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#1 2017-05-29 08:35:24

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,486

Solar plus turbine...

This is a rather neat summary of solar plus turbine technologies:

https://w5.siemens.com/italy/web/pw/Pow … e_COMP.pdf

Do people have a view on which of the solar collection technologies would work best on Mars i.e. parabolic trough, line/fresnel or solar tower?

Which one could be produced on Mars with least effort?

Would a Mars ISRU design be simpler?

Could we work with less efficient methods e.g. aluminium or polish steel reflectors?

Here are some examples of home made small scale steam engines.

https://www.youtube.com/watch?v=Pv6GVUoFcD0

https://www.youtube.com/watch?v=AXPG2aioAE8

Steam engine technology looks well within the scope of a settlement of under 100 people with access to CNC lathes, 3D printers, and small scale Mars ISRU steel production.

A mini forge:

https://www.youtube.com/watch?v=xMuCId2Uo6U

And this is a great video on small scale steel making:

https://www.youtube.com/watch?v=gDy1jx6mLgs

I see no reason why the early Mars community couldn't have something similar but more automated and less messy. I think there was a reference to a 64 pound bloom - about 29 kgs. If you had a couple of small scale furnaces producing say 200 kgs of steel a week, or 10 tonnes a year, that would probably suffice for a community of 100. I appreciate that the video depicts a first stage in the process of steel making.

Here's a very small scale generator:

https://www.youtube.com/watch?v=3aE5xiUwLgw

And a  larger one:

https://www.youtube.com/watch?v=85OmZU3dZpA

Anyway, for me solar plus steam seems an obvious way to power the industrial revolution on Mars.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#2 2017-05-29 09:23:04

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,800

Re: Solar plus turbine...

This is another somewhat fanciful solar scheme--one that works for a half Sol at a time. My primary objection isn't use of solar power as a resource, but the huge amount of infrastructure required. This scheme should be demonstrated as viable on Earth, since it "could replace" much of the other infrastructure of power generation. Not.

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#3 2017-05-29 15:15:44

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,486

Re: Solar plus turbine...

You don't seem to get it...a Mars ISRU energy generation scheme has a close-to-zero mass import requirement. More than that, once the technology has been refined, there is no reason why it can't be replicated many times.

Solar plus turbine has been demonstrated on Earth but it clearly is not as efficient as gas, nuclear, coal, direct PV or wind. But that's irrelevant on Mars. The main issue is whether you can avoid a mass import penalty and whether the Mars settlement can make the energy generation equipment.

Oldfart1939 wrote:

This is another somewhat fanciful solar scheme--one that works for a half Sol at a time. My primary objection isn't use of solar power as a resource, but the huge amount of infrastructure required. This scheme should be demonstrated as viable on Earth, since it "could replace" much of the other infrastructure of power generation. Not.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#4 2017-05-29 17:11:41

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,885

Re: Solar plus turbine...

I will agree that the future needs for power for insitu resource ultilization will require some sort of means to create the energy beyond what we bring on the first few missions as what gets brought needs to be along the likes of mars processing equipment and items needed to build a mars colony with after those first few.

Along the lines of nuclear the means to make thorium reactors would be tops of what we would ship to mars as well Since we know that excess power allows for growth to occur.

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#5 2017-05-29 18:31:05

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,486

Re: Solar plus turbine...

There's a lot of talk about and designing of thorium reactors, but not much actual building of them. And I doubt that any reactor building project on Earth could be done with less than 100 people completely focussed on it. In my judgement, solar steam power is a much more doable prospect. People do build steam turbines in their back gardens...they don't build thorium reactors.

If we have any sense we will be sending people to Mars with all the equipment they need to make solar reflectors, a steam engine, turbine and electric motor.

Generation doesn't need to be huge.  A community of 20 that could build say 5 x 10 Kw turbines over two years would be well on the way to energy independence. 


SpaceNut wrote:

I will agree that the future needs for power for insitu resource ultilization will require some sort of means to create the energy beyond what we bring on the first few missions as what gets brought needs to be along the likes of mars processing equipment and items needed to build a mars colony with after those first few.

Along the lines of nuclear the means to make thorium reactors would be tops of what we would ship to mars as well Since we know that excess power allows for growth to occur.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#6 2017-05-29 20:00:38

kbd512
Moderator
Registered: 2015-01-02
Posts: 3,199

Re: Solar plus turbine...

Louis,

If you have to build a LFTR on Mars, you'll be supplying a few hundred people with electrical power and therefore have the human capital to devote to the project.  I've been on ships with boilers, gas turbines, and nuclear reactors.  In the two years I was aboard two different nuclear powered aircraft carriers, we never lost power and nobody on either ship had ever experienced a power loss.  On the ship with boilers, we lost power numerous times (once or twice per cruise) and the gas turbine powered ship only lost power once (the result of a mistake, IIRC).

