Considering the very probable depletion of liquid fossil fuels toward 2090 and the start of declination of oil production in 2020 through 2030, humankind will face the huge challenge of maintaining its economic growth and stable technological development without compromising the welfare of the future generations (sus­tainable development). In addition, the quality of life for people from developing and underdeveloped countries should be improved without compromising the life level of those people in developed nations. Kosaric and Velikonja (1995) point out that the solution to this problematic situation depends on how mankind develops and implements viable technologies for the industry, transport sector, and heat­ing based on alternative (renewable) fuels and feedstocks as well as ensuring the availability of sufficient amounts of renewable resources (energy and raw materi­als). Furthermore, man should develop and implement technologies for reducing the environmental pollution and CO2 emissions. For these reasons, the renewable energies may partially or totally replace the fossil fuels, especially if humankind does not choose the dangerous pathway toward the global development of nuclear energy as a primary source of energy.

The renewable energy sources correspond to those kinds of energy that are obtained from natural sources, which are practically inexhaustible due to the huge amount of energy that they contain and to their ability to regenerate themselves by natural means. Among the energy sources of one type, solar, wind, hydraulic, geothermal, and tide energy should be highlighted. The energy sources of a sec­ond type correspond to the bioenergy or energy from biomass. One of the main features of the renewable energies is that their utilization does not imply the net generation of polluting emissions, which contribute to the greenhouse gas effect or the destruction of the ozone layer. The renewable energy sources represent 7.68% of the total energy consumed in the world, with the biomass being the most exploited resource (Energy Information Administration, 2008). Two thirds of the biomass is used for food cooking and heating in developing countries (tra­ditional use of the biomass), e. g., through the use of firewood. The remaining third corresponds to the commercial use of the biomass for the industry (e. g., cane bagasse as energy source in sugar mills), generation of electricity (e. g., wood chips feeding small thermal plants), and transport sector (liquid biofuels produc­tion). The hydroelectric energy is the second most important renewable resource, whereas the contribution to the global energy consumption from such sources as the sun, winds, tides, and geothermal energy is marginal. A 59.2% increase in the consumption of renewable energy (corresponding to 828 million tons of oil equivalent) is expected in the period 2002 to 2030 (IEA, 2004).

One renewable solution in the search for alternative sources of energy for the world populace is the use of solar energy in the form of biomass (bioenergy). The global potential of bioenergy is represented by the energy-rich crops (mostly rep­resented by agroenergy) and lignocellulosic biomass (including the dendroenergy from forest activities). The conversion of these feedstocks into biofuels, either for electricity generation or for their use in vehicles, is an important option for exploi­tation of alternative energy sources and reduction of polluting gases (Sanchez and Cardona, 2008b), mainly CO2. The emissions generated by the combustion of biofuels are offset by the CO2 absorption during the growth of plants and other plant materials from which these biofuels are produced. In this way, the biomass utilization releases the carbon dioxide that was fixed during its growth, compen­sating the emissions generated in the current scale of time. In contrast, fossil fuel usage releases into the atmosphere the carbon dioxide that was fixed by the plants million of years ago, which implies a net increase in the amount of atmospheric CO2, provoking global warming.

Energy-rich crops comprise those crops that could be exclusively addressed to the energy production either as solid fuels for electricity generation or as liquid biofuels that can substitute for the fossil fuels (bioethanol, biodiesel). It is esti­mated that one hectare of energy-rich crops employed for liquid biofuel production can avoid the emissions of 0.2 to 2.0 tons of carbon into the atmosphere compared to the use of fossil fuels (Cannell, 2003). For the case of ethanol obtained from sugarcane in Brazil, its use may offset carbon dioxide emissions at a rate of 2 t C/ (Ha/year) related to the oil. This substitution is more appreciable in tropical coun­tries, whereas the offset is more effective for European countries if the electricity is produced from biomass. Kheshgi and Prince (2005) indicate that if the CO2 released during the alcoholic fermentation is captured and injected into the sub­soil or deeply in the ocean (where it is dissolved), ethanol production may lead to a net carbon dioxide removal from the atmosphere (CO2 sequestration) avoiding the emissions generated by the gasoline usage. Eventually, the environmental benefits can be enhanced if the feedstock employed is made up of residues or wastes.

The so-called lignocellulosic biomass includes agricultural, forestry, and municipal solid residues as well as different residues from agro-industry, the food industry, and other industries. The lignocellulosic biomass is made up of complex biopolymers that are not used for food purposes. The main polymeric components of biomass are cellulose, hemicelluloses, and lignin. For their conversion into a liquid biofuel such as ethanol, a complex pretreatment process is required in order to transform the carbohydrate polymers (cellulose and hemicellulose) into fermentable sugars. In contrast, for electricity generation, only the combustion of the biomass is needed.

It is evident that lignocellulosic biomass as feedstock for energy production is important. The lignocellulosic complex is the most abundant biopolymer on Earth and is present in such profuse materials as wood, sawdust, paper residues, straw, and grasses (Sanchez and Cardona, 2008b). It is estimated that the lignocel­lulosic biomass makes up about 50% of world biomass and its annual production has been estimated at 10 to 50 billion tons (Claassen et al., 1999). For instance, 35% of the material collected during the total wheat harvest in Europe corre­sponds to the straw, whereas 45% corresponds to the grain. In addition to the energy generation, the biomass utilization allows the economic exploitation of a wide range of residues from domestic, agricultural, and industrial activities. One of the main advantages of using lignocellulosic biomass is that this feedstock is not related to food production, which would permit the energy production without the utilization of a great number of hectares of land for cane, corn, or cassava pro­duction. Furthermore, the biomass is a resource that can be processed in different ways to produce a significant variety of products such as ethanol, synthesis gas, methanol, hydrogen, and electricity (Chum and Overend, 2001). However, some authors, such as Berndes et al. (2001), consider that the great scale implementa­tion of biomass energy would create serious social, economic, and environmental consequences, especially if dedicated energy crops are employed. For example, these authors estimate that the labor requirements for bioenergy production at a great scale in any country should not exceed 1% of the total labor force in order to make its production feasible. Grassi (1999) points out that the development of bioenergy production technologies in the European Union (EU) can represent the creation of 200,000 direct and indirect jobs as well as the reduction of 255 million annual tons of CO2 by 2010. Thornley (2006) summarizes the main environmen­tal, social, and economic advantages of employing biomass as an energy source. Some of these advantages are applicable to both developed and developing coun­tries. Among them, the reduction of greenhouse gas emissions, reduced use of agro-chemicals, diversification of rural economies, the potential for low-cost heat supply, and the potential income streams for farmers should be highlighted. On the other hand, this author presents some of the main consequences of bioen­ergy development: impacts on particular native species, the visual impact of crop growth and conversion plants, environmental emissions associated with thermal conversion plants, the uptake of significant amounts of water from below ground, and the requirement for policy support, among others. The need for policies that stimulate the development of technologies based on biomass through tax exemp­tions or subsidies should be emphasized considering the lower production and transport costs of fossil fuels.