Key Takeaways
1. DARPA successfully transmitted 800 watts over 8.6 kilometers using laser technology, setting a record for wireless energy transmission.
2. The system used an infrared laser beam focused on a compact receiver that converted laser energy into electricity via photovoltaic cells.
3. Advanced technologies like adaptive optics and beam-steering ensured stable energy transfer over long distances, achieving a conversion efficiency of about 20%.
4. Other companies, like PowerLight Technologies and Emrod, have also made significant progress in wireless energy transmission using different technologies.
5. Future phases of DARPA’s POWER program aim to scale the system to deliver up to 10 kilowatts over distances of 200 kilometers, potentially powering data centers.
Transmission of electricity without wires has been a dream for people for a long time, particularly after Nikola Tesla spent his final years working towards this vision. Since then, various companies have begun exploring technologies to make this dream a reality.
DARPA’s Achievement
The Defense Advanced Research Projects Agency (DARPA) of the US military has reached a significant milestone that puts it at the forefront of this research. They successfully transmitted 800 watts across a distance of 8.6 kilometers for 30 seconds using laser technology. This amount of energy is similar to what is needed to power a microwave or a small refrigerator. With this accomplishment, DARPA’s Persistent Optical Wireless Energy Relay (POWER) program has set a new record for the longest distance of wireless transmission so far.
How It Works
The system operated with a carefully focused infrared laser beam aimed at a compact receiver on the ground. This receiver utilized a parabolic mirror to concentrate the incoming laser light onto photovoltaic (PV) cells, which transformed the laser energy into electricity. This design was selected due to its simplicity, quick production time (built in less than three months), and its ability to keep the beam aligned over large distances with little dispersion or scattering from the atmosphere.
The system employed adaptive optics and beam-steering technology to stabilize the laser over long ranges and adjust for atmospheric disturbances, ensuring effective energy collection. The PV cells were optimized for the specific wavelength of the laser used, achieving conversion efficiencies of about 20%, which is quite good considering the distance and safety limits of the laser. Even at this long range, the beam maintained enough coherence and power density to transfer over 1 megajoule of energy in just 30 seconds.
Other Milestones
The agency has hit several other important milestones, for instance, in late 2024, they transmitted 230 watts over a distance of 1.7 kilometers for 20 seconds and also conducted tests over 3.7 kilometers.
Nonetheless, other companies have reached their own milestones too. PowerLight Technologies demonstrated an infrared energy transmission of 400 watts over a kilometer, sustaining the energy flow for over 12 hours. In a similar vein, Emrod, a company based in New Zealand, transmitted around 2 kilowatts over a few hundred meters with an efficiency of approximately 97% by utilizing microwave technology.
This demonstration was part of Phase 1 of the POWER project, which includes three distinct phases. The agency is currently focusing on refining beam direction, enhancing wavefront correction, and minimizing conversion losses.
For the upcoming phases, the program aims to scale up the system to deliver as much as 10 kilowatts of optical electricity over distances reaching up to 200 kilometers. This energy could potentially power a small to medium data center, consisting of about 500 servers, which can consume between 150 to 250 kilowatts.
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