E-mobility is on the rise: charging electric cars with solar power
With a share of just under 20%, the transport sector is the third-largest emitter of greenhouse gases in Germany, with road traffic accounting for the lion's share by far. Decisive reorientation is required in this area, not least in order to achieve the climate targets set by the federal government. Mobility must and will be rethought. The further development and promotion of electric mobility plays a significant role here, if not the key role. By using electricity as a source of energy, renewable energy sources such as photovoltaic systems can be made available in order to power vehicles. This enables CO2-free travel and ensures independence from rising oil prices.
Charging solutions for electric cars
As with fossil fuels, in the field of electromobility there are also different fuelling and charging options, depending on the technology integrated in the vehicle. However, there are a few more special features here. The charging process is basically determined by three factors: the charging capacity of the electric car, the output of the charging station and the corresponding connection or plug technology that connects these two parts. Since the performance of electric vehicles differs widely in relation to manufacturer and model, in the following we will concentrate on the wider influencing factor: the charging technology.
Charging technology as the biggest influencing factor
In the charging of electric cars, a basic distinction is made between direct current (DC) and alternating current (AC). This distinction is important, in that it determines the appropriate design of the charging station, its charging capacity and connection equipment.
Während nahezu alle Energiequellen des täglichen Gebrauchs über Wechselstrom verfügen, der Akku in den Elektrofahrzeugen allerdings nur Gleichstrom aufnehmen kann, muss zuvor eine Umwandlung des Stromes stattfinden. Erfolgt diese Umrichtung direkt im Elektroauto (“On-Board”), so spricht man von AC-Laden. Wird dieser Prozess durch Gleichrichter in der Ladestation übernommen, handelt es sich um einen DC-Ladevorgang.
Normal charging with alternating current
Das Laden über Wechselstrom, auch „Normalladen“ genannt, eignet sich besonders dann, wenn eine kostengünstige und universell nutzbare Ladelösung benötigt wird. Da die Umrichtung des Stromes hier nicht durch einen separaten Transformator in der Ladestation, sondern direkt im Elektroauto (“On-Board”) stattfindet, können AC-Ladestationen von allen Elektroautos genutzt werden. Die Ladeleistungen liegen hierbei zwischen 3,7 Kilowattstunden und 43 Kilowattstunden und eignen sich besonders für den privaten Haushalt und halböffentlichen Bereich wie auf Firmenparkplätzen, in Parkhäusern oder vor Supermärkten.
The standard European plug for AC charging is the so-called "Type 2 plug", otherwise known as the "Mennekes" plug after the company that played a major role in its development. Type 2 is derived from the IEC 62196-2 standard, which defines three types of plug for AC charging (Type 1 = single-phase charging; Type 2 = single- and three-phase charging; Type 3 = single- and three-phase charging with shutter). In contrast to conventional safety sockets, the Type 2 plug is designed for a large number of charging processes with permanently high currents. Additionally integrated pins enable communication between the vehicle and the charging station, and regulate the reference power according to availability and absorption capacity.
For vehicles with a lower battery capacity, AC charging can alternatively be carried out using the normal household socket or CEE socket (three-phase current).
Fast charging with direct current (DC)
In order to charge a vehicle again as quickly as possible, direct current is used instead of alternating current, as this allows significantly higher charging speeds. The necessary conversion of the current is no longer carried out in the vehicle itself; instead, the expensive and heavy rectifier and the power electronics are moved to the charging station. As things stand today, charging capacities of up to 350 kilowatts are already available. The corresponding plug types are the CCS plug for European or American vehicles, and the CHAdeMo plug for Asian vehicles.
The CCS plug is basically an extension of the Type 2 (AC) plug described above, with the addition of two poles for quick charging. While these two additional poles are exclusively responsible for the current flow, the already familiar (upper) section of the Type 2 plug is still used for communication and safety.
CHAdeMo ist ein Akronym für „CHArge de Move“ und stellt sozusagen das asiatische Gegenstück zum europäischen CCS-Stecker dar. Im Gegensatz zum europäischen Standard ermöglicht dieser die bidirektionale Ladung, das heißt es kann Energie aus dem Fahrzeug rückgespeist werden (“Vehicle-to-Grid”), beispielsweise zur Notstromversorgung.
