By D.A. Barber
The problem for PV generated electricity is that the sun only shines on average for about 8 hours per day. But the sun shines in space all the time and if that energy could be redirected to the surface, would it not go a long way boosting the use of solar power?
The concept of space-based power was first introduced in 1941 by science fiction author Isaac Asimov in his short story "Reason", and was later scientifically put forth by Peter Glaser in 1968.
It was not until 2009, when California startup Solaren proposed a space-based solar power project that the concept was starting to be taken seriously by the energy industry and the company signed an agreement with Pacific Gas & Electric to buy 200MW of power from any future working project. If successful, this project would be the first implementation of space-based solar power (SBSP).
Then in a 2011 report, the International Academy of Astronautics indicated scientists from around the world believed harvesting the sun's energy in space could turn out to be a cost effective way of delivering some of the world’s energy needs. That report concluded that orbiting power plants collecting energy from the sun and beaming it to Earth could become feasible within a decade or two.
There has even been a proposal circulating to launch satellites containing only ultra thin inflatable mirrors in a lower polar sun synchronous orbit of about 600 miles. These satellites would contain no power conversion equipment nor would they transmit power to a ground station. Instead, the mirrors would redirect sunlight to ground-based PV solar farms at night to increase their efficiency and get around the storage issue.
Now, space-based power is again being touted. At the third annual ARPA-E Energy Innovation Summit in February 2012 - sponsored by the U.S. Department of Energy with Bill Gates and former U.S. President Bill Clinton as some of the speakers - space-based power was cited as one of the breakthrough technologies seen as having a real future.
Solar Space-Power
Though the concept of space-based power was first proposed in 1968, the concept was officially explored by the US Government in a 1997 NASA study. The October 2007 National Security Space Office report, “Space-Based Solar Power as an Opportunity for Strategic Security,” was compiled through internet discussions with more than 170 university, scientific, technical, legal, and energy business experts around the world. The consensus was that space-based solar was technically feasible as a result of advances in PV cells and robotics for construction.
But the design the report considered would be far too expensive for the private sector to tackle and instead the report suggested that the first systems would need to be developed not to utilities, but by the government as an “early adopter and to incentivize other early adopters much as is accomplished on a regular basis with other renewable energy systems coming on-line today.”
The most immediate suggested use by the US government would be to beam power to troops at forward military bases in war zones.
“SBSP and its enabling wireless power transmission technology could facilitate extremely flexible ‘energy on demand’ for combat units and installations across an entire theater, while significantly reducing dependence on vulnerable over-land fuel deliveries,” concludes the report.
Nevertheless, private companies have been eyeing the possibilities.
Space-Power Satellites
In 2009, California startup Solaren proposed a space-based satellite power project that would work basically the way the 2007 U.S. government report sketched out such as a typical space-based solar power system: The idea is to launch a network of solar power satellites into orbit around the Earth. The electricity would then be converted into microwaves suitable for transmitting through Earth's atmosphere at frequencies of probably 2.45 or 5.8 GHz and beamed to a variety of ground-based station locations. That beam would be converted into usable electricity and then delivered to customers over existing transmission lines.
The appeal of solar from space comes in mainly the form of higher efficiency.
Because space-based PV panels are unaffected by the filtering effects of the atmosphere and can collect rays 24 hours a day, the World Radiation Center has estimated that rays collected in space would be 144 percent more powerful than those collected on the surface. And the U.S. National Security Space Office’s 2007 report estimated that one kilometer of space-based PV panels could collect an annual supply of energy “equal to the energy contained in all of the known recoverable conventional oil reserves on Earth today.”
Solaren has been planning since 2009 to generate such power from PV panels mounted on satellites in Earth's orbit. At last report, their satellites would beam the energy to a receiving station in Fresno County, California. In fact, the company had already received a vote of confidence when Pacific Gas and Electric Company, California's biggest utility, announced a deal in early 2009 to purchase 200 megawatts of electricity from Solaren beginning in 2016.
