Material Insights · Understanding the Material World

Biomass and biofuel stores: Engineering and performance

Cheap, simple stores that slowly leak their energy

What this tab covers Engineering and operating performance: round-trip efficiency, whether power and energy can be scaled separately, footprint and siting, and safety.

Bio-stores are cheap and simple but leak energy over time; they buffer seasonal harvests rather than serving as precise grid storage.

Round-trip efficiency

Mixed

There is no electrical charge and discharge; the relevant loss is energy lost while in store. Covered chip piles lose about 0.7% of dry matter a month, so six months could cost roughly 4% (calculated). Liquid biofuels lose little energy if kept dry and stable. Charcoal's big loss happens before storage, in the kiln.18

Covered chip pile, six months about 4% dry matter loss (calculated)1

Power and energy decoupling

Favourable

Fully decoupled: the pile or tank sets energy, and the boiler, engine or turbine sets power. Biogas is the exception: one manufacturer's membrane gasholders range from about 10 to 16,700 cubic metres and work at very low pressure (up to about 70 mbar), so they buffer hours of production, letting a biogas engine run at peak-price times rather than store seasonally.6

Membrane gasholder volume (manufacturer range) 10 to 16,700 m36 Gasholder pressure (manufacturer data) up to about 70 mbar6

Footprint and siting flexibility

Mixed

Biomass is bulky. Indian thermal plants co-firing pellets have missed targets because of inconsistent pellet supply, seasonal residue availability and limited storage in the monsoon months. Liquid biofuels fit existing fuel depots with some material changes: biodiesel attacks zinc, lead and some plastics, and ethanol attacks natural rubber, some plastics and some older fibreglass tanks.457

Safety and thermal runaway risk

Unfavourable

Self-heating is biomass's version of thermal runaway: pellets and chips can heat to the point of ignition. Carbon monoxide build-up in pellet stores requires confined-space procedures, gas checks before entry and permanent ventilation, as the UK HSE warned in 2012 after at least nine deaths in Europe. E85 vapour in tank headspace can be flammable below about minus 2 C to minus 22 C, depending on the blend. In the EU, large depots fall under the Seveso III directive, whose entry for petroleum products and alternative fuels sets thresholds of 2,500 t and 25,000 t.2359

E85 headspace flammable below about minus 2 C to minus 22 C, by sample5 Seveso III petroleum products and alternative fuels 2,500 t lower tier; 25,000 t upper tier9

Sources

  1. Info-sheet 4: Storage of forest chips (SECURE-BIO-SUPPLY), S. Lieskoski Abo Akademi University, 2025
  2. Safety alert: Risk of carbon monoxide release during the storage and transportation of wood pellets UK Health and Safety Executive, 2012
  3. COFORD Connects note: storage and handling of wood pellets COFORD (Ireland), 2016
  4. Biodiesel Handling and Use Guide, Sixth Edition (NREL/TP-4A00-86939) NREL (renamed National Laboratory of the Rockies in 2025) / US DOE, 2023
  5. Handbook for Handling, Storing, and Dispensing E85 and Other Ethanol Blends US Department of Energy, 2016
  6. Ecomembrane gasholder catalogue (manufacturer data) Ecomembrane (via Consorzio Italiano Biogas), 2020
  7. Decarbonising coal: co-firing as a viable pathway to cleaner thermal power generation (reporting CAQM and Ministry of Power data) Renewable Watch, 2026
  8. Can woodfuel (charcoal and firewood) be modernized in Africa? (Njenga, Mwampamba, Mendum) ICRAF / Global Landscapes Forum, 2018
  9. Directive 2012/18/EU (Seveso III), Annex I legislation.gov.uk (EU directive text as adopted), 2012