Data from national administrations are, in most cases, inadequate both in quantity and quality. Energy statistics are frequently restricted to the commercial (and thus more easily measurable) component of the energy picture. In developing countries, there is often a lack of expertise as well as financial and human resources for adequate data collection and estimation, a task rendered more difficult by the decentralised, mostly rural, and largely non-marketed nature of bioenergy use. The variety of sources, the lack of uniform definitions and methodologies, and the use of different units and conversion factors, make comparison between countries and assessment of time trends a difficult task . Even where the figures and values presented or estimated by national and international statistics are well established, the structure of the bioenergy database is affected by the following problems :
• Coverage: Different international agencies produce periodic statistical data (i.e. FAOSTAT, UN-ECE, IEA, OLADE, EUROSTAT) on products related to bioenergy but with very heterogeneous approaches and without truly covering bioenergy. Those statistics are based on a few and selected biofuels only (e.g. FAO covers charcoal and “Wood Fuel, including wood for charcoal” as sub-category of roundwood removals; EUROSTAT covers biomass as renewable energy source with a sub-category called “wood and wood waste” that includes, in spite of the definition, also lingo-cellulosic biomass from agro-residues; IEA publishes data on Primary Solid Biomass inclusive of wood and non-wood biomass but keeps estimates of sub components such as wood, black liquor, agricultural residues, etc. The data on biofuels, and woodfuels in particular, have also to fit into the structure of the energy and forestry statistics which are the main basis for modelling and forecasting work that is undertaken in the technical organizations involved. For instance, data on black liquor (the most important form of wood energy in many developed countries) are omitted in FAO statistics. In addition, key agrofuels are not considered at all in most of the statistics.
• Disaggregation: most existing information on biofuels and woodfuels is focused on biomass consumption and do not pay sufficient attention to other related aspects such as production and supply sources. Regardless of the importance of non-forest supply sources of wood energy and the large use of recycled products, the supply side is not disaggregated in the FAOSTAT database. On the other hand, although there is a clear shift of wood energy demand from traditional to modern uses, with considerable repercussions for the whole wood energy systems, information on the sectors of utilization is also absent in most databases. Only IEA statistics are consistently disaggregated by sector. Another important but equally neglected aspect concerns the distinction between urban and rural consumption patterns.
• Definition incompatibility: the main terminology currently used by the above agencies is not adequate for the proper collection, collation, exchange and presentation of biofuel data yet. The absence of a comprehensive framework and clear sets of definitions limit the possibility of comparison and exchange with other data sources on bioenergy.
• Uncertainty of conversion factors: bioenergy accounting covers primary data from various sources. Energy sources and commodities may be measured by their mass or weight or even volume, but the essential factor is the energy content related to these sources and commodities. The uncertainty of conversion factors limits the possibility of comparison and exchange with other data sources.
Therefore there is a strong need for a unified terminology which will improve data collection and exchange in order to enable assessments and policy analysis at a national and international level. To develop an adequate database for bioenergy, the following aspects need to be taken into consideration:
• supply sources: including forestry and agriculture, biomass processing industries (wood industry and agro-industry) and end-use products of the society as well as biofuel preparation activities (i.e. charcoal production)
• demand (users side): including the main demand sectors (residential, commercial, industrial sectors and heat and power generation) as well as the distinction between urban and rural areas
• trade: including import and export of biofuels.
The basic idea behind such a terminology is to create a suitable framework for the identification of the amount and type of bioenergy flowing from different supply sources to meet end users needs. Thus the fuel or product used to transport energy is the basic parameter to be accounted and properly classified. Whether in commercial or non-commercial terms, these fuels should always be considered goods or commodities that are valuable and capable of meeting demand effectively.
Bioenergy balances are derived from conventional energy balances, which are commonly used for the representation of data on production, conversion and consumption of all individual fuels in a table or diagram. Bioenergy balances include quantitative summary data on biomass used as fuel for energy production.
Bioenergy balances allow the analyses and understanding of all the operation and process units of biofuel cycles from production up to the use of energy generated with them.
Unfortunately, bioenergy balances are not commonly used by planners and policy makers. The following figure (Fig.1) gives an overview on biomass to biofuel flow within a given bioenergy system2 considering the intermediate activities involved such as preparation, conversion and trading (import and export).
