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In Depth

Space-based solar farms power up

About the author

Emmet writes about robotics and space. Editor-At-Large for Robotics Business Review's "Robots and the Law" and a regular contributor to Space Quarterly magazine. His work has also appeared in The Economist, Wired News, Red Herring, and Robotics Trends.

SBSP concept (Copyright: Mark Elwood, SpaceWorks Enterprises, Inc.)

(Copyright: Mark Elwood, SpaceWorks Enterprises, Inc.)

It would solve our energy needs overnight. But with huge technological and financial challenges, can space-based solar power ever take off?

“Ex-Nasa scientist seeks visionary billionaire to help change the world.  High risk venture. Return not guaranteed. GSOH a plus.”

John Mankins, the scientist in question, has not yet reached the point of placing a classified ad, but it could soon be an option. The 25-year veteran of the US space agency is the man behind a project called SPS-Alpha, which aims to loft tens of thousands of lightweight, inflatable modules into space. Once there, they will be assembled into a huge bell-shaped structure that will use mirrors to concentrate energy from the sun onto solar panels. The collected energy would then be beamed down to ground stations on Earth using microwaves, providing unlimited, clean energy and overnight reducing our reliance on polluting fossil fuels. The snag? It is unproven technology and he estimates it will take at least $15bn- $20bn to get his project off the ground.

Mankins initially had research funding from an advanced concepts arm at Nasa, but that money dried up in September 2012; hence his continuing search for a benefactor.

“I can't think of a better solution than to find somebody who is very wealthy, very visionary and willing to make this happen,” he says.

But not everyone shares Mankins' optimism. Space-based solar power (SBSP) is a topic that divides the scientific world into extremes. On one side are people like Mankins who believe it is the only solution to our ever increasing energy demands, whilst on the other is a sizeable chunk of the scientific community who believe any money put into solar power should remain firmly on the ground.

High times

SBSP has its roots in the 1941 short story Reason, by Isaac Asimov, which depicts a space station – run by robots – collecting energy from the sun to distribute to Earth and other planets. No further thought was given to the idea until the late 1960s, when aerospace engineer Peter Glaser began to investigate its potential. In the following decades, various concepts were put forward but none took off. At the same time Nasa and the US Department of Energy also became involved, funding bits and pieces of research and commissioning reports into its feasibility. Most of these concluded that SBSP was too “high risk” and too costly.

But in recent years, SBSP has once again begun to attract attention with projects emerging in the US, Russia, China, India and Japan, amongst others. All are driven by increasing energy demands, soaring oil and gas prices, a desire to find clean alternatives to fossil fuels and by a burgeoning commercial space industry that promises to lower the cost of entry into space and spur on a host of new industries.

“SBSP is the ultimate energy source for the world and eventually it's going to replace nearly everything else,” says Ralph Nansen of US-based advocacy group Solar High, with some of the characteristic hyperbole that defines both sides of the SBSP debate. “I don't think there's any doubt that within the next century we will be getting the majority of our power from space. It's just a question of when.”

Nansen is calling for the US government to invest in SBSP research and development as a matter of urgency. 

“England dominated the world economy during the industrial revolution because of coal. The United States dominated the world economy after the discovery of oil in Brownsville, Texas in 1901. I'm confident that whoever develops SBSP will have a similarly dominant position in the world economy,” he says.

Nansen, like other SBSP advocates, contends that instead of building huge solar farms on the surface of the Earth, which are at the mercy of fluctuating weather conditions and the cycle of day and night, mankind should fly a little closer to the sun. Specifically, they advocate building solar farms in geostationary orbit 35,800km (22,000 miles) above the Earth's surface. There, sunlight has an intensity of 1,347 Watts per metre squared - about 30% more intense than on the Earth's surface, meaning greater electricity production. And depending on its orbital position, an SBSP system could harness direct sunlight almost the entire year round, unlike terrestrial solar farms.

Of course, it is all well and good to collect the solar energy in space, but you still need to get it back to Earth. And since hooking a very, very long cable up to a 5 km (3.1 miles)-wide solar farm in space is not practical, most designs envisage wirelessly transferring the energy back via a concentrated microwave or laser beam to a huge receiving antenna (or “rectenna”) spread over several kilometres on Earth.

‘Kill it off’

All of which sounds simple. But two important issues need to be addressed if SBSP is ever to become reality - concerns about the efficiency of wireless power transmission (WPT) and the sheer cost of such ventures.

Even the most “cursory analysis” of SBSP shows that the advantages gained by moving the solar array into space is “not even nearly comparable” to the additional cost of operating in space and transmitting power back to Earth, says radio scientist Prof William A. Coles of UCSD's Jacobs School of Engineering. “No space-based power system would survive a cost-benefit analysis,” he says.

