Frequently Asked Questions About Renewable Hydrogen

Electrolysis is the electrochemical process that splits water (H₂O) into hydrogen (H₂) and oxygen (O₂) using direct electric current. If this electricity comes from renewable sources, the resulting hydrogen is referred to as renewable or green hydrogen.

• Overall equation: 2H₂O -> 2H₂ + O₂
• Theoretical minimum consumption: 39.4 kWh/kg H₂ (higher heating value).
• Actual industrial consumption: Between 50 and 70 kWh/kg H₂ due to ohmic and activation losses.
• Scalability: From a few kW to hundreds of MW, facilitating integration with wind and photovoltaic plants.

The three technologies differ significantly in terms of electrolyte, operating temperature and operational flexibility; alkaline electrolysis stands out for its cost and maturity, PEM for its dynamic response, and SOEC for its high efficiency.

• Alkaline (AEL): Uses a liquid electrolyte (KOH), operates at 60-90°C, offers high durability (>80,000 h) and low stack costs, but has a slow dynamic response.
• PEM (Polymer Electrolyte Membrane): Uses a solid membrane, operates at 50-80°C, offers high power density and excellent dynamic response, but requires expensive catalysts (iridium/platinum).
• SOEC (Solid Oxide): Operates at high temperatures (600-900°C), offers optimal energy consumption (<40 kWh/kg H₂), but has a lower level of commercial maturity (TRL 6-7).

The stack is the electrochemical core of the electrolyser, consisting of a series of individual cells stacked together, where water dissociation takes place. It is the most critical technological component and determines the project's life cycle.

• Voltage per cell: 1.8 to 2.1 V.
• Service life (modern alkaline): Between 60,000 and 100,000 operating hours (6-11 years at continuous full load).
• Efficiency degradation: 1-3 µV/(A·cm²·h).
• Financial impact: Its replacement (refurbishment) represents the largest maintenance (M&R) cost and directly affects OPEX when calculating LCOH.

A commercial electrolysis system currently consumes between 50 and 70 kWh for every kilogram of hydrogen produced, including the requirements of the stack and the parasitic consumption of its auxiliary systems (Balance of Plant).

• Thermodynamic limit: 39.4 kWh/kg H₂ (based on HHV).
• Current PEM systems: Around 52-55 kWh/kg H₂ under nominal operating conditions.
• European target (Clean Hydrogen Partnership): To reduce system-level consumption to below 45 kWh/kg H₂ by 2030 through improvements to the BoP and current density.

Hydrogen is mainly stored as compressed gas or cryogenic liquid, although solid alternatives such as metal hydrides and liquid organic hydrogen carriers (LOHCs) are also available. Its industrial design requires strict compliance with safety regulations.

• Compressed gas: At pressures of 200 to 700 bar in steel or composite cylinders (the most mature option).
• Cryogenic liquid: At -253°C using advanced thermal insulation systems.
• Large-scale stationary storage: Underground salt caverns (capacities ranging from GWh to TWh).
• Legal framework: Regulated in Spain by the APQ Regulations and ATEX Directives. ARIEMA provides specialised consultancy services for the legal authorisation of these facilities.

A fuel cell is an electrochemical device that continuously converts the chemical energy of hydrogen directly into electricity and water. Unlike a battery, it does not store energy but requires an external fuel supply.

• Electrical efficiency (PEMFC): 50-60% (this can exceed 80% in cogeneration applications by making use of waste heat).
• Advantages over batteries: Higher energy density per unit of mass, rapid refuelling in minutes and independence from the degradation cycles of electrochemical cells.
• Current limitations: Current capital costs and the need for an extensive hydrogen supply infrastructure.

The Balance of Plant (BoP) comprises all the peripheral auxiliary systems essential for the operation of the stack, including water purification, thermal management, power rectification and safety instrumentation.

