Power options for a Mars settlement

[john smith 19]

JohnSmithxxx (I forget the number attached to his handle) brought up the idea of salt storage a long time ago in this thread. He said something about salt in beer cans of all things, buried in a pit, and claimed it had been done. I consider him a high quality info source.

Thank you. I try to be accurate.

It was run by the US Navy Naval Research Laboratory in the late 70's/early 80's and was called "SolChem." It planned to use a cyclic chemical reaction (several were being looked at, ammonia was one of them) to move heat without needing insulated pipes.

The ultimate goal was to make the US Navy independent of oil supplies for its non-nuclear fleet by mfg synthetic fuel with systems mfg from materials available on CONUS. So the salt was a mix of Sodium and potassium chloride (IE Rocksalt) rather than some more exotic mix.

But salt dissolves easily with even a little water around so they planned to put it in beverage cans. OTS technology able to support very large volumes. To keep moisture out and ensure thermal transfer remained good after the salt had reached its melting temp (not something that would happen if it melted into a big pool then was frozen back again.    I can't recall if they were actually going with Aluminum or steel. the operating temp was about 500c, so Aluminum is possible but AIUI steel was still in common use for beverage cans at the time.

I question aluminum beer cans but following the idea, steam from the tower flows into the salt bunker, then to the turbines. After dark, the tower is cut out of the loop to avoid unnecessary cooling of the working fluid. This avoids the problems associated with molten salt. It might cut energy density but that sounds like a good trade for an early infrastructure.

However using steam in the tower as you propose complicates things. Nitrate salts melt around 700c and (IIRC) Solchem was targetting about 500c. If you match the operating temp of modern Super and Ultra-Supercritical steam turbines you can buy them OTS, like the 8000+ used in fossil fuel power plants around the globe, not the 390 of water moderated reactors.

[john smith 19]

Just realized I forgot my source: https://an.rsl.wustl.edu/merb/merxBrowser/an3.aspx?it=D1&ii=22771

Opportunity is currently in the midst of a severe dust storm though all subsystems are still operating as expected in RAM mode as of the Sol 5111 UHF pass. Solar array energy is approximately 22 W-hrs, with a measured tau of 10.8. This Tau measurement is the highest ever recorded from a ground station on the planet Mars. Dust factor was previously estimated at 3.27 as of Sol 5108.

22 W-hrs?

that's not a solar cell output that's a measure of energy in a battery. 

The output of a PV array should be in watts only.

[john smith 19]

What you are saying is just wrong, but you constantly repeat it. The figure of Watt-hours is integrated received power that day, NOT battery state of charge. Quit accusing others of ignoring something which is really just you misinterpreting something clear as day.

OK that makes a bit more sense.

The units are still quite odd.

So the average that day should be that figure divided by 24? that would give 0.9167w as the average PV array output.

Which doesn't seem like much.

[john smith 19]

I disagree that the reactor does not exist as yet, seems to me that modest size submarine reactors are pretty routine.
Weight is the main issue, mostly due to passive shielding that can be eliminated just by siting the reactor remotely.

Solar takes acres of cells to get reasonable power, so mandates a construction project right after getting there. Imho, that is a serious negative.

They're not that small as their typical size in 60MW, about the size of the few merchant ship reactors that have been built outside the former Soviet Union (the one for the NSS Savanah and one built in Germany IIRC)

And of course any naval reactors come under national security regulations.

So you've got a) A couple of reactors built 70 odd years ago or b)Modern one whose technology is a state secret.

Neither is exactly accessible 

[john smith 19]

The observation is correct, but the thing is that as you try to reject at lower and lower temperatures, the size of the heat exchangers increases.

If you can use the colony as the heat sink (e.g. taking hot showers or cooking soup or even keeping the habitats warm) then maybe some of that mass is free.

I think that's what JS may have been aiming for.

Exactly.

Mars is damm cold    The power engineers "Low grade waste heat" is the ECLSS engineers fish tank and greenhouse temperature management supply. 

In chemical engineering it's sometimes called "Scavenging," but people feel that's a bit pejorative.
Let's call it "re-purposing" heat. 

[john smith 19]

The argument against wind power is that the surface winds are too low and would need either a very tall tower or a balloon. Hmmm.

A new form of cogeneration? Mars is so power poor ya gotta take what you can get. Actually this emphasizes an important point. There is probably no one solution.


Diversification can only be a good thing until real people (not us armchair guys) get their hands dirty over time. Then they'll have ground truth knowledge of what works best under different circumstances. Theory is great but experience is better.


An minor nit Ive thrown out on occasion. Needs for expedition 1-3 are entirely different than later. 1-3 are strictly about survival and initial build out. The next several (or many) synods are about more than survival but not yet about thriving. That's when the technology shakeout will happen. Once they know what works and what doesn't, the stage will be set for Mars to thrive. This applies to everything, not just power.


