Fukushima Legacy Pt. I: Japan Plans Mankind's First Solar Farm
May 8, 2014 4:39 PM
(Source: Toho Films)
Or maybe it's just building Sol
In the 1980s, Japanese youth were delighted by the science fiction fantasy of Akira. While mostly Earth-bound, the novel briefly touched on a technology made by Japan for World War III dubbed the satellite orbital laser (SOL) platform.
I. JAXA Dreams of Solar Power Satellites (SPS)
Now that fiction appears to be creeping closer to reality, albeit in more peaceful form (or so Japan says).
The pie... err sun in the sky idea is one of the proposals Japan is eyeing in hopes of replacing its nuclear power facilities without bankrupting the nation. Prior to
the March 2011 tsunami
, Japan generated 31 percent of its electricity via nuclear power.
But in the aftermath of
Fukushima Daiichi's (Fukushima I) disastrous partial meltdown
three reactor units
, Japan is
eyeing a flight from nuclear power
, apparently in acknowledgement that
its utilities are too incompetent or corrupt
easily avoidable disasters
the Fukushima debacle
Nov. 2011: In Tokyo, protesters march in opposition of nuclear power. [Image Source: AP]
But it has no significant remaining fossil fuel deposits, so it is currently focused on alternative energy power generating schemes such as offshore wind and solar power.
By far the wildest of these plans is a government plan which involves putting large arrays of concentrating mirrors in orbit, converting the solar energy to microwave power, and beaming that power to Earth in a fiery beam.
The Japan Aerospace Exploration Agency
(JAXA) has released a proposal calling for a space-based solar power station. The plan calls for construction of a 100-kilowatt demo unit to begin by 2020. That would be followed 2 Megawatt and 200 Megawatt semi-commercial scale units in the 2020s and 2030s. The final goal is to have a working 1 Gigawatt demo unit actively producing power by 2040.
The 2 km x 2 km central solar panel unit would break the record for largest manmade satellite set by the International Space Station which is 1/10th of a km long. [Image Source: John MacNeill]
It probably goes without saying that such a scheme is unprecedented outside the world of science fiction, although the
Pentagon as recently as 2008 made similar, but more ambiguous calls for space-based solar power development
. If completed in that timeframe, the power system could revolutionize the way mankind consumes power, potentially taking a place
alongside fusion power
as a driver of the future global economy.
There is some cause to take the JAXA plan seriously. Japan was the
first nation to successfully deploy a space sail
-- an exotic form of solar propulsion that was popularized by American technologists and science fiction writers. The sail worked, and propelled a small satellite.
For Japan, which is
suffering a crisis of declining population
, being the first to implement such a crucial technology could provide economic salvation. But conversely if the project slips from its impressive roadmap and/or proves a costly boondoggle, it could be a further burden on a back of a nation that expects its working age population to fall in half over the next 90 years.
II. Roots of Satellite Solar Were Made in the USA
While Japan wants to make Tokyo the space solar power capital of the world, the roots of this technology lie in a pair of American innovators.
American aerospace engineer
was the first to propose that a solar power satellite (SPS) system with power transmission could be a viable power generation scheme.
Peter Glaser (far left on the left image; left on the right image) is the American forefather of satellite solar. [Image Source: MIT Lib. (L); NSS.org (R)]
Among the benefits he outlined in
a 1968 paper
-- the first on the topic -- were that space-based solar would be immune to weather-based outages (with the right transmission technology), would be subject to much stronger solar rays, and would take up far less land area.
The original design for a solar power satellite, published by Peter Glaser. [Image Source: Science]
In the 1960s, the
U.S. National Aeronautics and Space Administration
(NASA) and a top defense contractor, Raytheon Comp. (
), began toying with wireless power harvesting and the idea of space-based solar collection. Raytheon built a helicopter capable of flying on microwave power, which it demoed in 1964. By 1975, an end-to-end conversion efficiency of 54% was demonstrated.
But ultimately the project was deemed too costly and shelved. At the time the state of global solar panel and electronics was to nascent to make the project a financially compelling alternative to ground based solutions like wind turbines.
Today the progress of technology -- via
ever more efficient solar panel efficiencies
parabolic generation technologies
-- may be sufficient to make SPS finally worth doing.
III. Microwaves -- the Key to Solar When the "Sun Don't Shine"
And researchers think they finally have the answer to a decades old question of what transmission technology to use. For decades a high power laser beam -- which would have a short wavelength in the 1-µm range -- was considered a leading candidate, but it was eventually cast aside as water vapor molecules in clouds would block it.
Instead, researchers turned to perhaps the oldest well-researched
wireless electric power transmission technology -- microwave generation
. Nikola Tesla in 1901 began building the 57-foot Wardenclyffe tower to transmit electricity via microwaves to airships in the New York City airspace. The tower was housed on Shoreham, a town in New York’s Long Island.
