FAQ: Does the amount of delivered power vary with the distance between the transmitter and receiver?

Written by on Thursday, April 19th, 2012

The efficiency of wireless power delivery via laser does vary with distance, though the impact is much more pronounced near the ground than when delivering power toward the sky or space.

While not directly related to distance, the primary factor affecting efficiency is whether the receiver collects all of the transmitted light, or if some of the light “leaks” past the receiver. This is determined by the design of the transmitting optics and the size of the receiver. There may be reasons other than efficiency that also drive the size of the transmitter and receiver.

Assuming that the receiver is large enough to capture any light that makes it that far, the remaining factor is absorption and scattering by the atmosphere. Power transferred from point to point near the ground can suffer significant energy losses due to turbulence and dust. We can reduce that effect by elevating the transmitter and receiver so that the beam remains a reasonable distance, perhaps 100 feet, above ground level.

Power beamed near vertical suffers comparatively little energy loss because it quickly gets away from the ground effects. Scattering will depend on atmospheric conditions (e.g., dust, clouds). Absorption in the wavelengths we use is small. We can design for any range from millimeters to many kilometers, and we are working on system designs to beam power from the Earth’s surface to satellites and the lunar surface — it is possible to transmit power at reasonable efficiency over hundreds, or even thousands, of kilometers under the right conditions.

8 comments

  1. Steve Tait says:

    So a Solar Power Station (SPS) at the Earth-Moon L4 or L5 Lagrange points, could beam power to a receiver on the lunar surface? With a reasonable efficency?

    Isn’t there a competition from NASA for powering lunar stations during the lunar night cycle?

  2. Tom Nugent says:

    Steve,
    Yes, in general you could beam power from anywhere within the Earth-Moon system to anywhere else either directly or with 1-2 relays.

    NASA’s lunar night competition seems to be intended for energy storage technologies, and not for wireless power delivery.

  3. Although used most publicly for astronomy, I would imagine adaptive optics techniques could be used to mitigate the effects you describe in this post, right?
    For vertical applications, a beacon, a wavefront sensor and a corrector (like a deformable mirror or spatial light modulator)could be used to maximize the throughput and for horizontal situations, I would think an iterative process, without the beacon, could maximize the signal…
    Have you thought about using AO in future designs either to increase the power to the satellite/UAV or reduce the power sent from the transmitter?

  4. Tom Nugent says:

    Michael, yes adaptive optics can help with some (but not all) of the atmospheric effects to improve the amount of power delivered, and is something we’ve considered. One issue to consider is the cost of AO versus the performance improvement it delivers.

  5. Tom,
    I agree on both counts. Not to toot my own company’s horn, but when considering costs, MEMS device manufacturing is scalable and if wireless power delivery becomes as ubiquitous as you and I hope, it can become pretty inexpensive to put together a module that would essentially bolt on to a transmitter.

    Thanks for responding to my comment!

  6. Blake says:

    Is the system as effective sending power from the moon/space station to earth considering the adverse ground and atmosphere effects.

  7. Caddtech86 says:

    I’ve read about some reccent breakthroughs in Maser technology; is this being considered as an alternative to laser beamed energy (ex: Maser electric propulsion)?

  8. Malachi Carre-Smith says:

    Reuters recently posted a video covering the technology you are developing, and mention use for powering UAVs, lunar stations and orbiting platforms (fascinating potentials); but the title of the video is what caught my eye:
    “Laser beaming could make power lines obsolete” – is there consideration to replace power lines with laser-beamed power or is this just an optimistic projection?
    If there is consideration along these lines (harhar), theoretically could a laser move enough power from point to point to satisfy the needs of a community/city block/building etc? Are there hazards involved for something that interferes with the beam (like a bird)? How does the efficiency of the transmitted power compare with an equivalent power line?