# Biomass and biofuel stores: Science and technology

Why living fuel piles rot, heat up and give off gas

Source page: https://www.materialinsights.org/energy/e_bio_store/sg-sci/

What this tab covers The physics and chemistry: how the energy is stored, which materials it needs (scarcity, toxicity, recyclability) and what makes it age.

Biomass and biofuels store solar energy captured by plants as chemical bonds. Unlike fossil stocks, many of these stores are biologically active and slowly lose energy, heat up or give off gas while they wait.

#### Mechanism
Mixed

Wood piles, chips and pellets hold energy in cellulose and lignin; pellets are dried and compressed to about 8% moisture to make them stable and dense. Charcoal is wood heated with little oxygen, which drives off water and volatiles but wastes much of the original energy: traditional earth kilns convert only about 10% and efficient kilns about 30%. Ethanol and biodiesel are liquid fuels kept in tanks like petrol and diesel, though ethanol holds about a third less energy per litre than petrol (35% calculated from DOE heating values; DOE's handbook rounds this to about 30%) and biodiesel about 7.5% less than diesel. Biogas is usually held for hours to days at very low pressure in membrane domes over digesters.^[3](https://www.coford.ie/media/coford/content/publications/projectreports/cofordconnects/cofordconnectsnotes/00675CCNPP42Revised091216.pdf)^[4](https://www.nrel.gov/docs/fy23osti/86939.pdf)^[5](https://afdc.energy.gov/files/u/publication/ethanol_handbook.pdf)^[8](https://www.globallandscapesforum.org/wp-content/uploads/2018/09/Can-woodfuel-charcoal-and-firewood-be-modernized-in-Africa.pdf)
 Pellet moisture entering storage about 8%^[3](https://www.coford.ie/media/coford/content/publications/projectreports/cofordconnects/cofordconnectsnotes/00675CCNPP42Revised091216.pdf) Charcoal kiln efficiency about 10% (traditional) to 30% (efficient)^[8](https://www.globallandscapesforum.org/wp-content/uploads/2018/09/Can-woodfuel-charcoal-and-firewood-be-modernized-in-Africa.pdf) Ethanol energy per gallon 76,300 Btu vs 116,900 Btu for petrol^[5](https://afdc.energy.gov/files/u/publication/ethanol_handbook.pdf) Biodiesel (B100) energy per gallon about 119,550 Btu vs 128,488 Btu for diesel^[4](https://www.nrel.gov/docs/fy23osti/86939.pdf)

#### Material scarcity and toxicity
Mixed

No critical minerals are involved; the constraint is sustainable biomass supply and land. Stored pellets give off carbon monoxide as fatty acids in the wood oxidise, which has killed people entering storerooms. Damp chip piles, especially at 30-50% moisture, favour fungal growth. Fuel ethanol blends must be handled as toxic because of their petrol content, ethanol vapour in tank headspace can be flammable, and biogas contains hydrogen sulphide.^[1](https://blogs2.abo.fi/wp-content/uploads/sites/264/2025/06/Infosheet4_Secure-Bio-Supply-eng.pdf)^[2](https://www.hse.gov.uk/safetybulletins/co-wood-pellets.htm)^[5](https://afdc.energy.gov/files/u/publication/ethanol_handbook.pdf)
 Pellet storage CO deaths in Europe at least 9 since 2002 (to 2012)^[2](https://www.hse.gov.uk/safetybulletins/co-wood-pellets.htm)

#### Degradation and ageing
Unfavourable

Chip piles lose dry matter to microbes: monthly losses of 0.1-2.7% in published studies, averaging 1.1% for uncovered and 0.7% for covered piles, with most loss early on. Pellets self-heat as wood fatty acids oxidise, and spontaneous ignition can occur if the temperature reaches about 250 C. Biodiesel oxidises: fuel meeting the minimum specification should keep for up to a year in clean, dry tanks, but minimum-spec B100 without antioxidants should be tested every 1-2 months. Ethanol absorbs water, and in high blends the petrol part can separate out.^[1](https://blogs2.abo.fi/wp-content/uploads/sites/264/2025/06/Infosheet4_Secure-Bio-Supply-eng.pdf)^[3](https://www.coford.ie/media/coford/content/publications/projectreports/cofordconnects/cofordconnectsnotes/00675CCNPP42Revised091216.pdf)^[4](https://www.nrel.gov/docs/fy23osti/86939.pdf)^[5](https://afdc.energy.gov/files/u/publication/ethanol_handbook.pdf)
 Chip pile dry matter loss 0.1-2.7% per month; average 1.1% uncovered, 0.7% covered^[1](https://blogs2.abo.fi/wp-content/uploads/sites/264/2025/06/Infosheet4_Secure-Bio-Supply-eng.pdf) Pellet self-ignition from about 250 C self-heating^[3](https://www.coford.ie/media/coford/content/publications/projectreports/cofordconnects/cofordconnectsnotes/00675CCNPP42Revised091216.pdf) Biodiesel storage life at minimum specification up to 1 year in clean, dry storage^[4](https://www.nrel.gov/docs/fy23osti/86939.pdf)