Regarding your steam generator example, how many of the people who built steam turbines in their back yards built turbines with multiple megawatts of output?

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#7 2017-05-30 13:40:34

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,486

Re: Solar plus turbine...

Did you not have personnel with specific responsibilities for monitoring and maintaining the reactors and the reactor/turbine interface?

kbd512 wrote:

Louis,

If you have to build a LFTR on Mars, you'll be supplying a few hundred people with electrical power and therefore have the human capital to devote to the project.  I've been on ships with boilers, gas turbines, and nuclear reactors.  In the two years I was aboard two different nuclear powered aircraft carriers, we never lost power and nobody on either ship had ever experienced a power loss.  On the ship with boilers, we lost power numerous times (once or twice per cruise) and the gas turbine powered ship only lost power once (the result of a mistake, IIRC).

Regarding your steam generator example, how many of the people who built steam turbines in their back yards built turbines with multiple megawatts of output?


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#8 2017-05-30 16:59:35

Antius
Member
From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Solar plus turbine...

Louis, neither your solar turbine nor any realistic nuclear reactor could be built on Mars using ISRU by 100 people.  You want to see a solution that you have already chosen for emotional reasons, and you are ignoring the inconvenient facts.  No amount of personal enthusiasm can turn a bad solution into a good one.

Have you taken a good look at the brochure that you linked to?  Hundreds of curved, polished aluminium mirrors, mounted on individual frames, each one carefully tracking the sun using its own electric motor.  That's in addition to the Boiler, the HP steam pipe work, steam drying equipment and HP and LP turbines.  This is precision engineering on quite a large scale.  Not something that can be built in a hobby workshop.

Then there is the issue of power density.  Those polished mirrors within the brochure will have a time averaged power density of about 100 watts per square metre at the Martian equator.  After generation losses, that drops to perhaps 20 watts.  You would need about 100m2 of those mirrors just to power an electric kettle.

This is the problem with solar power.  It is a diffuse energy source even on Earth.  Compared to fossil fuels and nuclear power, you need a lot more physical kit to get the same amount of energy out.  That makes it a bad deal compared to alternatives in most places.

Last edited by Antius (2017-05-30 17:10:29)

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#9 2017-05-30 17:39:39

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,486

Re: Solar plus turbine...

Antius -

I can only assume that you haven't followed the links I provided. People are making solar reflectors, furnaces, forges, steel, turbines and electric motors from scratch  in their backyards without hundreds of millions of dollars of support from NASA or Space X.

What could that sort of approach achieve on Mars (which has a v. similar range of resources to Earth) if we invested hundreds of millions of dollars into Mars ISRU?

You are confusing the hobby shop with what can be achieved on Mars.  Some of my links show hobbyists achieving incredible things with minimal resources but others show more sophisticated technology. There is no reason why on Mars we can't import 3D printers, CNC machines, "clean room" habs, and material purification equipment that will enable us to perfect these technologies.

Energy density is not the issue on Mars. If it was, we would be shipping coal to Mars.

The issue is what energy system can proficiently meet the needs of the Mars settlement at various stages in its development.

For Mission One I would accept that it's fairly balanced between solar and nuclear - because of the peculiar requirements of that first mission - but thereafter I think solar is the clear winner.

100M2?  You can't mean 100 metres squared (100x100 metres)... so I assume you mean 10x10 metres.  What's the problem with that? If that's what it takes to boil a kettle on Mars, so be it. Far less complicated than commissioning, monitoring and maintaining a nuclear reactor.

"a lot more physical kit" - that's an unsubstantiated claim and rather avoids the central question here. Even if you could show that nuclear uses LESS physical kit than say a methane powered turbine, you will still have to get your nuclear reactor from Earth to Mars - which will involve a huge expenditure of energy, mass and money.

Antius wrote:

Louis, neither your solar turbine nor any realistic nuclear reactor could be built on Mars using ISRU by 100 people.  You want to see a solution that you have already chosen for emotional reasons, and you are ignoring the inconvenient facts.  No amount of personal enthusiasm can turn a bad solution into a good one.

Have you taken a good look at the brochure that you linked to?  Hundreds of curved, polished aluminium mirrors, mounted on individual frames, each one carefully tracking the sun using its own electric motor.  That's in addition to the Boiler, the HP steam pipe work, steam drying equipment and HP and LP turbines.  This is precision engineering on quite a large scale.  Not something that can be built in a hobby workshop.

Then there is the issue of power density.  Those polished mirrors within the brochure will have a time averaged power density of about 100 watts per square metre at the Martian equator.  After generation losses, that drops to perhaps 20 watts.  You would need about 100m2 of those mirrors just to power an electric kettle.

This is the problem with solar power.  It is a diffuse energy source even on Earth.  Compared to fossil fuels and nuclear power, you need a lot more physical kit to get the same amount of energy out.  That makes it a bad deal compared to alternatives in most places.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#10 2017-05-30 19:56:49

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,885

Re: Solar plus turbine...

