Wireless Power Transfer
Powering the world with waves.
Happy 4th of July, America! Or for anyone reading this in another country, happy 4th day of the 7th month of the year that is 2018. Wow, it’s 2018, and here I am writing this post with a lap top computer plugged into a wall charging my low battery… and the power goes out. What a coincidence, right?! I’m literally writing a post about the feasibility of wireless power transfer, and I can’t finish it on time because my power goes out due to a heat-induced power overload on the local grid. But this incident actually ties nicely into the theme of independence and freedom this week. No, I’m not talking about America’s independence from Great Britain, but rather a freedom for the entire world; the freedom from wires, power lines, and cords!
Wireless power transfer is a means of power distribution by which power is emitted from a transmitter connected to a power source, to a receiver within a piece of power-consuming technology via either induction or electromagnetic waves. Due to it’s non-reliance on kilometers of power lines, wiring, and charging cords, wireless power transfer may turn out to be the Holy Grail in powering the Earth’s skyrocketing population with clean, reliable energy within the next half a century. Now, I know what some of you are thinking. “Brandon. I follow you because you write about space stuff. I don’t see anything about space yet in this article.” Well don’t worry. I’ll tie space into this article somehow, but first we’ll have to delve into the finer workings of wireless power transfer.
There are two classes of wireless power transfer; non-radiative and radiative. Non-radiative power transfer moves charge to a device using transmitting and receiving coils of wire known as inductors. When a transmitting inductor (charging port) is plugged into an outlet, the power running through it generates an alternating magnetic field, and constantly wants to impart this magnetic field on another coil of wire. When a device equipped with a similar coil is placed near this charging port, the alternating magnetic field from the transmitter is induced into that device’s coil (its receiver), generating a voltage which can be used to charge it. Non-radiative power transfer is actually used quite commonly today, appearing in chargers for smartphones, electric toothbrushes, and even electric vehicles.
This technology is no doubt useful from a convenience standpoint. No one wants to fish around a dark floor for a charging cord at night, or think about remembering to plug something in when its power is low. It’s much more convenient to just place your device on such a platform overnight, or whenever not in use, to maintain power. However, from a power transfer point of view, non-radiative power transfer kind of misses the whole point of going wireless. First of all, non-radiative power transfer has an incredibly short range. Because it relies on inductance, efficiency decreases exponentially with the device’s distance from the port. Father than just a few centimeters away, no useful power is transferred between most household wireless chargers and their corresponding electronic devices. Furthermore, non-radiative power transfer still requires the transmitter to be plugged into a wall outlet, which is connected to a power grid. Unless you have your own solar farm or array of wind turbines wired directly to your house, you are reliant on a local power grid comprised of thousands of vulnerable power lines, feeding thousands of other people’s daily power needs simultaneously. If a thunderstorm wreaks some havoc on this grid, a wireless toothbrush user may be forced to avoid drinking that extra cup of coffee to keep their breath tolerable.
Now, imagine a system that could literally “beam” power to millions of consumers directly from the plant where that power is produced, regardless of heat waves, thunderstorms, or weather phenomena of any kind. This Utopian pipe dream could be made feasible with the advent of radiative wireless power transfer. Radiative power transfer works by converting power, generated by a power plant or collected from natural sources, into electromagnetic waves (i.e. light). These waves are strategically directed and emitted using a transmitting antenna towards a receiver, which may be tens or even hundreds of kilometers away. If the beam is kept focused, radiative power transfer can exceed 95% efficiency, even at these distances.
There are generally two viable options regarding the wavelength of light used for radiative power transfer; visible light, and microwaves. Visible light (in the form of lasers) allows for extremely narrow beam widths, thus requiring smaller recieving instruments. Visible light also doesn’t interfere with existing Wi-Fi and cellular phone networks. However, lasers have the drawback of not being able to pierce through thick cloud layers or man made structures. This means that the receiver would have to have a direct line-of-sight to the transmitter for power transfer to occur, which may be rare depending on where the receiver is on Earth. High power energy transfer with lasers would probably also be dangerous to wildlife, humans, and structures.
