Bioreactor for Mars Base Power

[DeepSeaBase]

TL:DR

• Your mind will be blown.
• Bioreactor/diesel blows Solar out of the water.
• Bioreactor is approximately 5x more efficient than Solar Panels optimized for Mars. WITHOUT additional efficiency modifiers that can be applied to Bioreactors.
• Same area of flat bioreactor as Solar Farm (50km^2) = power for 277 astronauts.
• Bioreactor makes rocket fuel (solar panels do not).
• Bioreactor is modular and can be built on Earth and shipped to Mars.
• Bioreactor uses in-situ materials, solar panels cannot.
• Bioreactor recycles all its nutrients/materials.
• Bioreactor provides numerous other benefits to Astronauts.

 

So my first thread raised a lot of good questions, I want to attempt to answer them properly.

The main questions are:

1. How can this be more efficient than solar?
2. How can it be provided for? Nutrients, offworld elements, etc?
3. How can it operate?

Basically it comes down to this: is a bioreactor more efficient and practical than a solar farm or some radiogenic method, etc?

I say yes for the following reasons. First, why did I retitle this from "biodiesel"? Because I'm not sold on the closed-cycle diesel generator. There is an even better ethanol fuel cell that is a potential power source that uses elements easily extracted from Martian Regolith to act as the catalyst.

So first: technologies used.

1. Photobioreactor - https://www.researchgate.net/publication/318031436_Photobioreactors_for_the_production_of_microalgae
2. Direct Ethanol Fuel Cell - https://en.wikipedia.org/wiki/Direct-ethanol_fuel_cell
3. Or a Closed Cycle Diesel Generator - https://en.wikipedia.org/wiki/Air-independent_propulsion#Closed-cycle_diesel_engines

Measurement of success?

Generate power on a better scale than solar at less weight-cost than uranium using in situ materials if possible.

K, let's get started.

So the photobioreactor comes in many forms but its efficiency comes in its space savings and modular design. The module can be pre-built on Earth and shipped to Mars, an advantage to any set-up requiring more labor-intensive construction.

Tubular Serpentine Photobioreactors with linear-fresnel lens solar concentrators will be the probable type of photobioreactor used to accomplish biomass production.

Why? Because the linear-fresnel lenses will greatly improve efficiency. Such devices theoretically could be used to enhance solar panels, but the weight of a panel is higher than an empty tube and again, not modular or compact and can't be stacked (unlike bioreactors which can stack).

The important part of this is dry mass - an acre of open ponds of algae produces at most about 10 grams of algae per day per m^2 footprint.

Comparatively - the photobioreactors without additional equipment (such as the fresnel lens) produce 22 grams per liter per day.

Key Facts

• 20 m^2 = 1 gallon of fuel per day.
• Fuel can be biodiesel (a methyl ester) or ethanol.
• fresnel lens increases solar irradiance by 3.5x more than enough to make up for Mars's lower insolation.

For simplicity I'll keep to 1 gallon a day of either fuel type per 20 m^2. Therefore the module would be roughly a 5m x 5m module and can be constructed on Earth and shipped ready to operate on Mars.

How much energy does 1 gallon produce?

Roughly speaking you can get 10 kwh's per gallon of diesel. https://energyeducation.ca/encyclopedia/Diesel_generator

Key Facts

• Diesel engine produces approximately 10kwh's per gallon of diesel.
• 2.4 Gallons of fuel per Martian Day per 1kwh stead load.
• 2.4 Modules or round up to 3 modules fueling a diesel engine.

How does this stack-up with the Martian energy requirements?

Not sure...so I'll use this as a source: https://planete-mars.com/a-mars-colony-a-tentative-technical-analysis/8/

90KW per person or 3.75kwh per person. We can get 1 kwh from 2.4 modules so this conveniently works out to 9 modules.

Situation so far

I did not stack the modules, so we are going with a short footprint of flat modules, with 20m^2 footprints. If the modules are built upward you can greatly reduce this footprint further.

Rough calculation are 180 m^2 per astronaut on Mars.

Based on others' statements I've seen 50,000m^2 for solar panels quoted for a base of unknown number of astronauts. But... bioreactor modules using closed cycle diesel can provide for 277 astronauts with the equivalent footprint.

What about ethanol fuel cells?

There are strains of algae that excrete ethanol and other chemical processes can extract ethanol.

So how much energy is produced by an ethanol fuel cell?

Source: https://energiforskmedia.blob.core.windows.net/media/18529/direct-ethanol-fuel-cells-ethanol-for-our-future-fuel-cells-energiforskrapport-2015-137.pdf

Direct Ethanol Fuel Cells produce 6.4 kwh of electricity per liter. Again a gallon is approximately 4 liters, so 1 gallon per day = approximately 1kwh of electricity.

The advantage with direct ethanol fuel cells comes from the materials and the lack of complicated oxidizers for closed cycle diesel engines.

