Biochar
Biochar is the carbon-rich material produced in the SkyClean pyrolysis process. By transforming biomass into stable carbon, biochar enables long-term carbon storage while creating valuable opportunities for use in agriculture, construction materials, and other applications.
Biochar is a powerful climate tool
Carbon removal requires more than capturing carbon. It requires storing carbon in a form that remains out of the atmosphere for the long term.
By converting biomass into biochar, carbon that would otherwise return to the atmosphere can be stored for centuries or longer. This ability to create durable carbon storage is what makes pyrolysis a recognised carbon removal pathway.
SkyClean biochar quality
At SkyClean, biochar is characterised through laboratory analysis to verify its composition, stability, and suitability for intended applications.
No tar contamination
SkyClean’s pyrolysis process includes steps that prevent tar condensation on biochar. This safeguards against the risk of tar contamination on biochar, which has historically been a common challenge.
Carbon sink stability
SkyClean’s pyrolysis process ensures that 75-90% of the carbon in the biochar will be retained in the soil for centuries.
Positive soil properties
Biochar improves drainage in clay soil, retains water in sandy soil, and boosts carbon content in depleted soil. It reduces nitrogen leaching and preserves nutrients. Biochar from biogas fibres is particularly rich in phosphorus, making it a valuable source of recycled nutrients.
Safety and handling of SkyClean biochar
SkyClean biochar is supported by documented safety, transport, and storage assessments:
- No hazard classification under CLP and registered under relevant REACH requirements
- Evaluated according to UN transport test methods and not classified as dangerous goods
- Long-term storage trials and operational experience support safe storage when properly conditioned
Independently analysed
SkyClean biochar is independently analysed by Eurofins.
Eurofins laboratory testing verifies carbon content, composition, and potential contaminants. The results support both carbon storage claims and application-specific requirements.
Applications of biochar
Beyond carbon removal, biochar has potential applications across a range of industries.
Through collaborations with research institutions and industry partners, Stiesdal SkyClean supports the development and testing of new biochar applications, including:
Agriculture
Biochar can improve soil properties by enhancing water retention, nutrient availability, and soil structure. These characteristics make it suitable for agricultural and horticultural applications.
Construction materials
Biochar can be incorporated into concrete, cementitious products, and other building materials. This creates opportunities to combine carbon storage with the production of lower-carbon construction materials.
Infrastructure
Biochar can be used in asphalt and other infrastructure applications, providing an additional pathway for long-term carbon storage in the built environment.
Independent Danish research on biochar
A 2026 research project by the Technical University of Denmark (DTU) and Aarhus University investigated the environmental properties of biochar produced from different feedstocks. The study found that:
- Pyrolysis significantly reduced organic contaminants, including PFAS, dioxins, detergent residues, and plasticisers compared with the original feedstock.
- Biochar acted primarily as a sink rather than a source of PFAS, showing very limited impact on PFAS leaching under normal application rates.
- Biochar quality depends on both feedstock and process control, highlighting the importance of selecting appropriate biomass and maintaining consistent production conditions.
- Feedstock matters. Agricultural residues such as straw showed the lowest concentrations of heavy metals, while heavy metals already present in the feedstock remain in the resulting biochar.
These findings reinforce the importance of high-quality feedstocks, robust process control, and independent testing in the production of biochar suitable for durable carbon storage and agricultural applications.
Learn more about SkyClean biochar
To support transparent dialogue with customers, partners, authorities, and researchers, Stiesdal SkyClean has published a comprehensive white paper covering the production, properties, safety, and carbon storage performance of SkyClean biochar.
Frequently asked questions
Is biochar safe to handle?
SkyClean biochar is not classified as hazardous under CLP regulations and does not require hazard labelling. It is also not classified as dangerous goods for transport, based on relevant UN transport tests. Normal handling precautions still apply, especially if dust is generated. The Safety Data Sheet recommends gloves, eye protection, and a particle filter mask if ventilation is insufficient or dust occurs.
Is biochar stable when distributed on agricultural soil, or does it release the captured CO₂ rapidly?
