Wireless power transmission

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In March of this year, Mitsubishi Heavy Industries, in conjunction with Japan’s space agency, successfully completed ground tests for wireless power transmission over a distance of 500 meters. A huge milestone for the company and for this burgeoning industry sector, Japan’s vision of solar power transmitted from outer space by 2030 seems like it could really be achievable…

Here at Total World Energy, we have continually focused on the evolving innovations of solar technology – covering applications ranging from Solar Impulse, the solar aeroplane featured in our April issue, now breaking records in its round-the-world flight, to the SolaRoad in our January issue – a public causeway that generates electricity and has the potential to create sustainable road systems. In this issue we look at a technology that will facilitate the transmission of solar power from space – a feat that sounds completely fanciful but is, in fact, very close to becoming viable.

On March 12th this year, Mitsubishi Heavy Industries (MHI) conducted ground demonstration testing of its wireless power transmission (WPT) technology. With the successful completion of the test at the company’s Kobe facility, it has verified the viability of long-distance WPT and completed the transmission of 10kW of power from a transmitting unit by microwave.

The potential applications of wireless power transmission (WPT) once fully realised, are endless. A technology that would seem more at home in a science fiction novel, the idea was first envisioned by Nikola Tesla in 1899 and is now, over a century later, being fully developed.

MHI has taken significant steps towards turning the idea into a working reality – one part of a much broader drive by the company to create innovations and develop technology for the betterment of humankind. By their own admission they are on a ‘quest to contribute to social progress’ in a range of different fields – and environmentally clean energy is one vital cornerstone of this ideal.

Led by the Japan Aerospace Exploration Agency (JAXA), solar power satellites are an area of active research and development in the country. It has a 25 year ‘technology development roadmap’ that culminates in a one gigawatt solar power satellite that can send power back to earth by the 2030’s.

The space solar power system (SSPS) concept first emerged in the US in the 1960s, with Japan beginning on their version in around 2009. MHI, in partnership with the space agency, expects SSPS’s to be the power generation systems of the future.

For this ambition to be realised, Japan will need to deploy a solar collector weighing over 10,000 tons and measuring several km across. Part of the reason why Japan is making these important investments into WPT and SSPS technologies, aside from the country’s long history of being at the forefront of technological innovations and the evident environmental benefits, is that it is not a very resource-rich country and currently has to import significant amounts of fossil fuel.

Technology such as this could significantly reduce this reliance and is also much more reliable than earth-bound solar power – an SSPS system would not encounter reduced efficiency down to varying weather patterns.

In the tests, the reception of power 500m away at the receiver unit, was heralded by the illumination of LED lights, using part of power transmitted. The volume of power transmitted and distance travelled signify new milestones for Japan. The test was also successful in confirming that the control systems used to regulate the direction of the microwave beam worked well.

A spokesperson from JAXA said of the test that “this was the first time anyone has managed to send a high output of nearly 2kW of electricity power via microwaves to a small target, using a delicate directivity control device.”

The method tested by MHI is a far-field technique – otherwise known as ‘power beaming’. A transmitter device connected to a power source beams power by microwave to a receiver device where it is converted back in to electricity.

The concept was first thought of by the famous Nikola Tesla in 1899, with the first significant research being done following World War II after the development of cavity magnetrons – a device that can emit high-power microwaves.

Many years later and WPT is a well-proven technique, with experiments in the tens of kilowatts successfully performed at Goldstone, California in 1975 and Grand Bassin on Reunion Island in 1997.

One of the limitations of transmitting power over such long distances is that, using the method of microwave transmission, in order to ensure accuracy and efficiency, extremely large transmitter and receiver areas are necessary – explaining JAXA’s plans for a 10,000 ton solar satellite to beam the power generated.

Taking human safe power density in to consideration, a 10km diameter area is needed to safely receive and convert roughly 750 MW of power – equivalent to the output of a modern power station.

MHI see the benefits of WPT, once perfected, as wide-ranging. It could be used to transmit power to isolated areas in the wake of natural disaster, or in other hard-to reach areas where it is less practical to use cable connections, for example: the power from offshore wind farms.

In as early as the next ten years MHI see the technology being utilised for applications such as charging electric vehicles, but with such incredible innovations being made in the field of renewable energy, it really does seem as if, technologically, anything is possible in the future of power generation.

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