Everyone can decide for themselves what they want
Around half a billion euros from the second economic stimulus package are currently flowing into electromobility. Does this make sense? No question, says Dirk Uwe Sauer, Professor at the Institute for Power Electronics and Electrical Drives (ISEA) at RWTH Aachen University. Anyone who takes climate change seriously cannot ignore electric cars
Spectrum of science: Professor Sauer, when electric cars are talked about these days, the weaknesses of today's batteries quickly become the focus of discussion. How efficient are they now?
Dirk Uwe Sauer: In my opinion, the discussions about energy densities, power densities and ultimately the range of electric vehicles are going in the wrong direction. The question must be: What can we afford economically? In the case of a delivery or postal bus with fixed routes, for example, there is no question. If it drives 100 or 200 kilometers a day, the battery is dimensioned accordingly and run empty once a day. It pays for itself: If a battery like this goes through 300 cycles a year, it will last at least five, maybe even ten years. The average citizen has a different usage profile, he drives an average of 37 kilometers a day, mostly over short distances. Even if his electric car has a range of just 100 kilometers, this is unfavorable for the economy. He has to finance the battery and drive it around all the time. But two-thirds of the battery just dies.
Spectrum: Even a range of 100 kilometers would not be enough for most people.
Sour: Everyone can decide for themselves what they want. Today's batteries for electric vehicles have an energy density of 100 to 120 watt hours per kilogram. A converted Polo, for example, consumes 15 or 16 kilowatt hours per 100 kilometers. This gives you a range of roughly 65 or 80 kilometers per 100 kilograms. With a vehicle weight of 1.2 tons, maybe 300 kilograms are okay for the battery, which corresponds to 200 or 240 kilometers. However, this is usually not useful. So far there have only been practically one-offs on the market, where a kilowatt hour of storable energy costs around 1000 to 1500 euros. Realistically, prices could drop to 300 euros per kilowatt hour one day. With a range of 100 kilometers, i.e. 15 kilowatt hours of energy, 4500 euros are then due for the battery. On top of that there is VAT, handling, installation, guarantee, we calculate with a factor of about 1.8. This investment can be partially refinanced because electricity is cheaper than petrol. But that only applies if you actually drive and the battery is not just aging.
Spektrum: So what can we expect from electric cars?
Sauer: Today, e-mobiles can basically be used as city or second vehicles. And even in ten years, we will not have standard batteries that will allow us economical ranges of 300 or 500 kilometers. Ideally, the average family in 2020 will own an all-electric vehicle and a plug-in hybrid (this has both a combustion engine and an electric drive with a battery that can be charged from the mains, ed.) with an electric range of 30 to 50 kilometers. With the latter, she can then easily go on vacation. If the electrical infrastructure is available across the board, for example if we charge our cars while we work, we can easily save two thirds of the petrol that Germans use in traffic today with such vehicles. Serial hybrids also make it possible to optimize fuel consumption and exhaust gas cleaning, similar to modern ships or diesel-electric trains. The internal combustion engine runs exclusively to generate electricity, but at its optimum power point.
Spectrum: In the city, electric vehicles also get their energy onto the road more efficiently than previous vehicles.
Sauer: Gasoline engines are of course less efficient in city traffic than at constant speed overland or on the motorway due to their very dynamic operation. In addition, they cannot recover part of the braking energy through recuperation. On the other hand: In the urban e-mobile, additional consumers such as radio, light, perhaps the air conditioning system have an impact because relatively short distances are relatively long journeys.
Spektrum: Some readers commented on our article "The future is electric" that apparently there is still no solution for heating the interior. After all, the waste heat from the engine is almost completely eliminated.
Sauer: Little research has actually been done on these thermal problems. From a thermal point of view, today's vehicles are anything but optimal: the entire interior air is exchanged up to 30 times per hour. Similar to what was the case with house building for a long time, nobody gave this topic any thought. But the corresponding tools that were developed for other purposes can of course also be let loose on the car: thermal storage, windows with coatings, thin vacuum insulation elements, heat exchangers and so on. But even with batteries and electric motors, around 10 to 15 percent of the energy is lost in the form of heat. About one kilowatt of heat output could be gained from this.
Spectrum: How desirable is it anyway that electric vehicles become widespread?