#### Bio-energy stores compared^[1](https://blogs2.abo.fi/wp-content/uploads/sites/264/2025/06/Infosheet4_Secure-Bio-Supply-eng.pdf)^[2](https://www.hse.gov.uk/safetybulletins/co-wood-pellets.htm)^[3](https://www.coford.ie/media/coford/content/publications/projectreports/cofordconnects/cofordconnectsnotes/00675CCNPP42Revised091216.pdf)^[4](https://www.nrel.gov/docs/fy23osti/86939.pdf)^[5](https://afdc.energy.gov/files/u/publication/ethanol_handbook.pdf)^[8](https://www.globallandscapesforum.org/wp-content/uploads/2018/09/Can-woodfuel-charcoal-and-firewood-be-modernized-in-Africa.pdf)

| Store | Typical storage time | Main loss or risk | Key safeguard |
|---|---|---|---|
| **Wood chips** | Months | Dry matter loss 0.1-2.7% per month, fungi | Cover piles, store drier chips |
| **Wood pellets** | Months | CO off-gassing, self-heating | Ventilation, dryness, confined-space rules |
| **Charcoal** | Months to years | Large loss at production (kiln 10-30% efficient) | Efficient kilns |
| **Ethanol** | Months | Water uptake, flammable vapour | Water checks every 1-2 months |
| **Biodiesel** | Up to about 1 year (minimum-spec fuel) | Oxidation, cold-weather gelling | Antioxidants, keep above cloud point |
| **Biogas** | Hours to days | Methane leakage, H2S | Gas-tight membranes, upgrading |

#### Sources

1. [Info-sheet 4: Storage of forest chips (SECURE-BIO-SUPPLY), S. Lieskoski](https://blogs2.abo.fi/wp-content/uploads/sites/264/2025/06/Infosheet4_Secure-Bio-Supply-eng.pdf) Abo Akademi University, 2025
2. [Safety alert: Risk of carbon monoxide release during the storage and transportation of wood pellets](https://www.hse.gov.uk/safetybulletins/co-wood-pellets.htm) UK Health and Safety Executive, 2012
3. [COFORD Connects note: storage and handling of wood pellets](https://www.coford.ie/media/coford/content/publications/projectreports/cofordconnects/cofordconnectsnotes/00675CCNPP42Revised091216.pdf) COFORD (Ireland), 2016
4. [Biodiesel Handling and Use Guide, Sixth Edition (NREL/TP-4A00-86939)](https://www.nrel.gov/docs/fy23osti/86939.pdf) NREL (renamed National Laboratory of the Rockies in 2025) / US DOE, 2023
5. [Handbook for Handling, Storing, and Dispensing E85 and Other Ethanol Blends](https://afdc.energy.gov/files/u/publication/ethanol_handbook.pdf) US Department of Energy, 2016
6. [Can woodfuel (charcoal and firewood) be modernized in Africa? (Njenga, Mwampamba, Mendum)](https://www.globallandscapesforum.org/wp-content/uploads/2018/09/Can-woodfuel-charcoal-and-firewood-be-modernized-in-Africa.pdf) ICRAF / Global Landscapes Forum, 2018

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_bio_store/index.md)
- [Overview](https://www.materialinsights.org/energy/e_bio_store/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_bio_store/correlation/index.md)
- [Engineering and performance](https://www.materialinsights.org/energy/e_bio_store/sg-eng/index.md)
- [Economics](https://www.materialinsights.org/energy/e_bio_store/sg-econ/index.md)
- [Impact and additionality](https://www.materialinsights.org/energy/e_bio_store/sg-impact/index.md)
- [What to track](https://www.materialinsights.org/energy/e_bio_store/tracking/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_bio_store/links/index.md)