Studierendengruppe mit E-Autos auf einer Bergkuppe im Odenwald
“The play instinct is important”

Driving is in his blood! As a qualified test driver, Jens Hoffmann, Professor of Electromobility, sometimes puts his foot down – but only when on safe terrain, and he knows at least as much about braking as he does about accelerating: before joining h_da in 2021, Hoffmann, who earned his doctoral degree in automotive engineering, worked for Continental, where he was responsible for developing new braking systems. On occasion, his courses introduce students to the subject in a rather unorthodox way. In this interview for impact, he explains what he finds fascinating about e-mobility and why he nevertheless does not consider it a panacea for the mobility transition.

Interview: Christina Janssen, 4.12.2023

impact: You recently spent a foggy autumn Saturday with your students in h_da’s e-cars on Frankenstein Mountain. Do you do things like that just for fun?

Professor Jens Hoffmann (laughs): It’s definitely fun, and the play instinct is also important. Of course, the students should also learn something. We teach them the theory beforehand, and then they can decide for themselves which questions they want to examine in practice during the test drives. We then spent a day together with h_da’s electric vehicles on Frankenstein Mountain in the Odenwald, where they were able to try everything out.

impact: What, for example?

Hoffmann: We measured the power flows in each car: How high is the electric current, how high is the voltage in different situations? We did this on the mountain to find out how much energy is needed to drive from the lowest car park at the bottom to the very top. The students had to think about this beforehand and take climate control into consideration, for example: on such a cold, rainy day – how much energy does that alone consume? And how much energy do I recuperate when I drive downhill again? We tested this with all our university’s e-cars, from the small Renault Twizy to the big Tesla Model 3.

impact: Recuperate means recover, in this case energy?

Hoffmann: Correct. We can recover some of the energy that we used when we drove uphill. This is one of the innovative features of e-cars and something that standard cars with combustion engines cannot do.

impact: And the students had calculated this beforehand in the lab to compare whether their results were correct?

Hoffmann: It was initially a matter of estimating figures. This time, students were involved who were not automotive experts. I undertake similar activities at a higher level with students from the Master’s programmes in Automotive Engineering, Industrial Engineering, Mechanical Engineering, and Mechatronics. This time, we had Bachelor’s students from the Building Systems Engineering and Energy Economics programmes with us, so we made it a bit more of a game. We took some measurements, and then the students had to explain the results.

impact: And these are skills that students will require later on in their careers? I would like, for example, a route planner to calculate exactly how far I can drive with an e-car if there are x kilometres of uphill and downhill gradients along the way.

Hoffmann: Exactly. The latest electric vehicles can already do that. But the group of students who were with us on Frankenstein Mountain must also develop an understanding of the infrastructure needed to facilitate electromobility. That is why we are also conducting trials with wallbox chargers on campus: What do I do if everyone comes home with their e-cars at 6 pm, plugs them in and then charges them at maximum power until 9 pm? What happens if I want to charge three cars next to each other in one building? They now understand this. It’s always easier to try something like this out for yourself than to have it explained to you in theory.

impact: Where else are you taking your students?

Hoffmann: In December, we will visit the HEAG depot with this group to look at electromobility in buses. We will meet the project manager in charge. That will be interesting, now that the students have understood everything at the level of smaller vehicles and can ask the right questions.

impact: And you’ve also visited an airfield?

Hoffmann: Yes, we did test drives with another group on Griesheim Airfield, where you can really see how e-cars perform.

impact: But without taking off.

Hoffmann (laughs): Without taking off. It has a long runway, where we accelerated a Tesla from 0 to 200 km/h and from 200 to 0 km/h. That was really impressive. And from the measuring system we can see how much current flows through the car’s cables, for example, and how much power the engine produces. Why is acceleration as it is? Why does it level off at higher speeds? That’s where all our knowledge of automotive engineering comes in, as well as some aspects of electrical engineering.

impact: In your opinion, is electromobility the key technology for the mobility transition?

Hoffmann: No.

impact: So it’s a bridging technology?

Hoffmann: No. For me, hybrid technology is a bridging technology. Electromobility is here to stay, but there will be many different technologies in the future, and combustion engines won’t disappear either. The question is: What do we use for what? There is a lot of talk about hydrogen at the moment. Personally, I believe that we will need the hydrogen capacities which we will hopefully have at some point for other things than private mobility. Mobility will have many facets. And we won’t gain anything by replacing every single combustion engine with an e-car.

impact: Why not?

Hoffmann: Because it would be too much. We are obviously living beyond our means. Not just in Germany, but throughout the world. And then I must ask myself: At what point can or should it also hurt a little bit? My neighbours drive somewhere in their combustion engine car for five minutes and then come home again. That hurts me for the combustion engine alone because it doesn’t even have a chance to warm up properly in those five minutes (laughs). These are forms of mobility that we need to change, and not just by replacing combustion engines with e-cars. Because that also means tons of steel on the move – just with a battery instead. Everything must become lighter and more efficient. E-scooters are perhaps not the best example, but at least they are an attempt.

impact: Critics complain that environmental pollution goes hand in hand with the mining of raw materials for the batteries, too. Just not here in Europe.

Hoffmann: Of course, you must always look at the whole chain. But sometimes it’s a case of comparing apples and pears: for decades, production in the oil industry was messy and dirty, and the sector ignored social standards, but it nonetheless remained unquestioned. Electromobility, on the other hand, is still a young technology, and politics has yet to establish the right framework. And in the debate about rare earths, we should bear one thing in mind: a 500-kilo Tesla battery is not lost at the end of the vehicle’s service life. The raw materials that I used at the beginning are still at my disposal at the end. In contrast to burning a litre of fuel, where all that’s left over is CO2.

impact: Are the batteries fully recyclable?

Hoffmann: There are processes today that claim to recycle 95 to 98 percent. We need a technology that does this economically. At present, there is no money to be made from that. This will hopefully change when the current generation of e-cars needs new batteries in 10 to 15 years’ time.

impact: E-mobility is also possible on two wheels: in the “GAUSS Project”, you are working with an interdisciplinary team of students on a new h_da electric motorbike. When will it be ready?

Hoffmann: That will take a while yet. The team has set itself the goal of a 24-hour race. We hope to do that in 2025. But “GAUSS II” will no doubt do a few laps on the square in front of University Tower before then. 

impact: Thank you for the interview.