Mobile Energy Storage in a Mars Colony

JoshNH4H · 2011-11-20 22:27:57

Leaving aside for the moment the question of how the central colony will store energy for later use, I think we need to take a look at how energy will be stored when you can't connect your electrical wires directly to a solar thermal generator (which I favor as an energy generation mechanism, though that's not particularly central to this thread). In any case, there is going to be a need for energy, both electrical and thermal, when not connected to the colony. How might we go about providing this?

For shorter time scales, it should be possible to store the energy as a molten salt (or other compound; I would think that something a bit more volatile/organic than a salt would be a pretty good energy storage medium, though I do believe that in a discussion I had with Midoshi at some point, in a thread which is not currently available, we settled on Boric Acid as a good thermal energy storage material), and then either use the heat as heat or turn it into electricity using a Stirling heat engine/Brayton turbine, etc.

The pros to storing energy as heat is that it is comparatively efficient over short periods of time. Since the colony may or may not be able to manufacture high-purity Silicon (the process is relatively simple, but energy intensive), and certainly won't be able to dope it with enough precision to make it efficient, they will not be the energy source of choice for a self-sufficient colony. I've been over this elsewhere. The main point here is that there is going to be heat involved at some point, so it is a simple matter of transferring this heat to whatever material we want to store it in, with no chemical or electrical intermediary. The downsides are that the energy density of stored energy is pretty low, generally speaking significantly below 1 MJ/kg. Further, if you try to store the energy in that form for a long period of time it will generally be radiated away. Not having done calculations, I would guess a week or two on the outside if you design carefully (Is aerogel beyond the synthesis capabilities of an early colony?).

On the other hand, there is the possibility of using a chemical energy storage material. Magnesium, for example, will burn in CO2, though the energy density of chemical sources is generally high enough that carrying an oxidizer isn't a big problem. The downside is that it is often more difficult to make chemical energy storage materials, because you have to go through several reactions and they almost always require an input of electricity at some point, which is of a very low efficiency.

I guess it depends on the particular use, for example a long-term scouting rover will be more likely to use chemical fuels both for their lower mass and for their higher storeability, while for an automated cart designed to drive a few hours or a day to a depot of some kind molten salts will be very competitive for their high efficiency and reusability.

Edit: Ironically, I just hit 600 posts for the second time. lol.

Last edited by JoshNH4H (2011-11-20 22:28:30)

SpaceNut · 2011-11-22 22:54:11

Storing solar thermal energy then creating electricity later is not going to be efficient for sure but thermal is of a higher collection level than PV. Likewise collecting solar PV to storage is only slightly better but its the lower energy input of such a system that makes it less desireable in the cold of Mars when what we need is heat...

JoshNH4H · 2011-11-22 23:24:35

Well, batteries in general tend to be either of low power an mass to weight ratio or they tend to be pretty difficult to make. Further, Light->Thermal->Electricity could be fairly efficient, maybe 80-90% on the first step and then 20-30% on the second. Light->Electricity->Heat->Electricity is going to be extremely inefficient, though it doesn't make much sense to do things that way anyway.

Very true about needing heat. I think that energy storage for heat and energy storage for electricity may be two separate things.

SpaceNut · 2011-11-23 07:54:48

As noted there will be lots of pros and cons as manufacturing gets going but nicely put as each type of out come ( heat or electricity), will be created from differing methods when it comes to energy. The more diversity that we have the less depency on one form we will have as we face daily when it comes to cost.

I am sure that once the last setting of the board is re-established that not only will the topics come back to fill in the blanks for energy but so will the other 5000 posts that I had made since 2008 as well...hard to believe that many more entries we made since then..

Last edited by SpaceNut (2011-11-23 08:34:00)

JoshNH4H · 2011-11-23 10:46:27

I know for a fact that I had a four page thread that was almost entirely analysis of energy production that was active at the time that Newmars went down. And haha you think you lost a lot of posts, in 2008 I was a mere 600-post peon.

louis · 2011-12-06 20:39:49

I came down in favour of methane storage for a number of reasons. Of course, you have to produce your methane, but that is not too difficult if you have an electricity supply, using eletrolysis and the Sabatier reaction and based on carbon dioxide atmosphere plus water.

I think methane could be installed in artificial ice clathrates (i.e. methane trapped as bubbles in ice) on the Mars surface, avoiding the need for expensive storage facilities.

As long as you have a water source, a methane production facility and a power source (PV panels are v. mobile) you can set up anywhere on the planet.

SpaceNut · 2011-12-06 22:08:45

There is a need to understand what is the time span that is needed for the temporary storage and the volume or mass that can be still safely moved by the mobile energy staorage unit.

