Vehicles with combustion engines have been used for more than 100 years, and there has been an intensive shift in the automotive sector since 2017, as the figures from Statistics Austria clearly show.
We are already in the midst of a trend reversal away from the conventional combustion engine towards alternative drive and storage concepts. The passenger car sector is certainly considered a pioneer here, but the trucking sector is also changing, albeit with a slight delay. But what alternatives are there? What advantages and disadvantages do they have?
In this article I will try to bring some clarity to the complex topic of alternative drive concepts.
The different concepts
Electric drive with battery (BEV – Battery Electric Vehicle):
Probably the best-known form of alternative drive. The first e-vehicles already existed 100 years ago, but they did not catch on. It looks a little different today. The vehicle is operated fully electrically. Batteries store the energy and the vehicle is powered by electric motors.
Storage medium: high-voltage battery
Drive: electric motors
- Completely electric operation when batteries are charged with renewable energy, CO2 neutral
- No fuel consumption when stationary (traffic jams, traffic lights,…)
- High overall efficiency 65-70 %
Energy balance of the electric car with electricity from renewable sources
- Low-noise transportation
- Good acceleration
- Well-developed publicly accessible e-charging network for cars
- Low ecological footprint
- Currently lower ranges than conventional drive concepts
- Charging time
- High acquisition costs
- The publicly accessible e-charging network for trucks is not yet very extensive
Hybrid drive (HEV – Hybrid Electric Vehicle):
In hybrid drive technology, internal combustion engines are combined with electric motors. A distinction is made between parallel hybrid and serial hybrid:
- Parallel hybrid: Combustion engine and electric motor jointly drive the vehicle (mechanical connection), completely electric operation is possible in some cases.
- Serial hybrid: The vehicle is driven exclusively by an electric motor, the combustion engine drives the electric motor or charges the battery.
Storage medium: high-voltage battery / fuel
Drive: electric motor / combustion engine
- Long ranges
- Short charging time, as energy can be supplied via fuel
- Good acceleration
- CO² emissions when driving with a combustion engine
- Only the plug-in hybrid can be charged externally with renewable energy
- Higher maintenance costs
- High weight
Hydrogen propulsion (FCEV – Fuel Cell Electric Vehicles):
The vehicle is powered by electric motors, but unlike the BEV, the electrical energy is provided by the fuel cell. Hydrogen reacts with oxygen in a chemical process and generates energy. Usually, a small battery storage unit is also installed in the vehicle in order to cover peak loads as an intermediate storage unit and to recover braking energy during recuperation. Hydrogen can be stored and transported in the form of gas in tanks.
Storage medium: hydrogen
Drive: electric motor
- Short refueling times (similar to diesel/petrol vehicles)
- CO2 neutral in operation
- Long ranges possible
- Very manageable supply network (approx. 5 fuelling stations in Austria and approx. 100 in Germany)
- Very high acquisition costs
- Low overall efficiency (production of hydrogen to propulsion of the vehicle)
Energy balance of hydrogen fuel cell vehicle with electricity from renewable sources
Natural gas CNG (Compressed Natural Gas) / Autogas LPG (Liquefied Petroleum Gas):
The classic petrol engine is used as the drive. Usually in the form of a bivalent drive, i.e., the engine can be operated with both natural gas (CNG) and petrol. In order to achieve the appropriate energy density, the natural gas (CNG) must be pressurized (approx. 200 bar), which makes storage a little more complex compared to liquid autogas (LPG).
Advantages of natural gas (CNG):
- Lower pollutant emissions than conventional drive types (petrol/diesel) up to 80 % –> when driving
- Efficiency similar to a diesel engine
- Naturally occurring natural gas
- Fuel costs are cheaper than diesel and petrol
Disadvantages of natural gas (CNG):
- Very volatile as it is lighter than air
- Greenhouse gas –> methane contributes significantly to global warming
- Gas station network is not yet available across the board
- Due to the lower energy density compared to petrol (31.7 MJ/l) and diesel (35.8 MJ/l), there is an increased consumption requirement –> for comparison, CNG has an energy density of 21 MJ/l
Advantages of Autogas (LPG):
- Longer ranges than natural gas-powered vehicles (same tank capacity, range approx. threefold)
- Fuel costs are cheaper than diesel and petrol
- Gas station network is already well developed
Disadvantages of Autogas (LPG):
- Increased pollutant emissions compared to natural gas –> when driving
- Due to the lower energy density compared to petrol (31.7 MJ/l) and diesel (35.8 MJ/l), there is an increased consumption requirement –> for comparison, LPG has an energy density of 24.8 MJ/l
E-Fuel (electric fuel):
E-fuel refers to synthetically produced fuels. Basically, the infrastructure (filling station network) and vehicles (diesel/petrol) would remain the same, just not with conventional fuels, but with e-fuel. For this purpose, hydrogen is obtained from water in an energy-intensive process by electrolysis and combined with carbon from CO₂ in the ambient air or industrial exhaust gases.The basic idea is good, but the implementation is not yet sufficiently tangible.
- Infrastructure (filling station network) and vehicles (petrol/diesel) could continue to be used
- Refuelling time, transport, storage – similar to petrol and diesel
- Electrical energy is required to produce e-fuel – very inefficient
- Overall efficiency: Only about 10-35 % of the original electrical energy is converted into useful energy (vehicle propulsion).
- With the current German electricity mix (2018) 3-4x more greenhouse gases would be generated than with comparable fossil fuels –> for a climate-friendly balance, the electricity mix would have to be at least 90 % renewable energy!
- Due to the fact that mass production is not yet feasible, the prices are horrendous and the product is only available in very limited quantities
From the current perspective, taking into account the technologies that are available and mass-produced, the only alternative left in the short and medium term is the BEV (Battery Electric Vehicle) to replace conventional combustion engines. The drive technology is mature and considerable progress is still being made in the battery sector. It should also be noted that in the case of disaster, it is easier to achieve energy supply with electrical energy than with fossil fuels. Of course, diesel is currently the number one energy source in the event of a disaster, but there will probably be a shift in thinking here as well with the increasing electrification of vehicles.
In the long term, BEVs will largely take the place of conventional drives. For special applications where all-electric propulsion is not feasible or uneconomical, other technologies will have to be used, but most of these are not yet mature, too expensive, or simply not climate-friendly.
Two trends can already be seen in the commercial vehicle sector in terms of alternative drive concepts: inner-city distribution traffic with purely electric drives, long-distance transport with hydrogen fuel cell drives.