I have been looking at building something for solar for a while now but still either am lacking in some knowledge and or ability to be able to make the system still at this point.

Youtube Concentrated Solar Power and another
https://www.youtube.com/watch?v=N1-zjbRqYXk
Youtube Lecture - 16 Solar Concentrating Collectors

One of the best Do it youself sites is the http://www.builditsolar.com/ The Renewable Energy site for Do-It-Yourselfers

http://www.builditsolar.com/SiteSurvey/site_survey.htm

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#11 2017-05-31 06:19:17

Antius
Member
From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Solar plus turbine...

Louis, thank you for the links.  I have built solar heating systems in my workshop, though I have never attempted a steam engine.  Looking at your links, I am tempted to have a go at it.

I do not doubt for a minute that building small solar powered steam engines is possible on Mars, if we ship machinery and tools to a small base and devote enough man-power to it.  I am sceptical it will be an economical venture.  Here is why:
http://large.stanford.edu/courses/2015/ph240/kumar2/

1.    The EROI of solar thermal power systems in Earth’s deserts with 2.3x the solar constant of Mars is 19 before buffering (i.e. energy storage) and ~9 after buffering.  In this analysis, buffering is provided by pumped storage which is efficient but capital and energy intensive to build.  On Mars, a solar thermal system would almost certainly buffer by storing heat in rock bodies, which would provide better energy density and lower embedded energy than pumped storage, but there will still be energy cost involved in building the store and energy losses in using it.  EROI will naturally be lower because sunlight intensity is only 43% of Earths.

2.    Steam engines are quite inefficient, historically <10% efficient for locomotive steam engines.  With multiple stages and a condenser cycle, efficiency can increase to between 10-20%, but the mass and complexity of the engine increase progressively.  Efficiency problems occur due to the relatively low input temperatures and pressures into the expanders, heat transfer into the cylinder and pistons, pumping losses in the engine and for open cycles, loss of enthalpy still stored in the vented, saturated steam.  Some steam engines include multiple reheat cycles to get around the final problem, but again, you are adding mass and complexity to the device.  Smaller units are generally less efficient than larger units (due to heat transfer and pumping losses).  To minimise both thermal losses and pumping losses, it is advantageous to keep the power profile of the engine as flat as possible, i.e. run it at 100% 24/7.  In other words, for better EROI, build it big and run it flat out.  Is it a coincidence that this also improves plant economics?

The EROI graph referenced above comes from the Weissbach study and is referenced within the link.  Let’s make a few adjustments for a system on Mars: (1) Solar intensity is only 43% of Earth’s; (2) Small steam engines are used, rather than large turbine plants.  Let’s be generous and assume turbine efficiency was 25% and steam engine efficiency is 15%.  Piston steam engines are a lot heavier per kW than turbo-generator sets, but let’s ignore that for now; (3) Let us assume that solar thermal energy storage is a more efficient means of buffering than pumped storage.  Let’s say a power plant using this method on Earth would achieve an EROI of 12 rather than 9.  Results:

EROI = 12 x 0.43 x (15/25) = 3.1

On the plus side, we do not need to connect to a long-distance transmission system, which improves EROI by about 30%.  So final EROI is about 4.  The study also notes that the replacement rate of solar concentrators is an optimistic assumption, but let’s ignore that too.

If the solar collectors are built to gather bulk heat as an end use, rather than electricity, the EROI improves, as the system no longer needs a steam engine (which reduces energy investment) and avoids conversion losses in power generation.  So solar thermal systems are much more efficient at gathering bulk heat for end use.  EROI for a thermal energy harvesting system could be 30 or more.

louis wrote:

Energy density is not the issue on Mars. If it was, we would be shipping coal to Mars.

100M2?  You can't mean 100 metres squared (100x100 metres)... so I assume you mean 10x10 metres.  What's the problem with that? If that's what it takes to boil a kettle on Mars, so be it. Far less complicated than commissioning, monitoring and maintaining a nuclear reactor.

You still don’t think EROI is important?  In a practical sense, the amount of energy and materials embedded in an energy system has a strong bearing on capital cost.  That should,’t be surprising.  If something is twice the size, you would expect it to be twice as expensive.  This is why renewables need subsidies.  On Earth, renewable energy systems receive an artificial boost, because fossil fuel energy is available for their manufacture.  On Mars things are worse, because you will be using a low EROI energy source to manufacture low EROI energy sources and you need a lot more energy per capita to survive.

One final word on EROI: Why do you think PV system manufacturers are attempting to develop thin-film and printed organic solar cells?  Could it perchance have anything to do with reducing the energy invested (and therefore capital cost) of the modules?

I will talk about Mars-built nuclear reactors later on.

Last edited by Antius (2017-05-31 06:39:10)

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#12 2017-05-31 08:32:11

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,486

Re: Solar plus turbine...

