Published on March 11, 2014
Presented by: • D.ADHARVANA • IV ECE 10F81A0461 • GOKULA KRISHNA COLLEGE OF ENGINEERING • AP
This paper reports on the futuristic advances in power transmission through microwave. A Space Power Satellite (SPS) orbiting round the earth traps solar energy and generates electric power using photovoltaic cells of sizable area. SPS transmits the generated power via a microwave beam to the receiving Rectenna site on earth. A RECTENNA (RECtifying anTENNA) comprises of a mesh of dipoles and diodes for absorbing microwave energy from a transmitter and converts it into electric power. We can in fact directly convert solar energy into electrical energy with the use of solar cells, but this process will be affected by day/night cycles,weather, and seasons. We are aware of the fact that light is an electromagnetic wave. Light rays never diffuse in space & if by any means these rays can be transmitted from space to earth then it will be a perfect solution for our desired need of 24 hrs power supplies. This paper presents the concept & evolution of satellite power system, SPS2000 (a research work by ISAS) and the impact of Microwave Power Transmission (MPT) on space plasma. In near future conventional power sources cannot meet total power demand, for which SPS is a best solution.
WIRELESS POWER TRANSMISSION SYSTEM(WPT) BACKGROUND TECHNICAL SEESION ON SPS BASIC STRUCTURE OF SOLAR POWER SATELLITE TYPES OF WPT SOLAR ENERGY CONVERSION SPACE CRAFT SIZING LEO INSTEAD OF GEO EARTH BASED INFRA STRUCTURE(RECTENNA) SPS 2000 CONFIGURATION OF SPECTANNA ADVANTAGES FUTURE SCOPE
o 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.Tesla's objective was to develop the technology for transmitting electricity to anywhere in the world without wires. He filed several patents describing wireless power transmitters and receivers. However, his knowledge of electrical phenomena was largely empirical and he did not achieve his objective of WPT, although he was awarded the patent for wireless radio in 1940. o The development of WPT was not effectively pursued until the 1960s when the U.S. Air Force funded the development of a microwave-powered helicopter platform. A successful demonstration of a microwave beam- riding helicopter was performed in 1965. This demonstration proved that a WPT system could be constructed and that effective microwave generators and receivers could be developed for efficient conversion of microwaves into DC electricity. o The growing interest in solar energy conversion methods and solar energy applications in the 1960s and the limitations for producing cost-effective base load. power caused by adverse weather conditions and diurnal changes led to the solar power satellite concept in 1968 as a means to convert solar energy with solar cell arrays into electricity and feed it to a microwave generator forming part of a planar, phased-array antenna. o In geosynchronous orbit, the antenna 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.
The first technical session on solar power satellites (SPS) was held in 1970 at the International Microwave Power Institute Symposium at which representatives of Japan, European countries, and the former Soviet Union were present. Based on preliminary studies, a plan for an SPS program was prepared by an NSF/NASA panel in 1972 and the first feasibility study of SPS was completed for NASA/Lewis Research Center in 1974. Shortly after the "oil shock" of October 1973, Japan staned to implement the Sunshine Plan to develop renewable energy sources. Japan's Plan included, as a long term objective, the development of SPS. Back in the U.S. in 1975, a successful demonstration of microwave wireless power transmissions was performed at the NASA Deep Space Antenna facility at Goldstone, California. In this demonstration of point-to-point WPT, 30 kW of microwaves were beamed over a distance of one mile to a receiving antenna. Microwaves were converted directly into DC at an average efficiency of 82%, confounding critics who claimed that such high conversion efficiencies could not be achieved.
