From the Electrical Engineering geeks at IEEE Spectrum, May 21:
Practical Power Beaming Gets Real
Wires have a lot going for them when it comes to moving electric power around, but they have their drawbacks too. Who, after all, hasn’t tired of having to plug in and unplug their phone and other rechargeable gizmos? It’s a nuisance.
Wires also challenge electric utilities: These companies must take pains to boost the voltage they apply to their transmission cables to very high values to avoid dissipating most of the power along the way. And when it comes to powering public transportation, including electric trains and trams, wires need to be used in tandem with rolling or sliding contacts, which are troublesome to maintain, can spark, and in some settings will generate problematic contaminants.
Many people are hungry for solutions to these issues—witness the widespread adoption over the past decade of wireless charging, mostly for portable consumer electronics but also for vehicles. While a wireless charger saves you from having to connect and disconnect cables repeatedly, the distance over which energy can be delivered this way is quite short. Indeed, it’s hard to recharge or power a device when the air gap is just a few centimeters, much less a few meters. Is there really no practical way to send power over greater distances without wires?
To some, the whole notion of wireless power transmission evokes images of Nikola Tesla with high-voltage coils spewing miniature bolts of lightning. This wouldn’t be such a silly connection to make. Tesla had indeed pursued the idea of somehow using the ground and atmosphere as a conduit for long-distance power transmission, a plan that went nowhere. But his dream of sending electric power over great distances without wires has persisted.
To underscore how safe the system was, the host of the BBC science program “Bang Goes the Theory” stuck his face fully into a power beam.
Guglielmo Marconi, who was Tesla’s contemporary, figured out how to use “Hertzian waves,” or electromagnetic waves, as we call them today, to send signals over long distances. And that advance brought with it the possibility of using the same kind of waves to carry energy from one place to another. This is, after all, how all the energy stored in wood, coal, oil, and natural gas originally got here: It was transmitted 150 million kilometers through space as electromagnetic waves—sunlight—most of it millions of years ago.
Can the same basic physics be harnessed to replace wires today? My colleagues and I at the U.S. Naval Research Laboratory, in Washington, D.C., think so, and here are some of the reasons why.
There have been sporadic efforts over the past century to use electromagnetic waves as a means of wireless power transmission, but these attempts produced mixed results. Perhaps the golden year for research on wireless power transmission was 1975, when William Brown, who worked for Raytheon, and Richard Dickinson of NASA’s Jet Propulsion Laboratory (now retired) used microwaves to beam power across a lab with greater than 50 percent end-to-end efficiency. In a separate demonstration, they were able to deliver more than 30 kilowatts over a distance of about a mile (1.6 kilometers).
These demonstrations were part of a larger NASA and U.S. Department of Energy campaign to explore the feasibility of solar-power satellites, which, it was proposed, would one day harvest sunlight in space and beam the energy down to Earth as microwaves. But because this line of research was motivated in large part by the energy crisis of the 1970s, interest in solar-power satellites waned in the following decades, at least in the United States.
Although researchers revisit the idea of solar-power satellites with some regularity, those performing actual demonstrations of power beaming have struggled to surpass the high-water mark for efficiency, distance, and power level reached in 1975. But that situation is starting to change, thanks to various recent advances in transmission and reception technologies.....
....MUCH MORE