I have some big problems with your use of the word "economical".   Its meaning is not clear.  The paper references nuclear as having a much higher EROI than wind or PV. But the reality is that nuclear power is more expensive than wind nearly everywhere, and solar in many places already.  Why?  because EROI is not the only consideration. With nuclear you have to build in huge labour resources to manage the process. They are conveniently not counted as "energy", just as treating the diseases of coal miners or vetting by state security of nuclear workers or building new communities in remote areas where nuclear power stations are located are not counted as costs.

Also, EROI is a somewhat mystical concept. If we had factories, machinery, mining, robots and transport in Australia's Western Desert all running on PV energy, and this PV desert economy was able to produce PV panels, to talk about EROI is irrelevant (as irrelevant as considering whether land or sea is a "better" medium for transport). This isn't a fanciful observation: Tesla are moving in this direction by producing batteries in a desert factory that will run off PV panels. The batteries will be used to run electric vehicles and store solar power from Musk's PV roofing tiles. You can see a total PV economy taking shape. EROI is misleading because it does not give value to the fact you can seamlessly expand your energy surplus once you have a holistic solar economy. You can't seamlessly expand oil or coal energy...you have to find the energy and dig it out of the ground, and then build facilities to transport it around the world. As long as you have land available, as one tends to in a desert, the PV energy supply can just be expanded hugely.

In terms of Mars, the correct comparison is not between EROIs - instead we should use  "cost of total labour time (on Mars) plus total cost of delivery of energy system from Earth to Mars".  The value of labour time should be assessed in terms of the cost of delivery to Mars. So if it takes 100 hours of labour time on Mars to produce 10 Kws constant of power, then you look at the cost of delivering 10 Kws constant to Mars.

So let's say it costs $20000 x 1000 (kgs) to deliver 100 KWs of power to Mars, that would be $20 million. So for 10Kws, it would be $2million. So we would value the labour time at $2 million for a 10K Mars ISRU system, as it is displacing $2 million worth of tonnage delivery.

I think you will find in nearly every case that if we compare a reliable ISRU system, it will win out against the equivalent imported system as the imported system will also have Mars-based labour time costs. If we import a 10 Kw system that requires say 100 hours of deployment, maintenance and monitoring, then the total cost will be $4 million in our cost benefit analysis, because that labour is not being freed up to displace tonnage requirements. Of course the Mars ISRU system may also require labour time for maintenance and monitoring...this is what we would need to look at. My suspicion is that nuclear reactors will require a lot more labour time in terms of deployment and monitoring  than people are admitting to.

Ultimately, if the settlement can construct its own PV Panels then that will be ideal as they require minimal maintenance and monitoring. I see solar plus turbine as a possible stage on the road to energy self-suffiicency. But it may be we will cut through straight to PV panel production on Mars. Or stirling engines may offer a better bet.


Antius wrote:

Louis, thank you for the links.  I have built solar heating systems in my workshop, though I have never attempted a steam engine.  Looking at your links, I am tempted to have a go at it.

I do not doubt for a minute that building small solar powered steam engines is possible on Mars, if we ship machinery and tools to a small base and devote enough man-power to it.  I am sceptical it will be an economical venture.  Here is why:
http://large.stanford.edu/courses/2015/ph240/kumar2/

1.    The EROI of solar thermal power systems in Earth’s deserts with 2.3x the solar constant of Mars is 19 before buffering (i.e. energy storage) and ~9 after buffering.  In this analysis, buffering is provided by pumped storage which is efficient but capital and energy intensive to build.  On Mars, a solar thermal system would almost certainly buffer by storing heat in rock bodies, which would provide better energy density and lower embedded energy than pumped storage, but there will still be energy cost involved in building the store and energy losses in using it.  EROI will naturally be lower because sunlight intensity is only 43% of Earths.

2.    Steam engines are quite inefficient, historically <10% efficient for locomotive steam engines.  With multiple stages and a condenser cycle, efficiency can increase to between 10-20%, but the mass and complexity of the engine increase progressively.  Efficiency problems occur due to the relatively low input temperatures and pressures into the expanders, heat transfer into the cylinder and pistons, pumping losses in the engine and for open cycles, loss of enthalpy still stored in the vented, saturated steam.  Some steam engines include multiple reheat cycles to get around the final problem, but again, you are adding mass and complexity to the device.  Smaller units are generally less efficient than larger units (due to heat transfer and pumping losses).  To minimise both thermal losses and pumping losses, it is advantageous to keep the power profile of the engine as flat as possible, i.e. run it at 100% 24/7.  In other words, for better EROI, build it big and run it flat out.  Is it a coincidence that this also improves plant economics?

