Space solar seemed like a nutty idea back in the early 2000’s, but the nut is beginning to crack. A research team at the California Institute of Technology has just wrapped up a months-long, in-orbit test of three key space solar technologies, including a batch of 32 different kinds of solar cells. Perovskite solar cells made the cut for this initial test, but it’s complicated…
Space Solar Is Not Nutty, After All
Space solar refers to the idea of collecting solar energy from orbiting solar arrays, and beaming it down to Earth. That makes sense in a way, considering that solar power has been a feature of outer space activities since the 1950’s.
A space solar array could simply shunt that energy down to Earth, for use on the home planet anywhere in the world, 24/7/365, regardless of the weather.
Well, it’s not easy. Among the formidable obstacles are scale, cost, the delicate maneuvering required to unfurl a solar array in space, and the ability of the solar cells to withstand the tough outer space environment, including solar flares and geomagnetic activity. NASA also notes that space solar arrays would need to maintain a geostationary orbit, which means they would be located farther out in space than conventional satellites.
Nevertheless, science loves a challenge. The philanthropists Donald and Brigitte Bren are widely credited for kickstarting serious work on space solar in the US back in 2011, with a series of funding commitments to Caltech totaling more than $100 million. Northrup Grumman chipped in $12.5 million for several years, and the the US Air Force and the US Navy have also been exploring the space solar field (see more CleanTechnica coverage here).
As for NASA, they are taking a wait-and-see position, though just last week they noted that their current portfolio of activities includes several key technologies that apply to space solar, including autonomous systems and wireless power beaming, along with the capability to manufacture, assemble, and service solar arrays in space.
Space Solar Lessons Learned
In the latest development, last week the Caltech team issued a debriefing on its orbiting space solar test bed. Called SSPD-1 (short for Space Solar Power Demonstrator), the test launched on January 3, 2023 for a 10-month cruise.
The goal was to assess three key technologies, those being wireless power beaming, successful deployment, and of course, the all important photovoltaic technology.
There were definitely some bumps along the way but that was the point, so let’s zero in on those 32 different kinds of solar cells.
The solar cell portion of SSPD-1 comes under the name ALBA, which is not short for anything. In all caps it looks like an acronym, but it’s not. Alba is the word for dawn in Italian and several other languages. It is also the Scottish Gaelic word for Scotland, among other uses.
Be that as it may, ALBA tested almost three dozen different kinds of solar cells, including some described as “three entirely new classes of ultralight research-grade solar cells, none of which had ever been tested in orbit before.”
Aside from assessing how well the solar cells function, the SSPD team has cost-cutting on its mind.
“Space solar cells presently available commercially are typically 100 times more expensive than the solar cells and modules widely deployed on Earth,” Caltech notes.
“This is because their manufacture employs an expensive step called epitaxial growth, in which crystalline films are grown in a specific orientation on a substrate,” they add.
As a workaround, the SSPD team deployed processes similar to those used in fabricating conventional solar cells. “These processes employ high-performance compound semiconductor materials such as gallium arsenide,” Caltech notes.
What About The Perovskite Solar Cells?
Yes, what about them? Gallium arsenide solar cells are not particularly cheap, but they are proven to be durable for space applications, and the SSPD team has already begun exploring ways to bring costs down.
Perovskite solar cells could offer even more savings, and the team also notes that perovskite technology could be deployed in the form of large scale, flexible polymer sheets.
However, performance in outer space remains an open question.
The low-cost gallium arsenide solar cells in SSPD-1 performed consistently under solar flares and other space weather events, but the perovskite solar cells exhibited “tremendous variability” in response to the same conditions.
The next steps include fabricating and testing scaled-up versions, deploying “highly scalable inexpensive manufacturing methods that can dramatically reduce both the mass and the cost of these space solar cells.”
Perovskites To Space Solar: How Do You Like Me Now?
No word yet on whether or not perovskite solar cells will continue to have a hand in the SSPD space solar project. However, the low cost and flexibility of perovskite solar cells have motivated innovators to continue plugging up some holes in the technology.
Last May, for example, NASA reported that the results of a 10-month test of perovskite solar cells on the International Space Station. Though not a space solar project per se, the test did indicate that perovskites could be durable enough for operations on the Moon and beyond.
The flight sample was crafted and safety-tested all the way back in 2019. It was transported to the ISS in 2020 and returned to Earth in 2021, where it has been undergoing a series of assessments.
“A lot of people doubted that these materials could ever be strong enough to deal with the harsh environment of space,” observes NASA research engineer Dr. Lyndsey McMillon-Brown said.
“Not only do they survive, but in some ways, they thrived,” she adds. “I love thinking of the applications of our research and that we’re going to be able to meet the power needs of missions that are not feasible with current solar technologies.”
That’s of interest considering the torrent of new research activity leading to improvements in perovskite durability in the years since 2019. New research methodologies are also beginning to accelerate the pace of progress.
Earlier this month, for example, the University of Michigan reported on a new method for assessing how different additives can improve perovskite solar cell durability. Additive tweaking is a staple of perovskite solar cell research, but an understanding of the exact mechanism has remained elusive until now.
The research involved formulating new molecules with carefully controlled coordination numbers, referring to the atoms, ions, or molecules in a compound or crystal. Molecular weight and steric hindrance (a slowdown of chemical reactions) also got the same consideration.
You can find all the details in the journal Matter under the title, “Molecular design of defect passivators for thermally stable metal-halide perovskite films.”
“We found that carefully tuning these factors can result in an optimized binding affinity with perovskites, which simultaneously enhances grain sizes, defect passivation, and thermal stability of perovskite films,” the team reported. This innovative molecular design strategy marks a transformative step toward designing more robust and efficient perovskite photovoltaics.
We’ll have to wait and see if a space solar application emerges, so stay tuned for more on that.
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Image (screenshot): A wireless transmitter will beam space solar energy down to Earth, eventually (courtesy of CalTech).
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