Electric car and charging losses: How to avoid costs
Do you know how much electricity your electric car consumes? Sure, you think, the on-board computer shows the consumption. But unfortunately, that's not the whole truth. This is because energy is lost when charging electric cars, which is paid for by you but does not end up in the battery. And your on-board computer does not show this loss.
Charging losses cannot be completely prevented. But in times of energy shortages and rising electricity prices, special care should be taken to keep losses as low as possible. And this is actually possible for every user – you just have to know how.
Charging at home: This is how the ADAC measured
Basically, there are several ways to charge the electric car at home - each at different speeds. Charging can be done at the household socket with a charging capacity of 2.3 kilowatts, at the wallbox with up to 11 kilowatts or, with the approval of the grid operator, even with 22 kilowatts. And as another special option, there is charging at the wallbox with reduced charging power, either through a vehicle setting or with photovoltaic surplus charging.
In order to explain how much energy is lost at which point in the system and how users of electric cars can minimise these losses, the ADAC measured at the household socket, an 11 kW wallbox and with reduced charging power (vehicle setting).
The vehicle batteries were always charged by 20% under the same conditions and the amount of electricity at the calibrated electricity meter (including charging losses) was compared with the energy stored in the battery from the battery management system.
The results clearly show that depending on how charging is carried out – at home at the "normal" AC socket, at the wallbox with up to 11 kW or with half the power – the charging losses vary greatly.
Electric car: Charging losses during AC charging
|
Outlet Power / Loss |
Wallbox Power / Loss |
Wallbox reduced Power / Loss |
|
|---|---|---|---|
|
Renault Zoe |
2.3 kW / 24.2 % |
11 kW / 9.7 % |
No measurement |
|
VW ID.3 |
2.3 kW / 13.6 % |
11 kW / 9.0 % |
5.5 kW / 9.2 % |
|
Tesla Model 3 |
2.3 kW / 15.2 % |
11 kW / 7.7 % |
3.5 kW / 11.4 % |
|
Fiat 500e |
2.3 kW / 12.7 % |
11 kW / 6.3 % |
3.6 kW / 13.9 % |
If you compare the measurement results for charging at the socket with charging at a wallbox,it is immediately noticeable that the efficiency of charging at the wallbox is significantly better for all four test vehicles than at the socket. The difference is widest for the Renault Zoe, and least for the VW ID.3. The fewest charging losses are recorded in the Fiat 500e, which has apparently been designed for good charging efficiency.
In a third series of measurements, the extent of the charging losses was investigated when the wallbox is operated with reduced charging power on the vehicle's side. In practice, this can occur if a load management system distributes the available charging power to two or more vehicles, or if solar power is to be charged by the PV system. These measurements also clearly show that the higher charging power leads to fewer charging losses.
How can charging losses be explained?
Charging at the household socket
Because the traction batteries of the electric car can only store direct current, but alternating current is supplied from the power grid, the on-board charger must convert this electricity into direct current. Considerable losses are already incurred here. Further relevant losses occur in the 12-volt on-board electrical system. Reason: A number of control units are active during charging. 100 to 300 watts alone are needed to operate components to control the charging process.
To a not inconsiderable extent, a (long) supply line to the socket in the parking lot or garage can also contribute to the losses. Incidentally, charging losses of up to four percent are permissible in domestic installations (DIN VDE 0100 standard). This should be borne in mind, especially with older house installations. If in doubt, it is worthwhile to have the house installation checked by an electrician in advance to ensure that the supply line to the household socket is suitable for permanent operation.
On the other hand, the house distributor, the charging cable, the HV cables in the vehicle and the HV battery itself are low to negligible. As a rule, no temperature management of the battery is necessary for charging at the household socket.
In total, the charging losses at the household socket amount to 10 to 30 percent.
Charging at the wallbox
Charging at the home wallbox is normally three-phase (instead of single-phase) and therefore with a greater charging capacity. In addition, wallboxes are connected by the electrician in such a way that the supply line is designed more strongly and thus hardly any line losses occur. Conversion losses in the on-board charger are still the same.
The most important difference concerns the self-consumption of the vehicle electronics. This is much lower in comparison, as the battery is charged much faster via wallbox and therefore the operating time of the auxiliary consumers is significantly shorter.
In total, the charging losses at the wallbox are only 5 to 10 percent.
How e-car users can avoid charging losses
When charging with alternating current, the rule of thumb is: the higher the charging power, the shorter the charging process, the lower the charging losses. For cost reasons, it is therefore advisable to always charge at the wallbox with maximum charging power. The battery should always be full as quickly as possible.
No significant influence was found in measurements with different charging strokes. Regardless of whether the battery was charged by 20 or 50 percent, the charging losses differed only insignificantly from each other in the ADAC tests.
Even if the charging losses are slightly different for each electric car, the four vehicles measured cover a large market share of electric cars as examples. All four models are popular state-of-the-art vehicles.
The example of the Renault Zoe in particular shows how much it can be worthwhile to charge consistently at the wallbox: 14.5 percent fewer charging losses per year are clearly noticeable on the electricity bill. With an annual mileage of 10,000 kilometers, this can save around 120 euros per year.
If you're wondering how severe the losses are when charging with direct current at a public fast-charging station: With DC charging, the power conversion does not take place in the vehicle's on-board charger, but in the charging station. As a result, the charging losses described here are borne by the operator of the charging station. This is one of the reasons why the kilowatt hour for DC charging is usually somewhat more expensive than for AC charging. However, there is also another phenomenon at the fast-charging station: Heating the temperature of the battery when it is too hot or too cold also costs energy that does not end up in the battery. The ADAC will also address this topic and report on it soon.
What manufacturers can do about charging losses
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Manufacturers are to transparently present the charging losses incurred so that electric car users can comply with them.
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The efficiency of on-board chargers needs to be improved. AC charging reflects the majority of charging processes, so there is great potential to save energy here.
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The 12-volt on-board system should be reduced to an absolute minimum during a charging process.
Expert advice: Luis Kalb, ADAC Technik Zentrum