Of the billions of points of light burning in the distance, the nearest bears down on our tiny planet from only eight light minutes.
Bound to us by nothing but gravity and an intervening black void, once above the confines of our own atmosphere, the sun is a startling revelation. Sunlight can easily turn the surface of our dusty moon from gunpowder gray into a blindingly bright sphere. Although such reflected visible radiation represents only a fraction of our own star's massive power, the question is: How do we best harness such energy?
Our own star essentially represents one gargantuan energy well. It outputs some 27 trillion times the amount of all the commercial power currently produced on Earth. In fact, a one kilometer-wide band surrounding our planet receives nearly as much energy annually as the energy potential of the world's remaining, recoverable oil reserves. That's partly because sunlight in space packs 35 percent more energy than sunlight that is filtered through earth's atmosphere.
Researchers and science fiction authors have been kicking around the idea of harnessing such solar power in space for decades but to little effect. To date, the International Space Station — with the largest solar collecting array ever installed by humans in space — only produces energy for its own consumption.
Even though the technology to make space solar power a reality has arguably existed for decades, much of the world is still mired in fossil fuel technologies. As a result, humankind only produces the continual equivalent of some 5 terawatts (or 5,000 gigawatts) of electricity a year. In contrast, when in full operation, the average nuclear plant produces about a gigawatt of electric power in the same period.
But to make matters even worse, a billion or so of the world's 6.5 billion people consume half the planet's available electricity, at an average wholesale rate of 6 to 7 cents per kilowatt electric hour. (Meanwhile, another billion or so have no access to electricity at all.)
By 2050, Earth's population is expected to hit 10 billion. If it is to prosper, and if all its citizens are to be served more equally, it will need a continual projected flow of 20 terawatts of electricity.
Pie in the Sky
Space solar power could make up a lot of this energy shortfall, but the concept needs a Madison Avenue makeover. One of its biggest hurdles remains the perception that it is either a technological pipedream or is untenably expensive in absolute terms or relative even to other renewable resources.
"Space solar power faces enormous — and probably insurmountable — technical and economic challenges," said Steven Fetter, a physicist at the University of Maryland in College Park. "The largest solar arrays placed in space — the solar arrays for the International Space Station — cost $2,500 per watt-peak, 500 times more than solar arrays on Earth." (A watt-peak is a solar photovoltaic cell's maximum output under test conditions.)
Fetter also notes that this cost per watt-peak did not include the space station's launch costs. He concludes that space-based solar cannot compete with ground-based solar energy alternatives, even if launch costs are zero.
Policy analyst Jeff Kueter, president of the George C. Marshall Institute in Washington, D.C., is also pessimistic about current space solar prospects. Kueter says that space solar energy is one of many long-term alternative energy possibilities that need to be investigated. But like Fetter, he is adamant that neither space solar's economics nor the current state of its technology are mature enough to make it a viable energy alternative.
Fetter's own point about space solar launch costs is not without merit. Today, launch costs to place a 5,000-kilogram communications satellite into geostationary orbit can easily top $100 million. Space solar energy satellites would typically be 20 times larger.
In 1973, Glaser patented the first design for a space solar power satellite.
His basic concept involves arrays of kilometer-sized on-orbit satellites that first gather the sun's energy with the most efficient photovoltaic systems yet built. These arrays then convert that energy into a microwave beams that are fired at ground-based circular receiving stations — essentially arrays of dipole antennas (or rectennas) 10 to 15 kilometers in diameter.
The incoming microwave energy then could be re-beamed to other points via wireless power transmission, then rectified into plain vanilla electricity that feeds into the existing electrical grid, or even used to manufacture synthetic hydrocarbon fuels.
With the 1973-74 Arab Oil Embargo as a prod, both the U.S. Department of Energy and NASA studied the space solar concept. In 1975, a 30 kilowatt-microwave beam transmitted from a distance of 1 mile energized an array of lights at NASA's Goldstone Deep Space Communications Complex in California's Mojave Desert. The receiving antenna converted the microwaves directly into electricity with an efficiency of better than 80 percent.