• Economic impact: It accounts for between 40% and 60% of the total CAPEX of a commercial electrolysis system.
• Technical impact: It determines overall system efficiency due to its parasitic electrical consumption (pumps, cooling).
• R&D focus: The simplification and engineering of the BoP carried out by ARIEMA significantly reduces capital costs while optimising plant performance.

The colour code classifies hydrogen according to its carbon footprint and production method: grey hydrogen uses unabated fossil fuels; blue hydrogen includes CO₂ capture; pink hydrogen uses nuclear energy; and green hydrogen uses 100% renewable electricity.

• Grey hydrogen: Natural gas reforming (SMR). Emits 10-12 kg CO₂/kg H₂. Subject to regulatory penalties.
• Blue hydrogen: Gas reforming with carbon capture, utilisation and storage (CCUS). Emits 1-3 kg CO₂/kg H₂.
• Pink hydrogen: Electrolysis using nuclear energy. It has a low carbon footprint but is not classified as renewable in the EU.
• Green hydrogen: The only type that can be certified as an RFNBO under Delegated Regulation (EU) 2023/1184 for access to mandatory quotas and State aid.

RFNBOs are Renewable Fuels of Non-Biological Origin, the European legal category under which green hydrogen can be certified. Compliance with RFNBO requirements is mandatory to access regulated quotas and public funding mechanisms.

• Industrial quota (RED III): Requires 42% of the hydrogen consumed in industry to come from RFNBOs by 2030.
• Transport quota (RED III): A minimum of 1% RFNBO fuels in the transport energy sector by 2030.
• Commercial impact: Production projects that fail to certify their hydrogen as an RFNBO will be completely excluded from preferential markets and commercial support schemes (Innovation Fund, CfD).

Delegated Regulation (EU) 2023/1184 requires three principles to be met simultaneously: additionality of renewable plants, geographical correlation and temporal correlation of supply, as well as a 70% reduction in GHG emissions.

• Additionality: The associated renewable plant must have become operational no more than 36 months before the electrolyser.
• Geographical Correlation: Electricity generation and the electrolyser must be located within the same electricity bidding zone.
• Environmental Reduction: Total life-cycle emissions must be below 94 g CO₂eq/MJ compared with the official fossil fuel comparator.

Hourly temporal correlation requires official certificates to demonstrate that the green electricity consumed by the electrolyser was fed into the grid during exactly the same hour in which the hydrogen was produced.

• Regulatory deadlines: Monthly matching is permitted until December 2029; mandatory transition to hourly matching from January 2030.
• Technical requirement: Requires the procurement of high-granularity Guarantees of Origin (GOs) and the deployment of advanced IT metering systems.
• Exemption: Installations isolated from the general grid (off-grid) or connected via a direct line automatically comply with this principle.

The RED III Directive (EU 2023/2413) is the European legal framework that raises sector-specific renewable energy targets, introducing binding green hydrogen consumption quotas for industry and transport.

• Overall Target: A minimum 42.5% share of renewable energy in the European Union's gross final energy consumption by 2030.
• Administrative Simplification: Introduces "renewables acceleration areas", limiting environmental assessment and permitting procedures for electrolysers to a maximum of 12 months.
• Transposition: Requires Member States to adapt their national legal frameworks within strict deadlines.

Guarantees of Origin are electronic certificates that officially certify that one megawatt-hour (MWh) of electricity has been generated from renewable sources. They are the mandatory auditing tool for RFNBO hydrogen.

• Issuance and control: Managed in Spain by Red Eléctrica (the grid operator) and settled through the CNMC's official registry.
• Use in hydrogen: The electrolyser operator must acquire and formally cancel these GOs, demonstrating the traceability of its electricity supply.
• Legal requirement: Without the formal cancellation of valid GOs aligned with the Delegated Regulation, the hydrogen produced cannot be legally recognised as green hydrogen.