I think that Louis is onto something thou in that we can use the power to compress the mars atmospher to tanks for use later at the main base if not converted to methane after electrolysis into CO and Oxygen for the crew to breath. Electrolysis of on board water into Hydrogen and Oxygen as well is of benefit to the crew, with the hydrogen to be used in the conversion of CO into methane. With a water export back into the loop for another time.

In either cae each of the processes can thought of temporary storage of the used energy.

Not sure that Storing as a Gas hydrate (a crystalline solid consisting of gas molecules), usually methane, each surrounded by a cage of water molecules is going to work as the key is lots of water. It looks very much like water ice. Methane hydrate is stable in ocean floor sediments at water depths greater than 300 meters, and where it occurs, it is known to cement loose sediments in a surface layer several hundred meters thick.

http://en.wikipedia.org/wiki/Methane_clathrate

Methane clathrates are restricted to the shallow lithosphere (i.e. < 2,000 m depth). Furthermore, necessary conditions are found only either in polar continental sedimentary rocks where surface temperatures are less than 0 °C; or in oceanic sediment at water depths greater than 300 m where the bottom water temperature is around 2 °C.

http://www.killerinourmidst.com/methane … 0MHs2.html

Since the Mars we know is colder than 0c and water in the form of ice sublimes away there is no wa to store this external to the unit carrying the methane hydrate.

Grypd · 2011-12-07 05:41:30

There is the possibility of using flywheels as a means to store electrical energy. This will obviously have uses if you need electricity for peak uses. Still being able to create a fuel to be burnt either in an engine or converted in a fuel cell will be much more effective. This allows fuel depending on type to be stored long term and this can be tapped much more easily.

louis · 2011-12-07 19:18:21

SpaceNut wrote:

There is a need to understand what is the time span that is needed for the temporary storage and the volume or mass that can be still safely moved by the mobile energy staorage unit.
I think that Louis is onto something thou in that we can use the power to compress the mars atmospher to tanks for use later at the main base if not converted to methane after electrolysis into CO and Oxygen for the crew to breath. Electrolysis of on board water into Hydrogen and Oxygen as well is of benefit to the crew, with the hydrogen to be used in the conversion of CO into methane. With a water export back into the loop for another time.
In either cae each of the processes can thought of temporary storage of the used energy.
Not sure that Storing as a Gas hydrate (a crystalline solid consisting of gas molecules), usually methane, each surrounded by a cage of water molecules is going to work as the key is lots of water. It looks very much like water ice. Methane hydrate is stable in ocean floor sediments at water depths greater than 300 meters, and where it occurs, it is known to cement loose sediments in a surface layer several hundred meters thick.
http://upload.wikimedia.org/wikipedia/c … iagram.jpg
http://en.wikipedia.org/wiki/Methane_clathrate
Methane clathrates are restricted to the shallow lithosphere (i.e. < 2,000 m depth). Furthermore, necessary conditions are found only either in polar continental sedimentary rocks where surface temperatures are less than 0 °C; or in oceanic sediment at water depths greater than 300 m where the bottom water temperature is around 2 °C.
http://www.killerinourmidst.com/methane … 0MHs2.html
Since the Mars we know is colder than 0c and water in the form of ice sublimes away there is no wa to store this external to the unit carrying the methane hydrate.

I am not sure you are right to say that "water in the form of ice sublimes away" on Mars. Water as liquid water may sublime, but not ice, which is why there are glaciers on the surface of Mars. The glaciers contain huge amounts of water, which should provide plenty of material for artificial clathrates.

I am not sure that Wikipedia entry is completely right. I am sure I have read about natural methane clathrates on the surface of Earth. I will check that.

SpaceNut · 2011-12-07 20:49:07

This what I have read from other places

Mars the water ice sublimes away (goes directly from solid ice to gas, without any liquid phase between) and leaves the debris lines intact.

I feel that the Glaciers contain Methane clathrate as that would explain the methane in the atmospheric content as a function of the subliming of the water ice that trapped the methane. This happens as a result of the dust storms removing the soil that covers the glaciers which keep it from rapidly subliming....

JoshNH4H · 2011-12-07 22:21:25

First I would like to address louis' point about solar panels being portable: The high purity Si and high purity dopants (very rare elements at that, and required in precise quantities) needed to make PV panels are just not going to be available. That said, for a permanent installation, it will be pretty easy to cart over a concentrated solar power (thermal->electric) generator.

Seems like there have been several different methods of energy storage proposed here. Each has its own pros and cons. All chemical fuels are inefficient to make but are very energy dense and long-term storeable. Methane clathrate has seen little research and it may be relatively difficult to synthesize. This website suggests that you need precisely controlled temperatures and pressures of 25-30 MPa. That's a pretty high pressure. We might want to look at using Methanol ice instead, which can be made from Carbon monoxide which has been reacted with hydrogen gas with a catalyst. Put it in a pressurized bottle so it doesn't evaporate and burn it with NO2 (Or maybe a nitrate salt?) when you need it. That's a lot easier than making a methane clathrate at 250 atmospheres.

