Author Topic: Power options for a Mars settlement  (Read 143835 times)

Offline rakaydos

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Re: Power options for a Mars settlement
« Reply #840 on: 11/29/2018 06:53 am »
Or perhaps store the fuel as H2 rather than methane?

How hard would it be to ISRU an Zero Boiloff hydrogen tank?
not hard if itís gaseous.
You are saying Hydrogen becomes easier to contain as a gas than as a liquid? That seems odd to me.

Well, you don't have to worry about boiloff.
Ah- a technically correct answer. :p

Does gasous hydrogen have the same long term containment issues that liquid hydrogen does? I recall hearing of hydrogen leaking through solid metal, and similar issues.

Online speedevil

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Re: Power options for a Mars settlement
« Reply #841 on: 11/29/2018 07:09 am »
Does gasous hydrogen have the same long term containment issues that liquid hydrogen does? I recall hearing of hydrogen leaking through solid metal, and similar issues.
'no' - in that if you have 100 tons of hydrogen - a million cubic meters or so at STP, diffusion is not an issue, leaks are. (which can be captured by a light outer shell).

This is a sphere some hundred meters in diameter, or a twenty meters in diameter at ~200 bar.

As an example if made from Al, it would be of the order of 20000 tons (at either pressurisation).

In principle a thin film could contain it at near atmospheric pressure, but now you have to deal with a hundred million cubic meters - and ...

If you can find large lava tubes, this would be excellent, and ideal of course.




Offline CuddlyRocket

Re: Power options for a Mars settlement
« Reply #842 on: 11/29/2018 07:14 am »
Or perhaps store the fuel as H2 rather than methane?

How hard would it be to ISRU an Zero Boiloff hydrogen tank?
not hard if itís gaseous.
You are saying Hydrogen becomes easier to contain as a gas than as a liquid? That seems odd to me.

Well, you don't have to worry about boiloff.

Either way, it seems a very large investment in Hydrogen storage facilities in terms of both mass and/or continual power requirements when compared with the straightforward technical fixes to enable a methalox ICE to operate. Also, how much Hydrogen will you store and what happens when you run out? In all likelihood you're still going to have methalox stores and therefore still need some way of utilising them as an emergency power source.

Offline lamontagne

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Re: Power options for a Mars settlement
« Reply #843 on: 11/29/2018 11:58 am »
Or perhaps store the fuel as H2 rather than methane?

How hard would it be to ISRU an Zero Boiloff hydrogen tank?
not hard if itís gaseous.
You are saying Hydrogen becomes easier to contain as a gas than as a liquid? That seems odd to me.

Well, you don't have to worry about boiloff.

Either way, it seems a very large investment in Hydrogen storage facilities in terms of both mass and/or continual power requirements when compared with the straightforward technical fixes to enable a methalox ICE to operate. Also, how much Hydrogen will you store and what happens when you run out? In all likelihood you're still going to have methalox stores and therefore still need some way of utilising them as an emergency power source.
The main reason you produce hydrogen is to produce methane for propellant.  And almost all of the energy involved in the process goes to the electrolysis of the water to create the hydrogen.  The Sabatier process itself is exothermic, it loses energy since methane has less chemical energy available than hydrogen.  The hydrogen is an energy battery.
To avoid hydrogen boiloff, of methane boiloff for that matter, you need to reduce heat gain, and then use refrigeration to remove the heat that remains, rather than hydrogen phase change(boiloff).  Refrigeration using compression to remove energy from -250C and disperse it in an environment at-50C is an inherently inefficient process, using more energy than it removes, but it is thorougly understood and available technology.  An hydrogen tank in an underground vault with aluminium walls is essentally a thermos bottle, with the main thermal transmission mechanism being radiation.  Insulation, plus low emissivity coatings, can probably reduce heat gain to a very small amount.  So the compression energy should be low. 
This being said, I expect almost half of the energy used at the colony will be the production of propellant, at least for quite some time until local production starts exceeding imports.  If we stop producing propellant during dust storms, the solar arrays can be repurposed to food production, the other large power drain on the colony.  The few curves I have seen of solar irradience during dust storms seemed to mention a power drop of 30%.  If this is correct, then the need for a backup power source becomes non existant. 
It would be absurd to burn propellant to produce propellant, after all.
Anybody have a number for reduction of power during dust storms, taking into account a mechanism on the solar panels to remove dust accumulation during the storm?

