The recent news that Tesla's (NASDAQ:TSLA) battery swapping plan isn't working out doesn't come as a surprise to me. In previous contributions published both on EVWorld and Seeking Alpha in 2013, I pretty much anticipated this kind of outcome.

What is at first sight somewhat disconcerting is Elon Musk's decision to have bet on this mechanism while working real hard on battery super-duper charging (or hyper-charging) aiming in the near future at charging electric cars in five minutes.

I have trouble believing that Tesla's CEO wasn't aware at the time that progress in charging would soon enough make the swap idea completely meaningless. Why did then Musk pursue this course of action?

It seems like the battery swap show was in fact - as I argued in my EVWorld blog - thought of from the start as "a simple (although most effective) public relations event to captivate everyone's attention on the kinds of things Tesla is capable of doing."

But just as Shai Agassi's swap scheme encountered two major hurdles too difficult to overcome before it would become popular and widespread, namely general battery technological development and specific progress in advanced energy storage charging, Tesla should now be sufficiently careful not to rely on (wired) hyper-charging alone to meet its future goals.

As I argued almost two years ago, although super-duper charging may pave the way for the adoption of more electric cars, wireless super-duper charging is likely to change the world.

Summary

• After reviewing a number of recent scientific articles on wireless charging as applied to EVs, and despite many hurdles to overcome, I believe that this technology is around the corner.
• Of all the recharging mechanisms applied to EVs found in the literature, inductive coupling (or electromagnetic induction) appears to be the one that has received the most attention.
• Next I show that much progress is being made in the other types of wireless charging mechanisms such as magnetic resonance, radio frequency, and microwaves.
• I then attempt to inquire as to why Tesla Motors would not have shown interest in going wireless in battery recharging while sticking with its wired hyper-charging technology.
• Lastly, I suggest Tesla start thinking of developing wireless hyper-charging technologies to be ready to displace its wired hyper-chargers in the next 5-10 years.

This intuition led me in recent months to initiate an in-depth investigation on the state of the arts of energy transfer through wireless recharging. Already invented by Nikola Tesla more than one hundred years ago, wireless recharging is a technical application of Wireless Power Transfer or Transmission (WPT) which can be defined as "a system that can efficiently transmit electric power from one point to another through the vacuum of space or the earth's atmosphere without the use of wires or any other substance" (See: Chen et al, 2015).

Following an article accepted for publication just a few months ago on Renewable and Sustainable Reviews, a leading scientific journal in the field, authored by Akhtar and Rehmani (2015), this concept has since been refined to increase the distance, portability and efficiency under which it operates.

Thanks to recent advances in technology, "somewhat efficient transmission is possible in portable devices …, enabling an easier and controllable battery recharging mechanism for nodes especially in hostile and inappropriate environments." In this context, five potential wireless recharging techniques have been identified: (1) inductive coupling; (2) magnetic resonance; (3) radio frequency; (4) laser based system; and (5) acoustic energy.

In Table 1 I present the characteristics, advantages, weaknesses, efficiency (%) and applications of each one of them. Notice that no reference is made here to electric vehicles (EVs) as a possible application.

Table 1

Summary of potential wireless recharging mechanisms

(click to enlarge)Source: Akhtar and Rehmani (2015).

Definitions:

RF: Radio Frequency.

LOS: Line of Sight, the path between point A (Antenna 1) and point B (Antenna 2) in an outdoor wireless network. Three main categories of LOS exist: Full LOS, where there are no obstacles between the two antennas;  Near LOS, which includes partial obstructions such as tree tops between the two antennas; and Non LOS, where full obstructions exist between the two antennas (See: L-com.com).

SHM: Structural Health Monitoring.

UAV: Unmanned Aerial Vehicle.

However, in recent times many companies and research centers have shown a great deal of interest in development of this technology for different applications, including EVs.

From a somewhat different perspective, wireless charging technologies can be broken down in just three categories: Electromagnetic Induction; Radiation; and Electromagnetic Resonance, with Radiation further being sub-divided into radio waves, microwaves, laser, and ultrasound (See Figure 1).

Figure 1

Methods of Wireless Power Transfer

Source: Stanford.edu.

Speaking of EVs, of all the recharging mechanisms presented in Table 1 and Figure 1, inductive coupling charging (or electromagnetic induction) is perhaps the one that has received the most attention.

