A winning submission to the 2014 ExploraVision competition by Sarah Buelow and Henry Homiller
Solar energy is steadily increasing in popularity because it is readily available and plentiful. Individuals use solar energy to power or heat their homes, but do not generate enough electricity to make a significant impact on reducing our dependence on oil and other nonrenewable resources. If solar energy were harnessed properly, it would be possible to power the entire planet. Solar power could be harnessed more efficiently with a space-located orbital generator that allows for the removal of solar refraction and filtration that occurs in Earth’s atmosphere. Satellite systems can be designed to harness solar energy, but without proper extraction methods, the transfer of energy from space to earth is flawed, and impossible. Available technology requires the use of large and impractical rectifying antenna arrays for this task. Our proposed design incorporates 3D meta-material lenses capable of focusing radio waves with extreme precision, thus lowering the size of the array required while increasing the transfer efficiency.
The proposed satellite generator takes advantage of several different existing technologies; the foremost is the photovoltaic panel. Photovoltaic or PV panels are in use already, though their fabrication makes them less practical than they could be. PV arrays are designed to capture the energy of light, particularly from the sun, and generate direct current electricity. The basic principle used is that a semiconductor, such as silicon, when bombarded by a photon, can have one of its electrons ejected, allowing it to flow from atom to atom, and generating electrical power. The semiconductor is typically doped with another element to make it P-type or N-type, based on which charge it will carry. When P-type and N-type panels are put together in an array, they acquire a built-in electric field that guides the loose electrons in one direction, generating direct current. When conductive connections are attached to the apparatus, the electrons can be pushed through an available current path by the field. Other modifications can be made, such as non-reflective coating, to maximize light absorption. The largest downside of PV arrays is that they are still expensive; however, solar power technology is one of the most rapidly growing technologies in the world (Toothman, Alduos).
The second chief technology is the receptor of the energy being transmitted to Earth. The rectifying antenna, or rectenna, has been in use for some time. A normal antenna absorbs an electromagnetic wave, typically a radio wave, and transforms its energy into electricity. The distinguishing feature of this particular antenna is that, rather than a radio antenna, which absorbs the electricity purely for information, the rectenna is attached to a rectifier which turns the AC electricity into DC, for use in charging batteries or otherwise powering mechanisms. The use of radio waves being used to send power wirelessly has been demonstrated on a small scale with relative ease, such as a remote control helicopter, and is a rapidly expanding idea (Zhang, Huang).
Third, a new study in the use of meta-materials provides a way to focus electromagnetic waves using negative refraction, allowing for much more focused applications of this form of energy. Designed by researchers at MIT, a copper-plated structured dish can be 3-D printed and used to focus radio waves, defying what traditionally would be expected from the base shape, using the complex structure of the meta-material (Chu). Lastly, the present knowledge of space and orbital mechanics is necessary in order to place the satellite and maneuver it into a geosynchronous orbit, remaining above the same place on the surface.
History of Solar Energy
Photo credit: Pannon Inipi Creations
Solar energy has been used as far back as the times of the Ancient Greeks, Chinese, and Native Americans, although their methods were very primitive. Mainly, these peoples oriented their buildings toward the sun to warm them, not fully understanding at the time how solar energy worked. These peoples also used mirrors and other reflective surfaces to light torches and fires, and, in second century B.C. Greece, used the reflective properties of bronze shields to defend the city by setting enemy ships on fire. The first known solar-powered mechanical device was a steam engine designed by French engineer Auguste Mouchout in 1866, which began the influx in solar inventions over the next fifty years. Inventors such as John Ericsson, Charles Tellier, and Frank Shuman worked on solar energy methods with irrigation, refrigeration, and locomotives. It was not until many years later, in 1954, when researchers at Bell Laboratories developed what has become the modern edge of solar energy – the photovoltaic cell, which is capable of converting light into electricity (ScienceDaily).
Of course, the photovoltaic effect was originally discovered in 1839 by French scientist Edmond Becquerel while he was experimenting with an electrolytic cell. Over the years, solar power slowly improved. Willoughby Smith discovered the photoconductivity of selenium in 1873, and three years later, William Grylls Adams and Richard Evans Day found that selenium produced electricity when exposed to light. By 1883, American inventor Charles Fritts, described the first ever solar cells made from thin strips of selenium. As time passed on, more and more people discovered or proved different methods to harness solar energy into electricity by expanding on photovoltaic devices and photoelectric effect understandings. Bell Telephone Laboratories in 1954 provided the U.S. with successful solar cells, although the efficiency of these early solar cells was a whopping four percent. Hoffman Electronics worked on improving the efficiency, going from eight percent in 1957, to nine percent in 1958, and eventually ten percent in 1959. A year later that efficiency increased by four percent bringing it up to fourteen percent. NASA also jumped on board with solar technology in 1964, with the launch of the Nimbus spacecraft – a satellite powered by a 470-watt photovoltaic ray. Efficiency and cost continued to improve, making solar cells cheaper, and more efficient as time went on. By 1977, photovoltaic manufacturing exceeded 500 kilowatts. Solar energy was added to aircraft, satellites, vehicles, and buildings, and methods for harnessing solar energy slowly improved into what it is today (U.S. Department of Energy).
