Molly Ayala
Electric vehicles (EVs) are a promising solution for the decarbonization of the transport sector, but their market penetration remains weak. One of the most important considerations for potential EV drivers is the range of the vehicle. EVs have a shorter range than gas-powered vehicles, and charging stations are not as readily available. Traffic conditions can significantly impact the range of an EV. In urban areas, EVs perform better than internal combustion engine vehicles (ICEVs) due to their regenerative braking and high part-load powertrain efficiency. On the other hand, EVs are less efficient at higher speeds, and their range can be negatively affected by extreme temperatures.
How does traffic affect electric vehicle range?
| Characteristics | Values |
|---|---|
| Regenerative braking | Regenerative braking helps maintain a charge while operating in stop-and-go traffic. |
| Efficiency characteristics of the powertrain | BEVs are very efficient at full load and in the part-load area, where ICEVs efficiency drops significantly. |
| Relative contribution of auxiliaries | Auxiliaries directly consume battery energy, limiting the range of the vehicle, an impact that is maximized under certain traffic situations. |
| Speed | EVs are particularly affected by higher speeds as all but a few models lack multiple gears, causing the electric motor to spin at a faster and less efficient point. |
| Temperature | Extreme temperatures can have a significant effect on EV range. Very low temperatures negatively affect an EV battery's ability to hold its charge. |
| Idling | EVs are more efficient when idling than gas-powered vehicles, which waste about half a gallon of gas per hour when idling. |
| Battery age | As the battery ages, it loses some maximum charge potential, though proper maintenance can slow this degradation. |
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What You'll Learn
Regenerative braking
The process of regenerative braking involves the wheels being connected to the motor-generator, which spins its internal rotor as the car slows down, producing electricity. This electricity is then stored in the EV high-power battery, ready to be used when the driver next presses the accelerator. This process is known as kinetic energy recovery, and it has been used in F1 cars for years. When the driver wants extra acceleration, the stored energy is used to power the motor, boosting the power of the engine.
While regenerative braking is an innovative technology, it does have some drawbacks. For example, travelling at slower speeds means that a vehicle has less kinetic energy and requires less braking force, resulting in less energy being supplied to the battery pack. In some cases, manufacturers have suggested that coasting may be more efficient than regenerative braking. Additionally, while regenerative braking does a lot of the work in slowing the vehicle, it is important to have conventional brakes as well, and to bring your vehicle in for regular inspections.
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Efficiency of the powertrain
The powertrain of an electric vehicle consists of three major subparts: the motor unit, the controller with power electronics, and the battery pack with BMS. The efficiency of the powertrain is one of the main differentiation factors between electric vehicles and conventional vehicles.
Battery Electric Vehicles (BEVs) are very efficient at full load and in the part-load area, where the efficiency of Internal Combustion Engine Vehicles (ICEVs) significantly drops. This affects their optimum consumption point compared to a combustion engine. The high efficiency of BEVs during urban operation influences their overall optimum energy performance. The energy recuperation during braking reduces the apparent energy consumption of BEVs, particularly under stop-and-go conditions.
The efficiency of the powertrain can be improved by utilizing a dual-motor coupling powertrain (DMCP) system, which uses two motors to realize multiple drive modes and distribute the power of the two motors efficiently. The simulation results of the two proposed powertrains in three typical driving cycles demonstrate that the EVs equipped with both DMPGT and DMPAT have a higher overall efficiency than the EVs equipped with single-motor input powertrain.
Additionally, the improvement of powertrain efficiency for EVs enables less electricity energy consumption. Innovative heat dissipation techniques can also be employed to minimize energy loss to heat, and efficient electrical-to-chemical energy conversion and vice versa can be achieved through the use of optimization techniques based on battery characterization data.
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Energy consumption of auxiliaries
The energy consumption of auxiliaries in electric vehicles is an important factor influencing the overall range of the vehicle. Auxiliary systems refer to various components and functions within the vehicle that consume power, reducing the total power available for propulsion. These systems include heating, ventilation, and air conditioning (HVAC), entertainment systems, lighting systems, and the autonomous driving system.
The impact of auxiliaries on energy consumption is particularly notable in certain traffic situations. For example, in urban areas with low-speed traffic, the energy recuperation from regenerative braking improves the overall energy efficiency of electric vehicles. However, the use of auxiliary systems, especially HVAC, can still lead to significant energy consumption. Studies have shown that in electric buses during the summer, the energy consumption of auxiliary systems, mainly air conditioning, can account for around 50% of the total energy consumed.
