News Feature | October 11, 2016

Japanese Scientists Develop Long Distance Wireless Power Transmission

By Jof Enriquez,
Follow me on Twitter @jofenriq

A wireless power transmitting array used in a test in Japan in 2015. Image courtesy Mitsubishi Heavy Industries

Long-distance wireless charging may be something of a holy grail for gadgets, devices and electric vehicles, but Japanese researchers are a step closer toward making it reality, making wireless power reception antennas that draw power from space-based solar arrays.

Man-made satellites have long since been able to harness solar energy for electrical power. For instance, the International Space Station has four solar arrays to power its systems. But redirecting stored solar energy down to Earth, with its unpredictable weather, is technically daunting.

According to the Japan Aerospace Exploration Agency (JAXA), microwaves would work even if the weather is bad, and the agency last year worked with Japanese conglomerate Mitsubishi on an experiment that successfully transmitted 1.8 kilowatts “with pinpoint accuracy” to a receiving antenna (rectenna) 55 meters away using carefully directed microwaves, reported IEEE Spectrum.

At the Combined Exhibition of Advanced Technologies (CEATEC) show held recently near Tokyo, Japan Space Systems (J Space Systems) showed off its "rectenna" technology. These are flat, wireless power reception antennas tuned to the 5.8GHz frequency, which has successfully managed to transmit power over a distance of about 50 meters. It successfully delivered 1.8 kilowatts into an antenna that measured 1.2 meters square and managed to harvest 340 watts out from a receiver antenna that was 2.6 meters by 2.3 meters, according to a report from CIO.

The rectenna arrays shown at CEATEC are part of ground wireless power transmission (WPT) laboratory testing being conducted by J Space Systems for an ambitious project called Space Solar Power System (SSPS). J Space Systems, over the past few years, has been developing SSPS as an alternative future energy resource with the support of the Japanese government's METI (The Ministry of Economy, Trade, and Industry) and JAXA. When built, the SSPS solar arrays are designed to consist of "a large power generation/transmission panel suspended by multi-tether wires from a bus system above the panel. The upper surface of the generation/transmission panel is covered with solar cells, and the lower surface mounts transmitting phased array antenna elements and solar cells," according to J Space Systems.

Japanese scientists continue to develop more efficient arrays with minimal transmission losses. Orbiting solar arrays, like the SSPS spacecraft, could be many years down the line due to several technical and financial hurdles.

"It will take significant time and effort to overcome the many hurdles on the pathway to the realization of the solar space power system," says Japan's space agency, according to CIO.

But even the incremental technologies – such as "rectennas" – supporting that grand vision, could prove useful sooner. 

These microwave antennas or similar advanced technology could be used "at short range to send power around factories, enabling machines, sensors, and workstations to be easily reconfigured without having to run new power cables," writes CIO's Martyn Williams. "Another potential application sees balloons being used to send power down to areas hit by natural disasters where electric power is out, while the technology could also be used to send power up from the ground to a drone or similar object to keep it in the air."