Firewood and charcoal supply: Efficiency and losses
Why the kiln, not the road, wastes most of the energy
What this tab covers How much energy is lost while it moves and while it waits in storage or transit, and how much energy the transport itself consumes, in per cent.The big loss is not on the road but in the kiln, where most of the wood's energy is lost before the charcoal is even bagged.
Chart: Efficiency ranges
Whole chainLosses by measure
| Measure | Range | Type | What is measured |
|---|---|---|---|
| Simple kilns in low-income countries, energy efficiency | 10 to 22%2 | Whole chain | Share of wood energy kept in the charcoal |
| Traditional earth kiln, energy efficiency | 18%3 | Whole chain | Share of wood energy kept in the charcoal, Rwanda average |
| Casamance improved kiln, energy efficiency | 32%3 | Whole chain | Share of wood energy kept in the charcoal, Rwanda average |
| Kiln yield by dry weight | 12 to 40%3 | Whole chain | Kilograms of charcoal per kilogram of dry wood across more than 30 kilns (some exceed 40%) |
| Production plus end-use losses | 70 to 85%3 | Whole chain | Share of original wood energy lost in kiln and cookstove combined |
| Wood-to-charcoal ratio, Tanzania | 10 kg wood per kg charcoal4 | Whole chain | Approximate national ratio |
Holding periods and inventory
| Measure | Value |
|---|---|
| Kiln cycle, Kenya | Planning 2 to 3 days, drying 7 days, carbonising 7 days, cooling 1 day5 |
| Former FAOSTAT conversion factor (to 1997) | Charcoal weight multiplied by 6 to give wood equivalent8 |
| Losses from breakage and fines in transport | Not quantified in the sources found; FAO notes transport adds relatively little to the chain's greenhouse gas emissions2 |
| Fuel used by trucks per tonne-km | Not quantified in the sources found3 |
Sources disagree on the wood-to-charcoal ratio: FAOSTAT formerly converted charcoal to wood at a factor of about 6, while Tanzanian field estimates use about 10 kg of wood per kg. The gap reflects different kilns, wood moisture and whether volume or weight is measured.
Firewood, by contrast, loses no energy in conversion but is bulky and heavy, so it is rarely carried far; most is gathered and used within walking distance. Transport losses are mainly time: kiln cycles of two to three weeks, and the hours that women and children spend collecting wood (in one Kenyan study, women carried loads of about 50 to 60 kg from forests 1 to 4 km away).
Sources
- The charcoal transition: greening the charcoal value chain to mitigate climate change and improve local livelihoods FAO, 2017
- Review of technologies for the production and use of charcoal (Kammen and Lew) Renewable and Appropriate Energy Laboratory, UC Berkeley, 2005
- Environmental Crisis or Sustainable Development Opportunity? Transforming the Charcoal Sector in Tanzania: A Policy Note World Bank, 2009
- Sustainable Business Models for Tree-based Value Chains in Sub-Saharan Africa: Analysis of the Charcoal Value Chain in Kenya (Mutta) Swedish University of Agricultural Sciences (SLU), Formas project, 2020
- The revision of woodfuel estimates in FAOSTAT (Whiteman, Broadhead and Bahdon) FAO, 2002