What we mean by wireless energy transmission, is the possibility of transferring energy from one object to another, without the two bodies being connected with wires or other materials, that could establish a physical contact.From a first sight, it can be difficult to imagine a concrete application of this theory in our everyday life, but if we take into consideration different technological fields, that are closely related to our everyday life, we will quickly find out that this form of energy transmission is far more widespread than you might be thinking.
Nowadays, the most exploited physical phenomena to transfer energy from one point to another, without using traditional metal conductors, are the electromagnetic field (https://en.wikipedia.org/wiki/Electromagnetic_field) and the light in the form of a laser beam (https://en.wikipedia.org/wiki/Laser).
In a few words, the first phenomenon is the result of the movement of electric charges, such as electrons, which flow within a conductor, while the laser is the result of a process of concentration of various light beams in one, that is technically defined as the collimate. Since in this case, the light is not dispersed at all, its energy remains bounded in a very small space, that will follow the same direction of the laser.
Practically, the ability of electric charges to produce electromagnetic fields when moving, is exploited to induce electron movements, i.e. electric current, in devices located far from the source. Induction charging devices, such as cell phone batteries as well as, wireless charging devices, could represent the perfect example of this theory.
Even if these products aren’t particularly common yet, are deeply appreciated for the various advantages they offer compared to traditional power cables. First of all, you do not risk with the passing of time, to damage the connections between the device and the source of energy, as the device recharges without any physical contact. Secondly, the technology used to implement such a system, which is not that innovative, is basically very simple and cheap.
Limits of inductive charging
The main limit of this physical phenomenon is the impossibility of transmitting energy at distances greater than a few centimeters. Increasing the distance, even by very little, would require a very large amount of energy, resulting very expensive for an everyday usage.
What about the laser?
The problem described above, doesn’t affect at all the laser, which by its nature, is able to cover theoretically, unlimited distances. However, the laser today is not that popular for transferring energy remotely. In fact, whenever the laser beam passes through the atmosphere, that is full of water vapor, the beam losses its energy, that is progressively absorbed by the particles it encounters along its way. If the earth wasn’t cover of clouds, theoretically, it would be possible to transfer energy from one point in the space to the earth’s surface, without any problems. This possibility was in fact experimented in various physics experimental centers, to understand the actual technical feasibility of this project, involving the implementation of large photovoltaic geostationary plants, able to transmit the generated energy to a terrestrial receiving apparatus. But if we look at our reality, there are existing applications that exploit the laser properties mainly for transmitting information between two distant points, as it largely happens for instance, with computer optical devices.
The idea of transferring energy from a source in the space to the earth’s surface – exploiting the sun light radiation, being enormously more intense since is not filtered by the atmosphere – has not been abandoned yet. That’s why, this remains a subject of study and experimentation in various institutions around the world.
Experiments of wireless energy transmission
In March 2015, several experiments of wireless energy transmission have been carried out in Japan.
Instead of using the laser, that as it has been mentioned above, loses power when passing through water vapor, microwaves (https://en.wikipedia.org/wiki/Microwave) have been used. Exactly as it happens in millions of microwave ovens, the energy produced by the main device, the magnetron, is sent to the food to be heated in the form of an alternating electric field, with a frequency equal to 2,45 GHz. The Japanese Mitsubishi research center, is working on the component that directs the energy from the magnetron to the food, the so called waveguide. They are trying to obtain, on a larger scale, a concentrated and highly adjustable energy beam.
Experiments carried out until today, have allowed to transfer through microwaves, an output energy equal to 10 kW at a distance of about 500 meters. The objective of these tests is to find alternative solutions to the limits of the laser, since microwaves are less affected by the problem of losing energy by the absorption of water vapor.
What about installing a photovoltaic system in the space?
If we want to go back to the idea of installing a photovoltaic system in the space, as we have previously mentioned, it should be a geostationary structure for transmitting energy on a regular basis to the ground, and it should be positioned at an altitude of about 36,000 km from the earth’s surface. This distance, if covered by a microwave beam, requires a receiving apparatus on the ground of about 3 Km of magnitude. Always assuming that, one day we might be able to cover a similar distance with accurate microwaves, there will always be a problem. The problem is due to the low efficiency of the waves, while they are converting into electrical energy, as well as from the low performance of the hypothetical photovoltaic system mounted in the space, that should convert solar energy into electric energy.
Another interesting application, which could exploit microwaves to transmit energy at a certain distance, regards the power transmission system from offshore wind farms to the mainland. Today the limits of this wind renewable energy production technology, is that wind farms cannot be moved too far away from the coast, due the huge costs associated with the wiring work of sea cables, as well as for the energy losses this process would entail.