Sauer: If you take the problem of CO2 emissions and climate change seriously, there is no alternative to electric drives in the medium term, at least if you want to keep the current concept of private transport. Only the electricity sector has the chance to generate largely carbon dioxide-free energy, be it through renewable energies, CO2 sequestration or nuclear power. In any case, the power requirement is lower than some people assume. If the entire mileage of the approximately 46 million cars currently driving on German roads were to be completely converted to electricity, total electricity consumption would increase by 15 to 20 percent. Even with today's electricity mix, an e-vehicle in Germany already emits less carbon dioxide than a conventional one. And of course noise and fine dust pollution are also eliminated.
Spectrum: What would be the consequences for the electricity grids of a large-scale conversion?
Sauer: A smart grid infrastructure could lead to some useful effects, mainly related to balancing power. Once a high proportion of vehicles are connected to the electrical grid, they can be used to regulate excess or undersupply. A method of energy management that is practically free of charge for the vehicle owner is to simply shift the demand in time. A vehicle connected to the socket would be charged precisely when there is a surplus in the network. There is also the possibility that batteries will feed their energy into the grid if there is a shortage there, or absorb excess electricity from the grid. Their efficiencies are around 90 percent, and there are also small losses from the converters. This means that the battery is currently the electricity storage device with the highest efficiency and also surpasses the commonly used pumped storage power plants.
The recipients of the funds include RWTH Aachen University. It is a nationwide leader in the field of electrical energy technology: Six professors conduct research here at five institutes with a total of around 300 employees. There is a focus on battery system technology, electronics and electric drives as well as network system technology. Appropriately, the Faculty of Mechanical Engineering at the RWTH is the largest in the state and is traditionally heavily involved in automotive engineering. Other research centers are Darmstadt, the TU Munich, Karlsruhe and Münster, as well as Dresden, the TU Berlin and non-university institutions such as the Freiburg Fraunhofer Institute for Solar Energy Systems or the Center for Solar Energy and Hydrogen Research Baden-Württemberg in Ulm.
Spectrum: If a driver makes storage capacity available to the networks, it must be worthwhile for him, especially since his batteries also wear out.
Sour: It could actually be worth it. If the network operators pay for the use of such intermediate storage, the car owner would also have the guarantee that his batteries would not simply die. On average, electric vehicles will hardly consume 1,500 times the energy content of the battery over a period of ten years. Depending on how they are operated, the batteries can safely release their energy content 3,000 to 5,000 times. Every penny that can be earned through the use of this additional life reduces the costs for the vehicle owner. A three-tier management that covers the needs of the individual user through the regional low-voltage grid to the high-voltage grid would also ensure that everyone has a full tank when needed. And the problem of shortening the service life has essentially been solved with lithium-ion technology, lithium batteries can be charged or discharged at practically any charge level.
Spektrum: Federal Environment Minister Sigmar Gabriel hopes that by 2020 there will be one million electric cars - hybrids as well as pure electric vehicles - on Germany's roads. Is that realistic?
Sour: I think there will be more. The forecasts are based on an overly simple approach. I assume that many small city vehicles and plug-in hybrids in particular will come onto the market. These city vehicles form a class of vehicles that, in principle, do not yet exist in this form today. They will meet the basic needs of mobility in the city, for example trips to work, to university, to kindergarten or to the play group in the afternoon. However, they are not designed to be taken on long-distance vacations twice a year. In the Asian market, we see exactly such developments that lead to cheap vehicles - and they will come onto the market here. The question is who will do this business in the future. Keyword Tata Nano: The Indian small car can be built for 3000 euros, and for another 3000 to 5000 euros you can in principle immediately produce an electric vehicle with a range of maybe 80 kilometers. Changing social structures will also ensure the success of such cars, because the gap between low and high earners is widening. More and more people who can no longer afford a Golf, Focus or Astra will scale back their mobility requirements. The fact that someone keeps a large car in front of them that they rarely really use is becoming increasingly rare.
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Dirk Uwe Sauer is Professor of Electrochemical Energy Conversion and Storage System Technology at the Institute for Power Electronics and Electrical Drives (ISEA) at RWTH Aachen University. His current work focuses on battery technology for mobility applications of all kinds. In most cases, the research projects are carried out in direct cooperation or on behalf of industry. Sauer also organizes training events for industrial employees and conferences.
