# Biomass combustion and CHP: Efficiency

Why an open fire wastes up to 90% of its fuel

Source page: https://www.materialinsights.org/energy/e_bio_combustion/efficiency/

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.

Burning biomass turns anywhere from under 10% (an open fire) to 90% (a well-matched combined heat and power plant) of the fuel's heat into useful energy. Electricity alone rarely exceeds 40%, and plants below 1 MWe manage only 10-12%.

Chart: Efficiency ranges
 In service Commercial

#### Efficiency by measure

| Measure | Range | Type | What is measured |
|---|---|---|---|
| **Open fires and traditional stoves** | 10 to 20%^[3](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2015/IRENA-ETSAP_Tech_Brief_E05_Biomass-for-Heat-and-Power.pdf)^[1](https://cleancooking.org/news/10-16-2018-voluntary-performance-targets/) | In service | Heat in fuel to useful cooking heat (thermal efficiency); ISO Tier 0 (below 10%) is typical of open fires |
| **Improved biomass cookstoves (ISO Tiers 2-5)** | 20 to 50%^[1](https://cleancooking.org/news/10-16-2018-voluntary-performance-targets/) | Commercial | Thermal efficiency thresholds of ISO/TR 19867-3:2018: Tier 2 at least 20%, Tier 5 at least 50% (laboratory tests) |
| **Small back-pressure CHP plants (below 1 MWe)** | 10 to 12%^[2](https://task32.ieabioenergy.com/?p=4686) | Commercial | Heat in fuel to net electricity |
| **Dedicated biomass power plants** | 16 to 40%^[3](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2015/IRENA-ETSAP_Tech_Brief_E05_Biomass-for-Heat-and-Power.pdf)^[2](https://task32.ieabioenergy.com/?p=4686) | In service | Heat in fuel to net electricity: 16% at 2 MWe, 30-32% at 25-44 MWe, 36% at 350 MWe; over 40% for large condensing plants |
| **Co-firing biomass in large coal plants** | 36 to 44%^[3](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2015/IRENA-ETSAP_Tech_Brief_E05_Biomass-for-Heat-and-Power.pdf) | Commercial | Heat in fuel to net electricity (biomass burned alongside coal in a big, efficient boiler) |
| **Biomass combined heat and power** | 70 to 90%^[3](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2015/IRENA-ETSAP_Tech_Brief_E05_Biomass-for-Heat-and-Power.pdf)^[4](https://old.etipbioenergy.eu/images/ETIP_Bioenergy_Factsheet_Biomass_CHP_facilities.pdf) | Commercial | Heat in fuel to electricity plus useful heat, when heat demand is well matched |
| **Charcoal from earth mound kilns** | 12 to 16% by mass^[5](https://www.fao.org/4/x6796e/X6796E05.htm) | In service | Mass of charcoal per mass of wood loaded (Mozambique field measurements) |
| **Slow pyrolysis (carbonisation) under controlled conditions** | 35% by mass^[6](https://task34.ieabioenergy.com/?p=4482) | Record | Char yield from dry wood at about 400 C over hours to days |

#### Where the energy is lost

| Step | Loss |
|---|---|
| **Open fire: heat escaping around the pot, unburnt smoke and wet fuel** | 80-90% of the fuel's heat (calculated from 10-20% efficiency)^[3](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2015/IRENA-ETSAP_Tech_Brief_E05_Biomass-for-Heat-and-Power.pdf) |
| **Power plant: heat rejected in the steam condenser and flue gas** | 60-84% of fuel heat in electricity-only plants (calculated from 16-40% efficiency)^[3](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2015/IRENA-ETSAP_Tech_Brief_E05_Biomass-for-Heat-and-Power.pdf)^[2](https://task32.ieabioenergy.com/?p=4686) |

Bone-dry wood holds 18-20 MJ per kg, but wet wood far less (about 8.5 MJ/kg at 50% moisture) because water must be boiled off. An open fire heats the air around the pot, an enclosed stove channels hot gas against it, and a power station loses most of its heat at the steam condenser.

Size matters for power: a 2 MWe plant converts about a sixth of its fuel to electricity, a 350 MWe plant or a co-fired coal boiler 36-44%. Using the leftover heat (CHP) lifts total efficiency to 70-90%. Traditional charcoal kilns keep only 12-16% of the wood's mass, burning much of the rest to drive the process.

#### Sources

1. [Voluntary Performance Targets for cookstoves (ISO/TR 19867-3:2018 tiers for thermal efficiency, CO and fine particulate emissions)](https://cleancooking.org/news/10-16-2018-voluntary-performance-targets/) Clean Cooking Alliance, 2018
2. [Power generation and cogeneration](https://task32.ieabioenergy.com/?p=4686) IEA Bioenergy Task 32 (Biomass Combustion)
3. [Biomass for Heat and Power, Technology Brief E05](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2015/IRENA-ETSAP_Tech_Brief_E05_Biomass-for-Heat-and-Power.pdf) IEA-ETSAP and IRENA, 2015
4. [Biomass CHP facilities (factsheet)](https://old.etipbioenergy.eu/images/ETIP_Bioenergy_Factsheet_Biomass_CHP_facilities.pdf) ETIP Bioenergy (European Technology and Innovation Platform)
5. [Review of the existing studies related to fuelwood and/or charcoal in Mozambique, section 3.2 Charcoal production](https://www.fao.org/4/x6796e/X6796E05.htm) FAO
6. [Fast pyrolysis: key points (table of product yields by pyrolysis mode)](https://task34.ieabioenergy.com/?p=4482) IEA Bioenergy Task 34 (Direct Thermochemical Liquefaction)

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_bio_combustion/index.md)
- [Overview](https://www.materialinsights.org/energy/e_bio_combustion/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_bio_combustion/correlation/index.md)
- [Techniques](https://www.materialinsights.org/energy/e_bio_combustion/techniques/index.md)
- [Resources and labour](https://www.materialinsights.org/energy/e_bio_combustion/resources/index.md)
- [Impact on the biosphere](https://www.materialinsights.org/energy/e_bio_combustion/biosphere/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_bio_combustion/links/index.md)