The limiting factors in automotive electrification today are the speed to charge the battery and the energy conversion efficiency to usable work, such as the EV range or thermal management of the passenger cabin. Extreme temperatures significantly negatively affect the vehicle’s performance and battery durability. Energy harvesting can help the battery thermal management systems (BTMS) regulate the battery temperature in extreme ambients to optimize performance and range, increase the charging speed, or control the cabin temperature. For EVs to become truly mainstream, they must provide the performance drivers expect in all conditions, including extreme heat (100°F and above) and cold (20°F and below).
What is Energy Harvesting in EVs?
Energy harvesting, often known as energy recovery when applied to automobiles, is the process of drawing power from the surrounding environment and transforming it into usable electricity. This idea is applicable to any type of ambient energy, whether it is the sun, the wind, vibration, or thermal radiation. It can run MEMS sensors to keep an eye on a vehicle’s performance or ultra-low power MCUs to cut down on the use of a small load’s battery.
To address the more systemic issue of electric vehicle range and efficiency, the recovered energy is added to the primary energy load of the vehicle during operation. Another perk is that the battery and/or the interior can be warmed using the waste energy recovered from the charging process.
In order to safeguard the battery and improve its performance in extremely hot conditions, it is possible to harness solar energy, thermal energy, and electrodynamic energy as a supplement to the thermal management system.
Solar Energy Harvesting
The northern United States can experience temperatures below 0 degrees Fahrenheit in the depths of winter. The combustion process produces an unlimited heat source that may be used to warm the engine and cabin, making ICEs a highly desirable option. Electric vehicles lack this heat source, so electric resistance heaters are used to warm the cabin and battery, which work best between 25 and 35 degrees Celsius. These heaters draw their energy straight from the battery.
The use of a refrigerant with a boiling point below the ambient temperature has led to recent improvements in vehicle heat pumps, which produce three useful heat units for every unit of power consumed. Even if the sun sets earlier in the winter, it is still possible to harness some of its energy by installing photovoltaic panels on the car. Scientists have proven that using solar energy to power vehicles can increase their range by over 23%. The method also extended battery life by the same percentage as it shortened charge times and grid energy consumption by roughly 10%. In addition, the battery in an EV can be used to store energy and smooth out the power fluctuations caused by the sun.
Thermal Energy Harvesting
Extreme temperatures provide difficulties for electric vehicle thermal management, but they also offer the chance to take use of a high temperature difference to promote quick heat transfer. When temperatures soar, a thermoelectric generator can help ease the strain on primary battery power by converting the heat difference into electricity.
Due to the low quality of the heat required for this application (100-150°F), this method is only 5-10% efficient in absolute terms at high ambient to battery/cabin temperature differentials. However, the peak power draws associated with initiating the thermal management system are reduced by the use of supplementary heat.
Kinetic Energy Harvesting
Although solar and thermal energy harvesting are resilient enough to increase efficiency even at high temperatures, they are nevertheless subject to the availability of sufficient sunshine and stable environmental temperatures. Because of this, kinetic energy harvesting is a viable option for reusing the wasted energy created by the motion and characteristics of any vehicle in operation.
Regenerative braking is an application of kinetic energy harvesting, in which some of the energy released during braking is sent back to the battery using a piezoelectric material. There is a direct correlation between the driving potential (brake force) and the effective magnitude of energy recovery available to decrease primary battery power demand, just like there is with temperature differential in thermal harvesting. Up to 70% of kinetic energy lost while braking can be recovered using this method, making it significantly more efficient than thermoelectric generators.
Other devices that use kinetic energy harvesting to capture higher energy recovery loads with increased mechanical force are shock absorbers and vibration sensors.
Conclusion
Problems with battery life, decreased driving range, and passenger discomfort are just a few of the issues that can arise when temperatures rise to dangerous levels. Use of solar, thermal, and kinetic energy harvesting techniques can produce significant supplementary power sources to balance off peak demands experienced at the outset of thermal management system operation.
By harnessing otherwise wasted energy at the working envelope’s periphery, the sensors we’ve discussed above make it possible for severe temperature EVs to exist. Finally, the vehicle’s sustainability profile is further enhanced by the use of solar, thermal, and waste energy recovery.