Offline CuddlyRocket

Re: Power options for a Mars settlement
« Reply #844 on: 12/01/2018 05:39 am »
(Snip previous posts for length)

The main reason you produce hydrogen is to produce methane for propellant.  And almost all of the energy involved in the process goes to the electrolysis of the water to create the hydrogen.  The Sabatier process itself is exothermic, it loses energy since methane has less chemical energy available than hydrogen.  The hydrogen is an energy battery.
To avoid hydrogen boiloff, of methane boiloff for that matter, you need to reduce heat gain, and then use refrigeration to remove the heat that remains, rather than hydrogen phase change(boiloff).  Refrigeration using compression to remove energy from -250C and disperse it in an environment at-50C is an inherently inefficient process, using more energy than it removes, but it is thorougly understood and available technology.  An hydrogen tank in an underground vault with aluminium walls is essentally a thermos bottle, with the main thermal transmission mechanism being radiation.  Insulation, plus low emissivity coatings, can probably reduce heat gain to a very small amount.  So the compression energy should be low. 
This being said, I expect almost half of the energy used at the colony will be the production of propellant, at least for quite some time until local production starts exceeding imports.  If we stop producing propellant during dust storms, the solar arrays can be repurposed to food production, the other large power drain on the colony.  The few curves I have seen of solar irradience during dust storms seemed to mention a power drop of 30%.  If this is correct, then the need for a backup power source becomes non existant. 
It would be absurd to burn propellant to produce propellant, after all.
Anybody have a number for reduction of power during dust storms, taking into account a mechanism on the solar panels to remove dust accumulation during the storm?


I think we're going off-track. Let's recap from first principles: SpaceX's plan relies on ISRU methalox propellant manufacture on Mars. The time over which the methalox is produced is a lot greater than the time during which it is used and therefore there will be a need to store methalox on Mars. Any store of methalox can be used to generate power given the appropiate equipment (ICE generator, methane fuel cell, whatever).

The proposal then is to take such equipment to Mars so that the methalox stores could be used to generate power in an emergency. The methalox stores are not being created to act as a power source; it's just that they inherently have that capability providing you have the equipment. IMO it would be irresponsible not to have that equipment. Hopefully, it will never have to be used, but it's better than dying. You can over-size your intended power production and intended forms of storage (batteries etc). You can diversify it (solar, nuclear etc). You can switch off non-essential equipment if necessary (including methalox production - it would of course be insane to use the methalox stores to produce power to keep methalox production going). It would be extremely unlikely that you'll ever need to utilise the methalox stores to produce power - which is good as you don't want to use them for anything other than their intended purpose of propelling rockets. But extremely unlikely things occasionally happen, so it's as well to have as many back-ups as possible. The ability to utilise the methalox store is the final back-up; used when all else fails.

Given that, I don't see the purpose of producing and storing hydrogen. Methalox has to be created and stored. Hydrogen does not; it's not going to be used as propellant, certainly. So why are you going to the trouble and expense, in terms of both mass and finacial budgets, of creating such a store? I suppose you could produce it as part of the intended operation of the power system, to store power during the night or dust storms etc. That requires an examination of the engineering trades between this and batteries etc. But you still have to produce the methalox stores anyway, so still have the opportunity to, and therefore the responsibility of being able to, use them for emergency power, so you're not saving anything in that regard. (NB If you store hydrogen with the idea of using it to produce methalox at a later date then you'll need a higher capacity methalox production plant, which will be under-utilised most of the time and is more expensive.)

I suppose you might have another reason to produce and store hydrogen - perhaps for Martian blimps? - and if you have a store of hydrogen you can use it as a source of power in an emergency (and therefore should be able to by a similar argument in respect of methalox). But, I don't see such usages in the early days of any base/colony, whereas methalox is going to be used right from the beginning.

