Publications

Survey of Energy Resources 2007

Wood Fuels

From the 2004 Survey of Energy Resources it is evident that wood fuels make up about 50% (24 EJ) of the IEA estimate of 48 EJ classified as combustible renewables and waste (IEA, 2006). As was noted in the Wood chapter of the 2004 Survey, there are two very different populations using wood fuels. One, typically an OECD member country, uses highly-efficient combustion technology under tight regulations on emissions. The other (representing by far the majority - estimated at three billion people) uses small-scale appliances (three-stone fires or cooking stoves) that are both inefficient and highly polluting. The two populations are also different with respect to the estimation of their energy consumption; the former increasingly uses wood fuels that are traded commercially, while the latter still operates in an informal sector for which only estimates can be made.

Statistics on wood fuel use are poor in both developed and developing countries because of insufficient institutional awareness, resulting in different approaches to making estimates. There are many different aspects of government jurisdiction involved in the wood fuel sector. Moreover, the lack of reliable statistics exacerbates the problems of supply management and the mitigation of negative impacts from the use of wood fuels. For example, forestry departments are concerned with the total wood flow out of forests; energy department concerns are with estimates of household, commercial and industrial energy requirements, while environmental regulators may be concerned with resource depletion (soil, water and biodiversity) and emissions impacts, and by no means last, the health sector may be following the effects of household emissions on chronic diseases.

One of the most critical of these issues is that of indoor air pollution, which featured in a special session addressing household energy and health at the 14th meeting of the Commission for Sustainable Development (CSD-14). The World Health Organization (WHO) simultaneously released Fuel for Life: household energy and health (Rehfuess, 2006) in which the call for both improved stoves and the substitution of modern fuels such as LPG is made.

In the 2004 update of the UN Food and Agricultural Organization's (FAO) interactive Wood Energy Statistics (i-WESTAT) (Drigo and Trossero, 2005), there is a detailed analysis of the state of different statistical sources of wood fuels. With the advent of new technologies based on geographic information systems (GIS) and their integration with survey activities, the FAO has developed the Wood Fuel Integrated Supply/Demand Overview Mapping (WISDOM) methodology. WISDOM has demonstrated that accurate, and indeed exhaustive, wood energy statistics can be obtained at several levels, ranging from regions to local forests (Masera, Ghilardi, et al., 2006). The early applications of WISDOM are not yet sufficient to revise the information base, so the present analysis of wood fuel will continue to rely on the FAOSTAT database (FAO, 2006).

The current wood energy situation.
Wood Fuel is classed into three main commodities: fuelwood, charcoal and black liquor. Black liquor is the spent pulping chemicals and the lignin component of wood after chemical pulping. It is fired in a chemical recovery boiler and process steam and electricity are also produced. Fuelwood and charcoal are the traditional wood forest products, and even today almost half of all of the forest harvest is for energy, with the remainder for industrial use (lumber, veneer and paper). Some of this is indirect, in that timber that is harvested may first be converted into board and the residues, such as bark, trim ends, and sawdust, then transferred from the wood industry into the energy sector, as is the case with black liquor. As well as this secondary generation of wood energy, there is a tertiary source in the form of post-consumer residues that arise from the manufacture, use or disposal of wood products. This source often ends up in the municipal waste stream and in many OECD countries it is separated from the stream, either for recycling or for use in energy products.

Charcoal is produced by the thermal conversion of wood (and other biomass). This transformation has losses in the form of combustible gas and condensable materials (wood tar), which are not always recovered for either material applications or energy purposes. The energy efficiency of charcoal production ranges from 25% in Africa (using mainly artisanal methods) to 48% in Brazil which uses industrial kilns with extensive energy and materials recovery. The FAOSTAT forestry database uses a single conversion of 6 m3 roundwood solid volume equivalents for one tonne of charcoal, corresponding to nearly 50% efficiency.

The values for 2005 are comparable to those of the 2004 SER. Differences are most likely due to the general improvement in estimates at the country level, as the FAO forestry group improves the overall methodology. Given the relative imprecision of the estimates it is not possible to see trends that will have a major impact on the values of previous years.