The EROI graph referenced above comes from the Weissbach study and is referenced within the link.  Let’s make a few adjustments for a system on Mars: (1) Solar intensity is only 43% of Earth’s; (2) Small steam engines are used, rather than large turbine plants.  Let’s be generous and assume turbine efficiency was 25% and steam engine efficiency is 15%.  Piston steam engines are a lot heavier per kW than turbo-generator sets, but let’s ignore that for now; (3) Let us assume that solar thermal energy storage is a more efficient means of buffering than pumped storage.  Let’s say a power plant using this method on Earth would achieve an EROI of 12 rather than 9.  Results:

EROI = 12 x 0.43 x (15/25) = 3.1

On the plus side, we do not need to connect to a long-distance transmission system, which improves EROI by about 30%.  So final EROI is about 4.  The study also notes that the replacement rate of solar concentrators is an optimistic assumption, but let’s ignore that too.

If the solar collectors are built to gather bulk heat as an end use, rather than electricity, the EROI improves, as the system no longer needs a steam engine (which reduces energy investment) and avoids conversion losses in power generation.  So solar thermal systems are much more efficient at gathering bulk heat for end use.  EROI for a thermal energy harvesting system could be 30 or more.

louis wrote:

Energy density is not the issue on Mars. If it was, we would be shipping coal to Mars.

100M2?  You can't mean 100 metres squared (100x100 metres)... so I assume you mean 10x10 metres.  What's the problem with that? If that's what it takes to boil a kettle on Mars, so be it. Far less complicated than commissioning, monitoring and maintaining a nuclear reactor.

You still don’t think EROI is important?  In a practical sense, the amount of energy and materials embedded in an energy system has a strong bearing on capital cost.  That should,’t be surprising.  If something is twice the size, you would expect it to be twice as expensive.  This is why renewables need subsidies.  On Earth, renewable energy systems receive an artificial boost, because fossil fuel energy is available for their manufacture.  On Mars things are worse, because you will be using a low EROI energy source to manufacture low EROI energy sources and you need a lot more energy per capita to survive.

One final word on EROI: Why do you think PV system manufacturers are attempting to develop thin-film and printed organic solar cells?  Could it perchance have anything to do with reducing the energy invested (and therefore capital cost) of the modules?

I will talk about Mars-built nuclear reactors later on.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#13 2017-05-31 08:45:23

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,800

Re: Solar plus turbine...

What ever happened to the basic Zubrin concept of keeping things simple? Louis is to be commended for some of his creative thinking, but his ideas ultimately devolve into massive infrastructure projects requiring materials from Earth.

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#14 2017-05-31 11:57:01

kbd512
Moderator
Registered: 2015-01-02
Posts: 3,199

Re: Solar plus turbine...

Louis,

All ships I was stationed aboard had a substantial number of personnel assigned to maintaining the machinery.  The difference in reliability between the three methods of driving the ship through the water seemed to be related to the number of moving parts required to produce the mechanical power required to drive the screws.  I thought a boiler would've been mechanically simpler than a gas turbine or nuclear reactor, but that turned out to be an invalid assumption and the actual technology involved was a maintenance nightmare.

Your statement about energy density being unimportant completely ignores the primary problem for any power plant intended for use on Mars.  We're not shipping coal or petroleum products to Mars precisely because the energy density is so poor.  Solar is worse on Mars than Earth for continuous output and if mass and materials cost constraints mattered on Earth to the same degree that they do on Mars, you'd likely never see PV panels, wind turbines, or liquid hydrocarbon fuel use (for ground transportation or electrical power production) when nuclear power plants are available.

The real-world performance of steam vs gas turbine vs nuclear power plants is pretty obvious to anyone directly involved.  If you have the infrastructure and natural resources to extract and use liquid hydrocarbon fuels, then these sorts of power plants are the most well-developed of all current technologies, with examples that output tens of watts to tens of millions of watts.  No such infrastructure or natural resources exist on Mars, so manufacture of those fuels and the oxygen required for combustion is problematic at best.  Solar has none of the traditional problems associated with consumable fuels, but energy density and conversion efficiency is pretty low because the input is so diffuse.

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#15 2017-05-31 13:33:16

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,768
Website

Re: Solar plus turbine...

I would like to point out that "fuel energy density" is the correct measure of comparison on Earth,  but NOT Mars.  Here on Earth,  combustion air is free for the taking.  On Mars,  it is not.  Ignoring that is a VERY serious error. 

If you decide to use a fuel resembling coal or petroleum on Mars,  you have to ship BOTH the fuel and the oxidizer.  Since you have to ship the oxidizer,  its mass goes into the energy density figure along with the mass of the fuel.  The oxidizer outweighs the fuel by factors of 3 or more. 

If you create any of these reactants on Mars in order not to ship them,  the total energy required to create them must subtract from the fuel-oxidizer reaction's energy release to fairly compare.  (And you still must figure the oxidizer into the energy density,  precisely because it is NOT free for the taking.)  For most of the chemical items I've seen mentioned,  that net difference is negative,  because our means of creating oxidizers from neutral or reducing materials is crude and inefficient.  This is mainly because we never before needed to,  and so we have little experience doing so.   