Offline NH22077

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Re: Power options for a Mars settlement
« Reply #845 on: 12/01/2018 07:02 pm »
On a standard ICE the nitrogen in air moderates the fuels burn and imparts a great deal of power to the piston as it expands from the heat of the fuel burning. An ICE (at least a standard one) would explode if all it was fed was methane and pure oxygen. Going fuel rich or oxygen rich wastes a lot of resources. How would this be fixed? Feed it air instead of oxygen, cool and recycle the nitrogen and replenish the oxygen? How would cooling work?

I would build an ICE with the intake using outside air routed to a blower, to bring the intake manifold pressure up to 15psi.
The less complex method would be to inject gaseous methane & O2 into the intake manifold. With the exhaust routed outside.
Some EGR could be used to keep the intake charge warm. A more complex method would be to have separate methane & lox injectors on each cylinder. The liquid cooled engine would have a heat exchanger with the heat-pump for the Mars base's main ECLSS. That is if the ECLSS uses a water loop for heating & cooling. I would also have the genset indoors so a block heater & low temp bearings for the generator. Are not necessary, and that gives you a shirt sleeve environment for maintenance. In a room that could be sealed off if the valves sealing intake or exhaust went not in use go bad.

A conventional natural gas genset on Earth is about 35% efficient.

I also agree that it shouldn't be used except in an emergency.

Ned

Offline Dao Angkan

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Re: Power options for a Mars settlement
« Reply #846 on: 01/09/2019 10:42 pm »
So this is a long thread, I haven't read it all. Before I go indepth ... has pumped storage been discussed yet?

Offline NH22077

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Re: Power options for a Mars settlement
« Reply #847 on: 01/17/2019 12:26 pm »
So this is a long thread, I haven't read it all. Before I go indepth ... has pumped storage been discussed yet?

Hi Dao,
Yes, pumped storage has been discussed up thread. Less gravity will mean less output for the same storage & elivation compared to Earth. SpaceX 1st bases r probably going to be on flat low lying areas. Lower in the atmostphere means less radiation. Flat makes for safer landings.

Ned

Offline Paul451

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Re: Power options for a Mars settlement
« Reply #848 on: 01/18/2019 12:57 am »
Before I go indepth ... has pumped storage been discussed yet?

Yes, pumped storage has been discussed up thread. Less gravity will mean less output for the same storage & elivation compared to Earth. SpaceX 1st bases r probably going to be on flat low lying areas. Lower in the atmostphere means less radiation. Flat makes for safer landings.

We've probably also discussed that pumped storage is just a way of lifting and lowering mass. It doesn't matter what the mass is. Water is just convenient on some places on Earth because you have existing water sources, dams, pumps, etc. If there's nothing special about water at your site, you can just lift and drop any dumb mass. A lump of metal, a box of rubble, whatever, just substitute winches for pumps and gears for turbines.

(Reduction in gravity works both ways: in lower gravity you get less energy storage from any given amount of mass, but your equipment can also handle a proportionally larger amount of mass for the same size/mass/loading.)

I imagine that we've also discussed the inefficiencies of such systems. AIUI, net output is typically 80% of input, depending on the details of the system. But IMO, you should assume a locally made (ISRU) system will be cruder, and will be operated under less than ideal conditions, 70-80% might be a reasonable planning assumption.

("Under less than ideal conditions: You will often need to cycle the system in an inefficient way due to the supply/demand requirements of the base being more important than optimising the storage system itself.)

Offline meekGee

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Re: Power options for a Mars settlement
« Reply #849 on: 01/18/2019 04:09 pm »
Actually I ran simple numbers on a power generation scheme where trucks drive up and down a slope, bringing down dirt and leaving it there.

Several variants, such as regular trucks on a dirt path, a railway, and an aerial tram.

There's something there, but it isn't as easy as you'd think.
ABCD - Always Be Counting Down

Offline LMT

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Re: Power options for a Mars settlement
« Reply #850 on: 04/11/2019 03:02 pm »
Quantum Dot PV Update

OP:  record-setting (2017) experimental QD PV solar cell rated at 15.2 kW/kg

Mar. 19 2019:  commercial plant under construction, for production of QD PV solar cells and other QD devices.  Quantum Materials Corp / Amtronics CC.