In effect, the first commercially available wireless EV charger, released September 2013 by Evatran, uses inductive power technology and has been offered as an aftermarket retrofit product for the Volt and the Leaf. It has also been known that Nissan is developing a similar system for its Infiniti LE concept EV. Evatran doesn't seem to have stayed still though throughout these years. A recent news from China tells us about the initial investment of $1.6 million of Zhejiang VIE Science and Technology Company (a Tier 1 automotive manufacturer which services both China-based OEMs and the global automotive market) as the first phase of a partnership with Evatran to introduce wireless electric vehicle charging products into the largest auto market on earth.

Notice that other car makers are making significant progress in this regard as well. For instance, last year BMW and Daimler announced a partnership to develop wireless electric vehicle charging systems aimed at attaining an output of 7 kW while maintaining an efficiency of 90% which could cut by half (from 8 to 4 hours) the current recharge time of a BMW i3. This may not be as impressive considering the little time that the huge 85 kWh battery in the Tesla Model S already requires for recharging. But as a recent Green Car Congress article indicates, "the potential scale of the EV market is so large that the way people charge vehicles in the future needs to be fast and automatic, and cannot be accomplished in residential garages."

In principle, a distinction can be made between two types of wireless charging: static wireless charging (which occurs while the vehicle is parked in a garage or a parking lot) and dynamic wireless charging (which happens while the car is moving or operating at full speed). According to Rebecca Hough, creator of the Evatran's systems, static wireless charging should be seen as the first step toward dynamic charging which is likely to become a reality in the next five to ten years and together with autonomous driving could lead to a complete revolution in the transportation sector in one or two decades. Here she implicitly refers to an intermediate category of wireless charging, namely semi-dynamic wireless charging, which takes place while the automobile is moving slowly or stopped for short periods of time, such as at traffic lights, taxi lights, taxi stands and bus stops (See: Figure 2).

Figure 2

Three Categories of Wireless Charging

(click to enlarge)

Source: Elektromobilitaet-Regensburg, June, 2015.

If it's dynamic charging the direction we're heading, then, to be successful, chances are public wireless charging infrastructure will be necessary.

But, Evatran's CEO is of the opinion that dynamic charging will only make sense economically with a dedicated base of wirelessly equipped EVs such as residential and fleet ones with continuous charging needs on a daily basis.

In fact, in a comparison between plug-in and (stationary) wireless charging for an electric bus system, for example, a recent study published on the leading scientific journal Applied Energy authored by Bi et al, 2015 finds that the wireless battery can be downsized to 27-44% of a plug-in charged battery thus generating significant benefits to that system.

Next, Chen et, 2015, already cited above, makes a case for building an electrified-road (eRoad) infrastructure network aimed at solving the problem of running "to longer distances with only a small battery capacity", which could in turn result in advantages not only in terms of cost and space but also in relation to batteries' energy consumption, road wear and even lithium use. There, the e-Road is defined as a transportation infrastructure that can "deliver the electrical power to charge EVs efficiently while stationary or even in motion, using conductive or contactless charging systems". The e-Road could then be used as a common motorway for ordinary vehicles while providing electrical power to EVs.

Similarly, the Korea Advanced Institute of Science and Technology (KAIST) has aimed at developing an all-electric-bus to be charged wirelessly while stationary or in motion. In such a system, "power comes from electrical cables buried under the surface of the road, creating magnetic fields" and "the receiving device installed on the underbody of the [Online Electric Vehicle] OLEV … converts these fields into electricity." Moreover, to the extent that the bus is charged while in motion, it requires a smaller battery and the system offers smart technology to distinguish electric buses from regular cars, automatically switching on the power strip when OLEV buses pass along, but switching it off for other vehicles, thereby preventing [electric and magnetic field] EMF exposure and standby power consumption". Be aware that in this kind of wireless charging system "the length of power strips installed under the road is generally 5 to 15 percent of the entire road, requiring only a few sections of the road to be rebuilt with the embedded cables."

Nevertheless, Chen et al (2015) warn that this kind of charging infrastructure is still in early stages of development and that to be sustainably implemented in practice, the following advances are required: Efficient charging technologies; (ii) integration of these solutions into practical road infrastructure; and acceptable functionality and cost-effectiveness in maintenance management over the lifetime of the roadway.

Beware that nowadays much progress is being made in the other types of wireless charging mechanisms included in Table 1 above, which may also have implications on EV applications in the years to come. One example may be the work done by WiTricity, the industry pioneer in highly resonant wireless power transfer, which has recently announced a licensing agreement with Brusa Elektronik AG, a global supplier of EV power electronics. And, of course, it appears important to emphasize that WiTricity's patentedtechnology to create efficient and high performance wireless charging systems for EVs and PHEVs would already be in use by TDK Corporation based on a license agreement signed last year.

