Vehicle-cycle and life-cycle analysis of medium-duty and heavy-duty trucks in the United States.

Medium- and heavy-duty vehicles account for a substantial portion (25 %) of transport-related greenhouse gas (GHG) emissions in the United States. Efforts to reduce these emissions focus primarily on diesel hybrids, hydrogen fuel cells, and battery electric vehicles. However, these efforts ignore the high energy intensity of producing lithium (Li)-ion batteries and the carbon fiber used in fuel-cell vehicles. Here, we conduct a life-cycle analysis to compare the impacts of the vehicle manufacturing cycle for Class 6 (pickup-and-delivery, PnD) and Class 8 (day- and sleeper-cab) trucks with diesel, electric, fuel-cell, and hybrid powertrains. We assume that all trucks were manufactured in the US in 2020 and operated over 2021-2035, and we developed a comprehensive materials inventory for all trucks. Our analysis reveals that common systems (trailer/van/box, truck body, chassis, and lift-gates) dominate the vehicle-cycle GHG emissions (64-83 % share) of diesel, hybrid, and fuel-cell powertrains. Conversely, propulsion systems (lithium-ion batteries and fuel-cell systems) contribute substantially to these emissions for electric (43-77 %) and fuel-cell powertrains (16-27 %). These vehicle-cycle contributions arise from the extensive use of steel and aluminum, the high energy/GHG intensity of producing lithium-ion batteries and carbon fiber, and the assumed battery replacement schedule for Class 8 electric trucks. A switch from the conventional diesel powertrain to alternative electric and fuel-cell powertrains causes an increase in vehicle-cycle GHG emissions (by 60-287 % and 13-29 %, respectively) but leads to substantial GHG reductions when considering the combined vehicle- and fuel-cycles (Class 6: 33-61 %, Class 8: 2-32 %), highlighting the benefits of this shift in powertrains and energy supply chain. Finally, payload variation significantly influences the relative life-cycle performance of different powertrains, while LIB cathode chemistry has a negligible effect on BET life-cycle GHGs.

Environmental profile of thermoelectrics for applications with continuous waste heat generation via life cycle assessment.

Over the past few decades, rigorous efforts have been undertaken to develop novel thermoelectrics (TEs) with high conversion efficiencies. However, poor TE device efficiencies and use of scarce and toxic constituent elements in major TEs raises valid questions about their ecological effectiveness. We evaluate this efficacy by investigating environmental performance of seven TE modules, spanning five different TEs, on a diverse range of impacts (including toxicity and scarcity) over their life cycle (cradle-to-grave). Exhaustive inventory is developed for all modules, particularly their production and end-of-life stages, in the first-ever exercise of its kind till date, to assess their benefits for applications involving constant waste heat emission. Three end-of-life scenarios are considered to determine ecological benefits and pitfalls of recycling TEs, a first in LCA literature on thermoelectrics. The results show the dominance of specific constituent elements and large processing-related electricity consumption on impacts caused by production for all modules. Over their life cycle, TE modules are seen to exhibit large positive environmental benefits, barring some exceptions, highlighting their substantial eco-credentials independent of the TE used. Also, barring circular economy approach in some cases, no end-of-life treatment is observed to significantly influence modular environmental impacts. Subsequent calculations show ecological benefits from TEs to be comparable with those from commonly used renewables like solar and wind energy, with the findings repeated under scenario-based sensitivity analysis despite 50% reduction in conversion efficiency and 15% lowering in usage duration, further validating their ecofriendly potential. Simultaneously, two key challenges that hinder large-scale application of TEs - marginal ecological benefits (even on converting high fraction of waste heat to electricity) and high costs - are pointed out. This work concludes by highlighting the urgent need for addressing major negative contributors to production-related impacts of this platform to boost its prospects for commercial application and transform its ecofriendly potential into reality.