Temperature extremes, both hot and cold, also impact the energy consumption of auxiliary systems. In cold weather, electric vehicles may require additional power to maintain the ideal battery temperature of around 20 degrees Celsius. This can result in increased power consumption by the battery management system. Similarly, in hot weather, the AC system becomes more active to maintain a comfortable cabin temperature, leading to higher auxiliary power consumption.
The efficiency of the motor, drivetrain, and battery also play a role in determining the power available for propulsion after accounting for auxiliary systems. The overall efficiency of these systems influences how much energy is available for traction and how much is lost to auxiliary functions. Additionally, the energy transmission efficiency loss in the inverter, electric motor, and mechanical transmission system can further reduce the available power.
To optimize the range of electric vehicles, it is crucial to minimize the energy consumption of auxiliary systems. This can be achieved through various measures, such as using energy-efficient LED lights instead of traditional light bulbs and employing preconditioning during charging to reduce the power required by the thermal management system. By addressing the energy consumption of auxiliaries, electric vehicles can improve their overall range and efficiency, making them a more attractive option for consumers.
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Extreme temperatures
The impact of cold weather on EV range is evident in the real-world data collected through the EV Project. Researchers at Idaho National Laboratory found that Nissan Leafs driven in Chicago during winter had a 26% lower range (60 miles compared to 81) than those driven in Seattle during the fall. To mitigate the effects of cold temperatures, it is recommended to precondition the battery before a road trip or using a DC fast charger. While this process consumes energy from the battery, it optimizes the battery temperature for quicker and more efficient charging.
On the other hand, high temperatures can also adversely affect EV range. When the temperature climbs into the high 80s and beyond, the range loss and battery damage become more pronounced. On average, EVs lose about 15% of their range when the temperature reaches 95 degrees Fahrenheit. The elevated temperature strengthens the electric current, pushing lithium ions through the battery and creating tiny cracks that facilitate secondary reactions. This process consumes lithium and impedes the smooth flow of energy, reducing the battery's performance and range.
To minimize the impact of extreme heat, EV owners should adopt specific habits. These include parking in shaded areas, pre-cooling the vehicle while plugged in, using the air conditioning system sparingly, and prioritizing cooling the occupants rather than the entire cabin. Additionally, it is advisable to avoid charging in extreme heat, as the process itself can cause batteries to overheat. By following these practices, EV owners can help maintain the longevity and performance of their batteries in hot conditions.
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Battery age
The lifespan of EV batteries typically averages eight to 15 years, with factors such as climate, driving habits, and charging cycles influencing their degradation rate. The primary outcomes of battery ageing are capacity and power fade, which affect the range and performance of the vehicle.
Capacity fade, caused by degradation of electrolytes crucial for transporting lithium ions between electrodes, leads to a reduced driving range. A brand-new EV might initially offer a 300-mile range, but regular use could decrease the projected range to 250 miles or even less.
Power fade affects how quickly and responsively a vehicle moves and functions. A decline in peak power caused by an ageing EV battery can affect acceleration and essential automotive systems such as regenerative braking. Power fade also impacts the efficiency and performance of auxiliary systems such as climate control and infotainment.
Several factors expedite EV battery ageing:
- Temperature: Prolonged exposure to high temperatures increases internal resistance and accelerates degradation. Conversely, charging at extremely low temperatures can lead to lithium plating, which affects battery life and performance.
- State of charge (SOC): Constant overcharging or consistently maintaining a battery near or at full capacity shortens its lifespan.
- Charging habits: Fast charging strains the battery and accelerates the ageing process, as do frequent deep discharges.
- Driving style: Aggressive driving, such as rapid acceleration and frequent hard braking, can drain your electric vehicle's battery much faster than smooth and steady driving.
To mitigate the effects of battery ageing, strategies such as optimal charging, advanced BMS, and proper storage can be employed. Maintaining correct tyre pressure is also crucial for reducing rolling resistance and improving an electric vehicle's mileage.
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Frequently asked questions
Traffic has a significant impact on the range of electric vehicles (EVs). EVs perform better in city driving due to their regenerative braking systems, which help maintain their charge in stop-and-go traffic. In contrast, EVs are less efficient at higher speeds, and their range can be negatively affected by highway driving.
Electric vehicles are more efficient when idling than gas-powered vehicles. Their regenerative braking systems allow them to maintain their charge and even gain range while braking or going downhill. Therefore, sitting in traffic does not dramatically decrease an electric vehicle's range.
In addition to traffic conditions, several other factors influence the range of electric vehicles. These include the age and charge level of the battery, extreme temperatures, vehicle maintenance, and driving speed. Proper maintenance, regular checks, and keeping tires properly inflated can help maximize the range of an electric vehicle.