The concept of the Solar Power Satellite (SPS) is very simple. It is a gigantic satellite designed as an electric power plant orbiting in the Geostationary Earth Orbit (GEO) as shown in Fig. 1. and fig 2. It consists of mainly three segments. 1) Solar energy collector to convert the solar energy into DC (direct current) electricity 2) DC-to-microwave converter, 3) Large antenna array to beam the microwave power to the ground. The solar collector can be either photovoltaic cells or a solar thermal turbine. Fig. 1 Solar collectors
The DC-to-microwave converter of the SPS can be either a microwave tube system or a semiconductor system, or their combination. The third segment is a gigantic antenna array. The SPS system has that advantage of producing electricity with much higher efficiency than a photovoltaic system on the ground. Since SPS is placed in space in GEO, there is no atmospheric absorption, the solar input power is about 30% higher density than the ground solar power density, and power is available 24 hours a day without being affected by weather conditions. It is confirmed that the eclipses would not cause a problem on a grid because their occurrences are precisely predictable.
Two types of WPT: 1) Ground based power transmission 2) Space based power transmission But Space-based power transmission is preferred over Ground-based power transmission. Ground is (obviously) cheaper per noontime watt, but: • Space gets full power 24 hours a day .3X or more Watt-hours per day per peak watt .No storage required for nighttime power • Space gets full power 7 days a week – no cloudy days • Space gets full power 52 weeks a year – No long winter nights, no storms, no cloudy seasons • Space delivers power where it’s needed – Best ground solar sites (deserts) are rarely near users • Space takes up less, well, space – Rectennas are 1/3 to 1/10 the area of ground arrays – Rectennas can share land with farming or other uses
Two basic methods of converting sunlight to electricity have been studied: photovoltaic (PV) conversion, and solar dynamic (SD) conversion. Most analyses of solar power satellites have focused on photovoltaic conversion (commonly known as “solar cells”). Photovoltaic conversion uses semiconductor cells (e.g., silicon or gallium arsenide) to directly convert photons into electrical power via a quantum mechanical mechanism. Photovoltaic cells are not perfect in practice, as material purity and processing issues during production affect performance; each has been progressively improved for some decades. Some new, thin-film approaches are less efficient (about 20% vs. 35% for best in class in each case), but are much less expensive and generally lighter. In an SPS implementation, photovoltaic cells will likely be rather different from the glass-pane protected solar cell panels familiar to many from current terrestrial use, since they will be optimized for weight, and will be designed to be tolerant to the space radiation environment, but will not need to be encapsulated against corrosion by the elements. They may not require the structural support required for terrestrial use, where the considerable gravity loading imposes structural requirements on terrestrial implementations.
The size of an SPS will be dominated by two factors. The size of the collecting apparatus (e.g. panels, mirrors, etc) and the size of the transmitting antenna which in part depends on the distance to the receiving antenna. The distance from Earth to geostationary orbit (22,300miles, 35,700 km), the chosen wavelength of the microwaves, and the laws of physics, specifically the Rayleigh Criterion or Diffraction limit, used in standard RF (Radiofrequency) antenna design will all be factors. It has been suggested that, for best efficiency, the satellite antenna should be circular and the microwave wavelength should be about 1 kilometers in diameter or larger; the ground antenna (rectenna) should be elliptical, 10 km wide, and a length that makes the rectenna appear circular. Smaller antennas would result in increased losses to diffraction/side lobes. For the desired (23mW/cm²) microwave intensity these antennas could transfer between 5and 10 gigawatts of power. To be most cost effective, the system should operate at maximum capacity. And, to collect and convert that much power, the satellite would require between 50 and 100 square kilometers of collector area (if readily available ~14% efficient monocrystalline silicon solarcells were deployed). State of the art (currently, quite expensive, triple junction gallium arsenide) solar cells with a maximum efficiency of 40.7% could reduce the necessary collector area by two thirds, but would not necessarily give overall lower costs for various reasons.
