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There is extensive research on growing food on Mars, and I'm particularly interested in optimizing food production.

Given equal area in a greenhouse, is it more efficient to grow crops on Martian sunlight directly (590 W/m2), or to use solar panels and a grower lamp? There are certainly losses, but this may be offset by the relative efficiency of photosynthesis at varied light intensities.

As suggested elsewhere, it may even turn out that the most efficient method is through light-concentrating lenses.

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  • $\begingroup$ It's an interesting question, the problem I have with it currently is that you haven't defined efficiency. The way it's phrased you could substitute the word 'better' and it would ask the same thing, which is subjective. Efficient in what sense? $\endgroup$
    – GdD
    Commented Aug 9, 2022 at 15:47
  • $\begingroup$ Well, it’s more energy efficient to grow them with just sunlight as you have no losses in transfer. But it’s more time efficient if you use grow lights . Which do you want? $\endgroup$
    – Topcode
    Commented Aug 9, 2022 at 17:09
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    $\begingroup$ Lots of info these days on using different color LEDs on different parts of plants at different times to optimize growth. This has spread well beyond the original grow uses into more main line gardening... $\endgroup$
    – Jon Custer
    Commented Aug 9, 2022 at 18:06
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    $\begingroup$ Without some artificial lighting the weeks to months long Mars dust storms will be problematic. But lighting powered by solar will be problematic for the same reason. These storms tend to occur with known regularity so it may be possible to cache some produce and accept lost productivity; a regular time to do maintenance and upgrades? All hypothetical; we are a long way from any attempts and there is an abundance of problems to solve. $\endgroup$
    – Ken Fabian
    Commented Aug 10, 2022 at 3:01
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    $\begingroup$ Amount of calories per what though @MrMartin? Energy? Human labor? Water consumption? $\endgroup$
    – GdD
    Commented Aug 11, 2022 at 10:26

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Plants can only use a finite amount of light, and are adapted to growth under less than ideal growing conditions...even on Earth, they experience cloudy days, shade from other plants, etc. Many crop plants will be at or near light saturation even in Martian sunlight.

Noon sunlight on a clear day on Earth is about 2000 μmol/m2/s, so on Mars it will be about 890 μmol/m2/s. Per this table, spinach, in sunlight, has a light saturation point of 857 μmol/m2/s. Potatoes are can make use of more sunlight with their saturation point at 1145 μmol/m2/s, but they'll probably do fine. Tomatoes at 1985 μmol/m2/s might benefit from doing something to augment natural sunlight. And breeding and engineering may improve the ability of crops to make use of the dimmer sunlight on Mars.

However, your options are not limited to either sunlight or lamps, you can also install lamps in your greenhouses and use them to compensate for season (Mars has both an Earthlike axial tilt and an orbit eccentric enough to be significant), light-hungry crops, and for events such as dust storms. Solar concentration would be more difficult (due to its dependence on sun position) and would be unable to compensate for dust storms.

As for the relative efficiency of the direct sunlight vs. the LEDs, using a more optimal spectrum but going through multiple conversion steps: the LED option might still be a more efficient use of sunlight hitting the surface of Mars, but that's not really a resource in scarce supply. Growing plants with any proportion of natural sunlight is obviously a more efficient use of power generated by solar panels, if all else is equal. However, it certainly won't be...green houses using natural light might need more active heating, or have higher power requirements for things like maintaining their atmospheres, supplying water, etc. Unfortunately there's no clear answer here, it depends on too many other factors.

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  • $\begingroup$ Great answer, that's encouraging. But you're assuming constant "noon sunlight on a clear day", which is definitely not the case. Want to elaborate on year-round production? $\endgroup$
    – MrMartin
    Commented Aug 12, 2022 at 14:01
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    $\begingroup$ I am not making such an assumption, I'm simply taking that as the basis for comparison. The axial tilt of Mars is very similar to Earth's, and the variation in sunlight over the course of a day and the day/night ratio over the course of a year will be similar, just with a longer year. The eccentricity of the orbit has an additional effect, but small in comparison to the difference from Earth. The day/night ratio can affect things like flowering in some plants, and is another thing you could control with added artificial lighting (or artificial shade), if necessary for the crops you're growing. $\endgroup$
    – Christopher James Huff
    Commented Aug 12, 2022 at 16:18

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