By the end of the 1970s, NASA and the DOE jointly proposed placing dozens of gigawatt-level space solar satellites into geosynchronous orbit. The idea was deemed economically unfeasible, with top-end cost estimates ranging into the trillions. And so the idea largely languished until recently.
Then last year, a U.S. and Japanese team successfully transmitted a microwave beam at low power between Maui and ground-based receivers on the Big Island of Hawaii. The microwave beam traveled some 90 miles, or almost a hundred times further than NASA's three-decade-old Goldstone test.
Glaser, now a retired aerospace engineer, recently commented that he felt that sooner or later space solar power would not only see daylight but prove very useful on a global scale.
Time For a Commercial (Application)
Still, there has been no commercial space-to-ground demonstration of microwave beaming. But that should soon change.
This past April, Pacific Gas and Electric signed the world's first space solar power purchase agreement. Beginning in 2016, Solaren Corporation, a space solar power startup based in Manhattan Beach, Calif., will provide PG&E with 200 megawatts of space solar power per hour, or some 1,700 gigawatt/hours (GWh) per year.
That's significant, since one GWh roughly equals a sixth of Los Angeles' peak electric demand.
With a solar photovoltaic collecting array of an estimated kilometer in size, the satellite will use solar concentrators to focus sunlight onto a photovoltaic array. Energy from the photovoltaic array will then be converted into a radio frequency signal using solid-state power amplifiers. From there, it then forms a beam that can be transmitted to the ground.
Located in a rural part of Fresno County, Calif., the PG&E/Solaren rectenna will be hooked into an onsite substation that will gather up the solar electricity and adjust voltages at a so-called "delivery point." However, from the time the space solar power enters the PG&E system, the California utility projects that this new space electricity's 2016 wholesale price will be some 12.9 cents per kilowatt.
"Utilities are notoriously conservative, so we had to convince PG&E that we knew what we were doing," said Solaren's CEO Gary Spirnak. He refuses to give an exact cost for the project, except that it will be in the billions of dollars. And PG&E has only contracted to pay for energy it actually receives and none of the start-up costs.
Those costs will be huge. Spirnak, a former spacecraft project manager with the U.S. Air Force who later worked for both Hughes and Boeing, notes that Solaren will launch its estimated 100,000-kilogram geosynchronous space solar satellite in sections. This will require some three to four launches from Cape Canaveral; based on current launch cost estimates, the financial burden of launching such hefty payloads into geostationary Earth orbit would easily range into the hundreds of millions
Spirnak said many previous space solar designs planned on moving gigawatts of electricity over many kilometers in space, and so wiring would make up a third of their system's weight. In contrast, his own team patented a design that alleviates such heavy on-orbit wiring, making the whole system significantly lighter.
A possible competitor, Space Energy, an international space solar startup with offices in Switzerland and Canada, hopes to reduce its costs at the launch pad. This might be achieved by using more economical ways of accessing space, perhaps with the SpaceX Falcon 9 rocket (a new reusable commercial launcher). Space Energy already has some $10 million in seed capital, but is at least a couple of years away from building hardware for its projects.
Amaresh Kollipara, Space Energy's chief strategy officer, said plans call for a $180 to $280 million demonstrator satellite to be launched into low Earth orbit within two years of the venture being funded.
Before 2025, Kollipara and colleagues would like to see their first phase of operation fully implemented — that is, the on-orbit robotic construction of a space solar satellite stretching over several square kilometers. It would likely be divided into separate nodes that would either be linked physically or via laser transmissions.
Space Energy's current plan is to use such a platform to beam one gigawatt of microwave energy to the ground.
"There's no way we are going to displace other forms of electricity," Kollipara said. "Space solar will simply be one energy option. But Space Energy's potential target markets would be China, India, portions of western Europe and niche regions of the U.S."
Kollipara estimates the startup's end-to-end cost per kilowatt-hour will be some 15 to 25 cents. That's more expensive than power generated from hydroelectric and coal-burning plants, he said, but is on par with costs of terrestrial solar power and wind energy.
Although Kollipara is optimistic about bringing solar power to the masses, he believes that Space Energy could possibly partner first with the U.S. Department of Defense in an effort to find a less dangerous and more efficient way to deliver electricity to combat zones.
