ABSTRACT

                       Transmission and distribution of 50Hz or 60Hz electrical energy from generation point of to consumer end without any physical wire has yet to mature as a familiar and viable technology. Apart from a few demonstrations or feasibility study the research effort so far on Wireless Power Transmission is adequate. Moreover the reported work have not disclosed any design methodology and this has restricted further advancement in the research on Wireless Power Transmission (WPT). A unified consistent and coherent mathematical model for WPT has been synthesized. The output obtained from the model when applied to a case has been compared against technical specification partially reported in literature by feasibility study of the same case. In addition it is shown that a potential application of wireless power transmission would be in annexing the grid system from radial field to demand site in certain scenarios. Also the specific aspects upon which further research should focus have been identified so that WPT annexure can be viable in the discussed scenarios. The findings are expected to renew interest in WPT among the public in general and among researchers.

              Wireless communication using radio waves is a very familiar topic. However Wireless Power Transmission is yet to be so, though it’s history dates back to late nineteenth century. The year 1888 was marked by the demonstration on Wireless Power Transmission (WPT) of pulsed power generated at 500MHz. Since then a few only a few demonstrations and feasibility study have been published on discrete time intervals. Among these, the most important is a feasibility study reported by a French research group in 1997,a terrestrial WPT Project. The aim of their project was to deliver a 10KW load from a grid system through AC-DC-microwave-DC-AC conversion to a 0.7 Km distant, a small tourist spot across a mountain in La Re Union Island, an oversea territory of France. The project was termed as Grand Bassin WPT Model after the name of tourist village.

           The post-war history of research on free-space power transmission is well documented by Willin C Brown, who was a pioneer of practical microwave power transmission. It was he who first succeeded in demonstrating a microwave-powered helicopter in 1964, using 2.45 GHz in the frequency range of 2.4 - 2.5 GHz reserved for the ISM (Industrial, Scientific and Medical) applications of radio waves. A power conversion device from microwave to DC, called a rectenna, was invented and used for the microwave-powered helicopter.

            An important milestone in the history of microwave power transmission was the three-year study program called the DOE/NASA Satellite Power System Concept Development and Evaluation Program, started in 1977. This program was conducted for the study of the Solar Power Satellite (SPS), which is designed to beam down the electrical bower of 5 to 10 GW from one SPS toward the rectenna site on the ground. The concept of the SPS was first proposed by P. E. Glaser in 1968 to meet both space-based and earth-based power needs. The SPS will generate electric power of the order of several hundreds to thousands of megawatts using photovoltaic cells of sizable area, and will transmit the generated power via a microwave beam to the receiving rectenna site.

         The idea behind microwave power transmission is that solar power satellites (SPS), consisting of panels of solar cells stretching many square kilometers in space, convert the electricity generated from light into radio waves and beam them wirelessly to the earth. If the largest conceivable space power station was built and operated 24 hours a day all year round, it could produce the equivalent output of ten 1 million kilowatt-class nuclear power stations, which is rather impressive, and in 1983 a Japanese team succeeded in a first-ever experiment to transmit microwave energy through the ionosphere using two rockets. In 1995, a team led by Prof. Nobuyuki Kaya of Kobe University managed to transmit electricity from the ground to an airship in the sky. Japanese scientists say that if microwaves carrying electric power can be beamed uniformly over the earth, they could be used as a power supply for mobile devices such as cell phones. The power of the microwaves would have to be weaker than the regulatory standard to prevent any physical harm to people from the electromagnetic rays. The mobile phones now in use require up to approximately 800 milliwatts of power. To receive microwave energy, they would need an antenna about 25-30cm square. As it would not be feasible for a mobile handset to itself serve as the antenna, the options would be to reduce the power consumption or devise a large antenna.
             The fundamentals are already in place, but the Japanese say that the problem with microwave power transmission is the exorbitant cost of constructing an SPS - around 2.4 trillion yen in total as a rough estimate.