In our advanced modern era, energy efficiency is all the rage. In fact, consumers are ordering more Teslas today than traditional luxury sedans—such as Mercedes-Benz or BMW—as they seem to be sustainable in style. While the threat of running out of battery with no way to charge up has slowed adoption in some consumers, modern self-charging technology has helped electric cars rival gas-powered cars on the “miles until empty” front.
Electric cars can self-charge using a combination of regenerative braking, inductive charging, and solar panels. Each of these adds miles to the vehicle’s battery range before the owner has to plug in.
Although these self-charging methods help extend the range of an electric car’s battery, they will not provide enough energy to make the vehicle completely self-charging. Scientists are still working on ways to make a completely self-charging car a reality. For now, the only cars that can completely charge their batteries on their own are hybrids, which must use fuel to make this happen.
How Electric Cars Self-Charge
When you plug your electric car into an outlet or some other charging station, the lithium-ion battery stores energy used to power the electric motor. Without recharging, this battery can only store a finite amount of energy. Most normal lithium-ion batteries will have a range of about 250 miles before depletion.
While this is a good distance, it is not quite on par with gas-powered vehicles, which can typically get between 350 and 400 miles on a tank of gas before refueling is necessary. Fortunately, the most innovative electric cars have self-charging features that provide a boost to their battery and extend their range closer to that 400-mile mark.
Regenerative Braking on Electric Cars
Regenerative braking is the most prevalent and functional method for providing a boost to your electric car’s battery. Essentially, engineers have figured out a way of redirecting and storing wasted kinetic energy in your vehicle’s battery.
Kinetic Energy and Electric Cars
Kinetic energy is the energy of motion. A ball flying through the air is an example of kinetic energy. When you stand up and walk, you are producing kinetic energy. In the case of your electric vehicle, the act of its axles spinning and the car zipping down the highway is kinetic energy.
While kinetic energy is all around us, it does not equate to electrical energy, which is needed to power a battery. If so, your car’s motion would be able to power itself indefinitely, which we know is not possible.
Some form of stored energy is needed to put your vehicle into motion, as much of the kinetic energy produced is lost in other states. In many cases, the heat energy that radiates into the air is one of the main ways energy escapes.
Impressively, though, engineers have figured out ways to convert some of this kinetic energy back into electric power for future use through the process of regenerative braking.
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Converting Kinetic Energy to Electricity
When going uphill or working on getting your car up to the speed limit, you press the accelerator; this provides a signal to the battery to send the requisite amount of energy to the electric motor, which then powers your vehicle into motion (kinetic energy).
However, when going downhill or bringing your car to a stop, no electrical energy is required. As such, a tap of the brake gives your electric car’s motor the cue that it is not needed, and it switches from the engine to a generator. This electric motor’s generator uses the spinning of your vehicle’s axles (kinetic energy) and converts it back to electric power to be stored in the battery.
For a visual illustration, this classic scene (jump to 3:18) from the hit television show Breaking Bad shows how chemist Walter White creates a homemade generator to use kinetic energy to trickle charge his dead RV battery. The process of regenerative braking in your electric vehicle uses the same concept with your vehicle’s axles, only on a much larger scale, as a vehicle’s axle will spin much faster and more powerfully than a hand crank.
Can All Kinetic Energy be Converted into Electrical Energy?
An important thing to remember about regenerative braking is that it can convert some of your vehicle’s kinetic energy back into electrical energy, but not all.
If you are going on an extended downhill drive where gravity is powering your vehicle, and you can lightly ride your brakes, then you could restore a nice little chunk of energy to your battery. I can do this when we drive down Haleakala on Maui. Descending 10,000 feet recharges the battery after the long climb up. Likewise, if you are driving in the city and frequently have to brake to a stop, you can also generate a fair amount of energy through regenerative braking.
However, if you are cruising down the interstate at 75 miles per hour and your electric motor is consistently being used to power your vehicle, then most kinetic energy will be lost, and you will likely see very little recharging through this method.
