A hydrogen prototype becomes useful when its behaviour can be measured, explained and repeated. Producing gas or electrical power is one milestone. Demonstrating performance across a defined operating envelope requires a rig that controls the conditions around the stack and records what actually happened.
Good hydrogen test rig design starts with the questions the programme must answer. For engineering managers, university groups and start-ups working towards UKRI or Innovate UK milestones, those questions should shape the equipment specification, instrumentation and acceptance tests.
Hy-7 Limited is a hydrogen and CCUS engineering consultancy based in Surrey / Godalming, UK, offering remote and on-site support in the UK, Poland, the USA and worldwide. It was founded by Dr Marek Malinowski, whose hands-on experience in hydrogen and electrochemical systems dates to 2008. His background spans a PhD in Electrical Engineering (electrochemistry) and practical work on fuel cell and electrolyser systems.
What a hydrogen test rig must prove
A rig should establish performance, repeatability and operating limits. For an electrolyser, this includes hydrogen production, electrical consumption, gas quality and response to changing demand. For a fuel cell, it includes electrical output, reactant consumption, heat rejection and transient behaviour.
Define the measurement boundary. Stack efficiency and system efficiency answer different questions: pumps, cooling, rectification and gas treatment contribute to system consumption.
The rig must also demonstrate controlled responses to foreseeable faults. A successful test produces traceable evidence, including operating conditions, calibration status, uncertainty and any interventions.
Scope performance targets and the operating envelope
Translate the research objective into an agreed test matrix before selecting hardware. Specify current, voltage, temperature, pressure, flow, gas quality, test duration and expected rates of change. Define start-up, standby and shutdown conditions alongside steady operation.
Separate normal operating limits from protective trip settings and equipment design limits. These serve different purposes and require engineering justification.
Check available utilities early: electrical capacity, cooling, water, ventilation and discharge arrangements can constrain the programme. Agree acceptance criteria and measurement uncertainty with the team responsible for interpreting results. This makes the evidence usable when a project moves between researchers, partners or funding milestones.
Electrolyser balance of plant: the essential subsystems
The electrolyser balance of plant maintains the conditions that allow the stack to operate and be assessed. Its specification should follow the stack requirements, test objectives and site constraints.
Water treatment and feed
Specify feedwater quality against the stack supplier’s requirements, including relevant contaminants beyond conductivity. Select treatment, storage and wetted materials accordingly. Provide reliable circulation or feed control, suitable level protection and access for sampling. Consider contamination introduced by pipework, tanks and maintenance activities.
Power supply and rectifier
Match the DC supply to the complete voltage and current envelope, including start-up and part-load operation. Assess ripple, control response, isolation, earthing and fault behaviour. Measure electrical power at the agreed boundary; nominal supply ratings cannot establish the energy consumed during a test.
Gas-liquid separation
Size separators for gas flow, liquid circulation, pressure and transient conditions. Manage liquid levels and prevent carry-over into downstream equipment. Consider foaming, entrainment and changing gas density. Separator behaviour can influence pressure stability and the reliability of gas flow measurements.
Gas drying and purification
Define the required outlet specification before choosing treatment. Drying removes moisture; other purification stages address different contaminants. Include pressure loss, regeneration requirements, sampling and analyser suitability. Gas quality requirements should follow the intended experiment or downstream equipment, rather than an assumed universal hydrogen specification.
Thermal management
Develop a heat balance across the operating envelope. Account for stack heat, circulation equipment and changing coolant conditions. Control temperature at representative locations and examine gradients, warm-up and cooling failure. Cooling capacity alone does not demonstrate that temperature remains stable during a load change.
Pressure control
Define absolute pressures and permissible differential pressure across the stack. Coordinate control valves, regulators, separators and downstream restrictions. Assess blocked outlets, regulator failure and shutdown transients. Pressure relief provides protection against overpressure; routine pressure regulation requires its own control strategy.
Venting
Engineer hydrogen and oxygen discharge routes for normal operation, purging and foreseeable faults. Assess discharge location, backpressure, ignition sources, air intakes and possible accumulation. Avoid arrangements that allow the streams to mix. Vent routing must be considered alongside the building and ventilation design.
