March 16, 2015 7:00 pm JST
Infrastructure technology

Mitsubishi Heavy takes step toward long-distance wireless power

TAKASHI NISHIOKA and SHOJI YANO, Nikkei staff writers

TOKYO -- Mitsubishi Heavy Industries' wireless power transmission system is expected to have a broad range of applications, from transportation to offshore wind turbines. It may even make space-based solar power generation possible.

     The Japanese heavy equipment maker said Thursday it has succeeded in transmitting electricity wirelessly in a Feb. 24 test at its Kobe Shipyard and Machinery Works in Japan's western Hyogo Prefecture.

     Two large panels, 13 meters high and 8 meters wide, were set 500 meters apart on a pier. One was a transmission unit, the other a receiver. The system successfully converted 10kW of electricity into microwaves, which were sent to the receiver and converted back into electricity, which lit up lights on the panel. The test set a record for wireless power transmission in Japan both in terms of the power supplied and the transmission distance.

     The 500 meter span was nearly 10 times longer than the previous record. "We aim to apply this technology to a broad range of industrial uses," said Hiroaki Matsumoto, general manager of the space technology application department at Mitsubishi Heavy Industries.

     At present, most wireless power transmission systems use electromagnetic induction, which uses a magnetic field to send electricity between a transmitting and receiving coil. This method is used to recharge mobile phone batteries wirelessly and in other applications. Although this allows a large amount of power to be sent, transmission distances are short.

Spirit of the radio

Mitsubishi Heavy's use of radio emission technology using microwaves is aimed at transmitting power over longer distances. If the technology can be refined, power-assisted carts would no longer need cables to recharge their batteries, for example, and offshore wind turbines could send power to receiving panels on land, eliminating the need for undersea cables. It might even be possible to send electricity to isolated villages suffering a blackout due to a natural disaster.

     The U.S. and China are also working on wireless power transmission technology, but experts say Japan is far ahead. Wireless power is a hot topic among those looking to improve energy efficiency and aiming to develop a new industry.

     As the Internet of Things -- a plethora of Internet-enabled devices -- takes hold wireless power transmission is attracting attention. Japan's Ministry of Economy, Trade and Industry is keen on the technology, particularly from the standpoint of infrastructure management. Inside tunnels, sensors are installed on the walls to gauge how the structures are holding up. The ministry thinks the technology can be used to supply power to these sensors by sending a car equipped with a power transmission device through the tunnels. "It costs to affix power sources to each and every [sensor]. Wireless power transmission technology offers a wide range of industrial applications," said a ministry official.

Keeping control

System control technology is the key to wireless power transmission. Mitsubishi Heavy has achieved a high level of accuracy in transmitting electricity to the designated target. In the demonstration test, the company employed a microwave-generating oscillator, similar to the ones used in microwave ovens, to cut costs.

    Cost is the biggest hurdle to be overcome before the technology can be put to widespread commercial use. It will have to fall by about half. "We are aiming to put the technology into practical use in five years," said Kenichi Anma, an engineering manager with the company's space technology application department. As Mitsubishi Heavy has a number of infrastructure-related businesses, it believes wireless transmission could help it grow.

     The company is also working on a space-based solar power generation system using wireless transmission, together with other companies and the Japan Aerospace Exploration Agency. The idea is to construct giant solar panels measuring 2 square kilometers in outer space that would gather sunlight, generate electricity and transmit it to a receiving station on Earth. In theory, this would allow continuous power generation because a space-based system would be unaffected by the earth's weather. Such a system could in theory generate 1,000MW of electricity, equal to the amount produced by a nuclear power plant, according to the industry ministry.

     The costs would be enormous. To lift the solar panels, weighing a total of 25,000 tons into orbit, would take roughly 2,500 rocket launches. That comes to around 25 trillion yen ($204 billion), just for starters.

     But the industry ministry and its partners are looking for ways to make the transmission system smaller and lighter, hoping to begin testing in space by the late 2030s.

 

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