Electric Car Charging: Power Requirements and Optimization
When considering the electricity requirements for charging an electric car, it is essential to understand the amount of energy required to power the battery. The size of the battery, in kilowatt-hours (kWh), directly influences the amount of energy needed for a full charge.
Understanding Energy in Batteries
For a typical 70kWh battery, it will take a bit over 70kWhs to fully charge. Similarly, for an 85kWh battery, it takes a bit over 85kWhs. If you need to calculate for other battery sizes, the principle is the same: the larger the battery, the more energy it requires. This is due to the direct correlation between the battery's capacity in kWh and the energy needed for a full charge.
Comparing Power and Energy
It is important to distinguish between electrical power (measured in watts) and energy (measured in watt-hours). While watts represent the rate at which energy is transferred, energy is the actual amount of power that is used to charge the battery. The energy required to refill the battery is what you should be concerned about, not the power that charges it.
Similar to how gasoline energy is measured in gallons, the energy required to refill an electric car is measured in watt-hours. To determine the exact amount of energy needed, assess the state of your battery (i.e., how empty it is). This will allow you to calculate the watt-hours required to fully charge it.
Solar Power Integration
The maximum wattage of solar panels currently available ranges from 360 to 375 watts. While solar panels are ideal during the day, it is not practical to solely rely on them for charging an electric car. Instead, most electric car owners charge their vehicles using a battery storage system, often at night when they’re not using them during the day.
My system, for instance, consists of about 18 solar panels, designed to power most household needs during an electrical outage. However, the energy stored in the battery is used predominantly for charging the car, usually once a week.
Charging Profiles and Rates
The charging profile for an electric car can vary based on the type of charger being used. For home charging with Alternating Current (AC), a 7.5kW charger can provide exactly 7.5kW of power to the car.
Direct Current (DC) fast charging, such as the V3 Supercharger, can provide up to 350kW of power. Alternatively, commercial charging stations often offer a range of options, from around 7.5kW to 350kW, depending on the facility.
Minimum Charging Requirements
For the J1772 connector, which is commonly used with Tesla models, the minimum amperage is 6 amps, equating to 720 watts. However, since the ID charge in the vehicle uses several hundred watts and the battery thermal management system can use several thousand watts, it is unlikely that a Tesla can be charged at the 720-watt minimum under normal circumstances.
Under typical conditions, a standard 120-volt, 12-amp EVSE would be the most practical choice, providing between 720 and 1440 watts. In extreme temperatures, the required wattage might range from a few hundred to a few thousand watts to compensate for the additional cooling or heating needs.
Understanding these power requirements is crucial for optimizing the charging process and making informed decisions about the infrastructure needed for electric vehicle use.