contractor and owner interfaces
- Expansion allowance and spare capacity, if future hydrogen demand is credible
Have the selected supplier review the brief before procurement. Then obtain the electricity utility’s connection response, water and effluent approvals, fire-authority input, planning determination and sign-off from appropriately qualified electrical, mechanical, process and fire engineers.
What are the key figures to carry into an early feasibility study?
| Figure | Use and limitation |
|---|---|
| 9 kg pure water per kg hydrogen | Process minimum stated by the Environment Agency; not gross site intake. |
| Approximately 9 L treated water and 19 L potable water per kg hydrogen | IESO/York project example; treatment design and recovery may differ. |
| Approximately 2.5 MWe for approximately 500 Nm³/h | IESO/York cited vendor-data example; not a universal power ratio. |
| About 10,000 kg storage at 30 bar and roughly one acre total footprint | DOE large-scale example in which storage occupied most of the area; not a general site rule. |
| Example high-purity-water limits | 0.056 µS/cm conductivity maximum, 18.2 MΩ-cm resistivity minimum, 10 µg/L TOC, 1 µg/L sodium, 3 µg/L silica and 1 µg/L chlorine maximum in the IESO/York report; verify the selected OEM specification. |
Use these numbers to test whether a concept is plausible, not to release a final design. No single universal footprint, electrical connection or gross water-intake value is established by the cited sources.
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What are the most common planning mistakes?
- Using stack power as site power: compression, cooling, treatment and purification can materially change the connection requirement.
- Budgeting only stoichiometric water: treatment reject, purge, cleaning and discharge can make source demand substantially higher.
- Drawing equipment without maintenance routes: replacement lifts and isolation access must be shown before foundations are set.
- Leaving storage decisions until late: inventory and pressure can drive plot size, setbacks and fire strategy.
- Assuming one water-quality instrument proves compliance: conductivity alone cannot verify every contaminant limit.
- Comparing proposals with different battery limits: a smaller quoted footprint or lower load may simply exclude auxiliaries.
- Copying another project’s separation distance: local codes, inventory, pressure and risk assessment govern the final value.
- Ignoring seasonal conditions: source temperature, water availability, ambient heat and utility constraints can affect capacity.
Correct these issues by maintaining a live interface register, utility load schedule, water balance and plot plan through design development.
Frequently Asked Questions
Can an electrolyser use ordinary mains water without treatment?
Usually not without verification. Electrolyser suppliers specify feed-water quality, and municipal water may contain salts, silica, chlorine or organics that require filtration, reverse osmosis and polishing. Obtain a laboratory analysis of the actual source and have the OEM approve the treatment train.
How early should I contact the electricity utility?
Contact the utility during concept design, before selecting the final plot or promising a production date. Connection voltage, reinforcement, protection studies, metering and lead times can change the project schedule and capital cost, especially for multi-megawatt loads.
Does hydrogen storage always need to be beside the electrolyser?
Not necessarily, but moving storage changes compression, piping, access, separation and control requirements. A remote or shared storage arrangement may reduce the electrolyser plot while adding transfer equipment, operating interfaces and permitting questions.
What information does a contractor need before pricing foundations and buildings?
Provide certified equipment weights and dimensions, dynamic loads, anchor plans, maintenance and lifting clearances, drainage requirements, hazardous-area boundaries, ventilation data, cable routes and environmental limits. Preliminary vendor brochures are not enough for final structural or civil design.
