Solar Constant Calculator
The intensity of a star's light at any distance — the solar constant, 1,361 W/m² at Earth — and what a solar panel of a given size and efficiency would produce there, in continuous sunlight.
A star's luminosity spreads over a sphere, so intensity falls with the square of distance: 1,361 W/m² at Earth, 586 at Mars, 51 at Jupiter.
How the solar constant calculator works
A star's luminosity spreads over a sphere, so intensity falls with the square of distance: 1,361 W/m² at Earth, 586 at Mars, 51 at Jupiter. That inverse square is why solar power works well to about Mars and why every mission beyond Jupiter carries a nuclear source.
In space a panel sees the full solar constant with no atmosphere and no night — a 10 m² array at 30% gives 4 kW at Earth's distance, around the clock.
Formula: S = L / (4 π d²); P = S × A × η
Worked examples
| Inputs | Irradiance (W/m²) | Note |
|---|---|---|
| Earth | 1,361.17 | 1,361 W/m² |
| Mars | 586.06 | 586 — solar still works |
| Jupiter | 50.34 | 50 — nuclear territory |
FAQFrequently asked questions
What is the solar constant?
The Sun's irradiance at Earth's mean distance, above the atmosphere: 1,361 W/m². It is not quite constant — it varies about 0.1% with the solar cycle and 7% over the year as the distance changes.
Why does it fall with distance squared?
Because the same light spreads over a sphere whose area grows with the square of its radius. Twice as far, a quarter the intensity.
How much power does a panel make in space?
Irradiance times area times efficiency, with no night, no clouds and no atmosphere. Space-rated cells reach 30%; the same panel on the ground averages a fifth of its space output.
How far out does solar power work?
Comfortably to Mars, marginally to the asteroid belt, and Juno at Jupiter needed 60 m² of panels for 400 W. Beyond that, radioisotope generators.
What is the plate temperature?
The equilibrium of a black plate facing the star and radiating from both faces — about 330 K at Earth's distance. It is why spacecraft need thermal design, not just power.
Where these figures come from
- NIST — CODATA 2018 fundamental physical constants — G and the speed of light
- IAU 2015 Resolution B3 — nominal solar and planetary conversion constants — the astronomical unit, solar mass and planetary radii
- Royal Observatory Greenwich — the historic home of the prime meridian
Last checked: September 2026. Constants are CODATA 2018 (G, c) and IAU 2015 nominal values (solar and planetary parameters).