GHG balance of biomethane under RED II step by step: formula, components and reduction thresholds
How the GHG emissions of biomethane are calculated in the RED II directive: the formula E = eec + el + ep + etd + eu − esca − eccs − eccr, the components, the fossil fuel comparator of 94 g CO₂e/MJ and the required reduction thresholds.
Other language versions: polski.
The greenhouse gas emissions of biomethane are calculated according to the methodology of the RED II directive (Directive (EU) 2018/2001) by summing emissions at all stages of the chain: cultivation or extraction of the feedstock, processing, transport, distribution and use, and then subtracting bonuses. The result is expressed in grams of CO₂ equivalent per megajoule of fuel energy (gCO₂e/MJ) and compared with the fossil fuel comparator – 94 gCO₂e/MJ for transport fuels. Biomethane can be counted towards renewable energy targets if the reduction relative to this value reaches the required threshold.
The formula
In the RED methodology the total emissions of a fuel are:
E = e_ec + e_l + e_p + e_td + e_u − e_sca − e_ccs − e_ccr
| Symbol | Meaning |
|---|---|
| e_ec | emissions from extraction or cultivation of the feedstock |
| e_l | emissions from land-use change (in practice usually zero for wastes and residues) |
| e_p | emissions from processing (fermentation, upgrading, including methane losses) |
| e_td | emissions from transport and distribution |
| e_u | emissions from the use of the fuel (for biomass fuels usually zero, because the CO₂ is biogenic) |
| e_sca | reduction from improved soil carbon accumulation |
| e_ccs, e_ccr | reductions associated with CO₂ capture, storage and use |
The emission reduction relative to the fossil fuel is calculated as (EF − E)/EF, where EF is the emissions of the comparator fuel. For transport fuels EF = 94 gCO₂e/MJ; other reference values apply to heat and electricity.
Reduction thresholds
In simplified terms:
- biofuels and biogas in transport from installations that started operation from 1 January 2021 – a reduction of at least 65%;
- biomass fuels in electricity, heating and cooling – 70% for installations that started operation from 2021, 80% for installations that started operation from 2026 (the values apply to the criteria for support and for counting towards targets).
Detailed thresholds, cut-off dates and exceptions should be read directly in the directive and in the national transposing law.
What makes up the emissions of biomethane
- Feedstock. Wastes and residues (slurry, food waste) usually have zero or very low extraction emissions; energy crops contribute emissions from fertilisation, machinery and land-use change.
- Fermentation. Emissions from energy use and from methane leaks, above all from open digestate tanks.
- Upgrading. Energy use and methane slip.
- Transport. Delivery of the feedstock to the biogas plant, and of the gas to the customer.
- Bonuses. For slurry and for certain agricultural practices or for CO₂ capture.
Default versus actual values
The annexes to the directive contain typical and default values for selected chains (e.g. biogas from slurry, wastes, maize), differentiated, among other things, by the type of digestate storage (open or closed) and the way the off-gas is handled. Default values are conservative (usually worse than typical), so well-run installations often achieve a better result through actual calculations, which require data and a certification audit. The choice of approach depends on the gain from a higher reduction and the cost of verification.
Worked example (illustrative)
Assumptions: biomethane from a mixture of wastes; emissions e_ec = 0 (wastes), e_p = 18 gCO₂e/MJ, e_td = 3, e_u = 0, no bonuses. E = 21 gCO₂e/MJ. Reduction: (94 − 21)/94 ≈ 77.7%, above the 65% threshold. If the methane loss in upgrading rose and e_p went up to 40 gCO₂e/MJ, the result would be: E = 43; reduction ≈ 54%, i.e. below the threshold. This shows that limiting methane losses and emissions from digestate can decide compliance with the requirements. The values in the example are assumed; they do not come from measurements.
Certification
Emissions are verified by national or EU voluntary schemes (e.g. ISCC, REDcert) through independent certification bodies, which check data on feedstocks, energy use, losses and the supply chain. For the producer this means the need to keep records: the mass balance, delivery documents, measurement results and settlements.
Typical mistakes in the calculation
The most common errors are omitting emissions from digestate storage, assuming too optimistic a methane slip without confirmation by measurements, mixing units (MJ of biomethane versus MJ of feedstock), and treating values from one chain as universal for another. It is also worth remembering that the mass balance in a multi-substrate installation requires emissions to be assigned to individual streams (allocation), and an incorrect split can change the result. Input data such as the quantities and types of substrates, energy consumption and delivery documentation should therefore be collected systematically from the first day of operation of the installation.
Summary
The RED methodology means that the value of biomethane is linked to its carbon footprint: the lower the process emissions, the larger the margin against the threshold and the higher the commercial value. It is worth planning the installation with emissions in mind: leak-tight digestate tanks, low methane slip and renewable energy.
Sources
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