Bioenergy balances also show specific information on the biomass production sources which is vitally needed for management purposes in order to examine the production and degradation capacities of different biomass supply sources. They may also help in the assessment of competitions with other uses as well as environmental impacts in order to: a) determine their sustainable use and b) develop sustainable resource management systems.
In addition, they allow the analysis of conversion, trade and utilisation aspects of biofuels such as energy efficiencies and conversion losses.
Figure 1: Flow of biofuels from the source
Most biofuels and woodfuels in developing countries are traded through informal markets. For the increased, more efficient and cost effective biofuel utilisation, more intensive trading activities are necessary at the local as well as international level. These fuels should be considered as an important environmentally friendly source of energy. Compared to other renewable energy sources, biofuels involve a wide range of fuels. These differ in provenance, physical/mechanical properties (e.g. total moisture, particle size and particle size distribution) and chemical composition (e.g. total carbon, total nitrogen). In this context the lack of clearly defined biofuel properties as well as clear supply conditions are seen as major non-technical impediments to effective trade.
Standardisation of biofuel terminology and the classification of their properties, as well as measurement standardisation, is one of the tools to improve the situation. Having a biofuel terminology and specification available, which is well adapted to practical needs, will assist the development of a more effective biofuel market. If the properties of the traded product “biofuel“ are clearly defined and well known (for example for the different types of gasoline or fuel oil), more transparent markets and prices are likely. Based on a unified terminology, market expansion and cost reductions can be expected to follow because of the following effects:
• producers of biofuels get more concrete signals to guide the production of biofuels. They are able to optimise their production processes based on the demanded properties, and to reduce costs;
• energy provision systems and conversion technologies can be better designed, and they can operate more efficiently and environmentally soundly if fuel quality is defined within a narrow range.
With regard to the intended effects there are two relevant areas of standardisation to be taken into consideration:
• Definition of the relevant biofuel sources and trade forms by a detailed and transparent terminology of the biomass resources (i.e. the different types of forest products and by-products): The terminology, definitions and descriptions as well as the fuel specifications and classes which are applied in the different countries are characterised by tradition and by characteristics of the national fuel market and their need of information. Problems of the comparability of national terms and definitions can arise mainly because of differences in the national systems of nomenclature. These differences can be serious obstacles, hindering trading and comparison of solid biofuels within and across countries. Standardisation in the field of terminology and definitions as well as fuel specifications and classes can make a valuable contribution to facilitating trading and the assessment of the quality and value of biofuels, and to increasing their use as an energy source on the international and national level. The development of standards can also provide a vital input to any serious decision making on a host of topics linked in one way or another to biofuels.
• Identification and Classification of the most relevant biofuel properties to ensure a cheap and trouble-free conversion on a low emission level. Special emphasis is needed on total moisture, total ash, shape and particle size and density (see chapter 5).
Within the European Union there is general agreement on the need for European standards in the field of solid biofuels. Especially in those EU countries with a high (potential) share of solid biofuels, standardisation is regarded as an important issue to promote and increase the use of biomass as energy source. As a result of the ongoing discussions that are taking place the Commission of the European Community has mandated the European Committee for Standardisation (CEN) to initiate the development of European standards for solid biofuels  . A Technical Committee "Solid Biofuels" was established by CEN in Stockholm at the end of May 2000, and this is to undertake the drafting of more than 20 European standards on terminology, classification, sampling and testing.
Activities on standardisation have to be followed by the development of quality assurance systems. Theoretically, these can be introduced for all processes in the provision chain (i.e. in crop production, harvesting, preparation etc.). A major motivation for quality assurance is to fulfil legal limit requirements (e. g. emission limits), or to meet technical demands for the power plant (e. g. avoiding corrosion). To guarantee these basic conditions, chemical and/or physical parameters may be varied theoretically by crop production processes (e. g. modifying the total nitrogen of whole grain crops by Nitrogen fertilisation) as well as by harvesting/preparation (e. g. modifying the total moisture of wood by storage). Additionally, at the conversion plant technical means are available for e. g. emission reduction (e. g. primary and secondary measures for NOx-emission reduction). In practice quality assurance are of most interest for non-woody biofuels used in emission controlled plants.
2 Bioenergy systems include all the steps and/or unit processes and operations involved for the production, preparation, transportation, marketing, trade and conversion of biofuels into energy.