Passive Induction Self-Charging an EV
Another means of self-charging for an electric car is through the process of passive induction. While this differs from regenerative braking in that it will not recharge the battery while the vehicle is in motion, it is a way of charging the car without ever having to plug it in.
Passive induction is a means of wireless or cordless charging. By parking your electric car on or near an electromagnetic pad or station, charging can occur through the following process:
- An alternating current (AC) is run through an induction coil (may also be called a primary or transmission coil) in the charging station or pad.
- This electric charge creates a magnetic field, as defined by Oersted’s Law.
- The strength of the magnetic field fluctuates as the AC continually changes in amplitude.
- This changing magnetic field creates an electromotive force (Faraday’s Law of Induction).
- This creates an AC in a second induction coil (which may also be called a receiving or secondary coil) found in your car.
- A rectifier is then used to convert the AC received from the secondary coil into a direct current for storage in your car’s battery.
This process of passive induction is most common for charging mobile phones (think of those vehicles that charge your phone just by putting it on the center console). It is not yet widely adopted for charging electric cars themselves.
In addition, some people argue that having to park on or near an electromagnetic pad or station offers little convenience over actually plugging your car into an outlet, making the term “self-charging” dubious.
However, as this technology becomes more refined and widespread in areas such as supermarket parking lots, electric car owners have yet another resource at their disposal for cutting the cord with the electrical outlet.
Solar Panels on an Electric Car
As with most concepts related to renewable energy and sustainability, solar power finds its way on the list for electric vehicles. While it is not necessarily the most efficient means of charging an electric car’s battery, it has been attempted by a handful of automakers.
Lightyear Solar Panels
Using this concept, a series of solar panels are placed on the surfaces of the car to collect sunlight and convert it into electrical energy. Most efforts have offered little utility, with the solar panels both cumbersome and unsightly.
However, the Lightyear is one of the most innovative options for sun-powered vehicles; solar panels all along the roof, hood, and trunk are contained under safety glass to continually collect and convert light energy throughout the day.
Disadvantages of Lightyear Panels
The downside to the Lightyear is the same confronted by other automakers who have attempted to incorporate solar charging into their vehicles. There is simply not enough surface area on vehicles to capture sufficient sunlight to convert into electrical energy.
Even with the Lightyear’s revolutionary design, it only creates about seven miles of battery range for each hour it is working; this is sufficient for short commutes but offers little more than a minor supplement for longer road trips.
Another downside to solar charging is that vehicles must be parked outside, which offers a host of other drawbacks in the winter months and areas with high crime rates.
Finally, there is the concept of wind turbines. For the most part, wind energy is not very practical for electric vehicles, as they cannot be large enough to capture and convert a sufficient amount of wind energy. Furthermore, turbines located in areas to collect wind create additional resistance that requires more power to overcome, making the turbine a bit self-defeating.
However, some vehicle prototypes use a wind turbine generator to improve energy efficiency for vehicles cruising at stable speeds. The wind captured and converted under these conditions can help lower energy use by up to 15%.
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Why Can’t Electric Cars Be Completely Self Charging?
Outside of some very small electric toothbrushes that require minimal power, physicists have yet to figure out how to create battery-powered objects that are completely self-charging. This is because it takes energy to produce energy, and the energy created by the vehicle’s momentum is not sufficient to power the car in perpetuity.
Modern physicists agree that self-charging vehicles violate the principles of perpetual motion as defined by the Law of Conservation of Energy, with the following points making a brief explanation of why completely self-charging electric vehicles do not exist:
- “Getting up to speed requires energy—converting energy stored in the battery pack into momentum.”
- “Turning the generator to cause electricity generation requires energy, depleting the momentum.”
(Source: Green Transportation)
With this understanding, it can be seen how self-charging features in electric vehicles are still only supplements. In regenerative braking, momentum is lost as the generator works to convert kinetic energy into electrical energy.
