Harnessing Space Energy
by Yury Zaitsev
Moscow (RIA Novosti) Jan 12, 2009
European Union leaders agreed during the Brussels summit on global warming, to cut 1990 levels of carbon dioxide emissions 20% by 2020. However, some researchers theorize that global warming is ending and that world temperatures will cool in the foreseeable future.
Naturally, this does not mean that the world must scrap programs for cutting toxic emissions into the atmosphere. Humankind will face an environmental disaster if the volume of harmful substances continues to increase.
Although alternative sources of energy, now generating only 1-2% of all power worldwide, could solve the problem, even industrial countries are in no hurry to use them.
This can be explained by a number of factors. Alternative-energy sources are expensive. Traditional energy giants which do not want to lose their profits are pressuring governments not to implement them. It is also believed that our conservative society would find it hard to adapt to a new lifestyle.
Nevertheless, we cannot do without alternative energy sources. Only 0.0125% of solar-radiation energy could meet global energy demand, while 0.5% could solve many long-term energy problems.
The so-called external photo-effect, or external photo-emission, when light quantums hit materials and generate electrons is the simplest power-generation concept. In 1930, Soviet physicists from the Leningrad-based Physical Technical Institute used this method to generate electricity for the first time in history.
Although sulfur-helium solar batteries used at the time had an efficiency of less than 1%, more advanced solar batteries with 10% efficiency were developed by the mid-1970s. Their efficiency was raised to 15% by the mid-1990s and reached 20% at the turn of the century. This was made possible by streamlining silicon production from quartzites, the main solar-battery element. Incidentally, Russia abounds in super-pure quartzite.
Five years ago, the Dubna-based Joint Institute for Nuclear Research near Moscow displayed a solar battery with 50% efficiency. Scientists called their brainchild the Star Battery using nanotechnologies to facilitate the effectiveness of well-known processes.
A 0.5-mm thick silicon film is injected with tiny gold particles. The properties of this precious metal alter efficiency so much that two, rather than five or six, photons of light can now generate one electron. This method has clear practical applications: One square meter of a solar battery can now generate about 600 Watts; and its capacity can be boosted to one kWt.
Scientists from Dubna have made a super-condenser using the same substance. A cylinder with a diameter of three-centimeters can store 900 times more power than a car battery. This is important because solar power plants only operate during the day, while power is needed round the clock and must therefore accumulated inside high-capacity batteries.
The first commercial solar power plant was commissioned in 1985 near the town of Shchelkino in the Crimea in the Soviet Union and had a peak load of 5 mWt, or just as much as the world's first nuclear reactor. But the costly and inefficient power plant had to be shut down in the mid-1990s, as on Earth it could not work to full capacity. Consequently, we must consider building such power plants in outer space.
The Presidium of the Soviet Academy of Sciences discussed this issue soon after Yury Gagarin's trailblazing space flight in April 1961 and said it deserved every attention. In the years that followed, experts started designing numerous space-based solar power plants, especially during the global energy crisis of the mid-1970s.
But all of them had to be placed into geostationary orbits, specifically geosynchronous orbit directly above the Earth's equator (0 degrees latitude), approximately 36,000 km above sea level and with a period equal to the Earth's rotational period. Although these orbits are the most efficient routes for transmitting electricity back to Earth, there are not many parking places left, with numerous satellites launched by many countries, whose operation could be disrupted by such power plants. Moreover, it costs $35,000-50,000 to orbit one kilogram of geostationary payload. Any solar power plant would only recoup itself if launch costs are reduced to $100-200 per kilogram of payload.
Technically speaking, Russia would prefer a sun-synchronous orbit - a geocentric orbit combines altitude and inclination in such a way that an object on that orbit passes over any given point on the Earth's surface at the same local solar time. When launched, a solar power plant would have an apogee of 40,000 km above the North Pole, while its 500-km perigee would be located 500 km over the South Pole.
The power plant would transmit electricity eight hours a day to the most power-strapped northern Russian regions, while its batteries would accumulate electricity during another four hours.
The Keldysh Research Center's experts have come up with a concept for building low-orbit power plants that would transmit electricity to Earth. They estimate that 10 to 30 solar power plants could be built by 2020-2030. Each power plant would consist of ten 15-mWt modules. Under optimistic scenarios, up to 800 power plants could be orbited by 2050-2100.
Apart from the photo effect, there are other methods for converting solar radiation into electricity. This includes the thermodynamic method for converting solar energy into heat energy. A solar-radiation concentrator is focused on a heat absorber, which subsequently builds heats. Its working medium, namely, gas, oil or any other liquid, begins to boil, turns into steam and starts rotating the turbine that generates electricity. The efficiency of such method could reach 40% and more.
However, the use of metal-intensive systems, such as turbines, radiators and electric generators, increases power-plant weight.
They could convert electricity into UHF beams with frequencies ranging between one millimeter and one meter and transmit them back to Earth. In that case, not more than 2% of power would be lost in the atmosphere. The narrower laser beams generated and received by small units could also transmit power to the planetary surface. However, atmospheric laser-ray absorption could reduce power-transmission efficiency.
It would become necessary to develop an impressive array of vehicle-assembly buildings, aerospace transport systems and orbital tugs for delivering solar power plant components to their working orbits. In fact, this is the same mind-boggling task as the creation of orbital solar power plants themselves.
Russian scientists also suggest other scenarios for solving power-supply problems with the help of up-to-date space technology. There are plans to develop space platforms with solar reflectors for illuminating polar regions and opencast mines, for increasing crop yield, etc. Such reflectors would illuminate 30-km sectors for several hours before sunrise and after dusk any place in the world.
Japan and the United States are also developing orbital power plants. Tokyo wants to orbit a power plant by 2020, while Washington hopes to do the same at an earlier date.
In the next few decades, the space power industry will become a rapidly developing global economic sector and will eventually cost as much as conventional power plants on Planet Earth.
Yury Zaitsev is an academic adviser with the Russian Academy of Engineering Sciences.
See also Portable Solar Power and Earth4Energy.
Solar Space
Researchers at Rensselaer Polytechnic Institute have discovered and demonstrated a new method for overcoming two major hurdles facing solar energy. By developing a new antireflective coating that boosts the amount of sunlight captured by solar panels and allows those panels to absorb the entire solar spectrum from nearly any angle, the research team has moved academia and industry closer to realizing high-efficiency, cost-effective solar power.
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