Could Laser-based Wireless Power Transmission Be Taking Center Stage?
Though wireless power transfer research continues to gain momentum, laser-based wireless power is garnering great interest from both Ericsson, JAXA, and DARPA.
Wireless power transmission (WPT) technology could almost be called a “phase of interest” that most electrical engineers move through on their way to more practical design experience. Plagued by low efficiency, WPT on cursory evaluation appears to be a non-starter.
Yet, the research into WPT endures and is advancing, using both microwave and laser energy as a coherent medium. Specifically, research into laser-based power transmission has garnered significant attention in the past couple of years.
Both private and public institutions are seeking a way to reduce infrastructure costs, beautify our cities, and simplify power delivery.
The general basics of WPT. Image used courtesy of Electrical Equipment
Today, this article will look at how researchers, corporations, and government entities are approaching laser-based wireless power transfer.
To start, let's dive into the fundamentals of this technology.
Principles & Limitations of Laser-based Wireless Power
Laser-based wireless power systems are characterized as having high energy density, highly directive beams, long transmission distances, and small transmission apertures. The basic components required to set up a test unit for wireless power via laser consist of a transmitting laser system and a photovoltaic receiver system.
Recent research in testing the performance of laser-based systems for WPT centered around the efficiency of these systems, especially concerning microwave-based WPT systems.
Test setup and UUT measurements of a laser-based WPT system. Image used courtesy of Xu et al
The researchers found that the overall efficiency of their laser system, providing ~46 watts to an electronic load, was 7.9%. Comparatively, their microwave RF-based system produced 500 watts at the load and had an efficiency of 10.4%.
Despite these low efficiencies, major players in the industry continue to push forward with this technology. Recently, Ericsson and PowerLight Technologies demonstrated a 5G base station powered wirelessly by laser irradiation.
World’s First Wirelessly Powered Base Station
In partnership with PowerLight Technologies, Ericsson has made strides toward a commercial application of wireless power transfer using a laser.
Conceptual transmission of power with safety ring (purple). Image (video) used courtesy of Ericsson
Claiming a ‘world’s first’ proof-of-concept system, Ericsson built the wirelessly powered 5G radio unit system with three key objectives:
- Power an entire base station wirelessly
- Ensure base station up-time in the event of temporary power interruption
- Discharge the laser within milliseconds
The demonstration experiment details a safety ring surrounding the power beam and acts as a control element that disengages the transmitter if anything crosses the beam.
The laser conversion system in the receiver stores energy in a power distribution unit, which continues to power the 5G base station while the laser beam is interrupted.
While Ericsson and PowerLight are focusing on WPT here on Earth, some companies are looking into WPT in space.
JAXA’s Space Solar Power Systems Team Investigates Lasers
When looking beyond the private sector, the Japanese Aeronautical Exploration Agency (JAXA) is engaged in research to determine the viability of transporting solar energy from LEO and GEO satellite systems using both laser and microwave transmitters.
When dealing with space-based laser WPT systems, the alignment of the system to terrestrial receivers is critical. To facilitate this, JAXA envisions a beam-steering methodology using a pilot laser from the ground to drive a fast steering mirror and ultimately achieve an accuracy of 0.1 µrad.
A conceptual solar space-powered laser system (SSPS). Image used courtesy of JAXA
Several notable technical challenges stand in the way of realizing this system, including developing a space-grade laser system, improvements in the efficiency of electrical-laser conversions, and methods to deal with atmospheric effects.
Additional challenges to the SSPS system include getting the system into orbit and ensuring the system's safety on human/animal health.
DARPA Calls for Breakthrough Energy Web Dominance Proposals
Furthering the trend towards the development of laser-based WPT, DARPA recently placed a small business technology transfer (STTR) opportunity announcement seeking proposals to develop a "wireless energy web [PDF]."
This web is described as consisting of multiple dynamic nodes, powered by transmission on the ground, which is capable of receiving or relaying optical power. Proposed research areas are intended to address one of two challenges: the development of high-energy flux/high-efficiency optical conversion or the ability to relay optical energy from one node to another.
The end goal is to attain systems that have an energy flux of 1 kW/m2 scalable up to 100 kW/m2, along with relay systems that operate optically (without electrical conversion) between nodes and have "rigorously assured photon containment" to prevent accidental injury to personnel.
Although wireless power transmission systems currently lack the technical specifications that would make them commercially viable in 2021, they are far enough that serious merit is being placed on their development.
With the support of industry giants like Ericsson and the clear interest of world governments, wireless power transmission through laser-based mediums might be set to take center stage in the coming decades.
Interested in other WPT news? Read on in the articles down below.