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Monday, June 16, 2025

New records for sending power wirelessly

 DARPA program sets new records for sending power wirelessly 

Looking forward to a future where laser beams replace power lines, DAPRA's Persistent Optical Wireless Energy Relay (POWER) program has set new records for transmitting more power wirelessly over longer distances. Successful demonstration of new receiver technology is important step for revolutionizing power delivery at the edge. In the optical power beaming receiver designed for PRAD, the laser enters the centre aperture, strikes a parabolic mirror, and reflects onto dozens of photovoltaic cells arranged around the inside of the device which convert the energy back to usable power. When it comes to military and humanitarian operations, obtaining a steady, reliable source of power is of paramount importance and this has only increased over time. As a result, the world's major military forces invest a staggering portion of their budgets to supply electricity, fuel, power plants and all that goes with them as part of an increasingly complex supply line.

However, no matter how much power technology improves, there's still the ever-present problem of getting that power from Point A to Point B, a problem that is often insurmountable across the infamous last mile where power lines cannot be slung or pipelines buried and soldiers are often reduced to hauling jerry cans of fuel over rough country by hand and back muscle. To close this gap, DARPA's POWER program seeks to build transmission lines of light where laser beams carry power to where it is required as easily as we now send data through the air. In a series of recent tests in New Mexico, the Persistent Optical Wireless Energy Relay (POWER) program achieved several new records for transmitting power over distance. The team recorded more than 800 watts of power delivered during a 30-second transmission from a laser 8.6 km's (5.3 miles) away. Over the course of the test campaign, more than a mega joule of energy was transferred. Previously, the greatest reported distance records for an appreciable amount of optical power (>1 microwatt) were 230 watts of average power at 1.7 km's for 25 seconds and a lesser (but undisclosed) amount of power at 3.7 km's. Not bad for sending power near-instantaneously without wires.

The POWER Receiver Array Demo (PRAD) set the records for power and distance for optical power beaming; the graphic shows how it compares to previous notable efforts. “It is beyond a doubt that we absolutely obliterated all previously reported optical power beaming demonstrations for power and distance,” said POWER Program Manager Paul Jaffe after the results were confirmed. The DARPA-led team brought together industry and government, including the US Naval Research Laboratory and the High Energy Laser Systems Test Facility (HELSTF) at the US Army’s White Sands Missile Range. The system is built around what is called the Power Receiver Array Demo (PRAD), which is a ball-like structure which has a compact aperture to allow a laser beam to enter. This beam strikes a parabolic mirror that scatters the light and shines it on an array of dozens of photovoltaic calls. These convert the laser light back into electricity.

Energy is a fundamental requirement for military operations, and traditional means of getting energy to the edge (battlefields, disaster zones etc.) are often incredibly slow, risky and resource intensive. These tests, referred to as PRAD (POWER Receiver Array Demo), mark an important step towards the POWER program’s long-term goal of being able to instantly beam power from a location where it can be easily generated to wherever it’s needed, opening a novel design space for platform capabilities unbounded by fuel limitations. At the moment, DARA is concentrating on power and distance, so the present efficiency of the system being a mere 20% is acceptable, though there are plans to improve this as the technology is scaled up. Both the emitter and the receptor were situated on the ground for the test. However, the ultimate goal is to turn these into relays mounted on drones flying at high altitudes to direct the power where needed. By sending the beams up above the thickest parts of the atmosphere, losses can be cut down and obstacles like buildings, aircraft and birds avoided.

To achieve the power and distance record, PRAD used a new receiver technology with a compact aperture for the laser beam to shine into, ensuring very little light escapes once it has entered the receiver. Inside the receiver, the laser strikes a parabolic mirror which reflects the beam onto dozens of photovoltaic cells (a.k.a. “solar cells”) to convert the energy back to usable power. The receiver was designed by Teravec Technologies, led by principal investigator Raymond Hoheisel, with support from Packet Digital and the Rochester Institute of Technology. The technology is scalable to higher power levels and can be integrated into different platforms, such as unmanned aerial vehicles (UAVs), to support the long-term needs of the POWER program. Currently in Phase One of a three-phase development effort, the program is working on how to most accurately and efficiently direct power, correcting the beam wave front to maintain quality, making the system throttleable, and reduce conversion losses across the relays. By Phase Three, the goal will be to install the relays in conventional aircraft that will be able to deliver 10 kW of optical energy across 125 miles (200 km).

For the tests, both the transmitter and receiver were on the ground, which required the beam to go through the thickest part of the atmosphere, making the test results even more impressive. “It’s a lot easier to send a power beam directly up or down relative to the ground because there is so much less atmosphere to fight through,” Jaffe explains. “For PRAD, we wanted to test under the maximum impact of atmospheric effects.” While efficiency wasn’t the focus of this demonstration, the team measured more than 20% efficiency from the optical power out of the laser to the electrical power out of the receiver at shorter distances. The goal of the effort was to rapidly validate the capability of a new design to massively extend potential distance, so trade-offs were made to accelerate the design and build of the test receiver. The receiver was completed in about three months. "This demonstration broke through misconceptions about the limits of power beaming technology, and it is already spurring industry to reimagine what’s possible," said POWER Program Manager Paul Jaffe. With the PRAD testing successful, the POWER program has significantly reduced risk for a key element of making long-distance power beaming a future reality. The program is now moving forward to demonstrate the benefits of integrated relays and vertical power transmission and is seeking the creativity and innovation of potential partners to accomplish this as part of POWER Phase 2. A POWER Phase 2 Industry Day will be held on 29 May, 2025.The Industry Day will promote teaming arrangements between researchers; provide potential performers with information on whether and how they might respond to government R&D solicitations; and increase efficiency in proposal preparation and evaluation. The Industry Day registration deadline is 21 May 2025.

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