Microwaves may provide a much more realistic solution for radiative power transfer. Like radio waves, microwaves can travel through atmospheric disturbances and most solid structures unperturbed. This is why NASA doesn’t lose contact with the ISS in cloud cover, and why you can still listen to the radio during a thunderstorm. Furthermore, microwaves won’t burn your house down if the transmitter is misaligned by a fraction of a degree. The main drawback from using microwaves for power transfer is the size of the transmitting and receiving antennas required to keep power transfer efficiencies at respectable levels. To maintain a tight beam, such a system would have to utilize the shortest possible wavelength of light (to minimize diffraction) and largest possible antenna (to maximize directionality).
Got it? Great! Let’s power the entire Earth’s population in 2040.
Earth is bombarded with 1365 continuous Watts of solar energy per square meter every day from the Sun. Not all of this power reaches Earth’s surface however; much of it is reflected or absorbed by atmospheric haze or cloud cover. But in space (I promised I would tie it back in!), there are no clouds or atmospheric phenomena of any kind to block incoming solar radiation, allowing for much more efficient power collection. Utilizing a massive space based solar power collection system with multiple giant solar panel assemblies, it may be possible to provide power for the whole world’s energy needs. Each of these assemblies would be equipped with microwave power transmitter antennas, and would all orbit the Earth at different inclinations in order to supply power to everyone, irrespective of geographic location. What would it take?
The human race is a power hungry civilization, and that power need is growing rapidly with both technology level and population. Today, our species eats up ~10²¹ (A thousand-billion-billion) Joules of energy every year, averaging out to a power consumption of about 3.2*10¹³ Watts. This divides out to about 4.3 kilowatts per person; roughly the power consumption of a washer and dryer running simultaneously. Of course, as more nations advance away from deep poverty across the world, global power demands will become even more stringent. By 2040, it is not unlikely that the human population will have exceeded 9 billion, and the average person will require ~5 continuous kilowatts to meet their power needs. Factoring this in with both a realistic near future solar panel efficiency of 40%, and a radiative power transfer efficiency of 90%, we would need almost 100,000 square kilometers of solar panels. Dividing this power load between 100 different assemblies, each solar satellite would require a diameter of 35 kilometers.
This seems enormous, and it is, but also remember that powering the entire Earth’s population with merely the surface area of Maine is rather impressive. The size of these solar panels may also be mitigated by the advancement of other forms of clean energy, or even the advent of fusion power near the middle of the century. Wherever the power is harnessed or generated, it can then be directionally beamed to various power distribution stations around the globe with giant kilometer long antennas. These stations would then divide that power load among individual consumers, assuring that the average Earthling doesn’t need to own a kilometer-wide receiver dish to play Call of Duty 14.
Wireless power transfer has nearly infinite applications. Using radiative techniques, cars, phones, and households could all be powered effectively, decreasing the need for bulky batteries and eliminating the fear of not having enough charge. Almost no household electronics would ever require a cord. But there may be an even more critical application for the installment of a global wireless power transfer system. Last year, hurricane Maria decimated Puerto Rico’s electrical power grid, depriving 100% of the island’s 3.4 million citizens of power. Months later, the power grid still has not been fully restored, and replacing downed power lines with new ones is like rebuilding a house on the same active volcano that destroyed your last house. A wireless power transfer system, free of flimsy power lines, could outlast a natural disaster such as this. Even if a local power distributor was damaged in such a storm, a neighboring distributor could pick up the slack in maintaining power for the population. No one would be without power for more than a matter of minutes.
Our global method of power transfer is antiquated, and requires an overhaul. Utilizing sources of clean energy, it is feasible to set up a system which converts this harnessed energy to electromagnetic waves in order to wirelessly transmit that power directly from the source, to millions of consumers kilometers away with negligible losses in efficiency. One day, it may even be possible to do this from space, though it is more likely that we will combine multiple sources of power to meet our species’ growing energy needs. In conclusion, I’m sorry that this post is a couple days late. One day, the entire world will celebrate a global freedom from wires, charging cords, and power lines. Until then, I will continue to complain about this heat, and launch some bottle rockets upside down into an empty milk jug. Thanks for the read!
