REFERENCES</li></li></ul><li>INTRODUCTION<br /><ul><li> Solar power captured on the Earth is familiar to all. However, an alternative approach to exploiting solar power is to capture it in space and convey it to the Earth by wireless means.
Unlike systems for the terrestrial capture of solar, a space-based system would not be limited by the boundaries of the day-night cycle.</li></li></ul><li><ul><li>Space Solar Power (SSP) provides a source that is virtually carbon-free and sustainable.
The power-collecting platforms would most likely operate in geosynchronous orbit where they would be illuminated 24 hours a day
Wireless power transmission via solar power satellites promises the brighter, eco friendly future. </li></li></ul><li>IMPORTANT MILESTONES<br /><ul><li>Construction of a tower for WPT on Long Island, New York, in the early 1900s.
1968: Dr .Peter Glaser introduced the idea of a large solar power satellite system with square miles of solar collectors in high geo synchronous orbit
1973: Dr. Peter Glaser was granted U.S. patent number 3,781,647 for his method of transmitting power over long distances
1994: The United States Air Force conducted the Advanced Photovoltaic Experiment using a satellite launched into low Earth orbit by a Pegasus rocket
1998: Japan's space agency starts a program for developing a Space Solar Power System (SSPS), which continues to the present day</li></li></ul><li><ul><li>1999: NASA's Space Solar Power Exploratory Research and Technology program (SERT see section below) program begun
2001: Power Sat Corporation founded by William Maness
2001: NASDA (Japan's national space agency) announced plans to perform additional research and prototyping by launching an experimental satellite with 10 kilowatts and 1 megawatt of power
2009: Japan announced plans to orbit solar power satellites that will transmit energy back to earth via microwaves. They hope to have the first prototype orbiting by 2030
2010: "Analysis of Electromagnetic Wireless Systems for Solar Power Transmission" at the 2010 IEEE International Symposium on Antennas and Propagation</li></li></ul><li>Working model of Japanese Space Solar Power Plant SPS2000 in Sagamihara, Japan.<br />
DESIGN<br /><ul><li>LEO satellite: Approx. 1000Km altitude to reduce launch costs and to minimize size of transmitting antenna.
There are several advantages to SPS<br /><ul><li>Solar radiation can be more efficiently collected in space, where it is roughly three times stronger than on the surface of the Earth and it can be collected 24 hours per day
SPS does not use up valuable surface area on the Earth and can be beamed to areas with the highest demand at any particular time</li></li></ul><li>Four basic steps involved in the conversion of solar energy to electricity and delivery <br />Capture solar energy in space and convert it to electricity<br />Transform the electricity to radio frequency energy and transmit it to Earth<br />Receive the radio frequency energy on Earth and convert it back to electricity<br />Provide the electricity to the utility grid<br />
WIRELESS POWER TRANSMISSION (WPT) BACKGROUND<br /><ul><li> The vision of achieving WPT on a global scale was proposed over 100 years ago when Nikola Tesla first started experiments with WPT, culminating with the construction of a tower for WPT on Long Island, New York, in the early 1900s.
Recent studies indicate that collection and transmission of power from space could become an economically viable means of exploiting solar power within the next couple of decades</li></li></ul><li>INTRODUCTION TO LARGE SPS<br /><ul><li>Since 1967, Solar Power Satellites (SPS) have proposed to collect solar energy in</li></ul> space and beam it down to the Earth. With the energy crisis of the early 1970's, SPS was seriously considered as an alternative to producing electric power from fossil fuels<br /><ul><li>With worldwide demand for electric power increasing as well as concern growing over urban smog and the greenhouse effect, SPS is again attracting mainstream interest.</li></li></ul><li>Possible power generation of 5 to 10 gigawatts<br />“If the largest conceivable space power station were 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. This may lead to the eradication of Nuclear hazards and Global nuclear wastes.”<br />
TRANSMISSION<br /><ul><li>Solar power from the satellite is sent to Earth using a microwave transmitter.
The transmission is through space and atmosphere and received on earth by a huge antenna called the rectenna.
Recent developments suggest the usage of recently developed solid state lasers allow efficient transfer of power.
In comparison to laser transmission microwave transmission is more developed, has high efficiency up to 85%</li></li></ul><li>Microwave transmission is more developed, has high efficiency up to 85%, beams is far below the lethal levels of concentration even for a prolonged exposure. The microwave transmission designed has the power level well below the international safety standard (Frequency 2.45 GHz microwave beam)<br /> Efficiency of WPT systems is the ratio of energy flow, which is intercepted by receiving antenna to the whole radiating energy.<br />
For receiving these transmitted waves rectennas are set up at the Earth. An antenna comprising a mesh of dipoles and diodes for absorbing microwave energy from a transmitter and converting it into electric power.<br />Microwaves are received with about 85% efficiency and 95% of the beam will fall on the rectenna but the rectenna is around 5km across . Currently there are two different design types being looked at- Wire mesh reflector and Magic carpet. <br />
CHALLENGES<br /><ul><li>In geosynchronous orbit, the transmitter would direct a microwave beam of very low power density precisely to one or more receiving antennas at desired locations on Earth.
At a receiving antenna, the microwave energy would be safely and very efficiently reconvened into electricity and then transmitted to users.
Resolving or reducing significant uncertainties associated with microwave radiation effects and SPS design considerations</li></li></ul><li>Motivation towards improved technology and economic benefits<br />Proper agreement about SPS paths<br />Large no. of satellites would take up large section of space<br />Would require a network of satellites , this would require global co-operation among countries<br />
ADVANTAGES<br /><ul><li>Space gets full power 24 hours a day
Sunlight captured in space is many times more effective in providing continuous base load power compared to a solar array on the Earth
Geosynchronous satellites would take up large sections of space</li></li></ul><li><ul><li>Interference with communication satellites
The large scale of Space Solar Power will require international financing
Technology for an efficient wireless power transfer is still in the evolving stage
More expensive than Earth-based solar power and other energy sources now . </li></li></ul><li>EVOLVING WPT MARKETS<br /><ul><li>Roadway powered electric vehicles for charging electric batteries –Microwave generators
Solar power satellites in low-Earth or geosynchronous orbit or on the Moon to supply terrestrial power demands on a global scale.
High-altitude, long-endurance aircraft maintained at a desired location for weeks or months at 20 km for communications and surveillance instead of satellites, at greatly reduced costs.
Power is transmitted from distant sites to geosynchronous orbit and then reflected to a receiver on Earth in a desired location very economically without overhead lines.
Charging of mobile appliances may be easier through this mode of power transfer from earth stations</li></li></ul><li>CONCLUSION<br />There is little doubt that the supply of energy must be increased dramatically in coming decades. <br />Space Solar Power may seem futuristic at present, it is technologically feasible and, given appropriate conditions, can become economically viable. <br />WPT efficiency may be improved by using special current discontinuous distribution on the antenna. <br />
SPS is still more expensive than Earth-based solar power and other energy sources. Yet, even now, a small SPS system could be economically justified to provide otherwise unavailable emergency power for natural disaster situations, urban blackouts and satellite power failures<br />Wireless power transmission is still being considered as a next-generation power transmission system for the future<br />
REFERENCES<br />IEEE International Symposium on Antennas and Propagation, April 20, 2010<br />World Energy Council, "Energy for Tomorrow’s World - Acting Now", WEC Statement 2000, www.worldenergy.org.<br />WEC/IIASA, Global Energy Perspectives, Nakicenovic, Nebojsa, et al, Cambridge University Press, 1998.<br />