Abstract
With the central aim to reduce greenhouse gas emissions, agroforestry systems have become popular because they can provide biomass for bioenergy conversion and thus help replace fossil energy. This article compares the net energy balances of three biomass conversion techniques for an agroforestry system consisting of willows and two types of grassland biomass as well as separate stands of grassland and willow. The period of investigation was the second willow rotation (4–6 years after establishment). The biomass conversion techniques included combustion of hay (CH), integrated generation of solid fuel and biogas from biomass (IFBB), and anaerobic whole crop digestion (WCD). Compared to the first rotation (years 1–3), the net energy yield of the willow stands significantly increased. Nevertheless, the separate stand of willow had higher net energy yield than the agroforestry system. The IFBB technique led to an improvement in solid fuel quality through demineralization. CH and IFBB provided higher net energy yields than WCD.
Highlights
With the central aim to protect the climate system for the benefit of future generations, 197 parties ratified the United Nations Framework Convention on Climate Change [1]
Biomass- and area-specific methane yields of the IFBB press fluids did not show any significant differences between the grassland types (Table 3)
The biomass-specific methane yields showed a mean value of 285.4 LN CH4 kg−1VS for Clover Grass (CG) and 302.4 LN CH4 kg−1VS for diverse grassland mixture (DG)
Summary
With the central aim to protect the climate system for the benefit of future generations, 197 parties ratified the United Nations Framework Convention on Climate Change [1]. In 2015, the Paris Agreement stated the convention parties’ aim to keep the increase in global temperatures to “well below 2 ◦C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5 ◦C above pre-industrial levels” [2]. To reach this aim, a path to achieving net zero CO2 emissions is necessary [3]. While discussions are still ongoing regarding the criteria for measuring the sustainability of bioenergy conversion systems, the energy balance is considered a crucial criteria by most experts [9]
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