Solar power on Mars
Every base on Mars will be an off-grid power system on the hardest site there is. Weaker sunlight, dust that can darken the whole planet, seasons of unequal length and nights cold enough to kill a battery. Here is how solar works there, and a free tool to design for it.
Less sunlight than Earth, but not as little as people think.
Mars orbits about 1.52 times further from the Sun than Earth does, and sunlight falls with the square of distance. Above the atmosphere, Mars receives on average about 586 W/m², a little under half of what reaches the top of Earth's atmosphere.
Its orbit is also far more eccentric than ours, so the figure moves through the year: about 490 W/m² at aphelion and about 713 W/m² at perihelion. That 45% swing matters more to a Mars solar designer than any seasonal change on Earth.
What decides a solar design on Mars.
Dust is the weather
Mars has almost no water cloud to speak of. Its weather, for a solar engineer, is dust. Engineers describe it by optical depth, τ: around 0.5 on a typical day, around 1 when it is dusty, 2 to 5 in a regional storm and above 5 when a storm wraps the whole planet.
The direct beam fades exponentially with optical depth and with the length of the path through the air:
The saving grace is that Martian dust scatters light mostly forwards. Much of what leaves the beam still reaches the ground as diffuse light, so output in a storm falls a long way but rarely to nothing. One design consequence: as the sky gets dustier, more of the light is diffuse and the extra yield from tilting or tracking the array shrinks.
Dust on the panels
Dust also settles on the modules. NASA's Opportunity rover was designed for a 90-sol mission and ran for more than 14 years, helped by gusts of wind that cleaned its panels from time to time. The InSight lander's mission ended in 2022 as dust built up on its arrays. A crewed base will need a cleaning plan, whether that is people, robots, coatings or simply oversizing.
Four seasons of unequal length
Because of its eccentric orbit, Mars has seasons that differ in length by up to 52 sols. The southern hemisphere gets the extremes: a short, intense summer near perihelion and a long, cold winter near aphelion. The north gets a milder version of both.
The catch is that perihelion is also dust-storm season. The strongest sunlight of the year often arrives through the dirtiest sky.
Cold helps the cells and hurts the batteries
Solar cells produce more power when they are cold, and Mars is very cold. Batteries are the opposite. Keeping a battery within its safe temperature range through a Martian night can be one of the largest loads on the system, and it peaks exactly when there is no sun. A Mars energy model that leaves out battery heating will undersize everything.
Design for the worst sol, then the worst season
The night on Mars lasts about as long as an Earth night, so the daily battery cycle looks familiar. What is unfamiliar is the planet-encircling dust storm, which can last weeks to months. The design question is the same one I ask for every off-grid site on Earth: what is the hardest stretch this system must survive, and how much is it worth to carry the load through it? On Mars the answer is a balance of extra PV, extra storage, load shedding and backup power.
Land, rows and shadows
At higher latitudes the Sun stays low through winter, and tilted rows cast long shadows. Row spacing, and therefore land area, is set by the shortest sol of the year at that site. Land is plentiful on Mars, but every square metre has to be landed, laid out, kept clean and cabled.
Solar has powered Mars exploration for decades.
Most missions that have worked on the Martian surface have run on sunlight. The two largest NASA rovers use radioisotope power instead.
| Mission | Landed | Power | Note |
|---|---|---|---|
| Mars Pathfinder and Sojourner | 1997 | Solar | The first rover on Mars. |
| Spirit and Opportunity | 2004 | Solar | Opportunity, designed for 90 sols, operated for more than 14 years until the 2018 global dust storm. |
| Phoenix | 2008 | Solar | Arctic lander. Fell silent as the polar winter set in. |
| Curiosity | 2012 | Radioisotope | Independent of sunlight and dust. |
| InSight | 2018 | Solar | Mission ended in 2022 as dust covered its arrays. |
| Perseverance | 2021 | Radioisotope | Carried the Ingenuity helicopter. |
| Ingenuity | 2021 | Solar | The first powered flight on another planet, recharged by its own solar panel. |
| Zhurong | 2021 | Solar | China's first Mars rover. Entered hibernation in 2022. |
Mars-PVGIS
A photovoltaic yield estimator for Mars, in the spirit of the PVGIS tool engineers use on Earth. Pick a site, a season and a mounting, and see what an array produces per sol, across a Mars year, and against typical Earth yields. Then size the PV and battery to carry a real load.
Mars-PVGIS is a screening tool. Its method and assumptions are set out in full inside the tool. For detailed mission design, results should be checked against the Mars Climate Database.
Solar on Mars, briefly.
How much sunlight reaches Mars?
Above the atmosphere, Mars receives on average about 586 W/m², roughly 43% of the 1,361 W/m² that Earth receives. Because Mars has an eccentric orbit, this varies from about 490 W/m² at aphelion to about 713 W/m² at perihelion. At the surface, dust in the atmosphere reduces it further.
Can solar power work on Mars?
Yes. Solar power has run many Mars missions, including Sojourner, Spirit and Opportunity, Phoenix, InSight, Ingenuity and Zhurong. Opportunity was designed for 90 sols and operated for more than 14 years. The challenges are dust in the air, dust settling on panels, long winters at high latitudes, and keeping batteries warm at night.
What happens to solar panels in a Mars dust storm?
Dust storms raise the atmospheric optical depth, which cuts the direct beam sharply. Because Martian dust scatters light mostly forwards, part of the lost beam still reaches the ground as diffuse light, so output falls a long way but not usually to zero. A planet-encircling storm can last weeks to months, so a Mars power system needs storage, reserve capacity or both.
How big would a solar farm on Mars need to be?
It depends on the load, latitude, season, dust and how much storage you use. Mars-PVGIS sizes the PV array, battery and land area for a given load profile at any site on Mars, then checks the design across a full Mars year. Try it above.
Working on Mars power?
I am available for mission concept studies, research collaborations, talks and media on solar power on Mars.