Output through the sol
Output across the Mars year
Plotted by sol, the seasons show their true, unequal lengths. Plotted by Ls, each season gets the same width, as astronomers chart them.
PV and battery sizer
Enter a load and the sizer finds the smallest PV array and battery that carry it through the design sol at the site, dust, mounting and losses set on the left, then checks the result across a full Mars year.
Yield map: latitude × season
Daily kWh per kWp with your mounting, dust and loss settings, . Click a cell to jump to that site and season. Blue is the lowest yield, dark red-brown the highest; grey means polar night.
Four seasons, unequal lengths
Mars has four seasons, not eight. Its orbit is eccentric enough that they differ in length by up to 52 sols, and the Sun is about 45% stronger at perihelion than at aphelion.
| Ls | Northern | Southern | Sols | Earth days | Sun W/m² |
|---|
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. Perihelion season is also dust-storm season, so the strongest sunlight often arrives through the dirtiest sky.
Against Earth
Mars output converted to kWh/kWp per Earth year (× 365.25 / 686.98), next to indicative fixed-tilt yields for Earth sites. The Earth figures are approximate ranges, not computed here; check any specific site in PVGIS.
Method and assumptions
Orbit and Sun position
- Solar constant 1,361 W/m² at 1 AU, scaled by 1/r². Semi-major axis 1.5237 AU, eccentricity 0.0934, perihelion at Ls ≈ 251°.
- Declination from obliquity 25.19°. Sol = 24 h 39 m 35 s; year = 668.6 sols.
- "Today on Mars" uses the Mars24 algorithm (Allison and McEwen, 2000) without the small perturbation terms; accurate to roughly a tenth of a degree of Ls.
- Sol curve integrated over 144 steps of true solar time. Twilight is ignored.
Atmosphere
- Direct beam: Beer–Lambert, exp(−τ·m), with a spherical-shell air mass (dust scale height 11 km).
- Diffuse: Mars dust scatters strongly forward, so much of the light removed from the beam still reaches the ground. Modelled as (1 − e−τm) × 0.65 × e−0.2τm. This is a simplified fit of my own, chosen to land near published Mars surface radiation tables. It is not validated; treat results as screening-level.
- Typical-year dust: τ ≈ 0.5 in the aphelion season rising to ≈ 0.95 around Ls 250. Illustrative, not a measured climatology.
- Altitude: dust optical depths are quoted at a 610 Pa reference (≈ 0 km). Assuming dust is mixed evenly with the air, τ at the site = τ × e−z/11.1 km, the same factor as surface pressure. Olympus Mons summit sees about 15% of the reference dust column; the Hellas floor about 160%.
- Isotropic sky diffuse on tilted planes; ground albedo 0.25.
PV conversion
- kWh/kWp = plane-of-array insolation (kWh/m²) × temperature factor × soiling factor × (1 − system losses).
- Cold cells produce more: factor = 1 + coefficient × (25 °C − cell temperature). The −10 °C default is an assumption; real cell temperatures depend on wind, mounting and season.
- Soiling: panels lose a fixed share per sol and are fully cleaned at the interval set. Mars Pathfinder measured roughly 0.3% per sol; please verify against the source before relying on it.
- Spectral shift: dust reddens sunlight. Silicon copes reasonably; multi-junction space cells can lose more. Folded into system losses.
PV and battery sizer
- PV: the smallest array whose surplus on the design sol, after battery round-trip losses, covers every deficit on that sol; then the margin is added. Run in 96 steps of local time.
- Battery: the deepest overnight drawdown on the design sol once the daily cycle has settled, plus any autonomy sols, divided by depth of discharge.
- Year check: a continuous 669-sol simulation with the battery carried over from sol to sol, using the dust setting on the left. Turn on the global storm to see what a storm year does.
- Area: module area = kWp ÷ (1 kW/m² × module efficiency). Fixed rows are spaced so the row in front casts no shadow within the chosen window around noon on the shortest sol for that hemisphere. The 150 Wh/kg default for pack specific energy is a rough figure for current lithium-ion packs; check it against a real product.
- Not included: battery heating, which on Mars can be a large night load (add it to the load profile), inverter standby losses, and module degradation.
For real design work
- Mars Climate Database (LMD / ESA / CNES) gives modelled dust, temperature and surface flux by site and season: www-mars.lmd.jussieu.fr
- Mars24 timekeeping algorithm (NASA GISS): giss.nasa.gov/tools/mars24
- Appelbaum and Flood, "Solar Radiation on Mars", NASA Technical Memorandum (1989), is the classic reference for surface irradiance versus optical depth. Cited from memory; verify the reference details.
- Local dust climate is not modelled: Hellas, for example, breeds its own storms and is often hazier than its elevation alone suggests.
- Elevation: MarsTopo719 spherical-harmonic shape model of Mars (M. Wieczorek, from Mars Global Surveyor MOLA laser altimetry), via the SHTOOLS project, expanded to degree 179 (about 60 km resolution) on a 0.5° grid. Heights are measured from the Mars reference ellipsoid, not the gravity-based areoid MOLA uses, because no gravity model was reachable. Spot checks against MOLA elevations I recalled for ten sites agree within about 1.5 km; crater floors narrower than ~60 km read too high (Gale and Jezero by roughly 1.3 km).
- Mars-PVGIS is an independent tool, named in homage to the European Commission JRC's PVGIS for Earth and not affiliated with it.
- Map: Mars colour mosaic and named-feature list from Celestia Content (GPL-2.0-or-later), derived from spacecraft imagery and IAU nomenclature. Lander coordinates are approximate.