ABSTRACT
Current bioenergy systems generate around 50 EJ year−1, representing about 10% of the world’s energy supply (Haberl et al. 2006; Sims et al. 2006; Beringer et al. 2011; Offerman et al. 2011). Bioenergy systems are understood here to encompass complete biofuel life cycles: from seed to emissions and the disposal of wastes originating in the production and consumption of biofuels. Bioenergy systems have been divided in traditional and modern categories (Goldemberg and Coelho 2004; Sims et al. 2006; Kuchler 2010; Gurung and Oh 2013). Although the denitions of traditional and modern bioenergy systems are not very precise, it would seem that liquid transport biofuels, such as bioethanol and biodiesel, and puried biogas originating in the anaerobic digestion of biomass and woodchips used in power plants are in the category of modern bioenergy systems. Modern bioenergy systems currently supply worldwide about 10 EJ year−1 (Sims et al. 2006; Beringer et al. 2011). It would seem that traditional bioenergy systems produce bioenergy products such as wood, charcoal, dung cake, and crop residues used for small-scale cooking and heating. Worldwide, traditional bioenergy systems currently supply about 40 EJ year−1. Percentagewise, the share of traditional biomass in worldwide energy supply has been roughly constant since the 1970s (Grubler 2012). This chapter will deal with both traditional and modern bioenergy systems. Currently, biofuels are overwhelmingly terrestrial. However, there have also been proposals for algal biofuels. These will be dealt with in this chapter too.