A lot of the disagreement here is because of us thinking about but not acknowledging different phases of future history. Is there any way to fix this?

Good points. Yes Mars is very power poor. No coal or oil (and very little free oxygen to burn them with if they existed    ). I'm not sure how well people actually appreciate this fact.

[meekGee]

The argument against wind power is that the surface winds are too low and would need either a very tall tower or a balloon. Hmmm.

A new form of cogeneration? Mars is so power poor ya gotta take what you can get. Actually this emphasizes an important point. There is probably no one solution.


Diversification can only be a good thing until real people (not us armchair guys) get their hands dirty over time. Then they'll have ground truth knowledge of what works best under different circumstances. Theory is great but experience is better.


An minor nit Ive thrown out on occasion. Needs for expedition 1-3 are entirely different than later. 1-3 are strictly about survival and initial build out. The next several (or many) synods are about more than survival but not yet about thriving. That's when the technology shakeout will happen. Once they know what works and what doesn't, the stage will be set for Mars to thrive. This applies to everything, not just power.


A lot of the disagreement here is because of us thinking about but not acknowledging different phases of future history. Is there any way to fix this?

Good points. Yes Mars is very power poor. No coal or oil (and very little free oxygen to burn them with if they existed    ). I'm not sure how well people actually appreciate this fact.

Yup everything will be about power.  You can make all the plastics and glass and metal that you want from local resources, but every little thing costs power and there's no serious source other than nuclear and solar.

I am always wondering what the magic number is, in kWatt-hr/yr, per person, including everything from air to food to transportation to construction.

I've tried to ballpark it before based on terrestrial numbers, but it's not straight forward. I wonder if SpaceX has a firm estimate.

[lamontagne]

The argument against wind power is that the surface winds are too low and would need either a very tall tower or a balloon. Hmmm.

A new form of cogeneration? Mars is so power poor ya gotta take what you can get. Actually this emphasizes an important point. There is probably no one solution.


Diversification can only be a good thing until real people (not us armchair guys) get their hands dirty over time. Then they'll have ground truth knowledge of what works best under different circumstances. Theory is great but experience is better.


An minor nit Ive thrown out on occasion. Needs for expedition 1-3 are entirely different than later. 1-3 are strictly about survival and initial build out. The next several (or many) synods are about more than survival but not yet about thriving. That's when the technology shakeout will happen. Once they know what works and what doesn't, the stage will be set for Mars to thrive. This applies to everything, not just power.


A lot of the disagreement here is because of us thinking about but not acknowledging different phases of future history. Is there any way to fix this?

Good points. Yes Mars is very power poor. No coal or oil (and very little free oxygen to burn them with if they existed    ). I'm not sure how well people actually appreciate this fact.

Yup everything will be about power.  You can make all the plastics and glass and metal that you want from local resources, but every little thing costs power and there's no serious source other than nuclear and solar.

I am always wondering what the magic number is, in kWatt-hr/yr, per person, including everything from air to food to transportation to construction.

I've tried to ballpark it before based on terrestrial numbers, but it's not straight forward. I wonder if SpaceX has a firm estimate.

For our Mars settlement we calculated 1600 GJ/Y/person.  Food takes up a lot of that.  If there is absolutely no natural solar used, then it's even more.  Most serious designs I've seen are in that ballpark.

I have  spreadsheet, but it's mostly in French....

[Greg Hullender]

For our Mars settlement we calculated 1600 GJ/Y/person.  Food takes up a lot of that.  If there is absolutely no natural solar used, then it's even more.  Most serious designs I've seen are in that ballpark.

I have  spreadsheet, but it's mostly in French....

That's about  50 kW/person. Quite a bit more than the 9 kW/person (284 GJ/y/person) the average American uses. But the average American doesn't have to manufacture his own air. :-)

That suggests the first settlement is really going to need that megawatt reactor though.

[lamontagne]

For our Mars settlement we calculated 1600 GJ/Y/person.  Food takes up a lot of that.  If there is absolutely no natural solar used, then it's even more.  Most serious designs I've seen are in that ballpark.

I have  spreadsheet, but it's mostly in French....

That's about  50 kW/person. Quite a bit more than the 9 kW/person (284 GJ/y/person) the average American uses. But the average American doesn't have to manufacture his own air. :-)

That suggests the first settlement is really going to need that megawatt reactor though.

