Wireless Power: Here? Now?

Outside of very small applications, Nikola Tesla’s ideas about transmitting serious power without wires have not been very practical. Sure, we can draw microwatts from radio signals in the air and if you’re willing to get your phone in just the right spot you can charge it. But having power sent to your laptop anywhere in your home is still a pipe dream. Sending power from a generating station to a dozen homes without wire is even more fantastic. Or is it? [Paul Jaffe] of the Naval Research Laboratory thinks it isn’t fantastic at all and he explains why in a post on IEEE Spectrum.

Historically, there have been attempts to move lots of power around wirelessly. IN 1975, researchers sent power across a lab using microwaves at 50% efficiency. They were actually making the case for beaming energy down from solar power satellites. According to [Jaffe] the secret is to go beyond even microwaves. A 2019 demonstration by the Navy conveyed 400 watts over 300 meters using a laser. Using a tightly confined beam on a single coherent wavelength allows for very efficient photovoltaic cells that can far outstrip the kind we are used to that accept a mix of solar lighting.

Wait. The Navy. High-powered laser beams. Uh oh, right? According to [Jaffe], it is all a factor of how dense the energy in the beam is along with the actual wavelengths involved. The 400 watt beam, for example, was in a virtual enclosure that could sense any object approaching the main beam and cut power.

Keep in mind, 400 watts isn’t enough to power a hair dryer. Besides, point-to-point transmission with a laser is fine for sending power to a far-flung community, but not great for keeping your laptop charged no matter where you leave it.

Still, this sounds like exciting work and while it might not be Tesla’s exact vision, it sounds like laser transmission might be closer than it seemed just a few years ago. We’ve seen similar systems that employ safety sensors, but they are all relatively low power. We still want to know what’s going on in Milford, Texas, though.

34 thoughts on “Wireless Power: Here? Now?

  1. Imagine solar power satellites using a high power laser beam to convey energy to a earth receptor station… I bet there is a movie of such a setup going haywire.

    1. Two words: whisper dish.

      Dishes (and lasers) effectively change the location of the isotropic source (by a lot) meaning the power falloff from the distance to the *dish* is very small when you’re close.

      Couple two dishes together and it’s not hard to have zero power loss over a large distance before beam spreading kills your efficiency.

      Think of it like a flashlight on a wall. Yes, the beam spreads out as you back away, but the wall still collects all of the power, so there’s zero loss with distance until you get so far the flashlight beam is bigger than the wall.

      1. No such thing as zero loss, ever. Even in your flashlight example, a small amount of light will be scattered by particulates in the air, etc. So the best you can claim is most of the energy may make it to the target, but never 100%.

      1. No, they really are not. It’s just a beam of light. It has divergence just like any other beam of light. It’s not magic.

        A laser CAN have a very high surface brightness, and a very small apparent source size, so a beam of a given size (diameter and divergence, or etendue) can be more powerful than that from other light sources, but that’s all.

  2. In 1995 Rotring – the “former German manufacturing company of technical drawing tools”[1] – published “GEO Mission 1″ a kinda advergame with exactly that setup: Microwave or laser power receiver stations on earth, satellites in orbit and you managed everything from your desk (with Rotring pencils and what not on it) including re-aligning the receivers after an earthquake (I think), budgeting and so on…

    It came on one single 1,44MiB(?) 8,89cm floppy disk (3,5”) and ran on Windows 3.1 upward.

    If anyone has any Idea where to find a copy… I’d like to get my hands on one (not literally on a physical disk, a digital copy is fine ;-) ).

    The only reference I can find today are in a “PC Spiel” from October 1995 on Archive.org[2] and the archived homepage of [Prof. Dr. Jens H. Fischer] who “developed” the game (see [3])

    No reverse image search :-( and the original

    [1] https://en.wikipedia.org/wiki/Rotring
    [2] https://archive.org/details/PCSpiel1095/page/n14/mode/2up
    & https://archive.org/details/PCSpiel1095/page/n41/mode/2up
    [3] https://web.archive.org/web/20050419011743/http://home.foni.net/~jfischer/start.html (search for “rotring”)

    1. The IEEE Spectrum article is light on the details (as Spectrum is), but if you dig deeper into the company they’re shilling for, they use a 2 kW optical beam to generate that 400W output.

      They probably use a diode-pumped solid-state laser, or maybe a fiber laser, to generate that 2 kW of photons, and either of those do well to even get a 50% wall-plug efficiency. So, expect 4-5 kW system input power.

      Less than 10% end-to-end efficiency.

      “Has potential”, as 2nd-grade report card might read.

  3. If I’m not mistaken, Tesla’s procedure used the earth as a return to the generator station, and, used the atmosphere as a conductor of possibly very high frequency EM power. Don’t know for sure, wasn’t patented, or published.

    1. From what I have gleamed over the years from readings on his work, (some by him some by others), I am under the impression that Tesla was attempting to utilize the Schumann resonance or some harmonic of that. I am hard pressed to believe that Tesla would not be aware of or consider the inverse square law, I’m not sure if he was leaning to a high frequency ‘wave’ [i.e directionality increases] or a transient plasma, pulsed at the frequency of said Schumann or a harmonic of that.

  4. Everyone is missing the single, really good use case for this;

    Ion engine powered space probes/tugboats.

    One of the main limiters of in engines (in my understanding) is the power system, which is traditionally a bunch of solar panels. If you want more trust, you need more power, and that means more solar panels, which means more mass you have to accelerate, which cuts into your gains from more thrust.

    But, if you didn’t have to carry a bunch of solar panels with you, because there were large solar arrays in orbit to transfer the power, that would improve ion engine Thrust to Weight Ratio.

    Additionally, it’s unlikely to work as a destructive laser weapon (given you need to not destroy what you are powering), it will have minimal atmospheric losses due to being in orbit, the low electrical efficiency won’t matter as much given the super high value of the service, which also makes it cost effective.

    1. I watched a YT video the other day that FRBs (Fast Radio Bursts) detected by radio astronomers “could” be advanced civilizations powering solar sail type of space probes.

  5. Yo the transmission efficiency is really bad, combined with petty convenience… You know that people will waste every single resource in this world for the smallest amount of convenience. Give this to them and you will never have the efficiency of cables again. And no, they won’t all suddenly convert to renewables. lol.
    Not to mention you will have beams transmitting many watts through the air to contend with. Maybe wires aren’t so bad. And that giga-solar station in the sky, what’s the environmental impact of that? I remember seeing paintings of those in the 70s, and that kind of utopianism went out of favor for good reason.
    Transmitting however many watts your laptop uses across your house just so you don’t have to plug a cable into a wall a few feet away? Yeah horrifying, remind me to never ever visit your microwave oven of a house.

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