China is hoping to develop wireless energy transmission technology to power its high-speed trains and subways, in what it anticipates will be a world first.
Wireless energy transfer was an early dream in the field of electrical research, as demonstrated by the legendary inventor Nikola Tesla as early as 1891. However, technical issues and safety concerns have limited its applications to small devices such as mobile phone chargers and medical implants.
Today, at least two proposals for the construction of a rail line with a wireless power supply are under review by the Chinese central government. If the proposed technical solutions are considered feasible, a large national research project will be launched next year.
Scientists working on the projects are confronted with technological challenges that will not be surmounted easily or quickly. Among them is the fact that, while it is currently possible to transmit energy without wires, it is not very efficient, especially at high levels and long distances. China has the world's longest high-speed rail network, covering more than 11,000 km as of the end of last year.
There are also non-technical issues, including the high cost of the investment and strong opposition from both passengers and neighbours of the rail line, who fear high levels of radiation.
As the Chinese government is trying to promote its high-speed technology and rolling stock to other countries, wireless power transmission would enhance their export competitiveness. Overhead power lines that serve trains at present require frequent maintenance due to bad weather and rapid wear and tear. Trains themselves also require maintenance, and the expensive pantographs - the apparatuses mounted on carriage roofs that collect power through contact with the overhead transmission wires - must be replaced every few months. Furthermore, train delays come most frequently from physical breakages or electrical short-circuiting at the contact point. All of this adds significantly to operating costs. Chinese scientists are aiming at developing a system of power transmission that would require little maintenance and could function properly in almost any weather, including floods.
The race to develop this technology in Asia is tight. South Korean scientists, for example, are building a 1 MW experimental line but its capacity is still too low to be practical.
Government support is critical to develop such projects and overcome all the technical challenges. Upgrading an existing rail line with wireless technology would require massive investments and railways operators might stick with overhead wires due to budget concerns.