No simple “plug and play” for electric vehicles
SHC believes there is a paradigm shift to electricity as the primary propulsion source, mainly because of the much higher efficiency for the drive line
All the major auto manufacturers are including plug-in hybrids or all-electric vehicles in their model line-up. “Plug in” does not seem to be a simple issue of connecting the vehicle to one or other standard outlet. Europe, for a start, has several grid systems – owners will need a form of “travel plug” when crossing borders. Assemblers will also be challenged as they design world cars, which can be plugged in to the many more systems around the world. The quality of electrical power also varies, with some areas being subject to regular spikes and troughs in supply.
Vehicles like the Chevy Volt have on-board battery chargers that handle both 110-Volt and 220-Volt from a standard plug, as does the Leaf. The disadvantage of these systems seems to be the long time taken to recharge. Alternative systems in the US and Japan have the cord and plug attached to the wall rather than the car, and use higher power chargers. Here, the Yasaki plug seems to have emerged as a standard. When one starts considering the use of electric power for heavier commercial vehicles, the picture becomes even more complex, with a number of different standards and solutions.
Automotive Industries (AI) asked Lennart Josefson, director of the Swedish Hybrid Vehicle Centre (SHC), whether a common standard was emerging.
Josefson: There is standardization work going on in different regions, but as yet we see no common standard emerging.
AI: What are the safety aspects to be considered for recharging stations?
Josefson: There are several issues: protecting people from high voltage and currents, and minimizing the effects of short circuiting.
AI: Are power utilities ready for the introduction of electric vehicles?
Josefson: We will see several new commercial cars emerging as plug-in hybrids from late 2010 to 2012, including the Chevrolet Volt, and the Toyota Prius. In several cases prototypes have been running for some years. This will be the real test for hybrid vehicles. Sweden, and maybe Norway and Finland have a special situation when it comes to introducing plug-in hybrids. Many private homes have power outlets in garages for engine and passenger compartment heating. In addition, many employers in particular in the northern parts provide power outlets at parking spaces for engine preheating. Sweden and Norway at least also have sufficient capacity in the power grid to accommodate a large number of electric vehicles.
AI: Although research shows that most owners will have more than adequate range for their daily use, manufacturers continue to research ways of extending the range of EVs.
Early hybrids were, essentially, hydrocarbon-powered vehicles with an electric motor acting as a power fill-in. In the newer model, we are seeing electric vehicles with a hydrocarbon-burning motor as a back-up or range extender. Are we seeing a greater focus on electric motors as the primary source of propulsion?
Josefson: SHC believes there is a paradigm shift to electricity as the primary propulsion source, mainly because of the much higher efficiency for the drive line. This shift is hindered by the limited capacity (or rather capacity/weight) of the energy storage, batteries and maybe also partly by the high development costs. Our research focuses on finding the best hybrid electric or electric drive line combined with the energy storage. I think this development can be faster, but it is limited by physical laws for energy transfer in Li-ion batteries (i.e. they cannot be much better in terms of energy/weight ratio), and also the very high development costs
AI: What other range extension technology is in development?
Josefson: We are working on a EU-project to demonstrate the functionality of range extenders, with “small” secondary engines - ordinary internal combustion or Wankel engines. The idea is to find solutions where the savings on batteries for a pure electrical vehicle is larger than the additional cost for the secondary propulsion unit. At the same time, the range extender must meet other conditions, such as space availability and low vibration compared to a pure electric drive line.
AI: How soon will technology such as solar cells be commercially available?
Josefson: Solar cells are already available in cars, but their contribution is very limited. It can contribute to the temperature control of the vehicle or some auxiliary systems, but not the propulsion.
AI: What about gas turbines, or the revival of the Wankel engine?
We will be testing the use of a Wankel engine in range extender drives. The advantages of a Wankel are the small engine volume and the low vibration levels. The disadvantages may be the higher production costs.
AI: What different solutions/technologies are available for commercial vehicles?
Josefson: So far in Sweden there is little development of range extender solutions for commercial vehicles, although there should be a potential for light distribution vehicles.
AI: Which brings us to the conductive/inductive debate. Is it practical and economical to effectively reintroduce the tram systems by laying inductive cables along all the main routes? Vehicles would then be constantly charged and powered by the power in the system, and only rely on their batteries when they move off grid. This is seen by some as offering a solution for electric-powered commercial applications.
Josefson: We see cables in the streets used for continuous conductive charging as the best alternative. There may also be overhead wires for continuous conductive charging
AI: What work is SHC doing in this regard – and what are the implications for power utilities, local authorities and vehicle owners.
Josefson: SHC is not carrying out research on this, however there are two projects being run in Sweden to demonstrate the advantages of this system for commercial vehicles. The two manufacturers Volvo and Scania are working on a system with cables in the streets and are now preparing a demonstration site for this system. There is also a company Svenska elväg which is planning a demonstration site for trolley systems on highways. In both cases the continuous conductive charging is favored, where the efficiency for the cable to vehicle interface is a very high 99 %.
AI: How efficient are inductive systems – how much power is “lost” through magnetic transfer of power, as opposed to direct conductive transfer.
Josefson: One has to look at the total efficiency for a system and not only the interface between vehicle and electric cable or magnet. The efficiency for the inductive systems is strongly dependent of the distance between the two parts (magnets), but a typical figure is 80%
AI: Is there a conductive solution for commercial vehicles?
Trolley bus solutions have been in use for many years. New conductive and inductive charging prototype solutions exist, for example a inductive bus system in Switzerland (Luzern), with one magnet in the bus and the other magnet in the street at each bus station. There is also a Korean prototype system for continuous conductive charging