Bi-directional charging box connects e-cars to smart grid

February 19, 2014 // By Christoph Hammerschmidt
As a contribution to Germany's turnaround in energy policy, scientists have developed a device that allows electric energy to flow in both directions between the power grid and electric vehicles. The system enables electric vehicles not only to be charged but also to store energy and return it to the grid in times of high energy demand.

The 'Powerbox', developed by scientists from Technology Transfer Centre of the Würzburg-Schweinfurt Hochschule (FHWS) in northern Bavaria, is a building block of a Smart Grid. As such, it enables bi-directional energy flow between grid and electric vehicles. The prototype rolled out recently allows controlled charging and de-charging of battery electric vehicles and plug-in hybrids (PHEV). The box is designed to be connected to series production battery electric vehicles such as Mitsubishi's i-MiEV or PHEVs like the Mitsubishi Outlander.

The device is a European first, the research group around Ansgar Ackva claims. In Japan, Mitsubishi offers a comparable box since April 2012, which enables the i-MiEV to be utilized as an emergency AC power supply. In contrast to its Japanese counterpart which provides up to 1.5 kW, the FHWS system supplies up to 20 kW which enables the e-car to be utilized in small corporate grids. If energy flows in the opposite direction, the Powerbox enables fast charging within just half an hour.

The capability of storing renewable energies during low load periods and feed it back into the grid during peak load is regarded as a crucial precondition for the changeover towards renewable energies be a success. According to Siemens calculations, one million e-cars with an average battery capacity of 16 kWh (such as the Mitsubishi i-MiEV) can represent an energy buffer store of 16 GWh and thus supply 2 million households for a day.

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