Quantum Materials:  QD PV solution statement

Solterra subsidiary:  statement on QD PV automated flexographic printing 

Related:

Like the 2017 record-holder, a 2019 record-setting solar cell also leverages PEN substrate and Ag nanowire electrodes.  The active layer in this new record-holder is perovskite.  Rating:  29.4 kW/kg



Caveat:  Perovskite solar cell stability problems were noted in thread previously.
« Last Edit: 04/11/2019 04:22 pm by LMT »

Offline lamontagne

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Re: Power options for a Mars settlement
« Reply #851 on: 04/11/2019 06:01 pm »
Quantum Dot PV Update

OP:  record-setting (2017) experimental QD PV solar cell rated at 15.2 kW/kg

Mar. 19 2019:  commercial plant under construction, for production of QD PV solar cells and other QD devices.  Quantum Materials Corp / Amtronics CC.

Quantum Materials:  QD PV solution statement

Solterra subsidiary:  statement on QD PV automated flexographic printing 

Related:

Like the 2017 record-holder, a 2019 record-setting solar cell also leverages PEN substrate and Ag nanowire electrodes.  The active layer in this new record-holder is perovskite.  Rating:  29.4 kW/kg



Caveat:  Perovskite solar cell stability problems were noted in thread previously.

Interesting.  However, I would be concerned that the fairly low efficiency (10% if I read correctly) would mean that the overall cost of the panels to Mars would be higher because of support structures and such.
Perhaps if the support structure is produced in-situ then this would be advantageous?

Offline Dave G

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Re: Power options for a Mars settlement
« Reply #852 on: 04/11/2019 08:39 pm »
I think they will have two different types of primary power (nuclear fission and solar) and batteries for storage and electric motors.  While they could build an ICE why bother, they are less efficient than electrics and are consuming you fuel to go home. 

If you want emergency back up power, as a last resort use methane fuel cells so you can use the methane directly don't convert and store the hydrogen first.

I agree.

For some reason, it seems like most people talk about either solar or nuclear, like they're mutually exclusive. 
I think nuclear and solar tend to compliment one another. People are generally more active during the day.
That's human nature. I don't see why it would be different on Mars. So nuclear supplies baseline power at night,
while solar provides the extra power needed during daylight hours.

They'll also need some batteries to smooth out the load curve, but nowhere near the number of batteries they'd require for a solar-only system.

Also, for some reason, it seems like a lot of people are only familiar with hydrogen fuel cells. There are actually many different types of fuel cells. They even have fuel cells that run on gasoline. So given that they'll need to store methane and oxygen separately, using methalox fuel cells as an emergency backup power source seems like a natural choice.

Offline rakaydos

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Re: Power options for a Mars settlement
« Reply #853 on: 04/11/2019 09:06 pm »
The ARC reactor looks likeit would fit inside a 12m hull, with replacement tokomak sleeves being able to be shipped in a 9m Starship.

It wont be available for another 10-15 years, but that'll be right about the time mars colonization starts scaling up.

https://en.wikipedia.org/wiki/ARC_fusion_reactor

Offline Joseph Peterson

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Re: Power options for a Mars settlement
« Reply #854 on: 04/11/2019 11:05 pm »
I would like to add a point about Sabatier reactors and hydrogen storage.  In my experience most catalyst degradation occurs at startup.  Steady state operation is preferable.  If we add a hydrogen buffer between the electrolysis unit and the Sabatier reactor we can regulate hydrogen flow for a fraction of the mass regulating using batteries.  I believe it is reasonable to expect that early Martian colonies will have at least some hydrogen storage.

So roughly how big is this hydrogen storage buffer?

Assuming each Starship requires 240 tonnes of methane we need to produce 60 tonnes of hydrogen.  Assuming a 720 sol production period we need a buffer that can store 83.3 kg to allow a one sol buffer.  83.3 kg isn't a lot, but when every bit counts...

Offline Dave G

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Re: Power options for a Mars settlement
« Reply #855 on: 04/11/2019 11:22 pm »
I believe it is reasonable to expect that early Martian colonies will have at least some hydrogen storage.

Why?

