【正文】 arly not advantageous in terms of energy efficiency, . hydrogen in internal bustion engines or liquid hydrogen. Usually, a key instrument in strategies to promote sustainable transport is the introduction of alternative fuels. Frequently, the principal objective of introducing a different energy carrier is to utilise it for introducing renewable energy sources into the transport sector and/or improving energy security by reducing the dependence on oil. In this context, the main options as regards energy carriers for renewable energy sources are electricity, hydrogen, biofuels and biogas. Regardless of their respective strengths and weaknesses, as energy carriers in the transport sector, electricity and hydrogen have in mon the strengths of having high flexibility with respect to primary energy sources and the possibility of selecting between several renewable energy sources. In contrast, liquid biofuels and biogas, which are frequently seen as more immediately applicable alternative fuel options in the short term, are in practice (with acceptable conversion efficiencies) confined to a quite limited resource base of biomass. Since these energy carriers can relatively easily be generated from fossil fuels, the limited resource base poses a realistic risk, for instance in case the demand for biofuels/biogas outstrips the production capacity. The choice between hydrogen and electricity as fuels, and between their different paths, is a plex evaluation of various aspects, also involving assumptions on the longterm development of technologies with very different development trends, as seen today. The evaluation is further plicated by the fact that the electricity/hydrogen forms part of the electricity supply system and can only fully be analysed in this context.This article illustrates some of the problems in this context, highlighting issues of particular importance: energy efficiency, range, costs, and durability, among others. It concentrates on the vehicle and the generation of fuels, and does not include systems analysis of the electricity system. Instead the article intends to raise vehicle/fuelrelated issues that are significant for such an analysis. An overall conclusion is that it is not possible to make simple remendations on the choice between electric, hybrid and hydrogen vehicles e partly because of the difficulties in assessing the different dimensions, and partly because considerable variations exist between the different paths within the main options.2. Overview of fuel cycle of electricity and hydrogenElectricity may be used either directly as fuel in batteryelectric vehicles or plugin hybridelectric vehicles, or be converted into hydrogen and applied in internal bustion enginebased vehicles or in fuel cell vehicles. A mon feature, except for the internal bustion engine vehicle, is that they can be perceived as variations of electric drive, in which the electricity is either supplied from the grid via a battery (or similar electric storage technologies) or generated onboard either in an internal bustion engine (the plugin hybrid) or in a fuel cell.If electricity is used as fuel in batteryelectric vehicles (BEV), this is typically supplied from the public grid, stored onboard the vehicle (typically in batteries) and used in electric motor drives. In principle, the recharging can be achieved though existing sockets, and in this case the infrastructure is very inexpensive. This is, however, a solution which imposes many restrictions on the place and speed of the , in practice, more requirements and costs will be linked to this option, particularly if fast recharge is required and if the electricity consumption needs to be monitored. This is usually a very energy efficient option.Hybridelectric vehicles (HEV) are characterised by having both electric motors and internal bustion engines in its drive system (Graham, 2001。 Duvall, 2002。 Gage, 2003。 Lipman and Delucchi, 2003。 Boschert, 2006). The plugin hybridelectric vehicle (PHEV) is a hybrid which can be recharged from the grid. It can be perceived as a BEV supplemented with an internal bustion enginebased drive. In fact, the PHEV category contains a wide range of different options,defined by factors such as: impacts of different hydrogen options, but normally even the most efficient hydrogen pathways have greater losses than the least efficient option based on electricity as fuel.On the other hand, the vehicle range is usually considerable higher for hydrogen than for BEVs and this will in all probability continue to be the case in the future. This is linked to the costs and physical properties and the two storage mediums as described in detail below (Amos, 1998。 Kalhammer et al.,2007).A range of different options can be identified with regard to onboard hydrogen storage. Storage in the form of liquid hydrogen (LH2) can achieve ranges in the same order as conventional vehicles, but this option has extremely poor energy efficiency and other weaknesses in addition. From an energy efficiency viewpoint, the most attractive solutions at present are probably pressed gas tanks (CH2 storage) and metal hydride storages, but the latter of these still requires considerabledevelopment in order to reduce weight and costs. Infrastructure requirements and costs constitute a major drawback in conjunction with hydrogen. In this respect, hydrogen undoubtedly involves the greatest number of obstacles of all alternative fuels. This weakness in bination with the currently shorter ranges in connection with hydrogen vehicles have resulted in the exploration of options in which liquid fuels (gasoline, diesel, methanol etc.) are converted into hydrogen onboard the vehicle. This solution involves considerable energy losses and in addition, many technical problems as well as problems of reducing the volume.Hydrogen can be generated through other paths than via electricity, notably (in a renewable energy context) by con