And THAT is why the two power sources most often considered for use on Mars are solar and nuclear.  There really isn't anything else readily available that we already know how to do.  And unless you can stand the brownout or blackout during nights and dust storms,  you simply have to have at least some nuclear,  because the mass of batteries to be shipped is otherwise entirely prohibitive.

I'm sorry,  it really is that simple.  So why are we all still arguing about this or that power source?  You simply have to do some of both.  The only argument is over relative proportions in the mix. 

GW

Last edited by GW Johnson (2017-05-31 13:38:04)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#16 2017-05-31 14:28:49

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,800

Re: Solar plus turbine...

GW-

THX for being blunt. Your analysis is directly based on the thermodynamic considerations of the problem at hand. I think we had some similar "discussions" on this topic before, and the whole issue is elegantly simple when put into a block diagram. I hope I can summarize it below: well, shucks, I can't make this software accomplish my goals.
                              Energy input                                   Operating system        System efficiency       Energy Output
                          ---------------------------                   -------------------------                     
                          / construct solar panels/                   /Battery storage             /
                          / build solar mirrors     /                    /methane combustion    /
                          / build turbines            /                    / with stored oxygen     /  Less than 100%     
                          / lay out solar farm      /   --------->   /collect water; convert   / ---------------->       Not enough!
                          /manufacture methane /                    /to steam                     /
                          /build steam generator /                    /generate electric power/
                          /transport equip Mars   /
                          /manufacture oxygen    /

Last edited by Oldfart1939 (2017-05-31 14:30:19)

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#17 2017-05-31 14:36:13

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,800

Re: Solar plus turbine...

The point of the previous post is the solar-only energy system efficiency will be abysmal.

To paraphrase the first 3 Laws of Thermodynamics in layman terms: (1) You can't win; (2) You can't break even; (3) Things will always get worse.

A Mars expedition cannot be based on a semi-religious belief in the wonders of solar-only, no matter how many layers of obfuscation are piled on. You can always put lipstick on a pig, but underneath, it's still a pig.

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#18 2017-05-31 14:41:56

louis
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From: UK
Registered: 2008-03-24
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Re: Solar plus turbine...

I haven't ignored the additional combustion requirement on Mars. But as I understand it, perhaps you can correct me, nuclear reactors operating in space or on Mars will also have added mass because they won't be water or gas cooled. Isn't that right? All this proves is that operating on Mars is not as easy when it comes to steam engines and nuclear reactors.  Solar panels, I would say, are relatively unaffected, though we have to cope with the low temperatures and dust storms.



GW Johnson wrote:

I would like to point out that "fuel energy density" is the correct measure of comparison on Earth,  but NOT Mars.  Here on Earth,  combustion air is free for the taking.  On Mars,  it is not.  Ignoring that is a VERY serious error. 

If you decide to use a fuel resembling coal or petroleum on Mars,  you have to ship BOTH the fuel and the oxidizer.  Since you have to ship the oxidizer,  its mass goes into the energy density figure along with the mass of the fuel.  The oxidizer outweighs the fuel by factors of 3 or more. 

If you create any of these reactants on Mars in order not to ship them,  the total energy required to create them must subtract from the fuel-oxidizer reaction's energy release to fairly compare.  (And you still must figure the oxidizer into the energy density,  precisely because it is NOT free for the taking.)  For most of the chemical items I've seen mentioned,  that net difference is negative,  because our means of creating oxidizers from neutral or reducing materials is crude and inefficient.  This is mainly because we never before needed to,  and so we have little experience doing so.   

And THAT is why the two power sources most often considered for use on Mars are solar and nuclear.  There really isn't anything else readily available that we already know how to do.  And unless you can stand the brownout or blackout during nights and dust storms,  you simply have to have at least some nuclear,  because the mass of batteries to be shipped is otherwise entirely prohibitive.

I'm sorry,  it really is that simple.  So why are we all still arguing about this or that power source?  You simply have to do some of both.  The only argument is over relative proportions in the mix. 

GW


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#19 2017-05-31 14:55:07

louis
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From: UK
Registered: 2008-03-24
Posts: 5,486

Re: Solar plus turbine...

You can claim this is a belief rather than the product of analysis all you like.

Your analysis completely ignores the fact that the Mars settlement will have huge per capita productive capacity. Why? Because we will (if we have any sense) send them there with an array of machines which they can use to exploit Mars In Situ resources, rather than
just sending them as dumb actors. All the Mars resources - the iron ore, the land, the water and so on - are freely available, as freely as air on Earth.

With all that productive capacity available they can afford to be less efficient in producing energy than utility companies on Earth (which in case are normally competing with other energy providers).

But as I have explained you have to compare Mars ISRU with the full cost of importing energy from Earth. A ten tonne 100 Kwe nuclear reactor might cost, at $20,000 per Kg,  $200 million to ship to Mars (never mind the cost of developing and building it) and would displace 10 tonnes that could be used for other projects that could develop ISRU capacity.