The scheme might have worked, but in beginning in 1903 Tesla suffered a string of financial setbacks that ultimate scuttled the 57-foot tower. First, principle funder J. P. Morgan (cofounder of J.P. Morgan Chase & Comp. (
)) abandoned the project, after finding out that Mr. Tesla was really planning to use it for wireless power transmission (it's advertised purpose that he sold Mr. Morgan and other investors on was providing media and telephone signal transmission).
At the same time several of Tesla's key patents expired, drastically reducing the royalty income that he had been using to fund his research.
Wardenclyffe Tower was demolished, but its legacy lives on. [Image Source: The Oatmeal]
Tesla ultimately lost ownership of the tower and its wireless power transmission technology was never finished. During World War I the tower was wiped off the island on orders of the U.S. government, who reportedly feared it would be used a spotting landmark for German submarines. Today the tower site is
home to a new museum
But Tesla's microwave power transmission technology has provided JAXA designers with a way of skirting weather issues.
IV. The World's Biggest Manmade Satellite
The orbital SPS system would transmit microwave power down to Earth in a beam with a wavelength between 5 and 10 centimeters. At such a wavelength the beam would be able to penetrate clouds, ensuring continuous power access.
The signal would likely operate in the 1-10 Gigahertz range given the advantages in antenna size and minimization of atmospheric attenuation. The question is what bands in this region are applicable under the internationally agreed upon so-called "ISM" (industrial, scientific, and medical) band. The 2.45 and 5.8 GHz bands are
. The higher the frequency the smaller the antenna, so JAXA researchers are primarily targeting the 5.8 GHz band.
If the station uses the 5.8 GHz band, its antennas would likely be smaller than the 2.4 GHz Wi-Fi antennas. [Image Source: Internet Routers Blog]
Under the current plan, a two-sided 2 kilometer x 2 kilometer frame with over 11 million 0.6 meter x 0.6 meter panels would be used. These panels would be deployed with high efficiency thin film solar cells on the top, hooked up to phase controllers and power management systems. Each panel would produce around 400 watts of power. The bottom of the panel is dubbed the "rectenna". It features power amplifiers and hundreds of tiny Gigahertz antennas. Scientists are aiming to produce prototypes capable of producing 350 watts of power (an 87.5 percent conversion efficiency on that end).
When it comes to the amplifiers used to create the microwaves to beam to Earth, researchers are examining two possibilities --
(e.g. magnetrons, klystrons, or traveling wave tubes) and semiconductor amplifiers.
Vacuum tubes are one possibility for driving the amps. [Image Source: Classix Audio]
The latter is cheaper and more established, but limited at around 70 percent efficiency (still pretty good). Semiconductor amplifiers are still pretty expensive, but they can reach higher efficiencies and they are dropping relatively quickly in cost.
Alternatively, the finished station could make use of up to 100 million 10-watt GaN semiconductor amplifier chips. [Image Source: GaN Systems]
New amplifying circuits based on exotic semiconductors such as
are showing great promise. The plan could use as many as 100 million 10-watt semiconductor amplifiers, if that approach is adopted.
V. Gravity Gradient Stabilization and Retrodirective Beam Control Prove Crucial
Scientists are proposing a simpler early design that leverages the laws of physics to avoid using fuel. The downside to this approach is that the panel would be stuck in a static angle incident the sun, an angle that at times would be less efficient. To remedy this, JAXA hopes to later add large concentrating mirrors that orient themselves around the panel, directing sun at optimal angles onto it.
The first step -- the static panel -- includes a 10 kilometer long tethering electrical cable would link the massive panel to a smaller electronics control unit in higher orbit. That unit would coordinate the satellite and the ground receiver. During power transmission the ground station would beam up a pilot signal, and the rectenna would respond by tuning its antenna using a technology known as retrodirective beam control.
The idea of retrodirective beam control is that the satellite will likely not be precisely aligned with the ground station given the centrifugal and gravitation forces tugging it back and forth. By detecting the pilot signal, the control electronics of the rectenna will determine the phase across its face. It will then use this to produce a waveform optimized signal to beam down to Earth, allowing for more precise, on-the-fly directional targeting of the receiver site. Panels would be arranged in 2x2 groupings to allow for adjustment.
The station will eventually be supplemented with parabolic concentrators. [Image Source: JAXA]
The brains of the rectenna’s tuning also serve a vital second purpose. It would also act as a counterweight, in a sort of tug of war between the Earth's centrifugal force and the gravity on the lower panel satellite. This technique is known as
gravity gradient stabilization
and it would allow the satellite to ditch its active attitude-control system, saving millions of dollars in fuel costs.
