Abstract
In this paper vehicles (of different size and powertrains) are investigated for their optimum service life to minimise their greenhouse gas emissions and contribution to global warming. The method uses the best available energy production and usage data for life cycle analysis (more than well-to-wheel as materials, manufacturing, consumables and recycling/reuse is included) for conventional, hybrid, through to full electric types. Also accounted for is the change in vehicle use with age in a vehicle fleet, in which new vehicles replace older, scrapped ones in the market with significant improvements in fuel consumption (and CO2 emissions). Moreover, sensitivity analysis is performed to identify the options that are the most disruptive outside the expected present trend of around 5% per annum improvement in fuel/energy consumption. It is shown that depending on the vehicle size and type of energy source, the optimum vehicle life ranges from 8 years to more than twenty, with all electric having the longest optimum life. As the energy efficiency trend for new vehicles entering the market reduces, as it must according to the law of diminishing returns, vehicles need to remain in use for longer. On the basis of the median results from the projections, hybrid vehicles use the least long term (several model change overs) energy and produce correspondingly low CO2-e. Depending on the technology, BEVs will be considerably worse unless there are major reductions in the embedded energy in the battery. The sensitivity analysis allows for conclusions to be drawn about many alternative scenarios that may exist in different regions of the world. These findings indicate that government policy should subsidise hybrids, in preference to the present support for all electrics i.e. BEVs.