This means that at some point, even if the generator were always working on converting wasted kinetic energy (which it is not), then the battery would eventually get depleted as the energy used by the generator itself sucks from the initial power supply.
Mounted features such as solar panels and wind turbines decrease inertia energy; this lowers momentum. In turn, new energy must be consumed to replace the lost momentum, undermining the energy-producing features of such devices.
Self-Charging Hybrid Vehicles
If you see advertisements for a fully self-charging vehicle, you are likely looking at a hybrid. This is a bit misleading, as fuel is required to charge the battery. However, from the perspective of operating on a no-plug electric motor, hybrids can rightfully make this case.
Powered by dual gas and electric motors, hybrids generate enough electricity during operations to eliminate the need to charge their lithium-ion battery. Then, using this battery power, the car runs on its electric motor, greatly reducing the need for fuel, effectively creating a vehicle that never needs to be charged and only has to be filled up occasionally.
Let’s take a look at how modern hybrids can arrive at a self-charging status:
As mentioned, it takes energy to create energy, so one of the nifty ways modern hybrids have turned the automotive world on its head is through the use of the gas engine as an electrical energy creator instead of a kinetic energy creator.
Rather than powering an axle to drive momentum, the gas engine powers the generator that creates electrical energy. This is similar to the concept of how electric vehicles use regenerative braking to transfer kinetic energy back to the generator to produce electric power—only much more direct, efficient, and powerful.
The hybrid has two electric engines. The first is a generator that is powered by the gas engine. This generator powers the second electric engine, which is the drive motor used to turn the wheels.
You may be thinking: Wait, if the gas engine is only used to power a generator that powers a second motor to put the car in motion, how is that even a hybrid? Is that not just a more indirect route of having an axle powered by the gas engine?
The answer lies in the fact that the generator does more than just drive the second electric motor. It is constantly monitoring the state of the vehicle’s lithium-ion battery and making sure that it is charged sufficiently to power the car in electric mode. The various modes of a hybrid car include:
- Electric Mode: Uses energy stored in the lithium-ion battery to power the drive motor. When operating in this mode, a hybrid is functioning no different than a pure electric vehicle.
- Braking Mode: This is the exact same as the regenerative braking described throughout this article. When the vehicle is using inertia to go downhill and/or braking to come to a stop, kinetic energy from the axles is sent back to the generator to be converted to electricity and stored in the lithium-ion battery.
- Hybrid Mode: This mode uses fuel to power the generator motor, which simultaneously powers the drive motor and charges the lithium-ion battery.
- Fuel Mode: Uses fuel to power an axle while also sending energy to the generator to charge the battery; this is the least fuel-efficient mode and will likely only be used in situations when the battery is very low and significant power is required.
The vehicle will switch between modes due to several factors, such as the driving conditions or the amount of charge in the battery. The driver also has the option to manually switch to electric mode if the battery is sufficiently charged and will be doing a lot of city driving or other situations when significant horsepower is not required.
Based on the fuel engine powering the generator, hybrid vehicles never have to be plugged in. With the electric motor’s power from energy stored in the lithium-ion battery, fuel economy is greatly improved, with many modern hybrids getting a fuel economy of roughly 50 miles per gallon for a range of about 600 miles, nearly doubling that of a traditional combustion engine.
The Future of Self-Charging Electric Cars
Modern electric vehicles can self-charge using a combination of regenerative braking, passive induction, and solar panels. While these methods will not completely charge a battery, they do offer a nice supplement to help extend an electric car’s range.
Modern science has yet to discover a means of making an electric car completely self-charging. This is because it takes energy to produce energy. Some of the battery’s stored power will be lost during this conversion process, even if everything else were completely efficient, which it is not.
Hybrid vehicles use an electric motor to power their drive axle. They never require their battery to be charged, as the gas engine powers the generator that creates electricity for the battery to store. Although they are not 100% energy-independent because they have to be refueled on occasion, they do allow owners to cut the cord in terms of plugging in their vehicle, which can take hours on some electric models.