As Lt. Col. Paul Damphousse of the U.S. Marine Corps, and the chief of advanced concepts for the National Security Space Office in Washington, D.C., acknowledges, it's pretty difficult to move energy around a theater of war.
In Iraq, for example, electricity is still being generated by costly diesel fuel, at a price of some $10 per kilowatt electric hour. Meanwhile, large numbers of troops have been killed or wounded while protecting convoys transporting that diesel fuel. A fixed forward base equipped with space solar rectennas could save lives, money and might give the war fighters — or even the nation-builders — a competitive advantage.
A U.S. Department of Defense space solar power project, with an estimated top-end budget in the hundreds of millions, could also help the U.S. project what Damphousse terms "soft power."
"It's no real stretch to equate energy security with national security," Damphousse said. "Overpopulation and scarcity of resources translates into conflicts. So, we are not only in the business of war fighting; we are in the business of war prevention."
To that end, he said, a 2,500-kilogram space solar power satellite could see launch within the next five years.
In addition, space solar technology may provide a solution for developing nations that have both a need for energy and telecommunications but lack infrastructure.
"Once deployed, I doubt you would ever build a conventional communications satellite again," said James Mankins, a former NASA technologist and co-founder of the Virginia-based Managed Energy Technologies. "You would piggyback communications of all kinds around the edges of the power beamer. You could provide gigabits-per-second bandwidth at a bargain-basement price."
When the beams do finally hit the rectennas, these targeted developing nations could "leapfrog the infrastructure" by using ground-based wireless power transmission for both electricity and telecommunications.
"This is going to put a revenue-generating capability in space like nothing before," said Spirnak, who envisions follow-on benefits to include both easier access to space and a new emphasis on missions to the moon and Mars.
New Kind of Moonbeams
But why bother building satellites to capture solar radiation when in the eyes of at least one researcher the moon could act as a perfect collecting platform.
David Criswell, a physicist at the University of Houston, said we've already got a big satellite — a really big one. "The full moon represents 13,000 terawatts of reflected sunlight," said Criswell. "Tap a few percent of that, and you've got 20 terawatts, enough to power a prosperous world."
Unlike Earth, the moon has almost no atmosphere to block the full punch of the sun's radiation. So, why not use the lunar surface as one big solar collector and beam a portion of that energy back to Earth? Plus, Criswell said that the moon's silicon and metal content easily lend itself to making glass and fiberglass for the collecting equipment on site, drastically reducing costs — a good thing, given the projected costs, which are nothing short of astronomical.
Even so, the global benefits of such an economically challenging energy source arguably more than make up for the financial risks.
The first lunar solar power demonstrator project would involve arrays of solar converters, a microwave reflector and transmitter, mobile factory assembly units; and a habitat/manufacturing facility.
All the machinery would be operated from Earth using lunar robots and set up in staged deployments. However, lunar-workers (i.e. astronauts) would be on site for maintenance of the machinery and industrial research and development.
One scenario would involve pairs of solar collecting stations some 30 to 100 kilometers across, on the lunar nearside. With the exception of a new moon or a full lunar eclipse, this would ensure that one or the other would always receive sunlight.
Like power lines emerging from a generating station, solar-generated microwaves would be beamed back in power increments ranging from hundreds of megawatts to tens of gigawatts. Earth-orbiting microwave beam-redirecting satellites would then enable 24/7 power delivery to Earth-based rectennas.
And, in the process of powering Earth, the LSP could also energize small cities on the moon; or transmit power to drive electric ion propulsion engines on lunar space tugs operating between low Earth orbit and low lunar orbit. Eventually, high-frequency lunar solar power beaming stations could even transmit power to ion propulsion space tugs operating as far out as Jupiter.
Once Criswell's lunar project hits the "break even" point at an estimated $400 billion, he expects it to then start paying for itself.
"With its Apollo lunar missions, NASA has essentially been on a bunch of camping expeditions," Criswell said. "But if this lunar space power project were done with the intensity of the Apollo program, we'd be back on the moon within 10 years. And by 2050, we could have the entire world powered."
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