Sensors and instrumentation
Select instruments for range, accuracy, response time, wetted materials and service conditions. Measure where the result has physical meaning. Record whether gas flow is wet or dry and state reference conditions for normalised volumes. Provide calibration access and quantify uncertainty in calculated performance.
PEM, AEM and alkaline: different BoP requirements
Stack chemistry changes fluid handling and material selection. PEM systems typically require high-purity water. Conventional alkaline systems circulate alkaline electrolyte, bringing chemical compatibility, concentration management and electrolyte carry-over into the design. The underlying distinction between PEM, liquid alkaline and AEM technologies is described by the US Department of Energy.
AEM requirements depend on the specific stack: establish whether it uses water or an alkaline feed, and confirm contamination limits, including sensitivity to carbon dioxide where relevant.
Do not transfer a BoP design between technologies on rated power alone. Obtain the stack’s requirements for circulation, temperature, pressure differential, gas crossover and minimum load. Similar hydrogen output does not imply identical operating constraints.
Controls and data acquisition
Develop the operating sequence before writing code. Define permissives, start-up checks, normal control, alarm handling, protective trips and recovery after a fault.
A PLC programmed using TwinCAT can coordinate equipment and acquire data. The appropriate architecture depends on response times, interfaces and the required safety functions. Assess whether protective functions need independence from routine control; a software alarm alone does not establish adequate protection.
Synchronise timestamps and record commands, measured values, alarms and operator actions. Choose sampling rates that capture the dynamics being investigated. Preserve raw data alongside calculated results so that analysis can be checked later.
Safety: HAZOP, DSEAR/ATEX and operating procedures
Start hazard assessment while the process design can still change. Use a HAZOP appropriate to the rig’s complexity to examine deviations such as loss of flow, excess pressure, cooling failure and unintended gas mixing. Assign actions and verify their closure before commissioning.
For a workplace in Great Britain, assess DSEAR risks and determine hazardous area classification where required. Zoning and equipment selection should follow a competent assessment of releases and ventilation. ATEX equipment considerations form part of this work; installing certified components does not establish the safety of the complete installation. HSE guidance explains these relationships.
Position gas detection through assessment of release locations, dispersion, enclosure geometry and ventilation. Define and test the response to detection and ventilation failure.
Prepare SOPs covering operation, purging, maintenance, emergencies and restart. Address health risks from substances such as alkaline electrolyte through COSHH assessment, separately from fire and explosion risks, as explained in HSE’s DSEAR guidance.
Scaling from the laboratory to tens or hundreds of kW
Scaling an electrolyser test rig requires fresh mass, energy and pressure-drop calculations. Larger flows change separator behaviour, valve selection, pipe sizing and instrument performance. Greater thermal mass changes warm-up and control response, while higher electrical demand affects site infrastructure.
Review gas inventory, vent capacity, maintenance access and the consequences of utility failures. Validate critical subsystems before integrating the complete rig, then commission progressively against documented criteria.
Hy-7’s founder has worked on fuel cell and electrolyser systems from 1 kW to 200 kWnet, including 5 kW and 50 kW alkaline electrolyser prototypes at the Polish Academy of Sciences (INTiBS), fuel cell test rigs at AFC Energy, and PLC control of 1 Nm³/h PEM electrolysis stacks. That experience informs a practical focus on interfaces between stack, utilities and controls.
Common mistakes that weaken results
Recurring design mistakes include:
- Buying equipment before defining the test: available hardware then dictates which questions can be answered.
- Oversizing measurement ranges: low-load results become difficult to distinguish from instrument uncertainty.
- Ignoring auxiliary consumption: reported efficiency lacks a clear system boundary.
- Treating steady operation as sufficient: start-up, trips and shutdown remain unproven.
- Leaving documentation until handover: configuration changes and operating decisions become difficult to reconstruct.
Review the test matrix, process diagrams, instrument list and control philosophy together. Their interfaces often reveal gaps before fabrication.
Discuss your project with Hy-7 Limited
Contact Hy-7 Limited to discuss your hydrogen test rig design, electrolyser balance of plant or fuel cell testing project. Bring your stack requirements, research objectives and site constraints to establish a practical engineering scope.
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