Thermochemical biomass conversion: Efficiency

Seconds or hours of heating: how speed decides the product

What this tab covers How much of the energy available is actually captured or extracted, in per cent: theoretical limits, laboratory records, typical new equipment and in-service averages, each with exactly what is being measured.

Heating biomass with little or no oxygen splits it into gas, liquid and char: fast pyrolysis turns up to 65-75% of dry wood's mass into bio-oil, gasification about 85% into gas. Turning these into electricity or transport fuel leaves 25-40% as electricity or 14-18% of the mass as liquid fuel.

Chart: Efficiency ranges

Commercial Record

Efficiency by measure

Measure	Range	Type	What is measured
Fast pyrolysis, bio-oil yield (commercial practice)	65% by mass¹	Commercial	Bio-oil per unit of dry feed, about 1-2 seconds at around 500 C
Fast pyrolysis, best liquid yield	75% by mass²³	Record	Liquid per unit of dry wood feed (char 12%, gas 13%)
Slow pyrolysis (carbonisation), char yield	35% by mass³	Commercial	Char per unit of dry wood at about 400 C over hours to days, with 30% liquid and 35% gas
Gasification, gas yield	85% by mass³	Commercial	Gas per unit of dry wood at about 800 C, with 5% liquid and 10% char
Torrefaction, solid yield	82% by mass³	Commercial	Torrefied solid per unit of dry wood at about 290 C for about 30 minutes (18% leaves as gas)
Gasifier with gas engine, CHP	25 to 30%⁴	Commercial	Energy in biomass to electricity (0.2-1 MWe units)
Biomass integrated gasification combined cycle (IGCC)	30 to 40%⁴	Record	Energy in biomass to electricity
Gasification with Fischer-Tropsch synthesis	14 to 18% by mass⁵	Commercial	Distillate fuel per tonne of agricultural (14%) or forest (18%) residue
Microbial fuel cells, coulombic efficiency	55.6%¹¹	Record	Share of electrons in the organic feed recovered as current, best reported under optimised laboratory conditions

Where the energy is lost

Step	Loss
Pyrolysis char and gas (usually burned to heat the process)	about 25% of feed mass (12% char, 13% gas)²³
Water carried in bio-oil	about 25% of bio-oil by weight²

These processes break biomass into simpler fuels that are easier to store, ship or refine. Rapid heating to about 500 C for a second or two, with quick cooling of the vapours, gives mostly liquid; slow heating gives mostly char; higher temperatures with a little air or steam give mostly gas.

Bio-oil is not crude oil: it carries about 25% water and much oxygen, so it holds about 18 MJ per kg, roughly 40% of the energy of fuel oil by weight and 60% by volume, and must be upgraded with hydrogen before it can become transport fuel. Torrefaction (200-350 C) is a milder roasting that keeps about 82% of the mass as a dry, brittle 'bio-coal'. No quantitative efficiency data were found for hydrothermal liquefaction in the sources reviewed.

Sources

Torrefaction and pyrolysis (European Industrial Bioenergy Initiative factsheet EIBI-4) ETIP Bioenergy
IEA Bioenergy Update 29: Task 34 technology report on fast pyrolysis IEA Bioenergy
Fast pyrolysis: key points (table of product yields by pyrolysis mode) IEA Bioenergy Task 34 (Direct Thermochemical Liquefaction)
Energy Technology Essentials ETE03: Biomass for Power Generation and CHP (2007 cost estimates) International Energy Agency (copy hosted by nachhaltigwirtschaften.at), 2007
Progress in commercialisation of biojet / SAF (van Dyk, IEA Bioenergy workshop presentation) IEA Bioenergy Task 39 (hosted by DBFZ), 2023
Recent Applications, Challenges, and Future Prospects of Microbial Fuel Cells: A Review (Chakma et al., Global Challenges 9(5) 2500004) Wiley (open access, PubMed Central), 2025