Pressurized gas is very inefficient at long term storage because if you let the heat that is created from compressing the gas go, you lose about 50% of your stored energy.

Flywheels are good for the short term, and are pretty easy to make and have a fair energy density, but are hard to keep going indefinitely.

SpaceNut · 2011-12-08 20:27:52

Solar panels definitely easy to import and less of an issue as the insitu processing plants to get to being able to refine to the needed degree for use to make them is a matter of time and initial investment in a settlement and colonization of mars.

JoshNH4H · 2011-12-08 20:32:47

Solar panels are easy enough to import but importation for a colony is expensive and it would be a big drag on the Martian economy to pay for solar panels whenever they wanted to expand, and I wouldn't want to establish such an absolute dependency on Earth for power sources. Solar thermal power is very feasible and fairly simple to make in situ. Obviously the power sources for the initial missions and even the base are going to be imported, but a colony cannot and should not be importing something so basic.

SpaceNut · 2011-12-08 20:42:40

You bring up a very important question as to when does a population on Mars have to start paying there own way and not being paid to go for the exploration science aspects.

louis · 2011-12-09 21:19:24

Space Nut,

My view has always been that the colony can pay its way from day one (leaving aside the initial development costs of the rocketry and other equipment) - i.e. make an operating profit from sales of TV rights, sale of scientific data, meteorites, regolith, precious metals and stones (gold and diamonds)...

Later on there will be opportunities for more money making from: creation of art works by famous artists on Mars that are sold back on Earth (but not brought back to Earth), production of light luxury goods on Mars eg. watches and light scarves for sale back on Earth, university endowments, and "gap year" tourism.

Long term, solar reflectors to heat boilers and produce steam are probably the cheapest way to produce power on Mars using Mars materials. The colonists won't need huge amounts of energy for the first two or three decades when the number of colonists is likely to be under 100.

Terraformer · 2011-12-10 10:08:18

How much does ultralight solar mass, anyway? I'm thinking about the solar cells themselves, minus the support and glass covering, which can be made insitu. Perhaps a few kg would do for 100kw...

louis · 2011-12-10 17:21:10

Terraformer -

I have previously proposed that PV film be stretched between light weight tensors on Mars, above the dust damage height level. I am not sure we need protective coverings on Mars because the wind force is so low. Probably for Missions 1 and 2 we might be talking about importing encapsulated PV film but we should certainly experiment with unprotected lightweight film.

Once the colonies are established I think they can focus on producing solar reflectors to heat boilers - that won't require advanced technology.

GW Johnson · 2011-12-15 02:15:50

It only takes a few centimeters of dirt at 0.38 gee to provide the overburden pressure necessary to keep ice from subliming away in the near vacuum that is Mars's atmosphere. Water-as-ice is easily stored outdoors without a container, if you just bury it in a "shallow grave".

Methane clathrate is only stable at 2 C and 300-meter Earth ocean pressures, which is some 30+ atmospheres pressure. To store it without a container on Mars would require very deep burial indeed. A pressurized container on the surface would be the better deal, if methane clathrate is really what you want to store. Actually, plain liquid methane would be easier to deal with.

I don't think chemical energy storage has been adequately explored, for application here or on Mars. There's more in this world than just batteries and water electrolysis into H2 and O2. What, I dunno.

GW

louis · 2011-12-15 14:58:30

GW Johnson wrote:

It only takes a few centimeters of dirt at 0.38 gee to provide the overburden pressure necessary to keep ice from subliming away in the near vacuum that is Mars's atmosphere. Water-as-ice is easily stored outdoors without a container, if you just bury it in a "shallow grave".
Methane clathrate is only stable at 2 C and 300-meter Earth ocean pressures, which is some 30+ atmospheres pressure. To store it without a container on Mars would require very deep burial indeed. A pressurized container on the surface would be the better deal, if methane clathrate is really what you want to store. Actually, plain liquid methane would be easier to deal with.
I don't think chemical energy storage has been adequately explored, for application here or on Mars. There's more in this world than just batteries and water electrolysis into H2 and O2. What, I dunno.
GW

When you say "Methane clathrate is only stable at 2 C and 300-meter Earth ocean pressures" what do you mean exactly? Do you mean under 2C or above? or only at 2C? And does the other condition (pressure) have to be fulfilled as well or is it an alternative?

I would agree that chemical storage of electricity needs to be explored. A plus about Mars is that in the initial colonisaiton period one doesn't have to worry too much about environmental damage. An open pit of a chemical "soup" would be perfectly acceptable.