The EU's REPowerEU strategy aims to develop a robust market for 20 million tonnes of renewable hydrogen by 2030, divided equally between domestic production and international imports.

• EU industrial capacity: Planned deployment of 40 GW of operational electrolysis capacity in the European Union by 2030.
• Spain's target: Installation of at least 4 GW of electrolysis capacity in line with the objectives of its national Hydrogen Roadmap.
• Support mechanisms: Funding channelled through Clean Hydrogen Partnership programmes, the EU Innovation Fund, PERTE ERHA funding schemes and national IDAE calls for proposals.

The CBAM is a European Union environmental tariff that imposes charges on imports of carbon-intensive products, aligning their emissions costs with those of the European carbon market (ETS).

• Affected sectors: Steel, cement, aluminium, fertilisers, electricity and hydrogen.
• Full implementation: Transitional phase launched in 2023; progressive commercial implementation from 2026 onwards.
• Sector impact: Increases the import costs of ammonia and fertilisers produced outside the EU using grey hydrogen, helping to safeguard the competitiveness of EU renewable electrolysis plants.

H2Med is a major cross-border transport infrastructure corridor designated as a Project of Common Interest by the European Union, designed to provide an energy connection between the Iberian Peninsula and France and Germany.

• Subsea link (BarMar): A planned hydrogen pipeline between Barcelona and Marseille (350 km), scheduled to become operational by 2030.
• Design capacity: Transport of up to 2 million tonnes of renewable hydrogen per year (2 Mt/year).
• Strategic role: Strengthens Spain's position as a major net exporter of clean energy to the industrial regions of Central Europe, thanks to its highly competitive solar power generation.

The hydrogen sector in Europe has fully entered its "maturity test", consolidating the transition from pilot projects to large-scale engineering. According to data from the Clean Hydrogen Monitor, the average size of projects entering operation has increased from 2.9 MWel to ~18 MWel (an increase of 520%), with the first plants exceeding 100 MW expected to begin operations imminently.

This industrial scale-up has brought about a structural shift in the labour market: roles focused exclusively on basic R&D are giving way to strong demand for professionals specialising in project execution, construction and operations. The market is no longer looking for theory; it is looking for technical and operational viability.

The deployment of hydrogen-related infrastructure and industry has the potential to create up to 181,000 direct and indirect jobs in the country, where upskilling (updating existing skills) and reskilling (retraining mechanical, electrical and process engineers) are essential to prevent projects from stalling due to a shortage of technical professionals.

• Hydrogen Solutions Architect: A specialist in engineering and integration. Their role is to size electrolysis plants and design their technical integration with variable renewable energy sources and existing grids or industrial infrastructure.
• Chemical and Electrical Engineers: Core professional profiles in high demand for the design and sizing of processes and the critical electrical infrastructure required by large-scale production plants.
• Regulatory, Safety and Permitting Manager (Permitting Specialist): A role focused on legal and technical viability. These professionals have in-depth knowledge of complex regulations, specific safety codes (such as ATEX regulations) and the critical administrative procedures required to unblock projects and bring them to Final Investment Decision (FID).
• Plant and O&M (Operations and Maintenance) Technician – The sector's biggest bottleneck: Field-based technical professionals (operations, electrical and mechatronics) responsible for day-to-day management, commissioning, compression, storage and safe dispensing. Technicians specialising in electrolyser operations and maintenance are currently among the most difficult professionals to find in the labour market.
• Application and Infrastructure Value Chain Specialists: Professionals focused on the immediate and future needs of technical deployment, including fuel cell design engineers, storage and integration system technicians, and hydrogen refuelling station operators.

The levelised cost of green hydrogen production (LCOH) in Europe is currently estimated to range between €4 and €8/kg, directly influenced by renewable electricity supply prices.

