(ORDO NEWS) — The high efficiency, light weight and flexibility of the latest solar cell technology means that photovoltaics could provide all the energy needed for a long-term mission to Mars or even permanent settlement, according to a new analysis by UC Berkeley scientists.
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 24/7 operation.
Over the past decade, miniaturized kilocalorie nuclear power plant fission reactors have advanced to the point where NASA considers them a safe, efficient, and abundant source of energy, and a key factor for future robotic and human-assisted research.
Solar energy, on the other hand, must be stored for use at night, which lasts about the same time on Mars as it does on Earth.
And on Mars, the production of energy from solar panels can be reduced due to the ubiquitous red dust that covers everything around. NASA’s nearly 15-year-old solar-powered Opportunity rover stopped working after a severe dust storm on Mars in 2019.
A new study published this week in the journal Frontiers in Astronomy and Space Sciences uses a systematic approach to compare the two technologies against each other for a long mission to Mars, designed for six people and involving a 480-day stay on the surface of the planet before returning to Earth.
This is the most likely scenario for a mission that will shorten transit time between the two planets and extend surface time beyond a 30-day window.
Astronauts going to Mars need to minimize the weight of the power grid they take with them from Earth. Photovoltaic systems will be the best choice if the planned settlement site is in the yellow zone on this flattened map of Mars.
Also shown are the landing sites of previous missions to Mars, including Jezero crater (top right), which is currently being explored by NASA’s Perseverance rover. (Photo courtesy of Anthony Abel and Aaron Berliner, UC Berkeley)
Their analysis showed that for settlement sites on nearly half of the Martian surface, solar power is comparable to, or even better than, nuclear power when taking into account the weight of solar panels and their efficiency – assuming some of the daytime energy is used to produce hydrogen gas for use in fuel cells for feeding the colony at night or during sandstorms.
“Photovoltaic power generation, combined with certain configurations of energy storage in molecular hydrogen, outperforms nuclear fusion reactors on 50% of the planet’s surface, mainly in regions around the equatorial strip, which contrasts rather sharply with what has been repeatedly suggested in the literature, namely that it is there will be nuclear power,” said UC Berkeley bioengineering doctoral student Aaron Berliner, one of the first two authors of the paper.
The study provides a new perspective on the colonization of Mars and provides a roadmap for deciding what other technologies to use when planning manned missions to other planets or moons.
“This paper takes a global view of available energy technologies and how we can use them, what are the best use cases for them and where they don’t work,” said co-author Anthony Abel, PhD student in the Department of Chemical and Biomolecular Engineering.
“If humanity collectively decides that we want to go to Mars, such a system-level approach is necessary in order to do so safely and cost-effectively while respecting ethical standards. We want to have a clear comparison between the options, whether or not we decide what technology to use, where to go on Mars, how to go and who to take with you.”
Longer missions require more power
In the past, NASA estimates of the electrical needs of astronauts on Mars have typically focused on short missions that do not require energy-intensive processes to grow food, produce building materials, or produce chemicals.
But as NASA and executives from companies that are now building rockets capable of going to Mars, including Elon Musk, CEO of SpaceX, and Jeff Bezos, founder of Blue Origin, discuss the idea of long-term off-planet settlements, larger, more reliable power sources need to be considered.
The difficulty lies in the fact that all these materials must be transported from Earth to Mars at a cost of hundreds of thousands of dollars per pound, which makes light weight extremely important.
One of the key needs is power for biomanufacturing, which uses genetically engineered microbes to produce food, rocket fuel, plastic materials and chemicals, including drugs.
Abel, Berliner and their co-authors are members of the Center for the Use of Biological Engineering in Space (CUBES), a multi-university project to modify microbes using synthetic biology gene-injection techniques to provide the colony with the necessary materials.
However, two researchers found that without knowing how much energy would be available for a long mission, it was impossible to assess the practicality of many biomanufacturing processes.
So they set out to create a computer model of various power supply scenarios and likely power needs, such as habitat maintenance involving temperature and pressure control, fertilizer production for agriculture, methane production for rocket fuel to return to Earth, and bioplastic production for spare parts.
Against Kilopower’s nuclear system, photovoltaic cells were chosen with three energy storage options: batteries and two different methods of generating hydrogen gas from solar energy – by electrolysis and directly using photoelectrochemical cells. In the latter case, the hydrogen is pressurized and stored for later use in a fuel cell to produce energy when the solar panels are not operating.
Only photovoltaic power with electrolysis – using electricity to split water into hydrogen and oxygen – has proven competitive with nuclear power, being more cost-effective per kilogram than nuclear over nearly half the planet’s surface.
The main criterion was weight. The researchers assumed that a rocket carrying a crew to Mars could carry a payload of about 100 tons, excluding fuel, and calculated how much of that payload would have to be diverted to the power grid for use on the planet’s surface.
The journey to Mars and back will take about 420 days – 210 days each way. Surprisingly, they found that the weight of the power grid would be less than 10% of the total payload.
For example, for a landing site near the equator, according to their calculations, the weight of solar panels and hydrogen storage will be about 8.3 tons, while the weight of the Kilopower nuclear reactor is 9.5 tons.
Their model also defines how to tune the photovoltaic panels to achieve maximum efficiency under various conditions on Mars. For example, latitude affects the intensity of sunlight, and dust and ice in the atmosphere can scatter light at longer wavelengths.
Advances in Photovoltaics
Abel said photovoltaic panels are now very efficient at converting sunlight into electricity, although the best ones are still expensive. However, the most important novelty is a lightweight and flexible solar panel that facilitates storage on a departing rocket and reduces the cost of transportation.
Humans on Mars will have to use the only raw materials available – water ice, atmospheric gases, Martian soil and sunlight – to produce everything they need to survive. Researchers like those at CUBES are working on how to turn these raw materials into food, medicine, fuel and construction materials.
This flowchart shows how In-Situ Resource Utilization (ISRU) turns raw materials into a form that can be used to synthesize food and pharmaceutical products (FPS) and produce biopolymers (ISM) for crew use.
Waste is collected and reused (closing the loop, or LC) to maximize efficiency and reduce the cost of supply chain logistics from Earth. (Illustration courtesy of Aaron Berliner and Davian Ho, UC Berkeley)
“The silicon panels that you have on your roof, with steel construction, glass backing and so on, just can’t compete with the new and improved nuclear panels, but the new lightweight, flexible panels are suddenly very, very changing that conversation,” Abel said.
He also noted that the lighter weight means more panels can be brought to Mars, providing a back-up for any panels that fail. Although kilowatt nuclear power plants provide more energy, they require less, so if one of them fails, the colony will lose a significant part of the energy.
Berliner, who is also pursuing a degree in nuclear engineering, approached the project with a nuclear energy bias, while Abel, whose thesis was about new innovations in photovoltaics, leaned more towards solar energy.
“It seems to me that this work really stems from a healthy scientific and engineering disagreement about the merits of nuclear and solar energy, and that in fact this work is simply our attempt to clarify and resolve the dispute,” Berliner said. “And I think I lost, judging by the configuration we chose to publish. But it’s certainly a happy loss.”
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