But the rise in the commercial space industry has given SBSP advocates new hope for changing the economic equation. A 2011 report by the International Academy of Astronautics (IAA) found that SBSP could be commercially viable within 30 years, driven in part by the rise of private space companies.

Two names crop up with regularity in discussions about SBSP and commercial space: Planetary Resources –the wannabe asteroid mining company launched earlier this year - and SpaceX, the first commercial space firm to send a cargo to the ISS, founded by South African tech billionaire Elon Musk. If just one of these firms – which have already shown they see the potential return on taking on high risk projects in space – can be persuaded to focus its attention on SBSP, the technology has a fighting chance, advocates say. 

They point to the falling costs of launching things into space.  It currently costs around $20,000/kg ($10,000/lb) to launch anything into orbit. To send a rig that could be several kilometers across and weigh several thousand tons sets a price tag starting in the billions of dollars. And that is before you have had to assemble the solar panels, an operation that would likely take at least as much skill as assembling the International Space Station – a project that has a price tag of around $100bn.

But Musk has talked openly about how his company plans to build reusable launch vehicles and slash the cost of launching into space to $1,100/kg ($500/lb) or even lower, making the prospect of building giant structures in space seem a less fanciful notion. However, any SBSP firms hoping the entrepreneur may put his financial muscle – as well as his rocket systems – at their disposal may be in for a shock. Musk has previously been hostile towards the idea of SBSP, once saying “stab that bloody thing in the heart” to suggest the idea should be killed off once and for all. SpaceX declined our request for an interview.

Budding entrepreneurs may find more enthusiasm from Planetary Resources co-founder Eric Anderson, who sees its potential, but has no immediate plans to invest in SBSP research or development. 

“The only way to get solar energy that is truly plentiful, reliable, and available from anywhere is through SBSP, but the set-up costs are exorbitant,” he says. However, commercially-funded SBSP might take off if it is initially used to deliver power to markets and locations that are “insensitive to price,” such as military positions, disaster scenes, and search and rescue operations, he adds.

“You may pay an exorbitant fee relative to what you would pay from the grid but in the midst of a natural disaster, for example, you don't care about prices. That's how SBSP is going to start,” he says.

Then, once the concept is proven, market forces will take over, he predicts.

“Once the inherent advantages of space come through, SBSP will be ubiquitous, in terms of Earth getting its energy from space. But it will probably take decades,” says Anderson, albeit with one important proviso: “If the Japanese, the Russians, or the US work out how to harness [nuclear] fusion energy, I think that would certainly be equally, if not more, attractive.”

Beam me… down

Fusion energy has famously always been “50 years away”, as each experiment throws up new technological challenges. But it is perhaps better news for SBSP – at least on paper.

A series of reports over recent decades by agencies like Nasa and the National Security Space Office (NSSO) have largely concluded that – whilst expensive - there is no major technological barrier to getting SBSP off the ground. For example, solar cells are now a well understood technology that is only getting cheaper and more capable, increasing efficiency from 10 to 40% over the last four decades. New lightweight materials – including graphene and advanced polymers – have been developed. And, whilst many view the ISS as a cash cow soaking up millions of dollars of tax payers money, it has certainly taught us a thing or two about working in space and, crucially, assembling large structures up there. In addition, robotics – crucial for maintenance and perhaps the assembly of these solar plants – have come on leaps and bounds, driven by ever more sophisticated electronics and computing power.

However, there is still a crucial part of the system that needs attention: the wireless energy transmission. Although it sounds like a fanciful technology, wireless energy transfer has a long history. It was first being demonstrated in 1893 by inventor Nikola Tesla when he managed to wirelessly illuminate vacuum tubes by exploiting a phenomenon known as electrical resonance. Tesla was able to turn lights on and off from a distance by adjusting the frequency of the electromagnetic waves in their vicinity. Since then there have been various small scale demonstrations of wireless energy transfer for everything from military applications to powering televisions.

In theory, any electromagnetic wave can be used for wireless energy transfer. Radio transmissions work on similar principles and involve well-developed technologies. 

But what works across the surface of the earth won't necessarily work as effectively from space. For a start, the distances involved are greater. Furthermore, these giant, orbiting solar farms have to generate their own powerful laser beams or microwaves in space and them direct them accurately to the earth's surface –a complicated process that consumes some of the solar energy created by the system.

Any energy beam heading earthward from space also has the small matter of travelling through our planet's atmosphere to contend with.

Since the Earth's atmosphere is opaque at most frequencies in the electromagnetic spectrum, scientists need ways of beaming energy through the haze of gas and water droplets without too much energy being dissipated in the process. 

Visible light frequencies offer one opportunity. Microwaves offer another.

Out of the two, microwaves are the preferred choice as they work more efficiently over long distances than laser-based alternatives. Lasers can be blocked by bad weather and current designs for the devices used to generate and collect laser light are generally considered to be considerably less efficient than their microwave-based counterparts. 