• Competitive locations: Regions in southern Spain with abundant solar resources and long-term power purchase agreements (PPAs) can stabilise their costs at the lower end of the range.
• Fossil fuel comparator: Conventional grey hydrogen (SMR) operates at costs of around €1.5-2/kg, subject to natural gas price volatility.
• 2030 outlook: International agencies (IRENA, IEA, BloombergNEF) forecast costs converging towards €2-3/kg thanks to economies of scale in CAPEX.

The Levelised Cost of Hydrogen (LCOH) is primarily determined by five technical and financial design variables, with electricity costs representing the largest component.

• Electricity cost: Accounts for between 70% and 80% of the project's total LCOH.
• Capacity factor: The number of hours the plant operates annually to recover fixed investment costs.
• System CAPEX: The cost of the electrolyser and BoP (currently between €500 and €1,000/kW for AEL technology).
• WACC (Cost of Capital): An indicator determined by risk levels and financial structuring.
• Replacement OPEX: Financial planning for the periodic replacement of stack cells.

Commercial and R&D projects have access to non-repayable funding schemes provided through PERTE ERHA calls, European Innovation Fund programmes and IDAE RENOVAL funding schemes.

• Large-scale grants: Mechanisms such as cross-border projects designated as IPCEIs (Hy2Tech and Hy2Use) and approved by the European Commission.
• Basic research: EU funding channelled through the Clean Hydrogen Joint Undertaking (allocated €1 billion under Horizon Europe).
• Operating subsidies: Forthcoming institutional launch of hydrogen Contracts for Difference (CfD) auctions backed by the European Investment Bank.

Lenders require project risks to be mitigated through long-term hydrogen purchase agreements (off-take), stable electricity PPAs certified as additional, and operational guarantees from manufacturers.

• Financing structure: Transactions are predominantly structured as non-recourse Project Finance, without recourse to the sponsors' balance sheets.
• Manufacturer (OEM) guarantees: Technical guarantees are required covering availability, stack durability and controlled efficiency degradation.
• Financial metrics: The base-case scenarios of the technical due diligence must deliver a minimum Debt Service Coverage Ratio (DSCR) of between 1.2x and 1.3x, which is the current standard required by commercial banks for energy infrastructure with moderate-to-high risk. This ratio measures the project's ability to service its debt from operating cash flow.
• In hydrogen projects, due to inherent volatility and the lack of a mature commodities market, technical due diligence processes typically stress-test the financial models.

A Contract for Difference (CfD) is a public financial support instrument that guarantees a fixed or reference sale price (strike price) to the green hydrogen producer, protecting it against market uncertainty.

• How it works: If the market sale price falls below the agreed price (strike price), the public authority pays the difference to the producer; if it exceeds the strike price, the producer repays the surplus.
• Investment benefit: It completely eliminates the commercial revenue volatility risk for the plant, immediately improving the project's bankability and substantially reducing the cost of capital (WACC).

IPCEIs are Important Projects of Common European Interest, an exceptional legal instrument that allows Member States to grant higher levels of public funding than would ordinarily be permitted.

• Active programmes: The Hy2Tech and Hy2Use initiatives bring together strategic pan-European investments exceeding €5.4 billion in public funding.
• Eligibility requirements: Applicant projects must demonstrate a strong innovative nature with systemic impact, proven financial viability and formalised genuine collaboration agreements with partners from other European Union countries.

The price of electricity supply determines the project's viability: given the efficiency levels of commercial equipment, every €10/MWh variation in the electricity price increases the cost per kg of hydrogen by €0.55.

• Competitive scenario: A renewable energy PPA secured at a fixed price of €30/MWh places hydrogen production costs within economically viable ranges for replacing fossil fuels (€2.5-€3.5/kg).
• Risk scenario: Operating with exposure to the daily volatility of wholesale electricity markets, with average prices of €100/MWh, pushes the LCOH above €6/kg, making it impossible to secure commercial off-take agreements.

Hydrogen has unique physicochemical properties that define a distinct risk profile, but not one that is greater than that of hydrocarbons; its extremely low density allows it to disperse rapidly upwards in open spaces.

