Is Hot Weather Bad for Electric Cars?
The short answer is that EVs can perform relatively well in hot weather. However, extreme heat can significantly impact their range, potentially reducing it by up to 30%. To understand this better, we need to explore the effects of high temperatures on electric vehicles (EVs) and their batteries.
The Impact of Hot Weather on Electric Vehicles
High temperatures can negatively affect EVs through several mechanisms:
Battery Degradation
Higher temperatures accelerate chemical reactions that can damage battery components over time, including the electrolyte. This can lead to a loss of battery life and accelerated aging. Some experts suggest that temperatures above 86°F (30°C) can cause accelerated battery degradation.
Reduced Range
Hot weather increases the demand on an EV's battery's thermal management system, which can consume energy. Recurrent's study found that EVs experience a 2.8% range loss at 80°F (26.7°C), a 5% loss at 90°F (32.2°C), and a 31% loss at 100°F (37.8°C) when the outside temperature reaches 95°F (35°C), and air conditioning use can decrease driving range by up to 17%.
Increased Internal Resistance
Hot climates can increase the internal resistance of the battery, which can extend charge times.
Reduced Regenerative Braking Efficiency
Batteries may reduce their charge acceptance to avoid overheating, resulting in reduced regenerative braking efficiency.
Additionally, there is the risk of thermal runaway reactions, which can occasionally lead to fires and explosions.
How Electric Vehicles Cope with Heat
Unlike internal combustion engine (ICE) cars, which use engine energy to operate their HVAC systems, EVs use electricity directly. Current HVAC capabilities can provide a maximum of around a 40°F (22°C) reduction in temperature. For instance, if the HVAC system has 100°F (38°C) air to cool, it can reduce the temperature to a maximum of 60°F (15.6°C). So, 110°F (43.3°C) goes down to 70°F (21.1°C), and 120°F (48.9°C) goes down to 80°F (26.7°C).
The key is to use the HVAC system's cooling capacity effectively. A car with closed windows in the sun can have a cabin temperature far above the outside air temperature. Initially, rolling down windows and leaving doors open can quickly bring the cabin temperature to match the outside air temperature. However, this will also introduce ambient radiated heat from the surfaces inside the car that the HVAC system needs to cool.
The recirculate feature of an HVAC system allows it to continue cooling the air in the cabin rather than cooling hot air from outside. Initially, recirculate should be off when the HVAC system is first turned on so that the cooled air starts at the cooler outside air temperature, providing quicker and more effective cooling. Once the inside temperature is around the outside air temperature, recirculate should be used to more efficiently cool the cabin to a cooler temperature.
However, there is an energy in and energy out equation. If there is more inbound heat energy than the HVAC system can cool, cabin temperatures may never reach below the outside air temperature minus the cooling capacity of the HVAC compressor. In such cases, sun shades, tinting, and other infrared (IR) reflecting window treatments can be necessary.