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Themeninfos – A compact guide to energy research

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The direction taken by electromobility depends mainly on the storage technology used. Pictured: Electric car tanking on power.
© Anna Durst, BINE Informationsdienst
Electromobility
Themeninfo I/2017

The diagram shows the maximum range of presently available electromobile drive concepts compared to conventional drives (ICE) with a range of 1,000 km (according to the manufacturer). Battery operation is shown in green, while red represents operation with the combustion engine.
© WWU/MEET
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Electromobility - What drives us now and in the future

Highly efficient, low-noise and zero-emission: the electric powertrain offers dynamic mobility, can integrate renewable energies and makes the transport sector less dependent on crude oil as an energy source. However, which technology will dominate electric vehicles of the future: batteries or fuel cells? An either-or decision is not necessary.

The combustion engine has a 100-year development history and has become consistently more efficient and cleaner. Despite this, the car engine is about to undergo a breakthrough: the finite nature of fossil fuels, climate change and smog demand that we find alternative solutions. The engine of the future needs to be clean, affordable, easily available and convenient to use. Electric drives already meet many of these requirements today. They are quiet and low-vibration, and emit no pollutants where they are used. When they drive with power from renewable sources, more resource-saving, more climate-friendly transport becomes possible. Compared to combustion engines, electric motors are light and compact. The technology is well developed: it has a high degree of effectiveness and is robust and low-maintenance. Electric motors have a similarly long development history to combustion engines.

Therefore, it is not the drive technology that is inhibiting the dissemination of electric cars. It is far more the case that there is a great need for further development in storage facilities for electrical energy. With a diesel or petrol engine, a simple hollow chamber - the pressureless tank - is sufficient in order to store chemically bound energy for a range of hundreds of kilometres. The electrochemical energy storage systems are far more complex. Both rechargeable batteries and hydrogen storage systems combined with fuel cells have a higher volume in particular. In order to guarantee the same range as one litre of diesel, a rechargeable battery must for example be around 10 times as large and 20 times as heavy.

There is also still a lack of infrastructure. While petrol stations for petrol or diesel are to be found in the most remote areas, charging stations for battery storage systems or hydrogen filling stations are to date almost non-existent. This is why the change to other drive technologies is taking so long. Here, an important role is initially being played by hybrid systems, which combine petrol or diesel engines with electric motors. These also include electric vehicles with a so-called “range extender”. These vehicles drive on purely electric motors. If necessary, a combustion engine drives a generator which charges the battery.

The direction taken by electromobility is therefore decided to a large degree on the storage and conversion technology available. However, what is the current latest development in technology with regard to a battery and hydrogen tank with a fuel cell? What challenges are there? How can the wide range of requirements be met? This BINE Themeninfo brochure looks at these questions in detail and discusses the system core of battery, cells and components, as well as the materials used, integration into the grid and how an infrastructure can be created.

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Fuel cell, battery and hybrid

The electric vehicle drive concepts include hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), pure battery electric vehicles (BEV) and fuel cell electric vehicles (FCEV). They can differ significantly in terms of their driving ranges. Opinions differ as to whether hybrid electric vehicles are regarded as electric vehicles, as they can only achieve short electric driving ranges and are not charged via a socket. In North America and Asia in particular, the success of the hybrid electric vehicles shows that the electrification of the powertrain has already been positively received by customers.

In Germany, the market for vehicles with purely battery electric drives is growing slowly, but steadily. Until now, electric cars have become even more expensive to buy than combustion engine and hybrid electric vehicles, and fall considerably behind in terms of range. Further obstacles are the poorly developed infrastructure and the still long charging times compared to fuel tanks. Many people are worried that they might be left stranded while looking for a charging opportunity, and are afraid of converting. These challenges can be met in two ways: either the storage capacity of the traction batteries is further increased, or they are continuously re-charged while driving by the electrochemical conversion of hydrogen and oxygen from the air in a fuel cell (hybrid concept). Both strategies have already been implemented commercially, but have different advantages and disadvantages. For example, the charging duration of a vehicle at the local charging station is increased significantly when a high-capacity battery is installed in the vehicle. While there are various fast charging options available, even via inductive, i.e. non-contact, charging, these are still rare. Furthermore, the actual charging duration depends on the technical conditions.

In hydrogen-driven vehicles with a fuel cell, tanking with hydrogen does not take much longer than with standard fuel pumps. However, short journeys increase hydrogen consumption, as the fuel cell needs to be brought to operating temperature each time the vehicle is re-started. Therefore, the range fluctuates, depending on the driving profile. In addition, the hydrogen infrastructure is still insufficiently developed.

Combined advantages

In the future, neither of the two individual technologies will be able to fully cover the entire application spectrum of individual and goods traffic, as well as commercial vehicles. They complement each other with regard to energy efficiency, protection of resources and the different requirements of primary energy sources used. The application areas - fuel cells for long journeys and a sufficiently large battery for short and medium-length journeys - can be combined in a single vehicle in a complementary way. Therefore, the question of pioneering technology cannot be answered in general terms. In the long term, a coexistence of both concepts for the electric drive is likely.

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Author team

Prof. Dr. Martin Winter
Dr. Tobias Placke
Dr. Sergej Rothermel
Paul Meister
Andre Bar
MEET, WWU Münster

Dr. Wedigo von Wedel
NEXT ENERGY

Links

NOW GmbH
National Organisation Hydrogen and Fuel Cell Technology

nationale-plattform-elektromobilitaet.de
National platform for Electric mobility

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