Hello everyone! 
I wanted to start this discussion to clarify an important aspect that is often underestimated when we talk about home charging: energy losses.
The Problem of Losses
Many electric vehicle owners are surprised when they notice a discrepancy between the energy drawn from the electrical grid and the energy actually charged into the vehicle’s battery. This is completely normal and occurs with both the standard charging cable and wallboxes/home charging stations.
Practical Example with the Charging Cable
Let’s take the case of the supplied charging cable that charges at 10A (about 2.3 kW on a standard Schuko socket):
- Theoretical Power: 230V × 10A = 2,300W (2.3 kW)
- Actual Power Measured at the Battery: approximately 1.7-1.8 kWh
- Loss: approximately 0.5-0.6 kWh per hour of charging
Where Do These Losses Go?
Energy losses are unavoidable and are due to several factors:
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AC/DC Conversion: The car’s internal charger must convert alternating current (AC) from the grid to direct current (DC) for the battery. This conversion has a typical efficiency of 85-90%.
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Dissipated Heat: During charging, components heat up, and some energy is dissipated as heat.
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Battery Management (BMS): The battery management system consumes energy to monitor and balance the cells.
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Cables and Connections: Cables also have electrical resistance, causing small losses.
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Auxiliary Systems: Battery cooling, the onboard computer, and other systems may remain active during charging.
Why is it Important to Consider Losses?
1. Calculating Real Costs
When you calculate how much it costs to charge your car, you need to consider the energy drawn from the meter, not just the energy that ends up in the battery.
Example: If your energy contract costs €0.25/kWh and you charge for 10 hours with the charging cable:
- Energy from the meter: ~23 kWh
- Energy in the battery: ~17-18 kWh
- Real Cost: 23 kWh × €0.25 = €5.75 (not €4.50)
2. System Sizing
If you are considering installing a photovoltaic system or a wallbox, you need to factor in losses when sizing them.
3. Actual vs. Stated Consumption
The consumption figures stated by the manufacturer (e.g., 18 kWh/100km) relate to the energy in the battery. To know the “from the socket” consumption, you need to add about 10-15% for charging losses.
Wallbox vs. Charging Cable: Do Losses Change?
Yes, but not significantly:
- Charging Cable (2.3 kW): efficiency ~75-80% (higher losses due to longer charging times)
- Wallbox (7.4-11 kW): efficiency ~85-90% (shorter times = fewer losses from auxiliary systems)
Conclusion
Energy losses are an unavoidable physical reality. It’s not a defect of the vehicle or the charger, but an intrinsic characteristic of the charging process.
Practical Tip: If you want to monitor your real consumption, install an energy meter (like a Shelly EM) on the socket or wallbox. Only then will you have precise data on actual consumption from the grid.
Have you noticed these losses too? What charging efficiency do you observe with your car? Let’s discuss! 