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Glossary · Energy industry & energy transition

Biochar

Biochar biochar negative emissions Biomass carbon storage Climate protection

Definition and production

Biochar is a solid, carbon-rich material. It is produced when biomass is heated strongly in the absence of oxygen. This process is called pyrolysis; a related technique is gasification. In combustion, the carbon in plants would react almost completely to carbon dioxide. In pyrolysis, by contrast, part of it is retained in a solid, highly aromatic and therefore hard-to-degrade form. The higher the temperature and the longer the residence time, the further carbonisation proceeds. This lowers the hydrogen share relative to organic carbon. The molar ratio H/Corg is therefore regarded as the most important indicator of stability. The European Biochar Certificate (EBC) requires a pyrolysis temperature of at least 500 °C for certified biochar and limits H/Corg to below 0.7 or below 0.4, depending on the quality class.

Possible feedstocks include wood residues, straw, landscape management material, nut shells, harvest and processing residues, and other biogenic residues. Technically, sewage sludge or digestate can also be pyrolysed. However, such materials are permitted only to a limited extent or not at all for use as fertiliser products (see below). Pyrolysis yields three product groups: solid char, combustible pyrolysis gas and liquid condensates (oils, tars). Gas and oil are usually burned directly. The heat first keeps the process itself running. What remains can be used as process heat or for district heating, and in some plants also for electricity generation. The solid char is used in soils, substrates, animal feed, concrete, asphalt or other materials, provided that quality and contaminant levels allow it.

Why biochar matters for climate action

As plants grow, they take up CO₂ from the air and bind the carbon in their biomass. When this biomass rots or burns, the carbon usually returns to the atmosphere within a few years to decades. Biochar considerably delays this return, because a large part of its carbon can remain bound for centuries. If the biomass comes from sustainable sources and the overall balance is negative, biochar can contribute to negative emissions. It then counts among the methods of carbon removal.

A worked example shows the order of magnitude: one tonne of carbon corresponds to about 3.67 tonnes of CO₂, because the molecule additionally contains two oxygen atoms. One tonne of dry biochar with 80 percent carbon therefore contains, arithmetically, at most about 2.9 tonnes of CO₂. This figure is only an upper limit, however. What is deducted is the share that is eventually degraded after all, and the emissions of the entire chain: harvesting, transport, drying, the plant's electricity and fuel demand, methane and nitrous oxide emissions from the process, and application or incorporation. How much CO₂ per tonne can ultimately be credited therefore results only from a complete carbon footprint assessment and not from the mass of the char.

Distinction from related terms

  • Charcoal: It is produced in a chemically similar way but is mostly used as a fuel. When it is burned, the storage effect is lost. German fertiliser law nevertheless uses the term charcoal (Holzkohle) for the char from untreated wood that has been permitted so far.

  • Activated carbon: It is deliberately post-treated and is therefore particularly porous. It is used mainly for purifying gases and liquids. Biochar can be activated but does not have to be.

  • Compost and humus: They also contain organic carbon but are degraded biologically much faster. Biochar can influence humus formation but does not replace living soil.

  • CCS and BECCS: Here, gaseous CO₂ is captured and stored geologically. Biochar stores solid carbon in soils or materials. The plants are often smaller and more decentralised. On the other hand, later monitoring in soil is more difficult than for a well-monitored geological storage site.

Role in the energy system

Biochar is not an electricity product, but it bears on the question of what scarce biomass is best used for. Biomass can be stored and used in versatile ways: for heat and electricity, as a fuel or as an industrial raw material. A pyrolysis plant delivers less usable energy than full combustion, because part of the carbon is deliberately left in the char. In return, a carbon sink is created. The assessment thus shifts from pure energy yield towards a combination of energy and storage. In practice, coupling with heat sinks, such as heating networks or industrial plants, is more obvious than pure electricity generation. The EU methodology for biochar therefore contains requirements on the use of waste heat. The certification schemes can specify the details further. Biochar replaces neither storage nor grid expansion nor flexible consumers. However, it can be part of a resource strategy that assesses residues not only by their calorific value but also by their storage potential.