Oldfart1939 wrote:

The point of the previous post is the solar-only energy system efficiency will be abysmal.

To paraphrase the first 3 Laws of Thermodynamics in layman terms: (1) You can't win; (2) You can't break even; (3) Things will always get worse.

A Mars expedition cannot be based on a semi-religious belief in the wonders of solar-only, no matter how many layers of obfuscation are piled on. You can always put lipstick on a pig, but underneath, it's still a pig.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#20 2017-05-31 15:26:44

kbd512
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Registered: 2015-01-02
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Re: Solar plus turbine...

louis wrote:

I haven't ignored the additional combustion requirement on Mars. But as I understand it, perhaps you can correct me, nuclear reactors operating in space or on Mars will also have added mass because they won't be water or gas cooled. Isn't that right? All this proves is that operating on Mars is not as easy when it comes to steam engines and nuclear reactors.  Solar panels, I would say, are relatively unaffected, though we have to cope with the low temperatures and dust storms.

SAFE-400 and Kilopower are inert gas cooled, similar to the freon coolant, or whatever they use now, in an AC system.  The coolant is sealed inside a heat pipe attached to a radiator panel.  Each heat pipe is an entirely separate coolant loop, although several are connected to the same radiator panel, so losing one loop doesn't mean cooling capability is entirely lost.  The cores are basically blocks of ceramic metals or metals, so heat is conducted across the entire core so.  The cooling systems are designed such that loss of coolant from several heat pipes has no adverse affect on the ability to cool the reactor.  If enough loops are lost, then the reactor has to be operated at lower power, but it can still produce power.  The radiator panels are basically carbon.  The heat pipes are made from steel or Molybdenum alloys.  The neutron reflectors are typically Beryllium or BeO.

Larger reactors would use CO2 for coolant since there's no shortage of CO2 on Mars.

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#21 2017-05-31 16:20:46

Antius
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From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Solar plus turbine...

louis wrote:

I haven't ignored the additional combustion requirement on Mars. But as I understand it, perhaps you can correct me, nuclear reactors operating in space or on Mars will also have added mass because they won't be water or gas cooled. Isn't that right? All this proves is that operating on Mars is not as easy when it comes to steam engines and nuclear reactors.  Solar panels, I would say, are relatively unaffected, though we have to cope with the low temperatures and

No.  We have already examined the mass budgets for nuclear reactors deployed on Mars.  Radiators were part of that mass budget.  We are going over and over the same topics again.

What combustion requirements?  Combustion may be used to power vehicles on Mars and maybe even as an energy storage medium.  It will not be an energy source as there is no natural oxidizer on Mars and (so far as we know) no natural fuels.  I thought that was well understood by everyone here.

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#22 2017-05-31 16:42:26

Antius
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From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Solar plus turbine...

louis wrote:

You can claim this is a belief rather than the product of analysis all you like.

Your analysis completely ignores the fact that the Mars settlement will have huge per capita productive capacity. Why? Because we will (if we have any sense) send them there with an array of machines which they can use to exploit Mars In Situ resources, rather than
just sending them as dumb actors. All the Mars resources - the iron ore, the land, the water and so on - are freely available, as freely as air on Earth.

With all that productive capacity available they can afford to be less efficient in producing energy than utility companies on Earth (which in case are normally competing with other energy providers).

But as I have explained you have to compare Mars ISRU with the full cost of importing energy from Earth. A ten tonne 100 Kwe nuclear reactor might cost, at $20,000 per Kg,  $200 million to ship to Mars (never mind the cost of developing and building it) and would displace 10 tonnes that could be used for other projects that could develop ISRU

False.  It is not necessarily true that you cannot build nuclear reactors using ISRU on Mars.  There is nothing very magic about a nuclear reactor.  It is a steel pot with uranium in it.  No different to a boiler really.  The only thing that really would be extremely difficult on Mars is enriching uranium.  But HEU is so energy dense, that we could import it from Earth without seriously impacting reactor economics on Mars.  And there is always the option of carbon moderated, natural uranium reactors.  We were building those back in 1942.  Even if fast reactor cores were imported from Earth, the pressure vessels, heat exchangers and generating equipment could be built on Mars just as easily as solar dynamic power plants.  It is essentially the same kit, only the heat source is different.

When you have to start building energy systems on Mars using energy systems built on Mars, then the energy payback of those systems becomes extremely important.  A low EROI energy source would effectively be a head wind that prevents growth of the colony, because so much of your workforce and resources would go into just maintaining the energy supply you have.

Here on Earth, for millennia before the industrial revolution, human numbers and living standards remained more or less constant.  Most energy came from biomass and a large proportion of human work was spent maintaining that energy supply, producing food and fodda.  There wasn't enough spare energy to divert into investments that could generate much growth.  Total human numbers were about 500 million in Alexander the Great's day and were still only about 700 million when Elizabeth 1 sat on the English thrown, nearly 2000 years later.  Around 1800, human beings started mining fossil fuels and burning them in machines.  Suddenly, they had access to a high EROI energy source.  Within a century, human living standards and human numbers had exploded.