Here's a quote from Elon Musk:
Quote from: Elon Musk
Hydrogen has very low density. Itís a pernicious molecule that likes to get all over the place. If you get hydrogen leaks from invisible gas, you canít even tell that itís leaking. But then itís extremely flammable, when it does, and has an invisible flame.

If youíre going to pick an energy storage mechanism, hydrogen is an incredibly dumb one to pick. You should just pick methane. Thatís much, much easier...

Online ZChris13

Re: Power options for a Mars settlement
« Reply #856 on: 04/11/2019 11:31 pm »
Here's a quote from Elon Musk:
Quote from: Elon Musk
Hydrogen has very low density. Itís a pernicious molecule that likes to get all over the place. If you get hydrogen leaks from invisible gas, you canít even tell that itís leaking. But then itís extremely flammable, when it does, and has an invisible flame.

If youíre going to pick an energy storage mechanism, hydrogen is an incredibly dumb one to pick. You should just pick methane. Thatís much, much easier...
Hydrogen doesn't burn in Martian Atmosphere

Offline lamontagne

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Re: Power options for a Mars settlement
« Reply #857 on: 04/11/2019 11:34 pm »
I believe it is reasonable to expect that early Martian colonies will have at least some hydrogen storage.

Why?

Here's a quote from Elon Musk:
Quote from: Elon Musk
Hydrogen has very low density. Itís a pernicious molecule that likes to get all over the place. If you get hydrogen leaks from invisible gas, you canít even tell that itís leaking. But then itís extremely flammable, when it does, and has an invisible flame.

If youíre going to pick an energy storage mechanism, hydrogen is an incredibly dumb one to pick. You should just pick methane. Thatís much, much easier...
You have to have some hydrogen storage because electrolysis produces hydrogen and oxygen, not hydrogen and methane. That being said it is probably best to convert the hydrogen into methane as soon as possible.  You might also use it for steel production.

If you are going to store energy at the utility level, perhaps the best solution would be Pumped Heat Electrical Storage.
http://energystorage.org/energy-storage/technologies/pumped-heat-electrical-storage-phes
These installations use steel tanks and an inert gas such as argon as working medium, storing energy with an efficiency of 75 to 80%. A reversible compressor is used to both compress the working fluid and to extract the energy from the expanding gas. The use of materials readily available on Mars make this an attractive mid term storage solution.
« Last Edit: 04/11/2019 11:36 pm by lamontagne »

Offline spacenut

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Re: Power options for a Mars settlement
« Reply #858 on: 04/11/2019 11:45 pm »
Natural gas generators on earth are NOT internal combustion engines.  They are not efficient enough.  They are converted jet engines that do double duty.  A jet engine turns a generator from the front of the turbine.  The exhaust is then run through a steam boiler to generate steam to turn another turbine behind it, usually an old coal fired boiler.  Thus generation the maximum amount of electricity with both mechanical energy conversion as well as heat conversion to electricity. 

Now on Mars a small jet engine running metholox fuel with both a generator and a steam generator can produce a huge amount of electricity at night.  The excess water produced can be ran back into the water system and used as heat for the colony when after making steam electricty.  It is also far more efficient than fuel cells. 

These engines on earth are already replacing coal as the number one producer of electricity. 

Methane for rockets to return to earth will already be made.  Excess could be used to produce electricity at night.  Solar power for daytime and metholox production. 

When Mars gets really big nuclear power may have to come into play. 

Liquid hydrogen is colder and more subject to leaks due to the small atoms.  Would cost more to keep cold. 

A small jet engine generator system with steam turbine added is a whole lot quicker and cheaper to bring to Mars than as components are currently "off the shelf" and far less expensive with more bang for the buck than anything other than solar on Mars.  Solar will be required initially anyway. 
« Last Edit: 04/11/2019 11:50 pm by spacenut »

Offline Dave G

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Re: Power options for a Mars settlement
« Reply #859 on: 04/11/2019 11:48 pm »
That being said it is probably best to convert the hydrogen into methane as soon as possible.

Right.

That's why long-term hydrogen storage doesn't make sense to me, at least not at the scale required for an emergency backup for powering the colony.