Energy and environmental evaluation and comparison of a diesel-electric hybrid tractor, a conventional tractor, and a hillside mini-tiller using the life cycle assessment method

Currently, electrification, especially hybrid solutions, still represents the most promising option to improve energy efficiency, emissions, and productivity for agricultural machinery. Agricultural machinery in China's mountainous areas is represented by quantities of small conventional tractors and hillside mini-tillers (HMTs), which are highly fuel-intensive and polluting. Effective measures need to be taken to reduce their environmental impacts. Thus, a diesel-electric hybrid tractor (DHT) was designed and developed. The life cycle assessment (LCA) method was used to assess and compare the energy consumption and environmental impacts of the DHT, an internal combustion engine tractor (ICET), and an HMT in this study. Comparative results present that the ICET had the most contribution to acidification potential (AP), eutrophication potential (EP), and respiratory inorganics (RI), while the HMT created the most to primary energy demand (PED), global warming potential (GWP), and photochemical ozone creation potential (POCP). The DHT had the lowest contribution to six environmental impact indicators, 5.1%-68.9% lower than those of ICET and HMT. Among the six phases in the life cycle, the Pump-to-Wheel (PTW) phase consumed the most energy (65.9%-78.5%) and brought about the largest environmental impacts (54.2%-94.7%), followed by the Well-to-Pump (WTP) phase (4.0%-37.3%). Increasing the proportion of electricity generation from non-fossil fuels in 2030 showed positive effects on saving energy and reducing environmental impacts for the ICET, DHT, and HMT, with the DHT benefiting the most. Discoveries in this study can contribute to the research and development of the DHT and the electrification of small agricultural machinery.