Auckland-based New Zealand-based Emrod recently embarked on an experimental attempt to develop a tele-power model. It is a technology that has so far found specific applications in the space and military fields, but has never yet produced commercial alternatives to traditional public energy infrastructures. The attempt is considered important and valuable due to the implications – both in benefits and risks – related to a possible future large-scale use of a similar model of wireless power transfer (WPT).
Emrod worked with the support of the New Zealand government and in collaboration with the national distributor Powerco to design a prototype for use in a closed test facility. In a separate project it is carrying out a series of tests to direct electricity from a photovoltaic park on the North Island to a customer located several kilometers away.
Emrod's goal is to expand a wireless power transmission system where this is preferable or where conventional transmission and distribution systems via cable or other physical means cannot be exploited. Other companies such as Japan's Mitsubishi Heavy Industries and Singapore-based TransferFi are working on similar energy transfer projects using different technologies.
The model underlying the Emrod project is not new: energy is converted into electromagnetic radiation by a transmitting antenna, picked up by a receiving antenna and then distributed locally by conventional means. It is something similar to what happens in common radio systems, but in that case the amount of energy required to make the signal potentially usable is quite low. In fact, very little energy can be transferred to a single receiver, hence the need to use a signal amplifier in most audio systems. And also, in radio systems, the signal is distributed in all directions.
The idea of transmitting electrical energy through the air by creating a magnetic field between physically separate circuits was already the basis of many innovative experiments conducted in the second half of the nineteenth century by the inventor, physicist and engineer Nikola Tesla. The Tesla coil (or “resonant transformer”) was a device capable of producing alternating current electricity between resonant coupled electrical circuits, in systems operating at short distances. Tesla himself was however convinced that he could use this technology to develop long-range wireless energy.
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In Emrod's experimental project, energy is transmitted as a narrow beam of microwaves, in a targeted manner. This would allow us to overcome two fundamental limitations in Tesla's plan. One is how to charge people for the costs of an electricity that in theory they could simply collect from the air. The other is imposed by the very characteristics of the propagation of the energy flow of a wave in space, which is drastically reduced even at short distances from the source. Transmitting energy in a narrow beam rather than radiating it in all directions could partially solve these dispersion problems.
In the past, experiments related to wireless energy transfer have been successfully conducted for military applications and for use in space. A record still in force was set by NASA in 1975, when 34 kW of electrical power was supplied over a distance of 1.55 kilometers via microwaves at a frequency of 2.38 GHz. In its first attempts, Emrod will transmit “a few kilowatts” along a distance of 1.8 kilometers, and then progressively increase both distance and power. The expected final efficiency for this system is 60 percent, according to company founder Greg Kushnir, who believes it is a margin sufficient to make this system already commercially sensible today, in circumstances and places where the installation of traditional lines electric would be more expensive.
In addition to the system power source and the transmitting antenna, the Emrod model includes two other essential components. One is the antenna used at destination to convert microwaves into direct current, a type known with the name “rectenna” (contraction of rectifying antenna) and with a shape quite different from the classic antennas. To improve its efficiency, it will be built using “metamaterials”, composite materials containing small quantities of conductive metals.
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The other component is the relays, arranged to deflect the microwave beam to direct it to the rectenna. Relays – from the French relais, “relay” – are generally used to regulate electrical systems based on some variations in the circuits. A relay system, to understand, is the one that usually allows you to turn on the same light by activating buttons placed in different positions in the house. In the Emrod system the relays function as “lenses” necessary to refocus the microwave beam with minimal transmission losses. They can also redirect it if necessary, which means that the transmitter and receiver do not need to be in line of sight with each other.
There are risks involved in using this experimental wireless energy transfer technology. According to the company, a brief accidental exposure to microwave beams, given the relatively low energy density, should cause no harm to either people or animals. But to avoid the possibility of accidents, Emrod has nevertheless developed a coverage of the rays by means of special “laser curtains” arranged along the circuit. They should detect any interposition of birds or helicopters at low altitudes and temporarily and instantly stop the transmission of microwaves. The energy would be supplied even during the interruption thanks to the storage batteries placed at the receiving end.
