Green & affordable: new drive concept for sustainable mobility

In heavy-duty transport, there are good reasons for using the hydrogen-powered fuel cell: It offers long ranges without CO₂ emissions. By contrast, European passenger car manufacturers are almost unanimously relying on purely electric cars. IAV has developed a functional powertrain with a fuel cell that brings the breakthrough of this environmentally-friendly technology a step closer in passenger car transportation as well.

Vehicles powered by fuel cells do not produce any emissions that are harmful to the climate or to health if hydrogen is produced using regenerative energy. They also offer longer ranges than purely electric cars, with shorter refueling times. Nevertheless, the market has not been gaining momentum for years: Only a few manufacturers offer models powered by H₂ fuel cells, they are expensive to produce and the filling station network is sparse.

“Current fuel cell vehicles rely on large fuel cell systems with high total output covering all operating points,” says Dr. Dennis Backofen, Team Manager for Fuel Cell Model-based Development at IAV. “This brings with it various disadvantages, for example high costs, high weight and large space requirements, a high level of effort during application and, under certain circumstances, can lead to a short service life for the fuel cells.”

New fuel cell concept: only three load points

With the so-called LEAN fuel cell powertrain, IAV has developed an antonym – the full name “Low cost, Efficiency optimized, Attractive range and Non-complex” describes the basic idea: Instead of combining a large fuel cell with a small battery, IAV engineers are taking the opposite approach. “We use a small fuel cell with 40 kilowatts of power – in contrast, about 100 kilowatts are common in current fuel cell vehicles,” Backofen said. “Another energy source in the LEAN concept is a battery with a capacity of 22 kilowatt hours. In currently available models, values of two kilowatt-hours are more common.”

Through this approach, in addition to the costs as well as package, two other advantages can be generated: a significant reduction in the application effort and the aging of the fuel cell. Thanks to the large battery – which covers the dynamic requirements while driving – the fuel cell can be operated in only three operating points (close to idle with 4 kW, medium load with approx. 13 kW, full power with 40 kW).

«This significantly simplifies the application and greatly reduces the dynamic load on the fuel cell – which significantly extends its service life.»

Dr. Dennis Backofen — Team Manager for Fuel Cell Model-based Development at IAV

Drive concept for the compact class

IAV examined the performance of the new approach using a specific example. The starting point was a vehicle from the compact class weighing 1.6 tons, with a top speed of 160 kilometers per hour and a range of 700 kilometers in WLTP. The electrical energy storage system used is a so-called EMBATT battery with a storage density of 270 watt hours per liter – developed in a research project by IAV and partners with the aim of increasing the energy density of lithium-ion batteries to such an extent that purely electrical ranges of 1,000 kilometers are possible.

The optimized fuel cell is based on a current stack from mass production for which the developers assume various technical improvements by 2025, for example the reduction of activation, concentration and ohmic losses. The vehicle’s tank can hold 4.8 kilograms of hydrogen at 700 bar pressure.

Highway test: greater range than BEV

In a calculation, the developers compared the range and driving time of a Tesla Model 3 with the fuel cell vehicle. The result: At a speed of 130 km/h, the distance from Flensburg to Oberstdorf (983 km) can be covered with hydrogen in about eight hours and requires three refueling stops. If, on the other hand, the vehicle is purely battery-electric, the journey takes just under two hours longer with a total of four refueling stops. In addition to the faster refueling, the main reason for this is the greater range of the LEAN-FC-Powertrain vehicle at the stated speed compared with the battery vehicle.

The fuel cell variant also comes out ahead in terms of cost. Internal estimates of the prices for batteries, fuel cells and tank systems show that substituting the LEAN powertrain for the all-electric powertrain noticeably saves costs.

«With our concept for the C-segment, we remain recognizably below the forecast cost trend for fuel cells.»

Ralf Wascheck — Senior Vice President Fuel Cell and Hydrogen Mobility at IAV

“For many customers, this would be a conceivable option, especially since a top speed of 160 km/h is marketable,” says Ralf Wascheck.

LEAN fuel cell powertrain

lean fc modell

Fuel cell system: 40 kW, PEM fuel cell
Battery: IAV EMBATT, 22 kWh, 270 Wh/l
Tank size: 4.8 kg, 700 bar
Hybrid strategy: 3-point operation with constant load, battery recharging

(C-Class vehicle 1.6 t)
Hydrogen consumption (WLTP): 0.8 kg/100 km
Max. range (WLTP): 762 km
Max. speed: 160 km/h
Acceleration (0-100 km/h): 7.6 s

EMBATT technology

Powerful batteries for e-vehicles and alternative applications: As part of a research project, IAV is working with the Fraunhofer-Gesellschaft and industrial partners to develop a battery system that can be integrated directly into the vehicle chassis as well as processes for manufacturing the bipolar electrodes. Thanks to large-area electrodes in a stacked structure and efficient storage materials, EMBATT technology enables all-electric ranges of up to 1,000 km. The OEMs’ goal is to increase volumetric energy density to 500 Wh/l and significantly reduce manufacturing costs. EMBATT can contribute to this – as well as to the industry’s efforts to further reduce modules and complexity. There are already initial entrepreneurial approaches to the commercial further use of the technology.

The article was published in automotion 01/2021, the automotive engineering magazine of IAV. Here you can order the automotion free of charge.

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