The study forgets that Americans eat food.  America has 157 000 000 Ha of arable land, to feed 350 000 000 people, or 2 people per hectare.  Or in other words 5000 m2 of land is required to feed one person.  This land receives about 250 W/m2 on average, including angle effects, nighttime and clouds.  That's 5000 x 250 = 1 250 kW of power per person.  That power is necessary to feed the US population. So the real average power use is 1259 kW, not 9 kW.
Now most of that sunlight is wasted in reflection, evaporation and general weather losses. Much of the food produced is wasted, or eaten by competition. Winter losses and growth cycles losses also affect the production rates.
Greenhouses can be about 30 times more efficient that arable land in food production terms, at 60 tonnes per hectare.  So 1250kW / 30 is about 41 kW.  add that to your 9 kW and you get 50 kW.

On Mars there is no land, all food needs to be produced in greenhouses, and the light levels are 50% of those on Earth.  So the 50 kW per colonist is an optimist number, with the expectation that up to 50% of the food can be produced in natural sunlight greenhouses.  If all food must come from artificial grow rooms and vertical farms, the power usage will be even higher.

[daveglo]

The study forgets that Americans eat food.  America has 157 000 000 Ha of arable land, to feed 350 000 000 people, or 2 people per hectare.  Or in other words 5000 m2 of land is required to feed one person.  {snip}

Your math is WAY off. 

Firstly, land in farm production in the US is 895,300,000 acres (362,310,000 Ha), not the value you quoted.

Second, the US feeds far more than it's own population.  Bulk exports of raw products exceed imports by a ratio of almost 40:1.

The reality is that the number you're looking for depends in large part on what you can get away with.  A more general estimate using quality soils would be 1 acre (0.4 Ha) per person.  But of course, the soils on Mars are going to be much more of a challenge, just because of the volume of fertilizer needed to make it suitable for food production.

I would agree that power requirements are going to be a top issue.  The big question is how much power to do you need to get water, oxygen, methane, and nitrogen out of the martian environment?  THAT's the number you're really looking for.

[Ionmars]

The study forgets that Americans eat food.  America has 157 000 000 Ha of arable land, to feed 350 000 000 people, or 2 people per hectare.  Or in other words 5000 m2 of land is required to feed one person.  {snip}

Your math is WAY off. 

Firstly, land in farm production in the US is 895,300,000 acres (362,310,000 Ha), not the value you quoted.

Second, the US feeds far more than it's own population.  Bulk exports of raw products exceed imports by a ratio of almost 40:1.

The reality is that the number you're looking for depends in large part on what you can get away with.  A more general estimate using quality soils would be 1 acre (0.4 Ha) per person.  But of course, the soils on Mars are going to be much more of a challenge, just because of the volume of fertilizer needed to make it suitable for food production.

I would agree that power requirements are going to be a top issue.  The big question is how much power to do you need to get water, oxygen, methane, and nitrogen out of the martian environment?  THAT's the number you're really looking for.

The production numbers you cite are new to me, especially the 40:1 ratio. Do you have a reference?

[lamontagne]

The study forgets that Americans eat food.  America has 157 000 000 Ha of arable land, to feed 350 000 000 people, or 2 people per hectare.  Or in other words 5000 m2 of land is required to feed one person.  {snip}


Your math is WAY off. 

Firstly, land in farm production in the US is 895,300,000 acres (362,310,000 Ha), not the value you quoted.

Second, the US feeds far more than it's own population.  Bulk exports of raw products exceed imports by a ratio of almost 40:1.

The reality is that the number you're looking for depends in large part on what you can get away with.  A more general estimate using quality soils would be 1 acre (0.4 Ha) per person.  But of course, the soils on Mars are going to be much more of a challenge, just because of the volume of fertilizer needed to make it suitable for food production.

I would agree that power requirements are going to be a top issue.  The big question is how much power to do you need to get water, oxygen, methane, and nitrogen out of the martian environment?  THAT's the number you're really looking for.

Arable land, not farming land.  I don't think we will be grazing many cows out to pasture on Mars.
https://worldpopulationreview.com/country-rankings/arable-land-by-country

Err.... 0.4 Ha is awfully close to 0,5 ha.  5000 m2.  Wouldn't call that way off.  It's basically the same number.

Sorry, but no.  These are all fairly easy to extract.  the most difficult issue is getting plants to function.  Photosynthesis is extremely inefficient (but also almost magical!) and evapotranspiration takes ridiculous amounts of energy.

The entire planetary ecosystem has evolved over billions of years to operate with huge amounts of water and a power level based on 1200+ W/m2 peak.  You won't be able to do the same thing with 600 W/m2.

Regarding import export, it's awfully close to a null game, as far as I can see.

'Agricultural exports support more than one million American jobs, with roughly 70 percent of these jobs in the non-farm sector, such as in processing and agricultural manufacturing. Overall, U.S. farmers and ranchers export more than 20 percent of what they produce.'
vs
'American consumers seek a safe, diverse, and abundant food supply that is simultaneously affordable and available throughout the year. To help meet these consumer demands, the United States imports about 15 percent of its overall food supply.27 sept. 2022'

https://www.foodsafetynews.com/2022/02/rising-food-imports-into-u-s-call-for-a-global-prospective/

I can provide the entire breakdown of the energy use if you want, will just take a few hours to translate :-)

The (practically) only good thing about Mars is that it's so cold that you can cool grow rooms without needing compression and refrigeration, as we do on Earth. 

