Wireless electricity transmission achieves a new milestone: The longest distance to date

Transmission of electricity without cables has been a dream for humanity, especially after Nikola Tesla devoted his last days to work towards this goal. Since then, companies have also started looking for technologies that enable this possibility. 

The US military's Defense Advanced Research Projects Agency (DARPA) achieved a milestone that positions it as the most advanced in this research. The agency successfully transmitted 800 watts through 8.6 kilometres during 30 seconds, using laser technology, equivalent to the amount of energy required to power a microwave or a small fridge. With this achievement, DARPA’s Persistent Optical Wireless Energy Relay (POWER) program set the record for maximum distance of wireless transmission to date. 

The system used a precisely focused infrared laser beam that was directed at a compact ground-based receiver. The receiver employed a parabolic mirror to focus the incoming laser light onto a set of photovoltaic (PV) cells, which converted the laser energy into electricity. This design was chosen for its simplicity, rapid manufacturability (built in under three months), and ability to maintain beam alignment over long distances with minimal dispersion or atmospheric scattering.

The system relied on adaptive optics and beam-steering mechanisms to stabilise the laser over long distances and compensate for atmospheric turbulence, to ensure successful energy capture. The PV cells were optimised for the specific laser wavelength used, enabling conversion efficiencies of approximately 20%,  which is relatively high given the transmission distance and laser safety constraints. Despite the long range, the beam retained enough coherence and power density to transfer more than 1 megajoule of energy in just 30 seconds.

The agency has achieved some milestones in this regard, for example, in late 2024, the agency transmitted 230 watts over 1.7 kilometres during 20 seconds, and tested a distance of 3.7 kilometres.

However, other companies have also achieved other milestones. PowerLight Technologies has shown an infrared transmission of 400 watts over 1 kilometre, but sending energy for over 12 hours. Similarly, the New Zealand-based Emrod transmitted around 2 kilowatts over a few hundred meters, but achieved an efficiency of around 97%, using microwave technology. 

What comes next?

This demonstration was part of Phase 1 of the POWER project, consisting in three phases. The agency is now working on perfecting beam direction, improving wavefront correction, and reducing losses during conversion. 

For future phases, the program aims at scaling the system, to deliver up to 10 kilowatts of optical electricity, crossing distances of up to 200 kilometres. The energy equivalent to power a small to medium data centre, of about 500 severs, that can consume between 150 to 250 kilowatts.