DARPA Triples Wireless Power Beaming to 800 Watts for 5 Miles But 2028 Goals Are 5000 Watts for 120 Miles

The DARPA 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 kilometers (5.3 miles) away. Over the course of the test campaign, more than a megajoule of energy was transferred. The DARPA goal is to beam power over battlefield distances of 120 miles at 5 kilowatts of power using a network of drones.

Previously, the greatest reported distance records for an appreciable amount of optical power (>1 microwatt) were 230 watts of average power at 1.7 kilometers for 25 seconds and a lesser (but undisclosed) amount of power at 3.7 kilometers.

DARPA beamed 800 watts versus the old 230 watt record and beamed 8.6 kilometer versus the 1.7 kilometer distance record.

The DARPA-led team brought together industry and government, including the U.S. Naval Research Laboratory and the High Energy Laser Systems Test Facility (HELSTF) at the U.S. Army’s White Sands Missile Range.

This is a step to 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.

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 that reflects the beam onto dozens of photovoltaic cells (a.k.a. “solar cells”) to convert the energy back to usable power.

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.

Powering Drones and Making a Power Web

Mid-to-late 2025: Phase 2 contracts awarded. DARPA was soliciting partners for Phase 2, a six-month effort to develop an integrated subscale relay.

The culminating Phase 2 demonstration is planned for 2026 at the High Energy Laser Systems Test Facility (HELSTF) in New Mexico. An existing HELSTF laser will serve as the source to deliver and redirect power from a ground station through an airborne relay to a ground-based receiver.

DARPA’s long-term vision is to create a wireless energy web that can deliver power to drones and ground assets on demand.

Airborne relays: In Phase 2, a subscale relay will be hosted on an air platform like a helicopter or aerostat at an altitude of at least 1.5 km (0.9 miles).

Ground-to-air-to-ground: A laser beam will be transmitted from a ground source, redirected by the airborne relay, and then sent to another receiver on the ground. This demonstration will validate the system’s ability to correct and redirect the beam.

DARPA envisions the POWER program performers will create novel integrations of optical technologies to create an airborne relay capable of redirection, wavefront correction, and energy harvesting of optical beams. The aim of the final demonstration is to use three airborne relay nodes, hosted by existing platforms, to transmit energy from a ground source laser up to high altitude for long-range efficiency, and back down to a ground receiver 200 kilometers away. It is envisioned that the platforms will be operating at or around 60,000 feet to minimize atmospheric losses and enhance relay survivability. Efficient and precise redirection is necessary to avoid platform thermal challenges and to ensure the relayed beam effectively illuminates the desired target. To account for degradation of beam quality as the beam transits atmospheric disturbances, the relay must be able to correct the optical wavefront as needed to achieve system efficiency goals. Finally, the relays must be able to selectively harvest energy from the optical beam to provide on-board auxiliary power and thereby demonstrate necessary characteristics for future indefinitely persistent relay platforms. Proposals that leverage existing and emerging optical technologies in a novel way to achieve program goals in an effective low size, weight, power, and cost package are encouraged.

Long-term potential: Ultimately, this technology could provide unlimited range and endurance for drones by allowing them to receive power wirelessly from airborne relays.

The POWER program is envisioned as a three (3) phase program.

In POWER Phase 1, performers undertook relay technology development efforts. Their accomplishments reduced risks, validated component technologies and concepts of operations, and catalyzed the transition to Phase 2. The results showed that relays with greater than 90% throughput efficiency weighing less than 500 kg should be possible, and that they should be able to meet the needed pointing and safety requirements.

Investigations and prototyping of novel enabling technologies such as high-performance diffractive optics, lightweight additively-manufactured precision reflective optics with integrated thermal management features, liquid crystal spatial light modulation for adaptive optics, pickoff beam shaping for enhanced efficiency power harvesting, and high-performance inertial measurement units to close tracking and safety control loops faster all provided confidence that the integrated relays envisioned for POWER are technically possible.

In Phase 2, covered by this solicitation, the POWER Subscale Aerial Demonstration aims to take the existence proofs provided by the Phase 1 activities and integrate the three key relay functions of redirection, correction, and harvesting into a fully-integrated subscale system demonstration.

Phase 2 will serve as a risk-reduction effort informing a DARPA decision to proceed with a Phase 3 multi-relay demonstration.

The subscale phase2 prototype relay system will perform the following specific functions:
* Redirect: The relay must accept at least 5 kW of laser energy from one ground location at a slant angle (from zenith) not to exceed 45 degrees and deliver the energy to another location on the ground while being airborne at an altitude of at least 1.5 km. There must be active pointing and tracking systems operating to ensure maximized energy delivery at the user’s location.

* Correct: The relay must perform corrections to the effects of atmospheric disturbances encountered by propagation over the path to ensure maximized energy delivery at the user’s location.

* Harvest: The relay must demonstrate a pickoff capability covering the range of 0% to 20% of the energy going through the relay. The conversion of this energy to electrical power is not a critical demonstration in this phase of the program, but this capability will be critical to future program expansion. For Phase 2, implementing a method of measuring and dissipating the picked-off energy is sufficient.

POWER Phase 1 efforts concluded that an aperture of approximately 50 cm is suitable for Phase 3. Since Phase 2 will use a power level of 5 kW, rather than 50 kW, an aperture scaled for similar irradiance is recommended to maintain operational relevance. Therefore, an aperture of approximately 15 cm would provide sufficient scaling to the envisioned system. This aperture size is not a requirement, but rather a notional suggestion. Performers must choose an aperture size for this effort while also showing relevance to the future anticipated Phase 3. The wavelength of the laser for this effort is approximately 1.07 microns.

The final demonstration, in a future POWER Phase 3, will use three airborne relay nodes, hosted by existing platforms, to transmit energy from a ground source laser up to high altitude for long-range efficiency, and back down to a ground receiver after > 200 kilometers of propagation. The platforms will be operating at or around 60,000 feet to minimize atmospheric losses and enhance relay survivability and safety. Efficient and precise redirection is necessary to avoid platform thermal challenges and to ensure the relayed beam effectively illuminates the desired receiver.