A collection of LEO (Low Earth Orbit) space power stations has been proposed as a precursor to GEO (Geostationary Orbit) space power beaming systems. There would be advantages • much shorter energy transmission path lengths allowing smaller antenna sizes • lower cost to orbit • energy delivery to much of the Earth's surface. • assuming appropriate antennas are available, etc. Ultimately, because full engineering feasibility studies have not been conducted, it is not known whether this approach would be an improvement over a GEO installation. Fig. 4 Solar power satellite
RECTifying anTENNA rectifies received microwaves into DC current. A rectenna comprises of a mesh of dipoles and diodes for absorbing microwave energy from a transmitter and converting it into electric power. Its elements are usually arranged in a mesh pattern, giving it a distinct appearance from most antenna. A simple rectenna can be constructed from a Schottky diode placed between antenna dipoles as shown in Fig. 1. The diode rectifies the current induced in the antenna by the microwaves. Rectenna are highly efficient at converting microwave energy to electricity. In laboratory environments, efficiencies above 90% have been observed with regularity. In future rectennas will be used to generate large-scale power from microwave beams delivered from orbiting SPS satellites.
SPS2000 is a model of solar power satellites with microwave power output of 10 MW, which was proposed by the SPS working group of the Institute of Space and Astronautically Science (ISAS). The primary objective of SPS2000 research is to show whether SPS could be realized with the present technology and to find out technical problems.
The general configuration of SPS2000 has the shape like a triangular prism as shown in Figure 2. The power transmission antenna, spacetenna, is built on the bottom surface facing to the earth, and the other two surfaces are used to deploy the solar panels. SPS2000 moves on an equatorial LEO at an altitude of 1100km. A frequency of 2.45 GHz is assigned to transmit power to the earth. SPS2000 can serve exclusively the equatorial zone, especially benefiting geographically isolated lands in developing nations.
The Spacetenna has a square shape whose dimension is 132 meters by 132 meters and which is regularly filled with 1936 segments of sub array. The sub array is considered to be a unit of phase control and also a square shape whose edges are 3 meters. It contains 1320 units of cavity-backed slot antenna element and DC-RF circuit. Therefore, there will be about 2.6 million antenna elements in the spacetenna. The spacetenna is composed of pilot signal receiving antennas followed by detectors finding out the location of the rectenna on the earth, power transmission antenna elements and phase control systems. The left and right hand sides in Fig.4 correspond to parts of power transmission and direction detection, respectively. The antenna elements receiving the pilot signal have a polarization perpendicular to the antenna elements used in the power transmission so as to reduce effectively interactions between both antenna elements.
The SPS concept is attractive because space has several major advantages over the Earth's surface for the collection of solar power. The SPS would be used in 24hrs in all seasons This characteristic of SPS based power generation systems to avoid the expensive storage facilities. A SPS will have non polluting consequences of fossil fuel systems, nor the ecological problems resulting from many renewable or low impact power generation systems Economically, an SPS deployment project would create many new jobs and contract opportunities for industry. Space solar power would be the only means of acquiring direct solar energy to supplement the burning of fossil fuels or nuclear energy sources under the most extreme conditions of a global catastrophic volcanic winter
1. To store electricity during off peak demand hours. 2. The frequency of beamed radiation is planned to be at 2.45 GHz and this frequency is used by communication satellites also. 3. Minimizing the entire size as it will be massive. 4. To reduce high initial cost and time for construction 5. Reduce radiation hazards associated with the system.
In the future Rectenna stands as a milestone among non conventional energy resources. This technology is more reliable than ground based solar power. In order for SPS to become a reality several things have to happen: oCheaper launch prices oInvolvement of the private sector The economic case for a solar power satellite is most compelling if it can generate power that sells at peak, rather than average, price. Several new designs for solar power satellites were considered, in an attempt to maximize the amount of power produced at peak rates. This study has given researchers a remarkable insight into uncertain future of development of power from space.
1.Presented by: • D.ADHARVANA • IV ECE 10F81A0461 • GOKULA KRISHNA COLLEGE OF ENGINEERING • AP . 2. This paper reports on the futuristic advances ...
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