Review of mixed-technology vehicle fleet evolution and representation in modelling studies: Policy contexts of Germany and Japan

Many countries and stakeholders are increasing their uptake of renewable energy and alternative fuel vehicles to decarbonize. Many countries adopted a technology-neutral paradigm to promote the update of such vehicles. Despite paradigm similarities, developments differ, even in comparable countries such as Germany and Japan. The reasons behind these differences are yet to be explained, and the present work thus examines developments in both groups over the past decade, highlighting how grid-modelling studies can help to plan for future developments in this sector. The main contributions of this work are, first, in providing a better understanding of the outcomes correlating to different implementation approaches of a similar paradigm between countries over a significant timeframe; second, in identifying further areas of research for integrated transport and grid modelling studies; and third, in making policy recommendations toward a more efficient implementation of a technology-neutral approach. Key findings are that while the fleet grows faster early on with a top-down- (Japan) than a bottom-up approach (Germany), both achieved similarly-sized fleets over a decade. For both, technological immaturity likely limited growth. Also, meteorological factors may intensify geographical clustering of specific technologies. The impacts of energy policy on regional transport technology penetration merits further research.