Topic of the month August 2011

One million electronic vehicles should drive on Germany’s streets in 2020. This is the aim of the “Regierungsplan Elektromobilität, which was adopted by the German government in May this year. To reach this goal, there have to be registered at least 100.000 e-cars in three years and 500.000 e-cars in 2017 in Germany, a forecast of the “National Platform for Electro mobility” (NPE) says. The producers of electrically powered cars and its components as well as the power grid operators face challenges promptly.

Dominance of hybrid vehicles

In the category of e-cars the streets in Germany will probably be dominated by hybrid vehicles in nine years. The term describes a string of car models that usually use a combination of a combustion engine and an electric battery motor. Depending on whether the combustion engine provides the main part of the energy needed or only supports the electric battery motor, on differentiates between parallel hybrids, series hybrids and plug-in hybrids (battery can be recharged with a cable to the power grid). A meta-analysis of the ministry of economics of Baden-Wuerttemberg and the Fraunhofer institute states, that in 2020 pure electric vehicles will only reach 2, 58 per cent of all newly registered cars worldwide. Contrastingly hybrids would reach 17, 8 per cent. Anyway, the market will still be dominated by combustion engines.

Because of the electro mobility-offensive and similar initiatives in other countries as for example France and China, cable manufacturing firm Leoni expects an increasing demand for cables for e-cars as well as the charging infrastructure, says Helmut Kalb, vice president for the business division electro mobility at Leoni. One reason for that will be the dominance of hybrids among the electrically powered cars. Hybrids need more cables and wires as other cars, explains Kalb: “In addition to the conventional 12-volt-vehicle electrical system and the connection of the engine hybrid cars need a high-voltage wire set for the electrical drive train.” In contrast, pure electric vehicles would probably need as much or less cables than non-electrical cars, because they have to be smaller and more lightly, says Kalb.

The recharging of an e-car-battery (30 kW) would last about eight to ten hours with a normal charging set (capacity 3,7 kW) and one hour with a fast-charging (between 11 and 43,5 kW in low voltage system). (Siemens-Pressebild)

High voltage cables as solutions for e-cars

Cables for e-cars have to meet special requirements, says Kalb: “Cables for cars are operated with unusual high voltages (600 volt and more). Because of the high conduction demand they normally have big cross sections and have to ensure a sufficient shielding against electromagnetic emission.” However, there are no standards for cables in e-cars so far, Kalb says: “The wires are dimensioned individually to each application. A promising solution could be high voltage cables, says Kalb: “For the drive train – the connection from battery to power electronics and electrical engine – most of time we use single-wire shielded with big cross sections (25 mm²).” Auxiliary aggregates would be powered with multi-conductor seethed cables with average cross sections (4mm²).

No expansion but coordination of the grid necessary

The increase of the number of e-cars would probably lead to a rise in current consumption in Germany. But only marginal, as Torsten Wolf from Siemens AG explains: “The energy, necessary to recharge one million electronic vehicles would amount to not more than 0, 5 per cent of the power generation in Germany.” In case renewable energies would be developed as planed – envisaged is an increase of more than 100 billion kilowatt-hours per year until 2020 – this green power alone would be sufficient to power 50 million e-cars, Wolf says: “The supply of these cars with power from renewable energies is ensured.” An analysis of the Association for Electrical, Electronic & Information Technologies in cooperation with Pricewaterhouse Coopers arrives at the conclusion, that an expansion of the electricity supply network will not be necessary if one million e-cars are registered: “The grid requirements through an electro mobility-offensive are marginal in comparison to the challenges caused by the development of renewable energies.”

Special cables from Leoni. According to the company high voltage cables are a good solution for electronic vehicles. (Leoni AG)

However, the charging processes require coordination. Otherwise the electricity supply network could be overloaded, as Siemens-spokesman Wolf explains: A typical distribution transformer provides 630.000 volt-ampere (corresponds to about 630 kilowatt) and powers about 100 households. Home-charging sets for e-cars provide approximately 22 kilowatt (kw). In case 100 recharging sets would be run at the same time, they would need about 2200 kw – more than three times of what the distribution transformer can provide, says Wolf: “If there are high loading capacities, it is necessary to regulate the charging rate at a control room in order to avoid, that distribution transformers and distribution networks have to be reconfigured or expanded.” The solution is smart grids, says Wolf. Smart networks try to delay peak demands in downtimes in order to utilise the grid more equally. The control room would decide which car should be recharged at which time. Thereby an uncontrolled charging and an overload of the infrastructure can be avoided.

In future, it is conceivable, that e-cars could serve energy storage and return power to the grid, explains Wolf. Such an energetic recovery system will probably be available in the long term, Wolf states: “We see that well after the year 2020.” The process is technically nontrivial, the spokesman explains. For using it, smart grids have to be installed already.

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