Accounting: permanence, additionality, leakage

Biochar is not automatically climate-positive. Climate neutrality only means that emissions are offset arithmetically. A removal requires more: CO₂ must be removed from the atmosphere on a net basis, and the carbon must demonstrably remain bound for a long time. There is no general ban on using fossil energy for start-up, drying or transport. However, such emissions must be deducted in full and reduce the creditable quantity. Three further test criteria are important. Additionality means that the storage would not have taken place without the project. Leakage refers to displacement effects, for example when a residue previously replaced fossil energy and heating now takes place fossil-based elsewhere. Or when biomass is specially grown and this creates demand for land, water or fertiliser. Double counting occurs when the same storage is credited to several actors.

Biochar, too, is not unchanging. How long it lasts depends on the feedstock, the pyrolysis temperature, the H/Corg ratio, the particle size and the environment. A part is degraded comparatively quickly, while a stable fraction can persist for centuries. The EU methodology prescribes measuring the H/Corg ratio for each batch. For one of the assessment options, it calculates a permanence factor from this. The expected mean temperature at the place of use also enters into this factor: soil temperature in soil, air temperature in building materials. The warmer the place of use, the less carbon is credited. Only the cautiously estimated stable fraction is therefore credited.

Legal framework in the EU (as of November 2026)

Regulation (EU) 2024/3012 (CRCF) creates a voluntary EU framework for certifying CO₂ removals. Delegated Regulation (EU) 2026/285 of 3 February 2026 lays down the methods for permanent removals. It covers direct air carbon capture and storage (DACCS), the capture of biogenic emissions with storage (BioCCS) and carbon removal through biochar (Biochar Carbon Removal, BCR). According to the EU Commission, permanent removals are regarded as technologies that store CO₂ safely for centuries. The minimum requirements of the biochar methodology include that the char meets the requirements of the EU Fertilising Products Regulation for pyrolysis and gasification materials. This includes the restrictions on permissible feedstocks. Certificates under the CRCF are issued only by certification schemes that the Commission has recognised. Whether biochar certificates will be included in mandatory markets such as the EU Emissions Trading System remains open.

For use as a fertiliser product, Delegated Regulation (EU) 2021/2088 created component material category CMC 14 for pyrolysis and gasification materials. It sets out permissible feedstocks, limit values (for example for chlorine and thallium) and quality assurance requirements. Sewage sludges, industrial sludges and animal by-products are not permitted as feedstock. Biochar that meets these requirements may be traded as an EU fertilising product throughout the internal market. In Germany, by contrast, the national Fertiliser Ordinance (DüMV) continues to permit only charcoal from chemically untreated wood with at least 80 percent carbon in the dry matter, and only for limited purposes. Producers therefore choose either the national or the EU route.

Side effects and quality control

Biochar can improve water retention, soil structure and nutrient binding. However, these effects depend strongly on the site. Fresh char can temporarily bind nutrients, which is why it is often loaded with nutrients beforehand, for example with compost or slurry. On its own it is not a fertiliser. Depending on the feedstock and process control, it may contain heavy metals, polycyclic aromatic hydrocarbons (PAHs) or dioxins. This makes batch control, analytics and clear limit values necessary. Only with such quality rules does biochar become a reliable climate action option and not a poorly controlled disposal route.

Conclusion

Biochar shows that climate action, besides emission reduction, also involves the deliberate handling of carbon flows. However, the term alone does not reveal whether a specific project makes sense. For that, the origin and prior use of the raw materials, the integration of the energy, the material quality, the expected storage duration and the accounting method must be disclosed and independently verified. Only when all of this fits together is biochar a robust negative emission and not merely a carbon-rich product.

Sources

Related glossary entries

Edited by eCMS on 11.11.2026 15:52

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