Energy beams: Market for long-distance wireless transmission of power not yet viable

Tesla cars are named after the Serbian-American entrepreneur Nikola Tesla, born in 1856 in western Croatia. He was a prodigious inventor, filing over 300 patents, despite not completing a university degree. He is best known for his work on alternating current (AC) electricity, including induction motors and transmission systems.

He initially worked with telegraph technology in Budapest, and then in Paris with the first electric lighting systems from the Edison company. In 1884, he moved to New York with Edison before resigning the following year to found his own start-up.

Edison used direct current (DC) electricity at relatively low voltages. Tesla’s AC system used fluctuating current and was licensed by Tesla to the Westinghouse company.

Tesla and Edison publicly clashed in the late 1880s in the “war of the currents”. Tesla showed that only his AC system was capable of using high voltages for efficient long-distance power. Edison countered that Tesla’s high voltages were dangerous, with grotesque demonstrations of the electrocution of animals. Ultimately, both Tesla and Edison lost control of their respective companies. The industry moved through consolidation to adopt AC as the preferred technology for long-distance transmission over cables.

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Tesla also invented wireless transmission of electric power by induction. His solution is now routinely used to recharge consumer devices such as toothbrushes and watches. Placing the device on its wireless cradle recharges it without having to plug it in.

Inductive recharging is beginning to be used for electric cars and even buses. A vehicle’s battery is recharged simply by parking over a special mat, without any cable. A number of demonstrations in Italy, Sweden, Germany and Israel have even trialled recharging moving vehicles, by driving over a length of road embedded with inductive pads.

Tesla believed that electricity could be transmitted wirelessly not just a few centimetres, but over long distances and potentially worldwide. He successfully demonstrated illuminating light bulbs by simply connecting them to the Earth’s crust, wirelessly powered by a generating transmitter several kilometres away. His solution was, however, not viable because of incorrect assumptions about the conductance of the Earth. His approach was also highly inefficient. Large amounts of power were simply dissipated, because power was “broadcast” in all directions rather than being steered towards only those devices intended to receive it.

However, if Tesla’s vision could be implemented, we would no longer have the need for electric pylons and towers, and the cables strung between them or expensively buried underground. While existing national grid infrastructures might be replaced over time, new networks could extend current power grids. One application would be to transmit power from offshore turbines directly to shore, without having to lay undersea cables. Another would be to rapidly bring up an electric grid in an area devastated by natural disaster or war.

The US army and navy have experimented with wireless power using point-to-point microwave beams. The “Scope-M” project conducted last year successfully transmitted 1.6kWatts over a distance of about a kilometre, with 95 per cent efficiency.

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There are also a small number of wireless power start-ups. Powerlight, near Seattle, is trialling high-intensity laser beams. Viviz Technologies in Texas experimented with “Zenneck” electric waves that can propagate across the Earth’s surface, but then went bankrupt last year. Perhaps the most promising is a New Zealand start-up, Emrod, which uses high-frequency microwaves as in the Scope-M initiative.

Emrod has trialled a small system with New Zealand’s second-largest power company and successfully transmitted 2kWatts of power over a couple of hundred metres, in various weather conditions, with 97 per cent efficiency of the beam. They also trialled with Airbus and the European Space Agency, for beaming energy from space-based solar panels.

As with Edison’s challenges to Tesla and his AC system, one of the major challenges of microwave wireless power is convincing the public that the technology approach is safe. Emrod claims to follow applicable industry standards. The microwave beam is concentrated, an invisible cable in the air, rather than a broadcast system that transmits signals in every direction. Their system is designed to detect threats that could interrupt the beam – such as birds or drones – and temporarily pause.

Emrod’s promoters maintain that their approach can readily be scaled up in both power and distance, using relay lens stations to periodically refocus the beam. Nevertheless, existing high-voltage transmission lines can each carry several hundred MWatt or more, a hundred thousand times as much power as the current microwave beam prototypes. Emrod plans further trials of a scaled-up solution next year and in 2025.

The potential market for safe, long-distance wireless transmission of power is extremely attractive. However, practical commercial systems have yet to be demonstrated and it may yet be some time before Tesla’s vision is accomplished.