If you want to build a civilisation on Mars, you need to develop native high EROI energy sources.

Last edited by Antius (2017-05-31 17:01:09)

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#23 2017-05-31 16:55:12

louis
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From: UK
Registered: 2008-03-24
Posts: 5,486

Re: Solar plus turbine...

GW's point was there is additional complexity (meaning more mass) to operating a steam engine on Mars, if you are using a hydrocarbon fuel.  I was simply pointing out there is additional complexity (meaning more mass) to operating a nuclear reactor on Mars from the point of view of coolant. I wasn't the one trying to describe things in these terms.

Clearly, it is understood that in a solar energy scenario, the methane and oxygen are products of solar energy deployment - either PV panels or solar reflectors/concentrators. To say that methane is not an energy source, is a bit like saying coal gas is not an energy source or petroleum is not an energy source, because both require processing from different materials (involving deployment of energy).


Antius wrote:
louis wrote:

I haven't ignored the additional combustion requirement on Mars. But as I understand it, perhaps you can correct me, nuclear reactors operating in space or on Mars will also have added mass because they won't be water or gas cooled. Isn't that right? All this proves is that operating on Mars is not as easy when it comes to steam engines and nuclear reactors.  Solar panels, I would say, are relatively unaffected, though we have to cope with the low temperatures and

No.  We have already examined the mass budgets for nuclear reactors deployed on Mars.  Radiators were part of that mass budget.  We are going over and over the same topics again.

What combustion requirements?  Combustion may be used to power vehicles on Mars and maybe even as an energy storage medium.  It will not be an energy source as there is no natural oxidizer on Mars and (so far as we know) no natural fuels.  I thought that was well understood by everyone here.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#24 2017-05-31 17:08:29

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,486

Re: Solar plus turbine...

I've never said it will be impossible to build a nuclear reactor on Mars. I've said it will be beyond the capability of a small settlement, say 100 people.  For every 100 Kw of additional power, you are going to want to import ten tonnes of nuclear reactor.  That's a lot of tonnage denied to other purposes. If you are saying you can build a nuclear reactor on Mars in a small settlement, then the issue is how much labour time per Kw of output is required - that will be the main test (apart from usage suitability). I can only go by the incredibly high costs of nuclear reactor construction to assume there is a lot of complexity in the construction process.

The proof of the pudding would be in the eating and I think PV panel manufacture would be hard to beat. 



Antius wrote:
louis wrote:

You can claim this is a belief rather than the product of analysis all you like.

Your analysis completely ignores the fact that the Mars settlement will have huge per capita productive capacity. Why? Because we will (if we have any sense) send them there with an array of machines which they can use to exploit Mars In Situ resources, rather than
just sending them as dumb actors. All the Mars resources - the iron ore, the land, the water and so on - are freely available, as freely as air on Earth.

With all that productive capacity available they can afford to be less efficient in producing energy than utility companies on Earth (which in case are normally competing with other energy providers).

But as I have explained you have to compare Mars ISRU with the full cost of importing energy from Earth. A ten tonne 100 Kwe nuclear reactor might cost, at $20,000 per Kg,  $200 million to ship to Mars (never mind the cost of developing and building it) and would displace 10 tonnes that could be used for other projects that could develop ISRU

False.  It is not necessarily true that you cannot build nuclear reactors using ISRU on Mars.  There is nothing very magic about a nuclear reactor.  It is a steel pot with uranium in it.  No different to a boiler really.  The only thing that really would be extremely difficult on Mars is enriching uranium.  But HEU is so energy dense, that we could import it from Earth without seriously impacting reactor economics on Mars.  And there is always the option of carbon moderated, natural uranium reactors.  We were building those back in 1942.  Even if fast reactor cores were imported from Earth, the pressure vessels, heat exchangers and generating equipment could be built on Mars just as easily as solar dynamic power plants.  It is essentially the same kit, only the source is different.

When you have to start building energy systems on Mars using energy systems built on Mars, then the energy payback of those systems becomes extremely important.  A low EROI energy source would effectively be a head wind that prevents growth of the colony, because so much of your workforce and resources would go into just maintaining the energy supply you have.

Here on Earth, for millennia before the industrial revolution, human numbers and living standards remained more or less constant.  Most energy came from biomass and a large proportion of human work was spent maintaining that energy supply, producing food and fodda.  There wasn't enough spare energy to divert into investments that could generate much growth.  Then human beings started mining fossil fuels and burning them in machines.  Suddenly, they had access to a high EROI energy source.  Within a century, human living standards and human numbers had exploded.  If you want


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#25 2017-05-31 17:49:47

SpaceNut
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Registered: 2004-07-22
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