Manufacturers are currently focussing their efforts on the full or partial electrification of the car. In doing so, they receive support on the political level, where CO2 regulation is constantly being intensified. Apart from the fact that electric mobility is already extremely advanced in terms of technology, it is in its pure form that the most rapid success can be achieved in the short term when it comes to meeting environmental targets. Hybrid cars that combine a combustion engine with an electric drive are seen as an intermediate solution, and there are also other alternatives to fully electric cars.
The hybridisation of cars, combining a combustion engine with electric energy, has been established for some time now. Hybrid electric vehicles make a significant contribution to reducing emissions in road traffic.
The approach when it comes to plug-in hybrids is to combine strengths to save on fuel. Such a vehicle runs on a combination of an electric motor and combustion engine, bringing these two systems together in an optimal way. The electric motor contains a lithium-ion battery that can be plugged into a socket and recharged fully or partially within a short time. The principle is to facilitate environmentally conscious electric mobility for short distances in everyday life with the aid of a combustion engine for longer journeys. Most journeys of up to 55 kilometres can be made with a plug-in hybrid vehicle using only electric power, silently and with zero local emissions.
Most electric hybrid vehicles use a parallel hybrid drive. A plug-in hybrid vehicle is powered by the electric motor alone or in combination with the combustion engine. If both are needed, they work side by side, i.e. in parallel, to enable maximum performance. Both the electric motor and the combustion engine are smaller in a hybrid vehicle than in a vehicle that has only one or the other.
In a serial hybrid drive, the two motors – combustion engine and electric motor – do not work side by side, but one after the other. As a rule, the combustion engine supplies energy to an electric generator, which in turn powers the vehicle or charges the battery. In this case, the combustion engine is not directly connected to the drive. The principle of the serial hybrid is also used in the “range extender”, in which the vehicle is always driven by the electric motor. If the energy in the battery runs short, the combustion engine starts up and functions as a generator for the electric motor.
Electrification of engines is an important step on the way to emission-free mobility. Those who do not yet wish or are unable to switch completely to electric mobility, however, have other options for being more environmentally conscious on the road. Modern technologies are making combustion engines more economical. With mild hybrid drives, the combustion engine is supported by a starter generator and a small lithium-ion battery. On straight or sloping roads, the combustion engine switches off and the car “coasts” emission-free. In addition to this, the mild hybrid system recovers energy through recuperation when braking. A mild hybrid car cannot be driven using only the electric motor, however.
Cars that run on petrol and gas are called gas hybrids. They have a long range and are more environmentally friendly than pure petrol or diesel, but occupy only a very small niche.
A natural gas hybrid car can be powered by two fuels – natural gas or biogas (both methane gases), and petrol. In normal operation, the car runs on gas. When this runs short, the system switches automatically and imperceptibly to petrol, thereby ensuring a range of up to 1000 kilometres. This bivalent technology avoids dependence on natural gas stations, of which there are not many available. While the engine is running on gas, it is compressed and transported to the cylinders where it mixes with air and burnt. This is the same principle as the burning of petrol. Natural gas vehicles are more environmentally friendly than pure combustion engines, and the gas, which is sold in kilograms, is cheaper than petrol or diesel. The tanks used are filled via two separate adjacent nozzles.
LPG is a liquefied gas made up of butane and propane. It is a by-product of oil production that is more environmentally friendly and cheaper than fossil fuels. Very few cars are manufactured to run on LPG, however, and converting a petrol car into a bivalent vehicle is only worthwhile for frequent drivers. An LPG hybrid vehicle runs on liquefied gas by default. Once the gas tank is empty, the system automatically switches to petrol operation. LPG vehicles are not very common in Switzerland, as they are not available for sale within the country.
E-fuels are synthetic fuels that are produced with electricity from water and carbon dioxide. They are climate-neutral. The main advantage of e-fuels is that they could be used for existing cars with combustion engines and distributed via the petrol station infrastructure. No changeover would be necessary, and CO2 emissions would be reduced immediately all over the world. This is particularly relevant in view of the fact that it will take decades before all cars with combustion engines are replaced by electric vehicles. In addition to this, e-fuels could also be used for ships and aircraft. The production process is still energy-intensive, time-consuming and expensive, however, and is not being promoted on the political level. This is why few car manufacturers are focusing on this technology.
With the exception of Porsche: together with Siemens Energy and other international companies, Porsche is developing and implementing a pilot project in Chile that will result in the world’s first large-scale facility for the production of synthetic, climate-neutral fuels. Around 130 000 litres of e-fuels are due to be produced in a pilot phase in 2022. The plan is then to increase capacity to around 55 million litres of e-fuels per year by 2024, followed by around 550 million litres by 2026. The background to Porsche’s undertaking, apart from the environmental arguments, is the fact that the cars are driven for a very long time and will be around for longer still as veteran cars.
Oliver Blume, Porsche’s CEO, says: “Electric mobility is top priority at Porsche. E-fuels for cars are a logical addition in this regard – provided they are produced at locations around the world where a surplus of sustainable energy is available. They are an additional building block on the road to decarbonisation. Their advantage lies in their ease of use: e-fuels can be used in combustion engines and plug-in hybrids, and supplied through the existing petrol station network.”
Despite being powered by hydrogen, fuel cell vehicles are considered to be electric as they have an electric motor on board. The fuel cell performs the function of an energy converter that converts hydrogen into electric energy. This is what ultimately drives the electric motor. As with the fully electric car, no local emissions are produced, only water vapour. The advantage of hydrogen vehicles is that it only takes a few minutes to refuel at special hydrogen stations. And compared with electricity, hydrogen is easier to store. The hydrogen station network is not yet very extensive, and only around six vehicles can be refuelled at one pump per hour, because of the pressure that has to be built each time.
Hydrogen is often referred to as the fuel of the future. It is extremely costly and energy-intensive to produce, however, as well as being significantly less efficient than electricity. On top of this, a completely new filling station infrastructure would need to be built.
E85 is the term used for a fuel that consists of 85% bioethanol and 15% unleaded petrol 95. Bioethanol is an alcohol produced from agricultural and forestry residues, biodegradable waste and renewable raw materials (grain, sugar beet, sugar cane, wood waste). E85 is well-established in Brazil, Sweden, the Czech Republic and the USA. A number of flexible-fuel vehicles (FFVs) in these countries run on this fuel.
In the production of bioethanol, the cellulose in the biomass is first broken down enzymatically into glucose. It is then fermented by yeast into bioethanol and distilled, before 15% of petrol 95 is added to improve the cold start quality in the combustion engine, as filling up a car with a pure petrol engine with E85 involves a risk of engine damage. The use of bioethanol in vehicles helps to protect oil reserves and processes biodegradable residues in a meaningful way. However, there is also criticism of this method because it means that agricultural land is used for fuel production instead of food production.