The signal would be beamed down to a small manmade island in Tokyo Bay. The island would be covered with roughly 5 billion rectifying antennas, which would convert the microwave power to DC current. An AC-to-DC converter would then transform the DC current to alternating current and send it via submarine cable to shore.
The receiver station will be built on a manmade island in Tokyo Harbor. [Image Source: JAXA]
Key objectives for the ground unit will be design efficient antennas to harvest the microwave energy as DC current and perfecting the art of the pilot signal. In laboratory experiments, researchers have achieved up to 80 percent efficiency at such wavelengths for a transmitter/receiver scheme. JAXA is aiming for something near that by the time the technology is fully commercialized.
VI. Parabolic Mirrors, Formation Flying
Eventually Japan would look to deploy helper parabolic mirror panels that would perform formation flying, concentrating power on the panel and increasing its efficiency. Anyone who's played the game
Dead Space 2
will get the basic concept here as the fictional Titan space station used a similar scheme, which acts as an in-game puzzle.
JAXA Professor Emeritus Susumu Sasaki in a post to IEEE Spectrum
Space agencies have some experience with formation flying, most notably in the docking maneuvers performed at the International Space Station, but coordinating a formation flight involving kilometer-scale structures is a big step from today’s docking procedures.
We would also have to make several other breakthroughs before this advanced type of SPS could be built. We’d need very light materials for the mirror structures to allow for the formation flight, as well as extremely high-voltage power transmission cables that could channel the power from the solar panels to the transmission unit with minimal resistive losses. Such technologies would take years to develop, so if one or more nations do embark on a long-term project to exploit space-based solar power, they may employ a two-phase program that begins with the basic model while researchers work on the technologies that will allow for next-generation systems.
is a hot topic in space exploration right now, but he's right, coordinating kilometer-size concentrators would be daunting task.
Whichever scheme is adopted, the plan is to place the satellite(s) in geosynchronous (GEO) orbit 36,000 km above the Earth. This would place them in the same orbit as most communications satellites, and allow for a steady, predictable, and stable orbit.
One side note -- many may be concerned about the health risks of the microwave power solution -- particularly given how much negligence the Japanese power industry showed in the Fukushima incident.
Mr. Susumu does a good job clarifying this. He points out that at the center of the beam the radiation levels will only be 1 kW/m^2. While that's above the
regulatory threshold of 10 W/m^2
, it's not even powerful enough to heat your coffee, must less roast man or beast, he explains.
The beam wouldn't even be powerful enough to heat coffee, so with basic protective equipment it should be safe for maintenance workers. [Image Source: StrangeCosmos]
Simple protective equipment should be sufficient to protect workers. By 2 km from the site, radiation levels will have dropped to within the regulatory thresholds.
VII. JAXA's Space Solar Roadmap
The roadmap of the trial is already coalescing:
Microwave power transmission is performed
Signal is sent 150 km (Earth-to-Earth) from Maui to the main Hawaiian Island.
Private, non-JAXA related, but of use to prove concept
Sponsored by the Discovery Channel
Filmed as part of a special
Led by NASA researcher
Sent 20 watts of power, produced by Maui solar panels
Received less an 1 microwatt (< 0.000005% efficient), but did receive some power
Earthbound testing of microwave beams with retrodirectional beam control
Expected to be dramatically more efficient
50 meter transmission tests
1600 watts with be sent via a 4-panel test unit
350 watts will be received (21.9% efficient)
Implemented by JAXA and
Japan Space Systems
Low earth orbit (LEO) testing using a space-based SPS demo unit
Will confirm or deny JAXA's hope that the
's charged high-energy particles (atmospheric plasma) won't intefere with the beam
Will also be used to gauge and mitigate any interference with ground based electronics
Begin construction on artificial island in Tokyo Bay to act a reception site
Construct and launch a 100 kilowatt semi-commercial test unit.
Construct 2 Megawatt and 20 Megawatt semi-commercial test units
Potentially construct more coastal receiver islands
Improve efficiency of satellite components
Build and launch a 1 Gigawatt-capable single-panel solution
Mr. Susumu acknowledges that the project is complex and its goals seem almost impossible. But with great risk, comes great reward, he says, remarking:
It would be difficult and expensive, but the payoff would be immense, and not just in economic terms. Throughout human history, the introduction of each new energy source—beginning with firewood, and moving on through coal, oil, gas, and nuclear power—has caused a revolution in our way of living. If humanity truly embraces space-based solar power, a ring of satellites in orbit could provide nearly unlimited energy, ending the biggest conflicts over Earth’s energy resources. As we place more of the machinery of daily life in space, we’ll begin to create a prosperous and peaceful civilization beyond Earth’s surface.
All eyes will be on Japan, particularly in 2018 and 2020 when it starts to test these technologies in space. If it succeeds mankind may have punched its ticket to nearly free power from the Sun.
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