These Direct Ethanol Fuel Cells use Iron, Nickel and Cobalt for their catalyst and those can be pulled from the Martian Regolith in sufficient quantity if needed to be replaced or repaired.

Key Facts:

• Direct Ethanol Fuel Cells are not much more efficient than the Diesel Generator.
• In-situ materials.

I'd say the ethanol fuel cell therefore could be more advantageous, but its power consideration comes from how much ethanol versus diesel per biomass can be generated.

CONCLUSION

My conclusion so far is that basically the bioreactor can provide for 277 Astronauts if it were the size of the solar farm.

I don't even want to bother explaining all the other benefits of having a bioreactor, and it's a given that all the materials for the bioreactor are recyclable while the bioreactor converts CO2 into O2 which gives you HALF of your return home fuel requirements.

Furthermore - the bioreactor can in fact make METHANE.

Dare I say...BOOM *mic drop*

NOTES:

I didn't give the exact figures for Solar panel efficiency, instead I compared solar panel performance on earth to the bioreactor performance on earth and considered it good enough. Since basically the two suffer the same inefficiency problems and wavelength optimizations are possible for both if you consider strains of algae versus materials of solar panels. Source: https://www.theecoexperts.co.uk/solar-panels/how-much-electricity

[swansont]

14 minutes ago, DeepSeaBase said:

Because the linear-fresnel lenses will greatly improve efficiency. Such devices theoretically could be used to enhance solar panels, but the weight of a panel is higher than an empty tube and again, not modular or compact and can't be stacked (unlike bioreactors which can stack).

How do you stack something that requires lenses to concentrate the light?

[DeepSeaBase]

15 hours ago, swansont said:

How do you stack something that requires lenses to concentrate the light?

Bioreactor tubes are stackable because biomass production doesn't fall-off as fast as solar productivity does in less light. The fresnel lens just enhances the irradiance for the entire stack of tubes or wherever its target happens to be.

Your question gives me an idea though.

The Bioreactor module, if was taller, could have walls that fold down when landed that contain mirrors, and the mirrors can shine up to the bottom of a higher stack. In this way the higher stack is illumined from below which if you think of those solar concentrators on the roof, that below target can be hit and funnel light (by mirror probably) into a lower stack.

Depends on if it's worth it to stack the modules.

For your statement though it was in reference to the amount of tubes that can be packed into a space. You can stack more and have effectively up to 2 or 3x the tubes on a square meter footprint and still not lose too much. The entire 'window' of the module would be the lens.

[swansont]

1 hour ago, DeepSeaBase said:

Bioreactor tubes are stackable because biomass production doesn't fall-off as fast as solar productivity does in less light.

But you claim "the linear-fresnel lenses will greatly improve efficiency."

So which is it? Is the efficiency greatly improved, or does it not matter much? You need to explain why this is so.

 

I will note that not of these claims are quantified, nor is any direct justification given for them. Just hand-waving.

[Ken Fabian]

I am not so interested in whether bioreactors and biofuels can work on the moon or Mars as whether it can help meet our near term and critical requirements for abundant clean energy here on Earth - but any technology to be used in space will have to be developed and proven on Earth first, so that isn't a conflict of interest.

The advantage of PV is you just expose it to sunlight and it makes electricity. No moving parts, can be plug and play, is low cost and exceptionally reliable, and likewise for associated equipment. Available solar area isn't usually the limiting constraint, so energy yield per m² is not a deal breaker; by all measures the yield from PV in most places is very good right now. There are biofuel successes but they tend to rely on the natural advantages of being on Earth - crops that grow readily in existing soils with natural rainfall, open ponds for algae cultures, availability of power and other supply. The concentrator type and other closed bioreactors are not as efficient and effective as claimed; the first link noted that getting tubular bioreactors from energy negative to energy positive is an ongoing challenge. Just the energy requirement for keeping the fluids well mixed seems to be a major hurdle. Failure to be energy positive is a big problem here on Earth, but would be a bigger problem on Mars. That doesn't sound like something that will make 5 times the energy production than PV to me.

PV is demonstrably energy positive but biofuels from tubular bioreactors are not, which makes the claims of superior energy delivery look wrong. Not clear what nutrients would be required but sources will be essential. It doesn't look like any kind of plug and play kind of technology, but would need constant attention, ie farming. It is also not clear what the steps and requirements are between biomass or ethanol gain in a ferment fluid and usable fuels ie dry burnable biomass, diesel grade oil or distilled ethanol of purity suited to fuel cells but they will be there - at a cost to overall efficiency and energy output. In space you will need the Oxygen if you burn anything or use fuel cells; it may be from CO2 recycled, possibly by bioreactor, but in a closed system it will add yet more associated equipment and energy use.

I like the enthusiasm for biofuels but it is a long way from being a replacement - let alone clearly superior replacement -for PV. Not on Earth, not in space.