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November 2, 2016

What Do Cleanrooms, Mars, and Cooking Have in Common?

Contamination Control News

Mars Astronaut

A Shimmering Red Presence in the Clear Night Sky*

The year is 2035 and Mark Watney, botanist and mechanical engineer, casts a wary eye over the latest weather report. A dust storm with intense winds is approaching and it’s time for him to move to safety. The rest of his team sets out but Watney doesn’t make it. Sheer bad luck combines with an accident to ensure that Watney is left stranded, facing a tenuous future alone on Mars.

Mars? Wait, are we talking about Ridley Scott’s film The Martian? Right now, we only have access to the Red Planet in our imaginations but, if Mars One, a group backed by SpaceX and Lockheed Martin and advised by some of the biggest names in planetary science, astrogeology, and theoretical physics, has its way, humans could be on our way out into the solar system sooner rather than later.

Mars One is a multi-national initiative devised by co-founder and CEO Bas Lansdorp with a goal of creating a viable human settlement on Mars as a stepping-stone along our voyage further out into the universe. And in order to set up a Martian colony, Mars One is working with a variety of aerospace industry leaders, from Paragon Space Development Corporation to Astrobotic Technology Inc., in sourcing materials. Crew selection began back in 2013 and, by the end the third round of selections this year, trials will have whittled down contenders to an initial twenty-four individuals who will live and train together until the anticipated launch date in 2026.(1) During their prolonged training they will develop the skills they’ll need to repair equipment, provide medical assistance, and to grow food in the harsh environment of space and on-site on Mars.

Grow and cook food? The most sobering part of the Mars One mission is that the selected participants are on a one-way trip – for those who survive the journey, there is no way home.

The Mars One roadmap to launch is ambitious and calls for a rover and communication satellites to be in place in 2022, cargo missions setting out in 2024, and the first crew landing in 2027. And, although this might seem like a generous time frame, the schedule is in reality quite tight, and not completely devoid of challenges. Aside from the difficulty of choosing folks with no qualms about forsaking this world on a one-way ticket to set up the first extra-terrestrial colony in the history of humankind, there’s also the big question of how to power this venture. Once the personnel, components, and funding are in place, there’s ‘just’ the question of the provision of power – the colossal energy required not only to get to the planet but also to survive there long term.

In Andy Weir’s novel, The Martian, abandoned astronaut Watney learns to burn hydrazine to make water and retrofits a rover with solar cells to facilitate on-planet transport. Solar cells? That’s already this is yesterday’s technology! Here on Earth, solar cells are ideal for use in architectural projects – domestic roofs, the tops of commercial buildings, vehicle charging systems, and exciting possibilities for smart freeway ‘paving’ that could in time replace asphalt. But in the Mars One mission, solar cells are already passé. Welcome to the exciting world of thin film solar photovoltaic panels…

The technician is testing film solar cells

Flexible enough to be rolled up between uses and light enough to be easily transported safely to Mars, thin film solar photovoltaic panels (PV panels) will be working hard once they hit terra firma. Mars One engineers anticipate that sheets of these panels will be deployed to create the power needed for mission critical operations – from the life support units that generate water and breathable air to the living units designed to accommodate the settlers. Given the amount of ice in the ground soil on Mars, Mission One expects to create potable water by heating 60 kilograms (approximately 132lbs) and capturing the evaporate. After the water vapor is condensed for storage, the dry soil will be discarded. Seems simple, but it’s a very power-intensive process. Then there is also the extraction of nitrogen and argon gases from the Martian atmosphere, to be mixed with oxygen and injected into the habitation zones to create breathable air. So, even with this simplistic overview, it’s clear that these PV panels have to be tough…

The production of the cells – applying semiconductors and electrical interconnecting layers to a substrate – must be completely contaminant-free and requires use of specialized Class 5 cleanrooms

