FAQ: Does the amount of delivered power vary with the distance between the transmitter and receiver?
Written by Tom Nugent 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.