Proof of Sustainability and Proof of Origin

What’s the difference—and which one do I need for what?

As of February 2025

Anyone buying or selling in the biomethane market will encounter two terms that sound similar at first glance but mean fundamentally different things: sustainability certificate (NNW) and certificate of origin (HKN). Both certify something about a quantity of gas—but each certifies something different. This article explains what these two types of certificates entail, how they differ from one another, and when to use which one.

The Sustainability Certificate (NNW)

What does it certify?

The sustainability certificate verifies that a given quantity of biomethane meets the EU’s legally mandated sustainability criteria. Essentially, it comes down to two questions:

• Does the biomass come from a sustainable source? (e.g., no deforestation, no use of protected areas)
• How much greenhouse gas is saved compared to the fossil fuel benchmark?

Only when these criteria are verifiably met may the gas be legally classified as “sustainable.” Without a valid sustainability certificate, biomethane does not count as renewable energy for regulatory purposes—regardless of how it was actually produced.

What is it used for?

The NNW is the key to accessing government incentive programs and meeting statutory compliance requirements:

• Eligibility for the greenhouse gas reduction quota (GHG quota)
• Tax benefits under the Energy Tax Act
• Proof of compliance with the biofuel quota in the transportation sector
• Eligibility under FuelEU Maritime or other sector-specific regulations

In short: Anyone who wants to market or use biomethane for regulatory purposes needs an NNW.

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Nabisy – Mandatory system for sustainability certificates & GHG quota

Nabisy is the central registry in Germany when it comes to sustainability in the biofuel sector. For many market participants, it is crucial primarily for one reason:

Nabisy for biofuel quota trading

Distributors of biogenic fuels (e.g., bio-CNG/bio-LNG) can generate GHG quotas and participate in quota trading. This requires that the necessary documentation be correctly maintained in the system.

Nabisy serves as a platform for managing sustainability certificates, transferring them along the supply chain, and invalidating them as needed.

What specifically do I need to know as a producer or trader?

To use Nabisy, you first need an account. This must be requested from the BLE. For traders/suppliers (Lfr) and producers (SSt), certification under a voluntary system is mandatory. Once the account is set up, it can be used to generate (SSt), accept, share, or invalidate certificates (Lfr).

Important: Without a functioning Nabisy setup, marketing through quota-relevant applications can quickly be blocked—even if the biomethane is technically flawless.

Requirements for Issuers and Recipients

Anyone wishing to issue sustainability certificates must be certified by an EU-recognized certification system (e.g., ISCC EU or REDcert EU) and register as an economic operator in Nabisy. Only after a successful audit and active certification can NNWs be generated and transferred in the system. The recipient—whether a trader or end user—must also be registered in Nabisy to receive and process certificates.

The Certificate of Origin (HKN)

What does the certificate of origin certify?

The Certificate of Origin does not certify sustainability characteristics, but rather the nature of a quantity of gas: Where does the gas come from, how was it produced, and what are its characteristics?

Typical information included in a certificate of origin includes:

• Source facility (location, facility type)
• Substrates and raw materials used
• Energy content and gas quality
• Quarter and region of feed-in
• "Green Gas" products for end customers: Energy suppliers use this label to identify gas rates as renewable
• Corporate sustainability reporting: e.g., to document Scope 1 emissions
• Direct marketing of specific biomethane grades (e.g., by raw material or region)
• Contractual requirements between buyer and seller
• Documentation of material flows and sustainability information
• EU-wide traceability
• Prevention of double counting and fraud
• The organization and certificate must be registered in the UDB by the VS
• The company’s lead user must accept the invitation to the system and validate access
• Initial stocks must be registered before transactions can be posted
• All subsequent trading, processing, and production transactions must be recorded on an ongoing basis
• For gaseous fuels in the integrated gas network: monthly injection volumes must be entered and verified by the DSO/TSO; a transaction is not recorded until it reaches the exit point of the integrated network
• Requirements for the Mass-Balance-Based Supply of Biomethane (February 2025)
• dena Biogas Registry – Guidelines (January 2024)
• dena Biogas Register – Criteria Catalog (December 2024)
• dena Product Matrix (January 2025)
• Nabisy FAQ, Version 04/2025 (BLE)
• Nabisy – Information for Plant Operators and Suppliers (BLE)

The HKN is therefore a certificate of origin. Put simply, it confirms:

“This amount of energy comes from a renewable source.”

