book_cover_big.gifA hybrid car is a car that uses more than one power source in order to propel the vehicle. These sources can be combustion engines (of course), an electric motor, a sail or human power. In this blog we will focus on HEV’s (Hybrid Electrical Vehicle), vehicles where an electric motor and an internal combustion engine will do the work. Several configurations are possible with the electric motor and the combustion engine[1]. HEV’s are not just applied in cars but also in diesel locomotives or in city public bus transportation. The biggest limitation of a HEV is its action radius. However, from studies it is known that 80% of the car owners on average drive less than 40 km per day. It is in these situations that HEV’s can work out quite OK.

But why would we ride an HEV in the first place given the limitation in action radius? There can be several advantages of HEV over pure combustion engine propelled cars. These advantages are mainly visible in terms of reduced particles, nitrogen di-oxide and noise generation but then locally. That local impact should not be underestimated as cities are often struggling with the environmental quality and traffic plays an important role in this.

But of course an HEV needs electrical re-fueling. Here we can ask three important questions[2]:

  • 1) Will a HEV generate less greenhouse gases than a traditional fossil fuel powered car? A middle size car will consume about 5 to 6 liter of Diesel per 100km. A similar size HEV needs about 20kWh/100km. Calculation show now that the electricity needed by the HEV and delivered by a coal fired power plant generates about the same amount of green house gases (770-840 gr/kWh) as the fossil fuel powered car per 100km. And of course, when the power plant is using renewable electricity generation then the balance will turn quickly more favorable for the HEV in terms of green house gas generation. This may turn out to be the biggest advantage of HEV’s, not only from an environmental point of view but also from a reduced dependency on oil imports point of view.
  • 2) Can the power grid handle the extra load to charge the HEV’s? This question is answered for the situation in Germany. It is expected that it will take at least till 2020 before there will be one million HEV’s on the road. They will consume about 2 TWh/year[3] and that is only 0.3% of the total yearly electricity production in Germany.
  • 3) Will the cost price of an electrical km be competitive with a fossil km? Actually yes. Again assuming a fuel consumption of 6 liter/km and a price of 1.2 Euro/liter, the fuel cost per kilometer is then 7.2 ct. The HEV needs 0.2 kWh/km, thus assuming that we pay the same amount per kilometer, the driver has a budget of 7.2/0.2 = 36 ct/kWh. Compare this with the actual price for electricity of about 18 ct/kWh and you have to conclude that electrical driving is indeed cost effective and can potentially be much cheaper than fossil fuel transportation.

Thus, all in all no roadblocks for HEV as long as it concerns the environment, the power grid and the economics.

 Copyright © 2008 John Schmitz


[1] Such as a serial or a parallel configuration of the power sources, see for more details: Robert Bosch GmbH, “Autoelektrik, Autoelektronik, Friedrich Vieweg &Son Verlag/GWV Fachverlage GmbH, Wiesbaden (2007)

[2] Recently a German study that addresses these and many other questions appeared that is worth reading: Höpfner U., Merten F., Elektromobilität und erneuerbare Energien, IFEU Heidelberg und Wuppertal Institut, Wuppertal, Nov 2007. The data I mention under 1, 2 and 3 come from that study.

[3] Assumed here is 2000kWh/HEV and that is about 10000 km per year

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