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Inductive & night recharging

Friday 15th April 2011
Project inductive charging. Courtesy:

As Siemens unveils a plug-free contactless system for recharging electric cars with live tests to be run in Berlin, US researchers shows that for plug-in hybrid electric vehicles (PHEVs) ozone, a known pollutant harming respiratory systems and sensitive plants, can be reduced on average, when electric vehicle charging is done at night.

Siemens system, part of project Green e-motion, does not require plugging into recharging point but uses inductive charging, in which a current flowing through an electric coil in the charging station generates a magnetic field that induces an electric current in a second coil in the vehicle, recharging the battery.

The system, demonstrated at the annual technology exhibition Hannover Messe, was developed with the car maker BMW. In June it will be tested live in a project funded by the German Environment Ministry and involving several vehicles in Berlin.

According to Siemens, the non-contact technology works if drivers make only a short stop to recharge. Associated charging stations can be easily put into practically any setting, making them nearly invisible so protecting against vandalism and wear and tear.

Lack of an extensive and reliable recharging system is a big obstacle to increasing use of electric vehicles that must recharge their batteries more often than combustion engines vehicles need to refuel.

A number of moves to create a suitable infrastructure, including installing recharging points in homes and car parks and setting up “battery swopping” stations where drivers can drop off a spent battery and pick up a charged one are being considered.

Siemens claims its inductive energy transmission technology make it possible to automatically recharge vehicles, such as taxis waiting at cab stands. The charging station is connected to the public grid by a primary coil, completely underground.

A secondary coil is attached to the car,  distance between the two coils being between 8-15cms. As the driver starts the charging process, an electric current flows through the primary coil. The resulting magnetic field induces an electric current in the secondary coil, which recharges the battery.

Electricity is transmitted from the grid through all of the components to the battery at an efficiency of more than 90%. The magnetic field is generated only in an exactly predetermined area between the two coils. Siemens says the strength of the field in and around the vehicle is far below international limits of 6.25 microteslas.

Starting in May, a prototype with a charging power of 3.6kW will be tested in an electric vehicle, followed by the Berlin trial  to determine improvements needed to enable technology integration in  mass-produced vehicles.

Siemens is also promoting the technology as a means of storing electricity from solar/wind generation, to balance  electricity grid loads.

MIT researchers work on PHEVs

Ozone forms as hydrocarbons and nitrogen oxides, and emitted into the air, react with sunlight. Two of the largest pollutant emitters are vehicles and electricity generating units (EGUs).

Plug-in Hybrid Electric Vehicles (PHEVs) have risen in popularity over the past decade as a result of cheaper fuel costs (versus gasoline), increased efficiency, and positive impact on the environment due to lack of exhaust fumes.

Charging PHEVs at night time is known to be more cost-effective and reliable; however, researchers publishing in Environmental Research Letters, now find that charging at this time also leads to lower levels of pollution on average across four cities and over four representative modelling days.

PHEVs can run off battery power and gasoline. When PHEVs run off battery power they emit no pollutants from their exhaust, but EGU’s, providing electricity to charge batteries, do give off pollutants.

Massachusetts Institute of Technology (MIT) and the University of Texas researcher modelled the effect of replacing 20% of the vehicle miles travelled (VMT) by gasoline-run cars with PHEVs, using three different electric car charging scenarios to study the emission of pollutants, specifically ozone, in the state of Texas.

There has been much debate regarding the best way to charge electric cars. First scenario in this study based on charging the car at off-peak times in the night. Second scenario involved charging to maximize battery life (charging just before use and only the amount of charge needed to complete the trip.) Third scenario involved charging battery when convenient for the driver (typically just after vehicle use.)

Results showed the overall levels of pollution, resulting from EGU emissions associated with charging, were lower than the level of pollution resulting from the emissions associated with 20% of gasoline VMT.

Despite night time charging shown to yield the highest amount of nitrogen oxides, it led to the least amount of ozone on average across all cities and hours modelled, as there is no sunlight for the emissions to react with.

By the time morning comes, pollutants are dispersed and diluted by other processes such as the wind.

Lead author Dr Tammy Thompson of MIT said “This further supports efforts to develop regulation to encourage night time charging; an example would be variable electricity pricing.

"As more of the fleet switches over to PHEVs and a larger demand is placed on the electricity grid, it will become more important that we design and implement policy that will encourage charging behaviours that are positive for both air quality and grid reliability.”


Above: The Solar Tree at the National Renewable Energy Laboratory (NREL) in Golden, Colorado, is the prototype of the future. Covering just two parking spaces, it is a pilot project that includes two integrated AC outlets charging hybrid electric vehicles that NREL has converted into plug-in hybrid electric vehicles. NREL researchers can use the array to charge their vehicles using the power of the sun. ©2009 Envision

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