However, WiTricity is not alone in development of this technology. Qualcomm would have started to work on it as far back as 2011, when it agreed with Renault to work together on wireless electric vehicle charging technology. Yet only about a month ago, it announced that it would engage in a similar partnership with Daimler. Qualcomm provides not only wireless electric vehicle charging technology for EVs and PHEVs but also WiPower technology that enables consumer electronics to charge wirelessly in-vehicle.

Another on-going effort is that performed by Nikola Labs Inc., a company that has developed a technology that converts specific radio wave frequencies (RF) such as WiFi, Bluetooth, LTE, 3G & 4G, into DC power. As of now, the technology has been integrated into phone cases for the iPhone 6 and Galaxy S6, capturing wasted RF energy and recycling it back into the phone to generate extra battery life, without any disruptions in call quality or data communication. Energous (NASDAQ:WATT) a wireless charging company that went public in 2014, also utilizes RF technology. But, unlike Nikola Labs' smartphone cases which harness and recycle the unused energy your phone creates by searching for cell towers and Wi-Fi routers, it requires a special transmitter to send energy to your phone. Time will tell whether this technology could be applied to EVs as well. Nonetheless, it has just been reported from China that UK researchers are currently exploring possibility of longer-range wireless charging for robots using microwaves, which could be thought of as either "a sub-section of radio waves" in Akhtar and Rehmani (2015) or a subcategory of the method Radiation in Figure 1.

Lastly, in March 2015 Japanese scientists announced they had discovered a way to transmit wirelessly space-based solar power. Using microwaves, they were able to deliver 1.8 kW to a receiving antenna 55 meters away. Their choice of microwaves over lasers was based on the grounds that unlike the latter, the former work fine through clouds. According to the Japan Aerospace Exploration Agency (JAXA), "this is the first time that anyone's been able to send such a high power output with this level of direction control". By the same token, it was also reported that "Mitsubishi (in partnership with JAXA) managed to send 10 kilowatts of power over a distance of 500 meters, using larger antennas with more of an emphasis on power over precision." The implementation time table for this technology is quite impressive. First, in the next five years or so, Mitsubishi hopes to be able to use this system for electric car charging and warning lights powering on transmission towers. Second, by 2018, JAXA would test the technology in space with a small satellite transmitting several kilowatts from low Earth orbit to a microwave receiver on the ground. Third, a 100 kW satellite would be put in orbit by 2021, followed by a 200 kW version by 2028. Finally, by 2031, a 1 gW pilot plant will be operational to be supplemented by a commercial space-based power industry beginning 2037.

In this context, in what follows I attempt to enquire as to why Tesla Motors would not have shown interest in going wireless in battery recharging while sticking with its wired hyper-charging mechanism.

To begin with, as a new article published in the latest edition of The Economist suggests, one reason would be that wireless charging is "inefficient and underpowered compared with the (wired) 'Superchargers' that Tesla has developed", considering that they "provide six times the wattage of wireless, and have already been installed at hundreds of places around the world." This, however, doesn't appear to be a solid argument given the hype that surrounds wireless charging nowadays and corresponding evidence that at least three major players (Evatran, Dynamic Momentum, and Qualcomm) will be soon be ready to take care of the recharging needs (with sufficient efficiency and wattage) of Tesla as well as those of other EV manufacturers.

This takes us to a perhaps more powerful (albeit flawed) reason for Tesla's disenchantment with wireless charging: The purported effects of the disrupting technology on EV battery use. As is well known, Tesla Motors will shortly become the largest battery producer on earth. Now, different kinds of electrified roads that seem to be around the corner are likely to downsize significantly wireless Li-ion batteries leading to an apparently non-trivial reduction in demand for such advanced energy storage devices. Would then be in Tesla's interest not to go wireless because of that? Not necessarily. Why? Because as roads electrify all over the world, chances are many more battery gigafactories will be required making Musk's dream about the emergence of hundreds of such plants in the years to come a tangible reality.

Last but not least, in an effort to ensure domination of the promising EV market, Tesla may simply dismiss any disrupting innovations altogether. And here I can only wonder whether the time has come for Tesla to start thinking of developing wireless hyper-charging technologies to be ready for displacement of its wired hyper-chargers in the next 5-10 years.