Microwaves are already commonly used on the surface of the Earth by telecommunications firms, and have an established history in space where they are used for satellite relays, and deep space radio communications with interplanetary missions, such as the Curiosity Rover on Mars. 

Microwave WPT systems are also considered to be safer for wildlife and humans than laser-based WPT, which the 2011 IAA report on SBSP noted has the potential to be weaponised. The IAA report estimates that energy levels at the very center of a microwave beam receiving antenna on earth would be between 200-250 W/m2 – or around 20-25% the intensity of mid-day sun at the equator.

The most ambitious experiment to date occurred in May 2008 when Mankins – along with Japanese researchers - demonstrated a microwave beam, similar to one that could be used to transmit energy to Earth, between two Hawaiian Islands 150km (100miles) apart. The distance was chosen because it is equivalent to the thickness of the atmosphere that a microwave beam from space would have to penetrate. 

But the experiment brought mixed results. “It was a good end-to-end test of key technologies at short range and that portion was quite successful. It was also the first use of solar power to drive such an experiment, so all the major aspects of the SPS technologies were tested together,” explains Mankins.  

“However, the power levels were much too low to actually transmit power over the full distance. Also, given the short time, the beam control system didn't work as we wanted.” 

‘Daunting task

Scientists like Tom Murphy, associate professor of physics at the University of California, San Diego, believe that anyone who wants to spend the $1m it cost to fund the experiment, would be better off saving their money.

“The problem with wireless power transmission is the diffraction of energy through the atmosphere. That's not something you're going to cheat on. Physics makes transmission cumbersome and that's always going to be the case with any SBSP system,” he says.

Even a cloud free sky contains water vapour. Each droplet takes its toll, scattering the radiation in the microwave beam causing significant energy loss between the orbiting solar farm and the terrestrial surface, says Murphy, who estimates that between generating microwave energy in space, beaming it to the ground, and converting back into electricity again, the entire process could be expected to operate with around 50% efficiency.

Murphy argues that even with new technologies and cheaper launch systems, SBSP will not become viable.

“The time scale, the expense, and the degree of complexity of doing something from space makes it so daunting a task that if you can at all achieve the same scientific result from the ground it's far and away a superior path,” he says.

It is a view that is backed up by the International Energy Agency (IEA) which is positive about the prospects for terrestrial solar power generation, but explicitly rules out SBSP in the long-term because the expense, “mostly due to the costs of putting the necessary elements into orbit, would be several orders of magnitude greater than the costs of generating electricity on Earth".

Another factor weighing against a bright future for SBSP is the resurgence of oil and particularly gas production in the United States, which could see the country become 95% energy independent by 2035, according to the IEA.

Money man

But, despite the critics – and seemingly against the odds - projects are still pushing ahead. At least on paper.

In September 2012 there was a flurry of announcements to coincide with the Space Power Symposium held in Naples, Italy. A division of the Russian Federal Space Agency (Roscosmos) revealed that it has a working prototype of a 100kW SBSP system in development; although no launch date was announced. And the China Association for Science and Technology (Cast) revealed more details of a 100kW SBSP demonstration, which it plans to put in low earth orbit is expected by 2025, followed by a fully-operational SBSP system in geostationary orbit by 2050.

Whether these ever get off the ground is another matter. SBSP concepts have a habit of launching with great fanfare but delivering very little. For example, in 2009 Californian regulators approved a 15-year contract with Solaren to supply 200 megawatts of SBSP to North American utility giant Pacific Gas and Electric from 2016. But in recent years the company has gone quiet about its plans. Solaren declined our request for an interview.

A similarly ambitious project, announced in 2009 by the Japan government, plans to send a 2km- (1.5miles-) wide, 1GW system into orbit. The project was launched in the wake of the Fukushima nuclear disaster, which generated a swell of public support for SBSP in Japan. But, reality – and budgets – has kicked in. The 6-year only received $10m, a drop in the ocean for a SBSP concept.

“People were very supportive of SBSP after Fukushima. But unfortunately we also need support from the decision makers. Our budget is limited and will be decreased because of the depression of the Japanese economy and the terrible disaster in Fukushima and Tohoku,” says Naoki Shinohara, professor of engineering at the Research Institute for Sustainable Humanosphere, at Kyoto University and part of the project. 

As a result, plans to test a small scale microwave link over 50m (160ft) in 2014 look like they will be delayed.

“I do believe in SBSP. And I do believe in this project,” adds Shinohara optimistically. “We hope to start generating power in space in 2030.”

This positive attitude is shared by Nasa veteran Mankins, who is now also chief technical officer of asteroid mining start-up Deep Space Industries. 

A self-proclaimed “concurrent entrepreneur” who likes “to keep busy”, Mankins', is still “actively seeking” funding for SPS-Alpha for a benevolent partner to bankroll the project.

“I haven't found the visionary billionaire quite yet. But I'm still looking.”

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