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RCS Database

Metrology

Metrology is the science of measurement. In the context of hydrogen infrastructure, it covers aspects such as hydrogen quality, calibration, quantity measurement, certification and taxation. It ensures compliance with quality standards across Europe and enables the entire infrastructure network to be interoperable. This includes the entire usage chain, from producers and refuelling stations to vehicles and applications. The legal basis for calibration and quantity measurement is the German Measurement and Calibration Act (MessEG) and the European Measuring Instruments Directive (MID).

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Quality

Calibration

GHG Reduction Quota

GHG Certification

AFIR Hydrogen quality and purification

Meaning of calibration, calibration standards and calibration bodies

GHG quota, GHG quota trading, quota price and fulfilment options

Meaning of certification, hydrogen colours and certification bodies

Quality

Hydrogen (H₂) quality and purity are especially critical in the field of fuel cell technology, as contaminants such as sulfur can cause irreversible damage to the fuel cell. The Alternative Fuels Infrastructure Regulation (AFIR) requires that public hydrogen refueling stations provide hydrogen that meets the quality standard set by EN 17124 (Grade D of ISO 14687: 99.97% H₂ purity, sulfur-free). This quality level is also anchored in the 10th Federal Immission Control Ordinance (10. BImSchV). ISO 19880-8 defines a protocol for achieving and monitoring hydrogen quality targets at refueling stations. Thermal applications, such as the use of hydrogen in combustion engines, have significantly lower requirements regarding gas purity and can operate with lower quality grades such as Grade F of ISO 14687. The classification into standardized quality grades for different applications thus reduces costs, simplifies handling, and lowers the risk of damage to components for all producers and users. Regular monitoring of hydrogen quality ensures its safe use in the intended application. This monitoring is conducted by independent approved inspection bodies (ZÜS). Information about approved inspection bodies is available from the Federal Institute for Occupational Safety and Health (BAuA): BAuA – Approved Inspection Bodies Sampling of hydrogen from the refueling station must follow the procedure described in ISO 19880-9, while measurement and verification of hydrogen quality must comply with ISO 21087 in accordance with the 10th BImSchV.
Purification

The most widely used method for hydrogen purification is Pressure Swing Adsorption (PSA). The safety of PSA systems is governed by ISO 19883.

Purification should take place at critical injection and withdrawal points, for example, when hydrogen is dispensed from a pipeline to a fuel cell vehicle via a refueling station.

Calibration

In order to ensure that customers and operators can rely on an accurate delivery quantity at the hydrogen refueling station (HRS), calibration of hydrogen dispensing is essential. Accordingly, HRS dispensers must be regularly tested for accuracy and correctness according to the German Measurement and Calibration Act (MessEG), typically every two years, using accuracy class 2.

The measurement must be carried out in accordance with OIML R 139 to ensure proper execution. The Organization of Legal Metrology (OIML) recommends applying error class 2 for hydrogen refueling stations, which allows a Mean Percentage Error (MPE) of 2% during calibration and 3% during operation. This means the actual amount of hydrogen may deviate from the indicated amount by a maximum average of 2% during calibration and 3% during regular operation.

OIML R 139

The International Organization of Legal Metrology (OIML) issues recommendations on various metrology-related topics, which are intended to be implemented into the national legislation of its member states. Accordingly, OIML R 139 “Compressed gaseous fuel measuring systems for vehicles” is a key standard in the field of calibration for hydrogen refueling stations (HRS).
OIML R 139-1 defines the metrological and technical requirements, while OIML R 139-2 outlines the metrological controls and performance tests.

Calibration Standards and Calibration Bodies

To perform a calibration, a calibration standard (i.e. a reference device) is used. According to § 45 ff of the German Measurement and Calibration Act (MessEG), the Committee for Rule Determination of the “Physikalisch-Technische Bundesanstalt” (PTB) is responsible for the development and validation of new calibration standards. The PTB has therefore developed a calibration standard using a Coriolis mass flow meter, which is intended to measure the amount of hydrogen during the calibration process. In addition, gravimetric measuring systems from Air Liquide and Linde are available, which can also be used as calibration standards.
However, gravimetric methods reach practical limits when calibrating heavy-duty refueling stations with up to 200 kg of hydrogen per refueling process.

The regular calibration of refueling stations is then carried out by the state calibration authorities, based on the PTB’s calibration standard, in accordance with § 40 MessEG. Additionally, other testing centers may be authorized by the competent state authorities to calibrate gas measurement devices. According to the German Measurement and Calibration Ordinance (MessEV), calibration must be performed every two years.

Coriolis Process

The Coriolis mass flow meter measures the mass flow of a gas or liquid using the Coriolis principle. In simple terms, the Coriolis mass flow meter consists of two metallic tubes that are set into vibration by actuators. Depending on the amount of mass flowing through the tubes, they oscillate differently, allowing the dispensed quantity to be determined based on the mass flow.

GHG Reduction Quota

Under the greenhouse gas (GHG) reduction quota (THG-Quote), companies that place diesel or gasoline fuels on the market are required to reduce their GHG emissions by an annually increasing percentage. This quota is defined in the Renewable Energy Directive (RED) and implemented nationally in Section 37 of the Federal Immission Control Act (BImSchG). The reduction is based on a reference value, which is calculated by multiplying a fossil-based comparison value by the energy content of all fuels and compliance options used by the respective company. The calculation method for GHG quotas is defined in the BImSchG. Compliance options include, for example, electricity-based fuels or electricity used in the field of electromobility.

GHG Certification

For the international trade of hydrogen (H2), its origin, production method, associated CO2 emissions, and quality must be certified in a tamper-proof manner. Initial standards for the certification of hydrogen are currently under development (ISO 19870-1 to 19870-4). These standards are primarily intended to serve the determination and calculation of the values required for certification.

At the regulatory level the certification of renewable hydrogen (RFNBO – Renewable Fuels of Non-Biological Origin) is possible in Europe due to the the Renewable Energy Directive (RED). The issued certificates are intended to reliably and securely document the amount of CO2 emissions. For this purpose, a dedicated calculation method has been developed by the EU. In the future, this method may conflict with the ISO calculation approach or other national methodologies, which could complicate the reliable certification of hydrogen on an international scale.

A unified extension of the certification process on both normative and regulatory levels would simplify the global distribution and sale of renewable hydrogen on the world market. Moreover, it could accelerate the development of hydrogen technologies in countries with high potential for renewable energy.

Digital Product Pass

The Digital product pass is intended to digitize and globally standardize the certification of storage containers and their contained gases and liquids in the future. These passports will include information such as composition/purity, country of origin, production method, and CO2 footprint. Particular emphasis will be placed on data security, transparency, and easy access. Corresponding systems are currently under development at the German Institute for Standardization (DIN).

Hydrogen Colours

The production method is a decisive factor in the certification process of hydrogen, as it significantly influences the CO2 footprint. Different methods release varying amounts of greenhouse gases.
Hydrogen is often categorized by different colors. However, this is misleading, as the definitions are imprecise and not standardized globally. Many experts consider it more effective to indicate the greenhouse gas intensity of hydrogen instead of using color codes.

Certification Bodies

Independent certification bodies currently exist that certify hydrogen using their own testing procedures. Examples of such certification bodies include CertifHy and TÜV.
To issue certificates in accordance with the requirements of the Renewable Energy Directive (RED), the certification systems of these bodies must be approved by the European Commission.

RCS is the abbreviation for Regulations, Codes and Standards. The goal of standardization is the planned unification of tangible and intangible objects, carried out jointly by interest groups, for the benefit of the general public.

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