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5. UWET proposal

The basic idea behind the Uniform Wood Energy Terminology (UWET) is to create a suitable framework for the identification of the amount and type of wood energy flowing from different supply sources to meet end user needs. Thus the fuel or product used to transport energy is the basic parameter to be accounted and properly classified. Either in commercial or non-commercial terms, these fuels should always be considered goods or commodities that are valuable and capable of meeting demand effectively.

Figure 1 presents a conceptual view of wood energy systems, showing how wood energy physically flows to satisfy demand. The figure introduces the three different supply sources: nature (forests and trees-outside forests), wood industries and society. The user's side is also presented, shared among the main demand sectors. Additional considerations regarding wood energy trade complete the picture.

As a complement to the general approach presented in Figure 1, a detailed scheme for classifying biofuels is presented in Table 2. The prime consideration behind the classification suggested in Table 2 is to recognize the basic site where biomass production takes place; in other words, to distinguish whether the biofuel was connected to forest, agricultural or municipal activity. Moreover the inclusion of a group on the use of agrofuels aims at distinguishing classical biofuels (generally related to forest exploitation) from later ones, basically oriented towards annual or pluri-annual plantation.

The groups on the supply side concern important sub-divisions which clearly identify the origin of biofuels. On the end user side, the variety of fuels that can be produced for each group can be observed, thus allowing for data comparison and verification on both supply and demand. The far right column of Table 2 lists the different types of primary, secondary and even tertiary fuels which can be used for heat, electricity and power generation. Secondary and tertiary fuels are often derived from raw biomass produced from various supply sources following the application of relatively complex transformation processes. Definitions of the main terms employed are provided in Section 5.2.

Figure 1. Wood fuel balance scheme, from supply source to end user

Table 2: Biofuel classification scheme

Production side, supply

Common groups

Users side, demand examples

5.2.1 Energy

5.2.2 Bioenergy sources

Biofuels: organic primary and/or secondary fuels derived from biomass which can be used for the generation of thermal energy by combustion or by using other technology. It comprises both purpose-grown energy crops, as well as multipurpose plantations and by-products (residues and wastes). The term "by-products" includes the improperly called solid, liquid and gaseous residues and wastes derived from biomass processing activities. The main definitions employed in UWET include three types of biofuel: woodfuels, agrofuels, and municipal by-products.

A. Woodfuels

Include all types of biofuels derived directly and indirectly from trees and shrubs grown in forest and non-forest lands. The definition of forest used in the FAO Forest Resource Assessment 1990 (FAO Forestry paper 124, p7) is rather broad and includes lands with a minimum crown cover of 20% in developed countries and 10% in developing countries. Woodfuels also include biomass derived from silvicultural activities (thinning, pruning etc.) and harvesting and logging (tops, roots, branches, etc.), as well as industrial by-products derived from primary and secondary forest industries which are used as fuel. They also include woodfuels derived from ad hoc forest energy plantations.

According to origin, woodfuels can divided into three groups: Direct woodfuels, Indirect woodfuels, and Recovered woodfuels, as presented in Figure 1 and defined as follows.

Table 3. Woodfuel importance


Supply side (sources)


(wood energy vectors)

Direct Woodfuels

Indirect Woodfuels

Recovered Woodfuels









Black liquor




Other (methanol, ethanol, pyrolitic gas)





XXX : very important

XX : important

X : less important or in technological development


E : currently estimated

NE: currently non evaluated

As regards the commodities to be considered in wood energy accounting, woodfuels can be divided into four types of products: fuelwood, charcoal, black liquor and other, defined as follows.

The present importance of different types of woodfuels, as well as the availability of data in FAO STAT current tables are summarized in Table 3.

B. Agrofuels

Fuel obtained as a product of agriculture biomass and by-products. It covers mainly biomass materials derived directly from fuel crops and agricultural, agroindustrial and animal by-products.

In the future, also more attention will be given to the definition of different types of agrofuels which so far have received marginal attention; not only regarding the terminology used but also for the development of improved data bases.

C. Municipal by-products

Refer to biomass wastes produced by the urban population and comprise two types: solid municipal by-products and gas/liquid municipal by-products produced in cities and villages.

For easy reference, Table 4 provides brief definitions of the main terms adopted.

Table 4: Definition of Biofuel Classifications Proposed

1st level

2nd level

Brief definition



Direct Woodfuels

Wood used directly or indirectly as fuel, produced for energy purposes


Indirect Woodfuels

Mainly solid biofuels produced from wood processing activities


Recovered Woodfuels

Wood used directly or indirectly as fuel, derived from socio-economic activities outside the forest sector


Wood-derived fuels

Mainly liquid and gaseous biofuels produced in forest activities and the wood industry



Fuel crops

Growing plants for the production of biofuels


Agricultural by-products

Mainly residues from crop harvesting and other kinds of by-products from agricultural activities left in the field


Animal by-products

Basically excreta from cattle, horses, pigs and poultry


Agro-industrial by-products

Several kinds of materials, produced chiefly in food processing industries, such as bagasse and rice husks

Municipal by-products

Solid and liquid municipal residues

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