Solar Power Transmission
The idea of having a space station that beams down solar energy to earth has been a popular topic in many sci-fi communities, but it may not be fiction for much longer. Officials in the US and Japanese government have begun funding research into the creation of real space-based solar power stations.
In Japan, the space solar power system (SSPS) and the Japan Aerospace Exploration Agency (JAXA) are currently working together with 16 other companies (including Mitsubishi) on a geostationary solar space station. The station would collect the solar energy by way of photovoltaic cells and then transmit this energy to earth via laser or microwave form. This would then be converted into electricity for commercial power grids or stored energy as hydrogen. This space station could potentially transmit one gigawatt of energy to earth – equivalent to the output of a large nuclear plant [Source: Scientific American]. The US, along with the small island nation of Palau, also are working in conjunction to create an orbital solar power station and are planning to erect a “rectifying antenna,” to demonstrate the effectiveness of this technology. The antenna would be 260 feet in diameter and would be set up to collect 1 MW, enough energy to power over 1,000 homes, from a satellite orbiting some 300 miles above [Source: Treehugger].
How it Works
There are three parts to the solar space station:
1. solar cells or heat engines to collect energy
2. microwave or lasers to transmit energy to earth
3. rectennas (rectifying antennas) to collect the energy and distribute the energy on earth.
Most of the countries have opted for photovoltaic cells in order to collect th energy from the sun. One of the greatest advantages of having these cells out in space is that they can collect energy all the time. In space, the sun’s rays are never compromised by clouds or increment weather like on earth. Therefore, these stations can collect 144% more energy than any terrestrial solar panels [Source: Wikipedia]. Of course, there needs to be a a way to transmit this energy wirelessly, since having cables from space to earth is impractical. Japan has opted for laser transmission. The lasers use plates built from a ceramic material containing chromium, which absorbs sunlight and neodymium, which converts it into laser beams. These new lasers outperformed earlier demonstrating a solar-to-laser energy conversion efficiency of 42% [Source: Treehugger]. On the other hand, many other countries have opted for microwave transmission. In fact, with the use of a rectifying antenna, the microwave-to-electricity conversion is about 90% [Source: Wikipedia], making it much more efficient than lasers.
Problems and Solutions
Of course with any new technological advances, there are always downfalls. One of the major downfalls of building a space solar power station is the huge cost and space to make the technology work. With a rough estimation of $21 billion, this could be one of the most expensive alternative energy sources. The money would go towards “thin-film condenser mirrors, solar panels and a microwave transmitter…, as well as a 100-unit laser array of 5,000 metric tons that would be 10 kilometers long” [Source: Scientific American]. While the intial cost is expensive, Suzuki and his colleagues are aiming to produce stable, cheap power and hydrogen at a target price of 6.5 cents per kilowatt-hour, which is in-line with conventional power generation [Source: Scientific American]. And since the space station itself is in space, it will not suffer the effects of weather, making maintenance and upkeep much cheaper.
Of course, because it is in space, there are many extraterrestrial problems like meteroid or space junk collisions that could throw the station off course. This leads into another huge safety problem: stray microwave beams. While in theory 95% of the microwave radiation is directed towards the antenna, if it were to miss or become misdirected, these beams could affect nearby towns. While science says that these beams are 10 mW/cm2 -completely withing the OSHA workplace standard [Source: OSHA] – scientists and developers have introduced a fail-safe beam targeting by using a retrodirective phased array antenna. A “pilot” beam is directed towards the antenna which sets up the phase front. The antenna then compares the pilot beam’s phase front with an internal clock in order to control the phase of the outgoing signal. This centers the beam directly on the rectenna. If the pilot beam is lost for any reason (if the transmitting antenna is turned away from the rectenna, for example) the phase control value fails and the microwave power beam is automatically defocused [Source: Wikipedia].
While there is still a long way to go until the actual station is completed, the Japanese and US government expect a demonstration of the technology to reach completion in three to four years. Should the demonstration go successfully, space-based solar power stations may not be a thing of fiction after all.