SIEMENS

As recently as five years ago, the idea that hundreds of thousands of electric cars could be on the road in Europe by 2020 was considered a futuristic scenario. Hardly anyone believed that the idea of driving with electricity could be implemented so quickly, and on such a grand scale. Times have changed, however, and work on readying electric cars for everyday use is proceeding at full speed. At the same time, some components of their energy source - the power grid - are being completely redefined (see article “From Wind to Wheels”, Pictures of the Future 2/2009). Two European regions in particular are leading the way to the future of electric mobility - Denmark and Germany’s Harz region in the country’s middle. Both already obtain a large portion of their electricity from renewable sources, especially wind. In Denmark, the figure is 20 percent; in the Harz, wind, biogas and solar facilities cover 50 percent of energy needs. As a result, both regions often face the same problem: too much wind energy.

When strong wind causes turbines to really get moving, they can actually meet more than 100 percent of each region’s electricity demand. To prevent the grid from overloading, wind facilities in Harz are shut down - much to the annoyance of their operators. Danish energy suppliers, however, are legally required to use the excess wind power, which they pass on to their European neighbors. What’s more, they have to pay transmission fees for the privilege. And the problem could get worse, since the share of electricity generated by wind power is increasing in both the Harz and Denmark. The latter hopes to have around 50 percent of its average electricity demand covered by wind by 2025.

Electric vehicles could help solve the problem by acting as a virtual surplus electricity storage system. Specifically, thousands of electric cars would recharge their batteries when winds are strong, primarily at night. Conversely, during periods of calm, they could resupply the grid at higher prices. It’s a great idea - but can it work? For example, how can electric cars and the power grid communicate reliably? How can vehicles be recharged quickly and safely? And how is everyone to be billed? Two major cooperative projects in Denmark and the Harz are seeking answers to these questions with the help of Siemens experts.

One project is headquartered at the Risø research center at the Technical University of Denmark (DTU), not far from the famous Viking Ship Museum in Roskilde. The center houses wind turbines, solar photovoltaic systems, a transformer station, and a vanadiumion liquid battery the size of a shipping container. Here, the energy consumers are electric heating units in the center’s office buildings, hybrid cars, and several small batteries that simulate additional vehicles. The research center thus has a miniature power grid that can be used to test the interaction between various components.

Risø is home to Denmark’s EDISON (“Electrical vehicles in a Distributed and Integrated market using Sustainable energy and Open Networks”) project, the world’s first major effort for bringing a pool of vehicles to power outlets. Practical testing will begin in 2011 on the island of Bornholm. “We’re focusing mostly on the question of how electric vehicles can be charged quickly, safely, and efficiently,” says Sven Holthusen, who is responsible for the EDISON project at Siemens’ Energy Sector. Holthusen and his colleagues analyze, for example, how a vehicle can be recharged at different types of charging stations or how a large number of batteries can be recharged simultaneously.

Holthusen knows that electric cars will become truly attractive to consumers only when they can travel long distances and be recharged within a few minutes. Electric cars these days are normally charged at an 11 kilowatt (kW) outlet. A typical battery with a 25- kilowatt-hour (kWh) storage capacity thus takes more than two hours to fully recharge. Increasing the charging power would lower the charging time. That’s why Holthusen’s team of researchers is developing 120 kW technology, which reduces the charging time to just a few minutes. However, with charging currents of up to 300 amperes and 400 volts of alternating current (a.c.), the load is equivalent to powering nearly 20 households.

“Heat generation during recharging with a.c. is one of the biggest challenges at the moment,” explains Holthusen, who is testing charge controllers that would be installed in powvehicles as well as those that would be part of charging stations. Onboard controllers offer the benefit of not having to be integrated into the power pump, which reduces infrastructure costs. Such controllers also ensure that each vehicle optimally controls the charging process in line with its battery’s requirements. External controllers, on the other hand, are better at dissipating heat, thus enabling higher charging currents.

No one knows which charging technology will gain the upper hand. That’s why Siemens is developing different technologies in parallel in its Inside Car and Outside Car electric mobility teams. The teams develop and test components for vehicles and grid technologies. Holthusen is also looking at direct current (DC), since it allows batteries to be charged without a controller. “However, DC is more dangerous, mainly because of the arcing that occurs in the event of a short circuit. Commonly used AC fuses cannot be used for protection in such a situation.” Holthusen is thus working on new, safe approaches for DC supply.