Energy Crop-Based Biogas as Vehicle Fuel—The Impact of Crop Selection on Energy Efficiency and Greenhouse Gas Performance

Abstract

Abstract:The production of biogas from six agricultural crops was analysed regarding energy efficiency and greenhouse gas (GHG) performance for vehicle fuel from a field-to-tank perspective, with focus on critical parameters and on calculation methods. The energy efficiency varied from 35% to 44%, expressed as primary energy input per energy unit vehicle gas produced. The GHG reduction varied from 70% to 120%, compared with fossil liquid fuels, when the GHG credit of the digestate produced was included through system expansion according to the calculation methodology in the ISO 14044 standard of life cycle assessment. Ley crop-based biogas systems led to the highest GHG reduction, due to the significant soil carbon accumulation, followed by maize, wheat, hemp, triticale and sugar beet. Critical parameters are biogenic nitrous oxide emissions from crop cultivation, for which specific emission factors for digestate are missing today, and methane leakage from biogas production. The GHG benefits were reduced and the interrelation between the crops changed, when the GHG calculations were instead based on the methodology stated in the EU Renewable Energy Directive, where crop contribution to soil carbon accumulation is disregarded. All systems could still reach a 60% GHG reduction, due to the improved agricultural management when digestate replaces mineral fertilisers.

Agricultural anaerobic digestion plants: What LCA studies pointed out and what can be done to make them more environmentally sustainable

“…In particular, a GHG saving when biomethane is used for transports was reported by Poeschl et al [71,101,102] (1.15 kgCO 2 eq/kg biomethane) and by Power and Murphy [115] (between 0.017 kg/MJ and 0.02 kg/MJ depending on the feedstock). The GHG performance of the different crop-based biomethane systems was calculated by 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 14 Börjesson et al [33]: the results range from 22 to 47 kgCO 2 eq/GJ biomethane when credit of increased soil organic carbon (SOC) content was excluded, and from −2 to 45 kgCO 2 eq/GJ biomethane when it was included. Berglund and Borjesson [34] included in the calculation of life cycle emissions of GHGs the changes in soil organic carbon (SOC) content.…”

Renewable energy from biogas with reduced carbon dioxide footprint: Implications of applying different plant configurations and operating pressures

“…From comparison of CO 2 footprint of four energy crops in Italy it is deduced that the lowest CO 2 footprint is associated with Miscanthus utilisation and the highest with maize [31,32]. Another study suggests that the lowest CO 2 footprint is obtained with ley, due to the remarkable accumulation of soil organic carbon (SOC) [33]. Slightly higher CO 2 footprint has maize and wheat and the highest hemp, triticale and sugar beet.…”

“…Energy crop-based biogas systems can achieve reduced life cycle CO 2 footprint, including negative life cycle CO 2 footprint, due to the significant soil organic carbon (SOC) accumulation via cropping rotations [33]. In general in the agro-biogas supply chain the CO 2 burden is reduced by applying SOC, more specifically by means of no-tillage practice, organic fertilisation and/or the large rooting system of crops.…”

Assessment of Novel Routes of Biomethane Utilization in a Life Cycle Perspective

“…Maize and sugar beet have the highest gross energy potential of commonly grown energy crops (Weiland, 2010). In addition, the cultivation of these crops produces the lowest specific GHG emissions of all energy crops (Hartmann, 2006; Börjesson et al, 2015). Maize cultivation is increasing within northern Europe due to the temperate climate, aided by the global warming effect, creating a need to manage this crop and its residues (Pöschl et al, 2010; Menardo et al, 2015).…”