Our proposition combines several existing ideas: the use of rectennas for wireless power, the use of solar energy production in orbit, and the study of meta-materials. By adding the technology behind the dish produced by MIT, we believe the idea for a wireless orbital solar generator is now reasonable, where it hasn’t been in the past. This opens up an entire new branch of power generation, which, with further development, could future proof the power industry with fully renewable methods of harvesting unused energy. The full task of the orbital generator is to translate energy from the sun into electricity on Earth. The first step is to capture the photons that make up the light coming from the sun by using conventional photovoltaic arrays, converting the energy into electric energy. This electrical energy would power a radio broadcaster, which would use the meta-material dish to create a focused wave that would travel through the atmosphere, reaching the rectenna array connected to the ground relay station. By keeping the orbital component in a geosynchronous orbit, the radio beam would constantly be focused on the rectenna, maximizing the efficiency of this final, most difficult step. The radio beam would then be transformed back into electric current and submitted to the power grid like any other power station.
The technology, while well on its way, is not quite at the level necessary to make the best use of an orbital solar generator. There are several fields that must be improved first. The study behind solar power is rapidly expanding already, and new, more efficient PV panels are being designed rapidly. Only a short time will need to pass before high efficiency, cheap, and lightweight arrays are available. In addition, the budding science of meta-materials has only just begun, and has no end of room to improve. Better designs than those that currently exist may allow even more precise focusing of radio waves, allowing for an improved efficiency in orbit-to-surface energy transfer, as well as smaller rectenna arrays. The more precise the focusing, the more energy can be successfully transferred, and the less area would be needed both on the ground for the receiving arrays, and in the air as required clear airspace. Along with a more precise electromagnetic broadcast, improvements in orbital control and telemetry will likely be in order. Faster, more accurate commands being sent to the satellite would keep it in the precise position overhead that would be required to be able to process the greatest amount of energy.
Photo credit: green_earth_by_Skivey.jpg
The primary effect of the orbital solar generator would be, of course, generation of solar energy that would be both more efficient and more reliable. Keeping a geosynchronous orbit has the benefit of allowing greater precision and efficiency of energy transfer, but will cause the recurrence of one of the chief problems of solar panels: night time power generation would be nonexistent. However, the time period for which there would be no power would be significantly less than that of a PV array on Earth. The curvature of the Earth as well as computerized rotation and positioning of the panels would allow the satellite to absorb light for a significantly longer period each rotation. This strategy also allows for the precision in the radio wave transfer. By allotting a small area of restricted airspace, the collected energy is made much more reliable, as clouds and weather will have less detrimental effects on the production of energy. The main negative effect would be the potential interference that the radio wave beam might cause in the surrounding area. The focusing nature of the meta-material dish will lower this, but it is impossible to tell at this stage in the development of the technology to what degree the interference would remain.
The power produced over the years of operation of the satellite would make the cost of materials worthwhile, and its lifespan could be greatly increased by use of space shuttle missions for repair and possible upgrade. The new methods of energy production made available would make a step toward cutting back on fossil fuel consumption and lead in to more reliable, sustainable energy.
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Jones, Susan. Solar Power of the Future: New Ways of Turning Sunlight into Energy. New York: Rosen Pub. Group, 2003. Print.
Toothman, Jessika, and Scott Aldous. “How Solar Cells Work.” HowStuffWorks. Discovery, n.d. Web. 11 Nov. 2013. <http://science.howstuffworks.com/environmental/energy/solar-cell.htm>.
Zhang, Jingwei, and Yi Huang. Rectennas for Wireless Energy Harvesting. Rep. University of Liverpool, n.d. Web. 2 Dec. 2013.
“Solar Power.” ScienceDaily. ScienceDaily. 19 Nov. 2013 <http://www.sciencedaily.com/articles/s/solar_power.htm>.
United States. Energy Efficiency and Renewable Energy. Department of Energy. The History of Solar. 2002. U.S. Department of Energy. 3 Dec. 2013 <http://www1.eere.energy.gov/solar/pdfs/solar_timeline.pdf>.
Chu, Jennifer. “New Metamaterial Lens Focuses Radio Waves.” MIT’s News Office. MIT, 14 Nov. 2012. Web. 03 Dec. 2013.
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