Currently, the Solaren project is still in search of the needed investments but the technology was singled out at the February 2012 ARPA-E (Advanced Research Projects Agency – Energy) Energy Innovation Summit as an up and coming technology.
Tethered Space-Power
Another space-based power concept is being proposed that does not require satellites in orbit but still involves collecting power well above the Earth’s surface using a tethered solar balloon-like device.
StratoSolar was founded by a small group of volunteer engineers and scientists in 2010, at which time they received a patent for the innovative PV kite system they had developed. What StratoSolar envisions is using a rigid buoyant platform with a PV array and permanently positioned like a kite at an altitude of 20 km in the stratosphere. The PV kite would collect the sunlight and transmit it down the kite’s tether through a high voltage cable to a ground station for distribution into the grid.
While the cost would be greater than ground-based PV facilities, StratoSolar believes there are enough advantages to consider tethering PV into the stratosphere in areas with persistent heavy cloud cover where a great deal more sun could be utilized above the clouds in the stratosphere. There could also be temporary applications in remote areas or areas that simple don’t have the ground space available for large PV arrays.
Conclusions
Generating power in space for use on Earth is an old idea that's never been tried, mostly because it's expensive. But power from solar satellites would produce energy almost continuously compared to ground-based PV systems which, even in the best desert locations, don’t generate power at night.
Yet, because of the technological obstacles, the 2007 U.S. government report recommended that the government should be the one to build a pilot project since only the government has the kinds of resources needed. But that was before the 2011 budget cuts at NASA, putting the U.S. space program in the hands of the private sector. Now, those launches will have to take place using either emerging private U.S. space developers such as the SpaceX Falcon launch vehicle or the capabilities of space programs run by other nations. And once in space, failures could not be easily serviced the way orbiting space telescopes have been repaired in the past by NASA Space Shuttle crews.
One fear expressed by SBSP advocates is that these satellites could be viewed by some world governments as a form of space-based weapon, as so put up legal roadblocks to prevent their deployment. The 2007 U.S. government report did suggest that such legal issues could be hammered out simultaneously with the technology development issues to “ensure that intangible issues do not delay employment of technology solutions”.
“An inventory should be created of who (individuals, corporations and organizations) has the expertise related to the various areas discussed in the studies and who is actively working on the research and development needed to make SBSP a reality,” concluded the 2007 report.
Though nothing has happened since on the US side, the report did acknowledge that there was “substantial interest and support” for SBSP in Europe, Japan, Canada, India, China, and Russia and suggested that this interest “can be leveraged to build or strengthen strategically stabilizing long-term partnerships.”
In fact, international interest has grown much more recently due in part to fears of the coming of “peak oil” and concern over climate change from fossil fuel use.
In September 2011, the US Council on Foreign Relations and the Aspen Institute in India called for a joint US-Indian feasibility study to develop a cooperative SBSP program to reach commercial viability within two decades. That “two decade” timeline was backed-up by a 248-page report released in November 2011, “Space Solar Power: The First International Assessment of Space Solar Power: Opportunities, Issues and Potential Pathways Forward,” by the Paris-based International Academy of Astronautics which concluded that SBSP is "technically feasible" within 20 years due to substantially improved technology.
Though the emphasis from the 5-year-old US government feasibility report stressed the military use of SBSP, a lot has changed in the world since then that point to other, more immediate uses of this technology that commercial companies could use to leverage the needed financial backing. While “plug & play” and “pay as you go” via cell phone customers PV power is seeing funding to reach developing areas that are years from being grid connected, SBSP has the potential to deliver “rapid response” renewable power to not only these developing regions, but also as humanitarian relief to areas struck by natural disasters and have lost their ground-based infrastructure.
If this SBSP technology continues to creep slowly forward, there appears to be a unique opportunity for those PV developers and manufacturers looking for utility-scale projects to invest in to try something new and partner with emerging private space vehicle start-ups or even the multi-national aerospace firms looking for a project to replace the drastic cuts in NASA contracts.