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How Many kW and kWh Does an Electric Car Need? A Guide to Power, Charging Times, and Costs
Wondering how many kW are needed to charge an electric car without knowing how many kWh its battery holds is like wondering how fast water should flow from the faucet without knowing the capacity of the pitcher you’re filling. Among the requests for clarification collected daily at charging stations Powy, confusion between power (kW) and stored energy (kWh) remains the most common question among those switching to electric vehicles. Distinguishing between these two quantities is essential for navigating the options between AC charging outlets (AC) and DC fast-charging stations (DC), calculating charging times, and avoiding unexpected expenses.
1. The Fundamental Distinction: kW (Power) vs. kWh (Energy)
The hydraulic analogy is the simplest way to understand how the recharge works:
- Kilowatt (kW) – power: This indicates the pipe’s capacity, that is, the instantaneous rate at which electrical energy flows from the charging station to the car. The higher the power in kW delivered to and accepted by the vehicle, the faster the charging.
- Kilowatt-hour (kWh) – energy: indicates the volume of water stored in the reservoir, that is, the total amount of electricity actually transferred and stored in the battery.
Basic energy formula:
Energy (kWh) = power (kW) × time (hours)
Example:
A charging station that delivers 11 kW of continuous power for 2 hours transfers:
11 kW × 2 hours = 22 kWh
Formula for calculating dwell time:
Charging time (hours) = energy required (kWh) ÷ actual power (kW)
Example:
To charge 45 kWh at a constant effective power of 11 kW:
45 kWh ÷ 11 kW = 4.09 hours (about 4 hours and 5 minutes)
2. Vehicle Speed Limits: Why the Charging Station Doesn't Determine the Speed on Its Own
The actual charging rate is always equal to the lower of the maximum power output of the charging station and the maximum power input of the car.
In AC charging (AC), the charging station powers the car's on-board charger (OBC), which converts the current from AC to DC before sending it to the battery cells:
- If you connect a car with an onboard charger limited to 11 kW to a 22-kW charging station at Powy on AC , the actual power draw remains capped at 11 kW;
- The charging station could deliver up to 22 kW, but the car's battery management system (BMS) limits the input to protect the vehicle's electrical system.
At DC charging stations (DC Fast, and HPC), the internal charger is bypassed: the charging station converts the power externally and sends it directly to the battery via the CCS2 connector, adjusting the kW output based on temperature and the remaining state of charge.
3. Charging times for actual models: from 20% to 80%
The range between 20% and 80% is the optimal operating range: below 20% and, especially, above 80%, the charging rate decreases for reasons related to the battery’s thermal and chemical safety.
Technical specifications of three popular models:
- Fiat 500e (city car): 37.3 kWh usable battery capacity (42 kWh rated capacity), 11 kW on-board “ AC ” charger, maximum charging power of up to 85 kW via “ DC ”;
- Tesla Model Y (midsize crossover): battery with approximately 75.0 kWh of usable capacity, 11 kW AC , peak power of up to 250 kW in DC ;
- Kia EV6 (800-V architecture): 77.4 kWh usable battery capacity, 11-kW AC , peak power of up to 240 kW ( DC ).
Estimated average charging times to go from 20% to 80%:
| Type of infrastructure | Dispensing | Fiat 500e (~22.4 kWh to charge) | Tesla Model Y (~45.0 kWh to charge) | Kia EV6 (~46.4 kWh to charge) |
| Heavy-duty outlet (3.7 kW) | AC single-phase | ~6 hours | ~12 hours and 15 minutes | ~12 hours and 30 minutes |
| AC Public Charging Station (11 kW) | AC three-phase | ~2 hours | ~4 hours and 5 minutes | ~4 hours and 15 min |
| AC Public Charging Station (22 kW) | AC three-phase | ~2 hours (11 kW charging limit) | ~4 hours and 5 minutes (11 kW vehicle limit) | ~4 hours and 15 minutes (11 kW charging limit) |
| Powy Fast Charging Station (50 kW) | DC continue | ~20 minutes | ~50 minutes | ~50 minutes |
| Ultra-Fast HPC Station (150+ kW) | DC continue | ~18 min (peak power 85 kW) | ~20 minutes | ~15 minutes (800 V architecture) |
4. Calculating Charging Costs: Formula and Practical Examples
The final cost of a charging session does not depend on the station's rated power, but on the actual amount of kWh drawn, multiplied by the unit price of electricity:
Cost formula:
Charging cost (€) = energy consumed (kWh) × provider rate (€/kWh)
Assuming a power draw of 36 kWh (equivalent to approximately 200–250 km of average range):
- at a public AC charging station (AC) (average estimated rate: 0.55 €/kWh): 36 kWh × 0.55 €/kWh = 19.80 €
- at a high-power DC charging station (DC Fast) (average estimated rate: 0.75 €/kWh): 36 kWh × 0.75 €/kWh = 27.00 €
The rate differential covers the infrastructure costs DC: dedicated substation transformers, high-power external converters, and fixed committed power quotas that are much higher than at a AC point.
For more details on units of measurement in the electric vehicle sector, see our Practical Guide to Charging Units of Measurement.
5. How to Choose the Ideal Power Rating for Your Parking Lot
For those who run a retail business, a hotel, or a company parking lot, choosing charging stations doesn’t always mean opting for the highest power rating available in the catalog. Installing ultra-fast charging stations in locations where cars remain parked for many hours creates inefficiencies in both supply costs and network management.
The most practical solution aligns power output with users’ averagedwell time. Through preliminary technical feasibility analyses, Powy determines the most suitable combination of AC and DC Fast stations. Based on the area’s characteristics and projected traffic volumes, Powy offers various flexible partnership options , handling installation, paperwork, and ongoing maintenance.
To learn more about how charging stations work and the main technologies available, check out our guide.
Frequently Asked Questions (FAQ)
On average, how many kWh does an electric car consume to travel 100 km?
An average electric car consumes between 15 and 18 kWh per 100 km on a mixed-use route. Compact city cars can consume less than 13–14 kWh/100 km in urban driving, while large SUVs or highway driving at 130 km/h can increase consumption to about 20–24 kWh/100 km.
Why does DC charging slow down above 80%?
The slowdown is controlled by the car’s control unit to preserve the battery. As the voltage in the cells increases, internal resistance rises, generating heat: to prevent overheating and premature wear, the system gradually reduces the power in kW delivered by the charging station.
Could plugging your car into a 300-kW HPC charging station damage it?
No, there is no risk. The charging station and the vehicle constantly communicate via cable before and during charging: the station indicates the maximum available power, but it is always the car that requests and draws only the amount of current that its battery can safely handle.
Disclaimer: These figures are approximate: power output and charging times may vary depending on the vehicle model and operating conditions (temperature, battery condition, available power). Always check your car’s specifications.
About Powy
Powy a company that owns, develops, and manages Italy's leading independent network of public charging infrastructure for electric vehicles.
Founded in Turin in 2018, Powy is at the forefront of the transition to more sustainable mobility, offering an innovative charging infrastructure that uses only renewable energy.
Powy 's network includes quick, fast, and ultra-fast charging solutions strategically placed in public and private parking lots, supermarkets, shopping malls, and transportation hubs to ensure maximum convenience and accessibility for EV drivers. Each station is equipped with advanced technologies to provide a reliable and efficient charging experience.
Press Office: press@powy.energy