• Key risks: It has a wide flammability range in air (4%-75%) and a low minimum ignition energy (0.017 mJ), requiring rigorous leak control in enclosed spaces.
• Advantages: Unlike LPG or petrol vapours, it does not form pools of flammable gas at ground level, and its thermal radiation dissipates rapidly into the atmosphere.
• Technical assurance: Engineering design that complies with current industrial safety codes ensures safe operation on a commercial scale.

Industrial plants are regulated by a combination of overlapping regulations that mandatorily govern the storage of chemicals, pressure equipment and fire protection.

• Mandatory national regulations: APQ Regulation (RD 379/2001) for gas storage, Pressure Equipment Directive (PED 2014/68/EU) and the Industrial Fire Protection Regulation (RSCIEI).
• Technical standards: Mandatory compliance with international manufacturing standards ISO 22734 (for water electrolysers) and ISO 19880.
• Permitting: Formal submission of an officially certified Detailed Engineering Design to the provincial industry authorities is required in order to obtain authorisation for commissioning. ARIEMA provides these consultancy services on a comprehensive basis.

An ATEX zone is a mandatory technical classification within the engineering design that identifies areas where there is a potential risk of explosive atmospheres forming due to the presence of flammable gas.

• Zone 0: Continuous presence or presence for extended periods of an explosive mixture (>1,000 hours/year). Typically confined to the interior of storage vessels and process lines.
• Zone 1: Occasional formation of an explosive atmosphere under normal plant operating conditions (10-1,000 hours/year). Areas around valves or purge points.
• Zone 2: Unlikely and very short-term presence arising exclusively from system anomalies or failures (<10 hours/year). External safety perimeters.
• Equipment requirements: All instrumentation installed within these areas must carry the appropriate ATEX marking and category certification for Group IIC gases.

As hydrogen is an odourless and colourless gas with a flame that is invisible in the conventional optical spectrum, automated safety monitoring requires specific sensors to be deployed and integrated into the control system.

• Sensing technologies: Electrochemical sensors (for accurate measurement of the Lower Explosive Limit), thermal conductivity sensors for high concentrations and industrial catalytic sensors.
• Installation criteria: Sensors must be installed at the highest points of enclosures and equipment rooms, where hydrogen accumulates rapidly due to its high buoyancy.
• Control logic: Detectors must be directly linked to the plant's Safety Instrumented System (SIS) to activate valve isolation, stack shutdown and emergency forced ventilation.

La fragilización es la pérdida de ductilidad y resistencia mecánica que sufren determinados aceros de alta resistencia al difundirse el hidrógeno atómico en su red cristalina, provocando roturas frágiles repentinas.

• Equipos sensibles: Afecta críticamente a las etapas de alta presión, tales como compresores de pistón, tuberías de distribución y recipientes de almacenamiento gaseoso severo.
• Mitigación técnica: Selección obligatoria de materiales idóneos conformes a las directivas del Reglamento del Mercado Interior del Gas Hidrógeno, priorizando aleaciones de acero inoxidable austenítico.
• Seguimiento institucional: Como especialistas integrados en la secretaría técnica del European Hydrogen Safety Panel (EHSP) de la Unión Europea, en ARIEMA analizamos continuamente el registro de incidentes asociados a este fenómeno metalúrgico.

Yes. The permitting and design of any commercial electrolysis facility requires a mandatory technical safety and risk assessment to certify the plant's operational safety.

• Mandatory documentation: Preparation of the explosion protection document, sizing of the emergency ventilation system and official classification of ATEX hazardous areas.
• Regulatory thresholds: Industrial facilities exceeding the storage limits established by the APQ Regulation or triggering the safety thresholds under the Seveso III Directive are required to submit advanced safety reports to the Civil Protection authorities. ARIEMA is responsible for the complete technical preparation of these engineering documents.