The high efficiency, light weight and flexibility of the latest solar cell technology means photovoltaics could provide all the energy needed for an extended mission to Mars, or even a permanent installation there, according to a new analysis by scientists. from the University of California at Berkeley. .
Most scientists and engineers who have thought about the logistics of life on the surface of the Red Planet have assumed that nuclear power is the best alternative, largely because of its reliability and 24-hour operation. and 7 days a week. Over the past decade, miniaturized Kilopower nuclear fission reactors have advanced to the point where NASA considers them a safe, efficient, and abundant source of energy and the key to future robotic and human exploration.
Solar energy, on the other hand, must be stored for use at night, which on Mars lasts about the same duration as on Earth. And on Mars, electricity production from solar panels can be reduced by the ubiquitous red dust that covers everything. NASA’s nearly 15-year-old Opportunity rover, powered by solar panels, stopped working after a huge dust storm on Mars in 2019.
The new study, published this week in the journal Frontiers in astronomy and space science, uses a systems approach to compare these two technologies head-to-head for an extended six-person mission to Mars involving a 480-day stay on the planet’s surface before returning to Earth. This is the most likely scenario for a mission that reduces transit time between the two planets and extends time on the surface beyond a 30-day window.
Their analysis found that for settlement sites on almost half of the Martian surface, solar is comparable to or better than nuclear, if you take into account the weight of the solar panels and their efficiency – as long as part of daytime energy is used to produce hydrogen gas for use in fuel cells to power the colony at night or during sandstorms.
“Photovoltaic power generation coupled with certain molecular hydrogen energy storage configurations outperforms nuclear fusion reactors on 50% of the planet’s surface, primarily in regions around the equatorial band, in contrast quite strongly with what has been proposed over and over again in the literature, which is that it will be nuclear power,” said Aaron Berliner, a bioengineering doctoral student at UC Berkeley, one of the first two authors of the article.
The study gives a new perspective on the colonization of Mars and provides a roadmap for deciding what other technologies to deploy when planning manned missions to other planets or moons.
“This paper gives a holistic view of available energy technologies and how we might deploy them, what are the best use cases for them, and where are they lacking,” said co-first author Anthony Abel, student graduated in the Department of Chemical and Biomolecular Engineering. “If humanity collectively decides that we want to go to Mars, this kind of system-level approach is needed to accomplish it safely and minimize costs in an ethical way. We want to have a lucid comparison between the options, that we’re deciding what technologies to use, where to go on Mars, how to get there and who to bring.”
Longer missions have higher power requirements
In the past, NASA estimates of astronauts’ energy needs on Mars typically focused on short stays, which don’t require energy-intensive processes to grow food, make building materials, or produce chemicals. . But while NASA and corporate executives now building rockets that could go to Mars — including SpaceX CEO Elon Musk and Blue Origin founder Jeff Bezos — are tossing around the idea of long-term colonies off of the planet, larger and more reliable energy sources should be considered.
The complication is that all of these materials must be transported from Earth to Mars at a cost of hundreds of thousands of dollars per pound, making low weight essential.
One of the main needs is electricity for bioproduction facilities that use genetically modified microbes to produce food, rocket fuel, plastics and chemicals, including drugs. Abel, Berliner and their co-authors are members of the Center for the Utilization of Biological Engineering in Space (CUBES), a multi-university effort to modify microbes using the gene insertion techniques of synthetic biology to provide the supplies needed for a colony.
However, the two researchers discovered that without knowing the power available for an extended mission, it was impossible to assess the practicality of many biofabrication processes. So, they set out to create a computer model of various power supply scenarios and likely energy demands, such as habitat maintenance – which includes temperature and pressure control – water production. fertilizer for agriculture, the production of methane for the rocket propellant to return to Earth, and the production of bioplastics for the manufacture of spare parts.
Facing a Kilopower nuclear system were photovoltaic systems with three energy storage options: batteries and two different techniques for producing hydrogen gas from solar energy – by electrolysis and directly by photoelectrochemical cells. In the latter cases, the hydrogen is pressurized and stored for later use in a fuel cell to generate electricity when the solar panels are not.
Only photovoltaic energy with electrolysis – using electricity to separate water into hydrogen and oxygen – was competitive with nuclear energy: it proved to be more profitable per kilogram than nuclear on almost half of the surface of the planet.
The main criterion was weight. The researchers assumed that a rocket carrying a crew to Mars could carry a payload of around 100 tons, excluding fuel, and calculated how much of that payload would need to be devoted to a power system for use on the surface. of the planet. A trip to and from Mars would take about 420 days, or 210 days each way. Surprisingly, they found that the weight of a power system would be less than 10% of the total payload.
For a landing site near the equator, for example, they estimated that the weight of the solar panels plus hydrogen storage would be around 8.3 tons, compared to 9.5 tons for a nuclear reactor system. Kilopower.
Their model also specifies how to adjust photovoltaic panels to maximize efficiency for different conditions at sites on Mars. Latitude affects the intensity of sunlight, for example, while dust and ice in the atmosphere can scatter longer wavelengths of light.
Advances in photovoltaics
Abel said photovoltaics are now very efficient at converting sunlight into electricity, although the most efficient ones are still expensive. The most crucial new innovation, however, is a lightweight and flexible solar panel, which facilitates storage on the outbound rocket and reduces transportation costs.
“The silicon panels you have on your roof, with steel construction, glass backing, etc., just won’t compete with the new improved nuclear, but the new lightweight and flexible panels suddenly change really, really this conversation,” Abel said.
He also noted that lighter weight means more panels can be transported to Mars, providing a backup for any panels that fail. While kilowatt nuclear power plants provide more power, less is needed, so if one fails, the colony would lose a significant amount of power.
Berliner, who is also pursuing a degree in nuclear engineering, entered the project with a bias towards nuclear energy, while Abel, whose undergraduate thesis focused on new innovations in photovoltaics, was more in favor solar energy.
“I feel like this article really stems from a healthy scientific and technical disagreement about the merits of nuclear power versus solar power, and that the job is really about trying to understand and settle a bet,” Berliner said. “Which I think I lost, based on the setups we chose to post this. But it’s a happy loss, that’s for sure.”
Other co-authors on the paper are Mia Mirkovic, UC Berkeley researcher at the Berkeley Sensor and Actuator Center; William Collins, UC Berkeley Professor-in-Residence in Earth and Planetary Sciences and Senior Investigator at Lawrence Berkeley National Laboratory (Berkeley Lab); Adam Arkin, director of CUBES and Dean A. Richard Newton Memorial Professor in the Department of Bioengineering at UC Berkeley; and Douglas Clark, Gilbert Newton Lewis Professor in the Department of Chemical and Biomolecular Engineering and Dean of the College of Chemistry. Arkin and Clark are also senior faculty scientists at the Berkeley Lab.
The work was funded by NASA (NNX17AJ31G) and National Science Foundation Postgraduate Research Grants (DGE1752814).