The stability of biochar, when applied to agricultural soil, depends on factors like the type of biomass, pyrolysis method, pyrolysis temperature, and the temperature of the soil where the biochar is stored.
Biochar from Stiesdal’s SkyClean pyrolysis is produced at a process temperature of 600°C.
The IPCC estimates that the average carbon retention for biochar produced at 600°C will be at least 89% after one hundred years at a soil temperature of 20°C.
The IPCC states that this assessment is conservative, as the breakdown of biochar increases with soil temperature, and the global average soil temperature is estimated to be around 10°C. In Den-mark, the average soil temperature is approximately 8°C, which would result in a retention rate above 90%.
Researchers from Aarhus University and GEUS have recently published observations of the microstructure of biochar from Stiesdal’s SkyClean plant, showing that the biochar has the same mi-crostructure as coal stored in geological formations for 10,000 years.
The stability of biochar produced through high-temperature pyrolysis for carbon storage meets the requirements for “permanent carbon storage” in the EU’s CRCF directive, defined as a carbon removal activity that, under normal circumstances and using appropriate management practices, stores atmospheric or biogenic carbon for several centuries.
Will we run out of green carbon if we store it in fields instead of using it for fuel?
Green carbon is carbon captured from the atmosphere by plants. It can be used for various beneficial purposes, such as fuel or chemicals, and it can also be stabilised and stored, effectively removing it from the carbon cycle in nature in the foreseeable future.
There is no risk of running out of green carbon, as plants capture billions of tons from the atmosphere each year. However, we need to consider how we use this green carbon.
The concentration of CO₂ in the atmosphere is currently around 420 ppm (parts per million), equivalent to 0.42 permille. For the past 10,000 years, the atmospheric CO₂ content has been around 280 ppm, and it is only in the last hundred years that we have exceeded 300 ppm.
Although it may not sound like much, the difference between the pre-industrial concentration of 280 ppm and the current concentration of 420 ppm is the main cause of climate change.
A concentration of 420 ppm in the atmosphere is too high to maintain a stable climate, and we risk self-reinforcing warming, which can have catastrophic consequences for humanity. Therefore, it is crucial to start removing as much CO₂ from the atmosphere as possible as quickly as possible.
Many scientists believe we need to reduce the concentration to about 350 ppm to have reasonable assurance that climate change will not spiral out of control. This requires not only stopping further CO₂ emissions but also removing around 500 gigatons of CO₂ from the atmosphere. Since we cannot simply stop emitting CO₂ overnight, the amount we need to remove is even higher than the 500 gigatons.
Plants already capture CO₂ from the atmosphere at a scale no technical solution can match. The challenge is ensuring that some of this carbon remains out of the atmosphere. Green carbon should therefore not be viewed solely as a feedstock for fuels and chemicals.
As energy systems transition towards electricity and non-carbon fuels such as hydrogen and ammonia, an increasing share of available biomass can be used for long-term carbon storage, helping to reduce atmospheric CO₂ concentrations.
Does storing biochar in agricultural soil make sense as long as fossil carbon continues to be burned? Would it not be better to burn biochar as a replacement for fossil fuel?
It may initially seem contradictory to store biochar while fossil carbon is still being extracted and burned elsewhere, but replacing fossil coal with biochar is not a long-term solution.
Efforts to address climate change have two main tracks.
First and foremost, we need to stop exacerbating the problem. This means reducing CO₂ emissions to the atmosphere as quickly as possible. We can do this by ceasing the use of fossil fuels.
These fuels should be replaced as much as possible with electricity, and where that is not feasible, we should use non-carbon-containing fuels such as hydrogen and ammonia.
Only in cases where neither electricity nor non-carbon-containing fuels are realistic alternatives, such as for larger aircraft, should we use carbon-containing fuels, and these should be based on green carbon.
The second track is the reduction of the atmospheric CO₂ content. We need to stabilise as much green carbon as possible and store it away effectively, removing it from the atmosphere.
We achieve this with biochar produced through pyrolysis.
Planning a pyrolysis project?
SkyClean supports projects from early concept and business case development to system delivery, integration, and operation.