[daveglo]

Well, I'll rely on a US source for data about the US:

https://www.nass.usda.gov/Publications/Todays_Reports/reports/fnlo0222.pdf

Page 4.

And I think you're missing the point.  You could feed a dozen people on an acre, or no one.  It's how WELL can you use it.  And that land-use efficiency coefficient is going to vary widely, and is strongly dependent upon light/heat energy input (whether natural or artificial) and fertilization (carbon, hydrogen, nitrogen, oxygen).

You want a good read on a system that lends itself to colonization-style agriculture, try searching for shipping container farming.  It's a hot topic.

https://www.freightwaves.com/news/want-your-own-farm-this-one-comes-in-a-shipping-container

[Twark_Main]

What you are saying is just wrong, but you constantly repeat it. The figure of Watt-hours is integrated received power that day, NOT battery state of charge. Quit accusing others of ignoring something which is really just you misinterpreting something clear as day.

OK that makes a bit more sense.

The units are still quite odd.

So the average that day should be that figure divided by 24? that would give 0.9167w as the average PV array output.

Which doesn't seem like much.

Technically divided by 24.66 hours.

And yes, it's not much. That power output was measured during a very dark dust storm.

[Twark_Main]

Now most of that sunlight is wasted in reflection, evaporation

That's not waste, it's water purification.

This is true on Earth too. If plants didn't "wastefully" evaporate (really, transpire) water, then we'd lose the source of 80% of rainfall on the land surface.

On a Martian greenhouse, you can recover both the water and the latent heat of evaporation with dehumidifiers. You can pipe the water to a final filtration step, and recuperate the low-grade heat for some purpose (eg space heating).

[meekGee]

For our Mars settlement we calculated 1600 GJ/Y/person.  Food takes up a lot of that.  If there is absolutely no natural solar used, then it's even more.  Most serious designs I've seen are in that ballpark.

I have  spreadsheet, but it's mostly in French....

That's about  50 kW/person. Quite a bit more than the 9 kW/person (284 GJ/y/person) <a href="https://www.npr.org/2022/04/12/1092045712/how-much-energy-powers-a-good-life-less-than-youre-using-says-a-new-report#:~:text=Americans%20use%20284%20gigajoules%20a,according%20to%20the%20new%20research.">the average American uses</a>. But the average American doesn't have to manufacture his own air. :-)

That suggests the first settlement is really going to need that megawatt reactor though.

50 kWatt-avg sounds right.  I got numbers from 10 and up, but there are so many variables.

How much is spent recycling CO2/O2?  Food growing? How much is expended on building stuff, like running tractors or tunneling machines...  Creating ISRU materials like plastics, glass, metal? Transportation?  Propellant? 

It's quite the list.

I think proceeding with 50 is a good starting point.

[lamontagne]

Probably a good time to repost this:

https://marspedia.org/Embodied_energy

The energy required to produce various goods.  This does not include labor, that could also be represented on Mars by energy usage to maintain the habitat and produce food for humans for a more complete picture.

Future improvements in automation will reduce the labor costs, however.

For the questions about nitrogen and such, see the first few lines of the table.

[lamontagne]

Going to rework the hydroponics energy figures and refine them a bit.
There are a lot of references to lettuce with the vertical farm growers, which have a fine yields as far as mass goes, but that include very little energy, as they are mostly water.

[john smith 19]

Anyway, getting back on-topic, Tau Theory's demise is great for would-be Mars colonists. It means that even in the deepest dust storm we don't need supplemental wind / nuclear / whatever. If we have a solar array sized for propellant production, it's plenty oversized for providing life support during a dust storm.

"Good news, everyone!"

Provided you ship 50x (not 50%, 50x) the size of array you need under normal circumstances. And ideally that needs to be shipped early because without it any crew will probably die. 

Which suggests there is a case for at least considering a secondary system provided it doesn't need too much development work.

That would include wind (a tall  tower with a windmill on top. That sounds like it could be engineered fairly easily) or geothermal (there are houses in the US that are at least partly heated by bore-hole heat exchangers) and it's pretty clear that at least one set of equipment to bore holes through rock is going to be needed anyway.

I'm no fan of mars-specific nuclear projects. If the USG supplied Kilopower units as GSE that would be viable but an actual "SX Reactor (TM)"  is ridiculous given the very steep learning curve in acquiring nuclear technology from scratch. Running on naural uranium to begin with would be a smart move (as most 1st generation designs were) to avoid the endless ITAR issues with enriched uranium, and the whole business of enrichment anyway.