What is the first thing you think of when it comes to electrically driven vehicles in a city or the urban environment? Probably, you have the usual road traffic in your mind. Traffic on many main and secondary roads between different blocks. Admittedly, it is almost the total proportion of the overall traffic.
However, there are further applications regarding eco-friendly transportation systems. Let us broaden the mental association and focus on the small fraction: Electric airport vehicles.
Why focus on airport vehicles?
City airports are not really in the foreground regarding green urbanization. The focus is more on sustainable buildings, road traffic, lighting or renewables. But even prior to every takeoff, there is already a lot of vehicle traffic on the airport apron.
It is not about small passenger cars but large-engined vehicles with significant differences in fuel consumption. Luggage tow tractors, passenger buses or cargo vehicles are responsible for ensuring the punctual takeoff. Most of these vehicles are commonly driven by a diesel engine. They cause noise and air pollution – unpleasant for all involved.
Many airports in the world, such as of Frankfurt (Germany), Portland (USA), Bangkok (Thailand) or Bangalore (India), provide charging stations for passenger cars on public parking lots. But the deployment of electric transport systems on the airport apron is still exceptional. Due to the constantly growing air traffic all over the world, electric airport vehicles would be a further contribution to improving the worldwide air quality, especially in and around cities.
Researching the deployment of electric airport vehicles
In order to lower the environmental impact and inconveniences for all concerned, the German Aerospace Center (DLR) investigated to which extent electric airport vehicles are able to replace conventionally driven vehicles. The investigation was carried out in practice – more precisely together with the international airport of Stuttgart within the scope of the research project eFleet.
The objective of the electric fleet was to achieve the same operational capability as with diesel vehicles. Furthermore, new options for interim charging and insights into the sizing of batteries were expected. With about 10.5 million passengers, Stuttgart has the sixth busiest airport in Germany but not even one of the 50 busiest in the world. It is certainly just right for this research project. Night flight restrictions are only applied for civil jet airplanes.
In a first step, the researchers prepared six electric-powered prototypes. Two luggage tow tractors, a freight tractor, a passenger bus, and a pushback tractor have been equipped with measurement. The collected performance data was used to compare them with the respective data of diesel vehicles. Furthermore, charging stations have been set up the immediate work environment. Finally, 100 drivers have been instructed in how to operate the new e-vehicles. The driving profile and the fuel consumption were recorded over a period of 28 months.
The driving profile and the fuel consumption were recorded over a period of 28 months. During this time, …
- … the electric airport vehicles covered a distance of around 90,000 kilometers,
- towed about 12,000 airplanes,
- conveyed 1.5 million pieces of luggage,
- and transported 300,000 passengers.
A closer look at the electric airport shuttle buses
The passenger buses eCobus 3000, manufactured by Cobus Industries GmbH, with a total weight of 20,400 kg and a passenger capacity of 112 people are powered with a Lithium-titanate battery with a capacity of 95 kWh. A permanent magnet synchronous motor nominal power of 160 kW sets the bus in motion. The batteries were charged between midnight and 5 o’clock in the morning. The shuttle drives at least 85 km with a single full charge.
How do electric airport vehicles perform on the apron?
Within a systematic analysis, the researchers analyzed the performance of the e-vehicles compared to the conventional ones. The practical implementation of the six electric airport vehicles was successful, even in shift operation. Apart from minor problems, the new fleet was fully accepted by the drivers.
Thanks to the applied recuperators, it was possible to reduce the specific energy consumption. The recovered energy during braking charged the vehicles’ battery. It was possible to increase the energy efficiency of about 50 – 80 percent depending on vehicle category and applied battery technology. The emissions can be reduced by 22 tons of CO2 per year and electric vehicle.
According to Stuttgart Airport, an enlargement of the fleet is not necessary thanks to the high availability. The researchers found out that a luggage tow tractor drives a maximum of 120 kilometers per day. A pushback tractor covers only a distance of about 40 kilometers.
“Electric drive is outstandingly well-suited to airport ground operations, as the distances traveled are manageable. After having carried out intensive testing, we are now taking the next step. Whenever cost-effectiveness, environmental impact, and operational safety meet, we will be relying on electric mobility in the future,” said airport CEO Prof. Fundel at the introduction of the vehicle.
How about the batteries?
Compared to diesel engines, the life cycle costs of electric vehicles are lower if lead acid batteries are used. The advantage of lithium batteries is the reduced weight and low maintenance requirements if compared to lead acid batteries. Unfortunately, live cycle costs for diesel vehicles are lower compared to lithium power supply.
“These airport shuttle buses are an exemplary step forward for the positive environmental impact of airports. The government of Baden-Württemberg massively supports electric mobility. The state is intended to become a pioneer region for sustainable mobility. I am therefore all the happier that with this decision the airport is keeping the role of a pioneer ‘fairport’ in the area of sustainability in Germany and Europe,” Mr. Hermann, Baden-Württemberg’s Minister of Transport and Infrastructure, notes.
Stuttgart Airport intends to switch the entire passenger transport and cargo system. Regarding this, only electric vehicles shall do the job on the airport apron by 2017. Charging stations with renewable power would make the entire transport 100 percent eco-friendly without harming the climate.
The research project was funded by the German Federal Ministry for Economic Affairs and Energy.