Rune · 2011-12-16 10:18:57

The way I see it, methane gas offers too many pluses to think of anything else. First off, you are already producing it for rocket fuel if you have any sense. The ingredients are simple and abundant as hell: atmosphere, energy, and water, and you can sabatier/electrolyze your way into liquefied methane and oxygen. Everywhere you have a settlement, you are going to have the three of them, or you are not going to have a settlement.

And you can run fuel cells out of the stuff, burn it in combustion engines, use as rocket fuel, even get gas burners for cooking. Pretty much a powersource for everything, scalable from tens of watts (fuel cell) up to megawatts (rocket engine or turbine engine/generator). And storage is pretty simple, pressurized tanks of methane and oxygen, preferably stored on opposing sides of the colony. Handling and transportation also don't seem an issue, we are pretty good about handling those on earth, you can move bottles of the stuff around by hand with a more than decent power density. And you are going to have to produce pipes for other things anyway. You can also forget about trying to store hydrogen, which is a bitch. And also on the plus side, none of the ingredients burn by themselves in martian atmosphere if there is an accident... I only see pluses, apart from the fact that you have to redesign all combustion engines to supply both oxidizer and fuel form tanks. That seems pretty easy.

Of course you are going to get a pretty awful efficiency out of the process, with much less than 50% of the input energy being able to be retrieved, compared to just using it as you produce it... but I don't think you can do any better here on Earth anyway.

Rune. No need to get complicated, methinks. So KISS.

GW Johnson · 2011-12-16 11:26:31

The methane clathrate is stable on Earth in deep cold water. Most of what we know about is in the 0-2 C range, hotter comes apart. Most of what we know about is 300 meters deep or deeper. Shallower is unstable.

I rather like the plain methane myself. If we will be using chemical propulsion, it make a lot of sense in the first stage, because the volume is lower (less structure). I dunno about Mars, but on Earth, the first stage of a rocket flight is thrust-limited, not Isp-limited. Lower-Isp fuels like methane make better sense because of their higher density.

It is the second stage that is more Isp-limited, where hydrogen itself makes more sense. Methane and oxygen are easier to process and store than hydrogen, so for practicality, all-methane-LOX makes a lot of sense, even for an upper stage.

GW

louis · 2011-12-16 12:36:41

Couldn't we just cover the clathrate in regolith and maintain the desired temperature range?

GW Johnson · 2011-12-16 14:27:34

Sure, but it's still deep burial for clathrates. It would be around 200 meters at 2C on Earth under a dirt overburden (that's figured at about 105 lb/cu.ft for loose dirt, vs 62.4 lb/cu.ft for fresh water). On Mars at 0.38 gee, it's almost 3 times that depth. That's a lot of digging. Building pressure tanks is probably easier.

One of the first things to import is probably a steel mill. Ha! Ha!

GW

JoshNH4H · 2011-12-16 15:35:35

GW- It was my understanding that relatively extreme temperatures were necessary for the production of clathrates but not necessarily for their maintenance. I was under the impression that once you created them if you cooled them down to ambient Mars temperature (~225 K, ~405 R, ~ -55 F), they would still be relatively stable at much more reasonable pressure.

That said, there is very little need to deal with any of this if one simply uses methanol as an energy storage medium. I just looked on wikipedia, as well; NO2 is a solid at ambient Mars temperatures. It melts (On Mars, presumably sublimes) at -11.2 C (471.5 R, 11.8 F- GW, do you prefer R or F? I know you use imperial, otherwise I wouldn't give either). One could actually conceivably make some kind of slush of NO2 ice within Methanol liquid. Throw it in a closed vessel under a few meters of regolith to get it to a pressure where Methanol liquid does not boil away (According to wikipedia, indirectly through the CRC handbook, we're looking at a vapor pressure of about 1 mb/.1 kPa/somewhat less than 1 torr at Mars pressure, so that's a very thin layer of regolith. Assuming a specific gravity of 2.5 (e.g., density 2.5 times that of water), the regolith layer would have to be 11 cm (4.5 inches) thick. That's almost nothing; hell you would be just as well off with a tank made of literally just about anything, and you would get a slight tank pressure, which makes getting the stuff out to burn it that much easier.

I think that's the best option in terms of chemical storage. Does anyone think that a methanol/N2O4 slush would be unstable at mars temperature?

louis · 2011-12-16 17:22:48

I obviously can't contribute much to the technical debate, but I am clear that there would be great value in finding a way of storing methane on the surface without the need to put it in pressure vessels. The reason is obvious: we are then relieved of the burden of either importing such vessels or trying to manufacture them on Mars. Remember, we don't have to worry much about the environmental impact of such storage - that's one great advantage of Mars: we have the space and lack of flora or fauna which will allow us to pursue such solutions in the early stages of the colony.

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#1 2011-11-20 22:27:57

Mobile Energy Storage in a Mars Colony

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