Solar beats nuclear at many potential settlement sites on Mars
Thanks to today's light, flexible solar panels, photovoltaics may be more practical for long stays

Date:
April 27, 2022
Source:
University of California - Berkeley
Summary:
While most missions to the moon and other planets rely upon solar
power, scientists have assumed that any extended surface mission
involving humans would require a more reliable source of energy:
nuclear power.

Improvements in photovoltaics are upending this calculus. A new
study concludes that a solar power system would weigh less than
a nuclear system, and would be sufficient to power a colony at
sites over nearly half the surface.



FULL STORY ==========================================================================
The high efficiency, light weight and flexibility of the latest solar cell technology means photovoltaics could provide all the power needed for an extended mission to Mars, or even a permanent settlement there, according
to a new analysis by scientists at the University of California, Berkeley.


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Most scientists and engineers who've thought about the logistics
of living on the surface of the Red Planet have assumed that nuclear
power is the best alternative, in large part because of its reliability
and 24/7 operation. In the past decade, miniaturized Kilopower nuclear
fission reactors have advanced to the point where NASA considers them
to be a safe, efficient and plentiful source of energy and key to future robotic and human exploration.

Solar power, on the other hand, must be stored for use at night, which on
Mars lasts about the same length of time as on Earth. And on Mars, solar panels' power production can be reduced by the omnipresent red dust that
covers everything. NASA's nearly 15-year-old Opportunity rover, powered by solar panels, stopped working after a massive dust storm on Mars in 2019.

The new study, published this week in the journal Frontiers in Astronomy
and Space Sciences, uses a systems approach to actually compare these
two technologies head-to-head for a six-person extended mission to Mars involving a 480-day stay on the planet's surface before returning to
Earth. That is the most likely scenario for a mission that reduces the
transit time between the two planets and extends time on the surface
beyond a 30-day window.

Their analysis found that for settlement sites over nearly half the
Martian surface, solar is comparable or better than nuclear, if you
take into account the weight of the solar panels and their efficiency --
as long as some daytime energy is used to produce hydrogen gas for use
in fuel cells to power the colony at night or during sandstorms.

"Photovoltaic energy generation coupled to certain energy storage configurations in molecular hydrogen outperforms nuclear fusion reactors
over 50% of the planet's surface, mainly within those regions around
the equatorial band, which is in fairly sharp contrast to what has been proposed over and over again in the literature, which is that it will be nuclear power," said UC Berkeley bioengineering doctoral student Aaron Berliner, one of two first authors of the paper.



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The study gives a new perspective on Mars colonization and provides a
road map for deciding which other technologies to deploy when planning
manned missions to other planets or moons.

"This paper takes a global view of what power technologies are available
and how we might deploy them, what are the best-use cases for them
and where do they come up short," said co-first author Anthony Abel,
a graduate student in the Department of Chemical and Biomolecular
Engineering. "If humanity collectively decides that we want to go to Mars,
this kind of systems-level approach is necessary to accomplish it safely
and minimize cost in a way that's ethical. We want to have a clear-eyed comparison between options, whether we're deciding which technologies
to use, which locations to go to on Mars, how to go and whom to bring."
Longer missions have greater power needs In the past, NASA's estimates
of the power needs of astronauts on Mars have generally focused on short
stays, which don't require power-hungry processes for growing food, manufacturing construction materials or producing chemicals.

But as NASA and leaders of companies now building rockets that could go
to Mars -- including Elon Musk, CEO of SpaceX, and Jeff Bezos, founder
of Blue Origin - - talk up the idea of long-term, off-planet settlements, larger and more reliable sources of power need to be considered.

The complication is that all of these materials must be carried from
Earth to Mars at a cost of hundreds of thousands of dollars per pound,
making low weight essential.



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One key need is power for biomanufacturing facilities that use 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 Utilization of Biological Engineering
in Space (CUBES), a multi-university effort to tweak microbes using
the gene-insertion techniques of synthetic biology to supply necessary
supplies for a colony.

The two researchers discovered, however, that without knowing how much
power will be available for an extended mission, it was impossible
to assess the practicality of many biomanufacturing processes. So,
they set out to create a computerized model of various power supply
scenarios and likely power demands, such as habitat maintenance -- which includes temperature and pressure control -- fertilizer production for agriculture, methane production for rocket propellant to return to Earth,
and bioplastics production for manufacturing spare parts.

Pitted against a Kilopower nuclear system were photovoltaics with
three power storage options: batteries and two different techniques for producing hydrogen gas from solar energy -- by electolysis and directly
by photoelectrochemical cells. In the latter cases, the hydrogen is
pressurized and stored for later use in a fuel cell to produce power
when the solar panels are not.

Only photovoltaic power with electrolysis -- using electricity to split
water into hydrogen and oxygen -- was competitive with nuclear power:
It proved 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
ferrying a crew to Mars could carry a payload of about 100 tons, exclusive
of fuel, and calculated how much of that payload would need to be devoted
to a power system for use on the planet's surface. A journey to and
from Mars would take about 420 days -- 210 days each way. Surprisingly,
they found that the weight of a power system would be less than 10%
of the entire payload.

For a landing site near the equator, for example, they estimated that
the weight of solar panels plus hydrogen storage would be about 8.3 tons, versus 9.5 tons for a Kilopower nuclear reactor system.

Their model also specifies how to tweak photovoltaic panels to maximize efficiency for the 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 that photovoltaics are now highly
efficient at converting sunlight into electricity, though the best
performers are still expensive. The most crucial new innovation, however,
is a lightweight and flexible solar panel, which makes storage on the
outbound rocket easier and the cost of transport less.

"The silicon panels that you have on your roof, with steel construction,
glass backing, et cetera, just won't compete with the new and improved
nuclear, but newer lightweight, flexible panels all of a sudden really,
really change that conversation," Abel said.

He noted, too, that lighter weight means more panels can be transported to Mars, providing backup for any panels that fail. While kilowatt nuclear
power plants provide more power, fewer are needed, so if one goes down,
the colony would lose a significant proportion of its power.

Berliner, who is also pursuing a degree in nuclear engineering, came
into the project with a bias toward nuclear power, while Abel, whose undergraduate thesis was about new innovations in photovoltaics, was
more in favor of solar power.

"I feel like this paper really stems from a healthy scientific and
engineering disagreement on the merits of nuclear versus solar power,
and that really the work is just us trying to figure out and settle a
bet," Berliner said. "which I think I lost, based on the configurations
we chose in order to publish this.

But it's a happy loss, for sure." Other co-authors of the paper are
Mia Mirkovic, a researcher at UC Berkeley at the Berkeley Sensor and
Actuator Center; William Collins, UC Berkeley professor-in-residence of
earth and planetary science and senior scientist at Lawrence Berkeley
National Laboratory (Berkeley Lab); Adam Arkin, CUBES director and the
Dean A. Richard Newton Memorial Professor in UC Berkeley's Department of Bioengineering; and Douglas Clark, the 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 Berkeley Lab.

The work was funded by NASA (NNX17AJ31G) and graduate research fellowships
from the National Science Foundation (DGE1752814).


========================================================================== Story Source: Materials provided by
University_of_California_-_Berkeley. Original written by Robert
Sanders. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Anthony J. Abel, Aaron J. Berliner, Mia Mirkovic, William
D. Collins,
Adam P. Arkin, Douglas S. Clark. Photovoltaics-Driven Power
Production Can Support Human Exploration on Mars. Frontiers in
Astronomy and Space Sciences, 2022; 9 DOI: 10.3389/fspas.2022.868519 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220427100529.htm

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