What is the HKN (certificate of origin) used for?

The HKN is primarily relevant in the voluntary and private sectors:

Important: The HKN alone generally does not qualify as fulfillment of statutory sustainability obligations. It supplements the NNW but does not replace it.

Where is the HKN managed? The example of the dena Biogas Register

In the German market, the dena Biogas Register operated by the German Energy Agency (dena) plays a central role in managing certificates of origin. It documents in detail the characteristics of biomethane—from raw materials and plant technology to greenhouse gas emissions. For every volume of gas fed into the grid, a quality certificate is issued that can be passed along the supply chain.

The registry deliberately goes beyond the minimum legal requirements: It enables granular quality differentiation, which is particularly valuable for premium products and sophisticated purchase agreements.

Requirements for Issuers and Recipients

To issue certificates of origin in the dena Biogas Register, plant operators must register as participants and have their plant data verified by an independent auditor. The recorded quality characteristics are documented and approved on a batch-by-batch basis. Recipients—that is, traders, utilities, or industrial buyers—must also be registered in the dena Biogas Register in order to receive, transfer, or invalidate certificates.

NNW and HKN in a direct comparison

The following table summarizes the key differences:

When do I need an NNW and when do I need an HKN?

In practice, the type of certification required—or whether both are needed—depends on the intended use:

Only NNW Required

If biomethane is used exclusively to meet legal obligations—e.g., for the GHG quota in the transportation sector or for tax relief—proof of sustainability is generally sufficient.

Only HKN required

If an energy provider wants to offer its customers a “green gas” product, or if an industrial company wants to document the source of its energy in its sustainability reporting, a certificate of origin is sufficient.

Combined Proof of Origin (NNW) and Proof of Sustainability (HKN)

In many commercial transactions, both NNW and HKN are transferred together. This allows the customer to account for the gas both for regulatory and sustainability purposes, as well as to transparently communicate its characteristics. This combination is particularly common among industrial customers with stringent reporting requirements, or when the final use of the gas has not yet been determined.

UDB – European system for sustainability data (increasingly relevant)

The UDB (Union Database) is the European system for collecting sustainability and supply chain data. It is gaining importance because it is intended to standardize documentation across the EU and will be made mandatory for all market participants.

What is the Union Database used for?

For producers and retailers, this means that in addition to national systems such as Nabisy, the UDB will also become relevant in the future.

How is the UDB structured?

The UDB is a central online platform operated by the European Commission (DG ENER). Economic operators can access the system in three ways: directly via the web interface, through a third-party service provider authorized by their certification system (Voluntary Scheme), or via their own IT connection using the eDelivery interface.

Organizational management is structured in three tiers: The European Commission operates and hosts the platform. Voluntary certification schemes (VS) handle the onboarding of economic operators, register their certificates, and serve as the central point of contact. Member States are responsible for integrating the gaseous value chain—in particular, DSOs, TSOs, and gas suppliers.

For whom will the Union Database (UDB) be mandatory?

The UDB is intended for all economic operators along the supply chain for renewable and recycled fuels: raw material collectors, producers, processors, traders, and suppliers. Certified operators in the liquid supply chain gain access through their respective voluntary scheme. Non-certified suppliers in the liquid value chain currently do not have access. In the gaseous value chain, DSOs/TSOs, suppliers, and large consumers are connected through the relevant Member States.

Requirements for Participants

Conclusion

Sustainability certificates and guarantees of origin are two different tools serving different purposes. The NNW opens the door to regulated markets and statutory crediting opportunities. The HKN provides transparency regarding the composition of biomethane and is indispensable for credible green product offerings and robust sustainability reporting.

Anyone active in the biomethane market should have a clear understanding of which certification is required for which use case—and how the German registries Nabisy and the dena Biogas Register interrelate in this context.

Would you like to know which certifications are relevant for your specific business model? agriportance would be happy to advise you.

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