As a pioneer of electromobility, Tesla has developed its own system in the form of the "Supercharger", which can be charged at up to 120 kW (DC). Installation and support are carried out by the US manufacturer itself, and use of the system is also reserved for its own vehicles. Vehicles from other makes can be charged at so-called "Destination chargers", which are mainly found in hotels, supermarkets or restaurants and have a lower capacity. Tesla uses the widely distributed Type 2 plug as the connection. An advantage of this connector is that it can be used both on standard European charging stations and - due to a different configuration of the contact pins - on Tesla Superchargers.
AC or DC – the charging capacity is what counts
Regardless of whether it is AC or DC - the connection technology includes not only the above-mentioned plug connections but also the appropriate cables. In addition to signalling devices for controlling the charging current and communication between the vehicle and the charging station, the main difference between the individual cables is whether the cables and plugs are fixed to the vehicle, have to be plugged in at both ends or are permanently installed in the charging station. The charging station must be selected according to the individual specifications.
Two factors are decisive for the selection of the right charging solution: the performance data of the battery technology and - since different vehicles have to be refuelled at the charging stations, especially in the commercial environment - the intended purpose or the availability time of the e-vehicles to be loaded.
If the charging time itself is uncritical, from a cost point of view the "classic" household socket (AC, 1-phase, 230 V) or a simple wallbox (11-22 kW) can be used to charge a vehicle. In spite of the longer non-availability of the vehicle associated with this, for reasons of cost this is the solution which is mainly used in the private sector. Three-phase connections (AC, 3-phase, 400 V) are also suitable in this respect.
In the case of more powerful engines, which usually have larger battery capacities and also need to be ready for use again quickly, the use of normal (22 kW) or fast charging stations (50 kW) up to ultra-fast charging stations (150-350 kW) makes sense. Here, too, the length of time the vehicles remain unavailable ultimately determines the choice of charging station. The use of normal charging stations with 22 kW is certainly sufficient and appropriate for charging a company car during working hours, or a service or emergency vehicle that is charged overnight at the depot.
Fast or ultra-fast chargers, on the other hand, are always necessary if the required energy is to be transmitted in the shortest possible time. Due to the high charging capacity, the vehicles to be charged are often available again after a short coffee break. This technology is therefore particularly suitable for charging processes at service stations, for demonstration vehicles in car dealerships, or visitor car parks on company premises. A quick-charging station is also useful in customer car parks where people only stay for a relatively short time (supermarkets, government offices etc.).
Since the necessary conversion of the current via additional hardware takes place directly in the charging station and higher currents have to be processed and possibly cooled, a greater investment can be expected here compared to normal charging stations.
Here is an overview of the various charging options commonly used in Europe:
|Power source||Output in kW||AC/DC|
|Three-phase current socket 16 A||11||AC|
|Three-phase current socket 32 A||32||AC|
|Type 2 (Mennekes plug)||11, 22, 43||AC|
|CCS Combo 2||50*||DC|
* Voltage and current are determined here by the installation specific to the vehicle.
At SENS every electric car can be charged with solar power
80 parking spaces are available for the staff and customers of STEAG Solar Energy Solutions GmbH. Four of these are reserved for electric cars. A 10-kWp PV system with a 15° south orientation has been installed on the company’s HQ, which covers almost the entire power requirements of the electric cars in summer.
Currently there are two charging stations in the car parks, each with a capacity of 22 kilowatts and two charging points per station. This means that four electric cars can be charged simultaneously. If this occurs, a load management system ensures that the power is optimally distributed to each electric car. Assuming an average working time of eight hours and thus an uncritical charging time, the 22-kW columns are, as mentioned above, completely sufficient. The charging stations are not only available free of charge to employees but also to customers. This creates added value for both staff and business associates.
The combination of normal and fast charging stations has its advantages
Everyday practice shows that a combination of normal and fast charging stations is often the most practical solution. In this case, particular attention should be paid to the appropriate selection of plugs and cables. Although the Type 2 plug is considered the norm in Europe, various e-mobility manufacturers will continue to use their own standard. Ultimately, it is a question of the wishes of the customer, but also of the company's own employees. They must be provided with the charging facilities they need.