Unlike its predecessor the crystalline silicon solar cell (c-Si), photovoltaic film is made by depositing multiple layers of material onto a substrate, with the thickness of the cells varying according to their use. Film thickness runs from a few nanometers to tens of micrometers and this slender profile allows not only for flexibility but also decreased friction, characteristics that lend it an advantage over the weightier and more rigid c-Si alternatives. The production of the cells – applying semiconductors and electrical interconnecting layers to a substrate – must be completely contaminant-free and requires use of specialized Class 5 cleanrooms. The wet chemical processing area for instance provides a contamination-controlled environment within the micron range for pre- and post-cleaning of samples and a texturing bath for solar cell texture. The optical lithography, as well as laser processing in which the thin films are scribed and the silicon wafer cells are edged, are also tasks that must be done within a cleanroom environment.

For the so-called ‘third generation’ photovoltaic cells, a multitude of different base materials may be used in the manufacturing process, and this spectrum demands careful thought in terms of resources for contamination-control. Copper zinc tin sulfide cells, for instance, are inherently different from organic solar cells or their quantum dot cousins, representing not only cost differences but also a spectrum of power efficiencies. And again, this is a major consideration in terms of the deployment of such technology in space exploration.

But, like the red Martian sands in a dust storm, the landscape is constantly shifting and evolving. As recently as 2015, a new world record was set for thin film solar efficiency. In an historic partnership between Solar Frontier and the New Energy and Industrial Technology Development Organization (NEDO), both of Japan, a 0.5cm squared cell topped out at an incredible 22.3% efficiency. To those outside of the industry, this conversion may seem low, but it actually represents massive incremental improvements. Let’s remember that when the technology was first introduced to market engineers were delighted to record production modules pushing the boundaries of conversion at a whopping 9%!

So where is the future of thin film technology and who is shaping it? Although specific vendor information for the PV panels is not made public through Mars One’s website, the chances are that their manufacturer is located in Asia.(2) According to Paula Mints, writing for Renewable Energy World, the 2015 top ten PV cell manufacturers were all based in China or Malaysia. Companies such as Trina Solar (China and Netherlands), Yingi Solar (China), Canadian Solar (bizarrely China), and Hanwha Q-Cells (China, Germany, and South Korea) are dominating the market with a full ‘46 percent of global module assembly capacity and 42 percent of cell/thin film manufacturing capacity.’(3) The US-based outlier, First Solar, ranks fifth on the top ten list, pulling in 4% of the global cell/module revenues of $32.1 billion in 2015.

But according to Finlay Colville of PVTech, an online news source for the international PV supply chain, Mars One might have less interest in current Tier 1 market leaders and more of an eye on emerging players. Colville believes the ultimate success of PV panels lies in ‘not just serving existing market demand, but also in directly influencing the landscape in the years to come.’(4) And if a company has its sights set on influencing the future landscape, it’s a safe bet to assume it’s focused on the most innovative and cutting-edge science. Exactly the kind of product necessary for the Mars missions. According to a report in Renew India Campaign, Solar Frontier’s thin film solar cells ‘generate more energy (kilowatt-hours per kilowatt-peak) compares to crystalline silicon in real-world conditions.’(5) But the question now is whether that ‘real-world’ extends beyond the reaches of our own small planet?

Do you have thoughts on thin film PV panels and their use in the space program? We’d love to hear them!

References:

  1. http://www.mars-one.com/mission/roadmap
  2. http://www.mars-one.com/about-mars-one/suppliers
  3. http://www.renewableenergyworld.com/articles/2016/04/2015-top-ten-pv-cell-manufacturers.html
  4. http://www.pv-tech.org/editors-blog/new-analysis-the-real-top-solar-pv-manufacturers-in-2016
  5. http://www.renewindians.com/2015/12/world-record-thin-film-solar-cell.html

Additional materials:

http://www.pv-tech.org/products/abbs_irb6640_robot_meets_thin-film_pv_class_5_cleanroom_standards

* “Mars tugs at the human imagination like no other planet. With a force mightier than gravity, it attracts the eye to the shimmering red presence in the clear night sky.” – John Noble Wilford, ‘Mars Beckons’, 1989, Random House

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