Solar chimeys - Feasible?

Bill White · 2003-11-28 14:03:03

I lifted this quote from the Silane Hopper thread:

You have to have an energy source to make silane, obviously. Mars Direct assumes a 3.5 tonne, 100 kilowatt (electrical) reactor. Any Mars outpost for 4 crewmembers and in situ resource utilization needs about 100 kilowatts of continuous power. That reactor converted only 5% of its heat to electricity. If a 15% Stirling engine were used the reactor would make 300 kilowatts, or a 100 kilowatt reactor could be made for closer to 1.5 tonnes.
* * *
-- RobS

Might we build a solar chimney with the nuclear reactor at the base? If we add the 15% Stirling engine as Rob S proposes that leaves 80% of the heat to be dissipated as "waste" and where will that heat actually go?

Elsewhere I have suggested that allowing that heat to transfer into the regolith might be a really bad idea if the settlement is built at a location with massive amounts of perma-frost a few meters underground. Transfer waste heat into the regolith and melt the foundation your settlement is built on.

If waste heat was dissipated with a cooling tower you could transform the cooling tower into a solar chimney and supplement with solar heated air. Another link and a very bare-bones link.

Look at the last link and visualize the chimney walls made from aerogel, or maybe a double layer aerogel thermopane with clear aerogel around the base to maximize greenhouse effects.

A current proposal to build a solar chimney on Earth. The high construction costs appear to be related to the need to build a tall durable tower yet with 3/8ths gravity and aerogel as the construction material perhasp a Marsian solar chimney would be feasible.

This link proposes using the space under the flat portions of the solar chimney for greenhouses to grow food. I suppose waste heat will need to be vented from Marsian greenhouses as well.

Shaun Barrett · 2003-11-28 20:18:10

Bill, I must say I do admire your lateral thinking in combining two separate ideas, nuclear reactors and solar towers, into one.
Martian insolation is only about 43% of Earth's but, supplemented by the waste heat from a reactor, the solar heat accumulator at the base of a solar tower might function well and produce a very considerable updraught to power the turbines.

Nice one, Bill! :;):

Bill White · 2003-11-28 23:11:02

More random thoughts on waste heat.

Early missions will house the crew in Zubrin's tuna can habitats. Even with TransHab, it seems to me that thermal insulation will not be absolute, thus the disposal of waste heat from things like cooking and human metabolism will not be a severe problem. Radiators to vent heat into the passing Marsian atmosphere would be easy to deploy as well, far easier than venting waste heat in the vacuum of space.

Permanent settlements will be a different story, perhaps. I remain concerned that if a buried settlement warmed the regolith on which it was built, perhaps the underlying permafrost could eventually melt, with disastrous consequences. Thus, even buried settlements need to vent waste heat into the scant Marsian atmosphere and perhaps insulate the walls and floors of any buried settlement to prevent heat from being transferred to the surrounding regolith. Aerogel enhanced kevlar blankets would seem ideal for keeping Marsian cold out and human warmth in.

Thus, I wonder, is there an opportunity to run Stirling cycle electric generators during whatever process is used to vent internal settlement heat into the atmosphere? It will be 68 to 72 degrees F inside and at least 50 - 80 degrees colder outside, right?

If generators were added to whatever radiator system was installed, perhaps a trickle of power could be added back into the overall power budget. Even with numerous nuclear reactors, any settlement's energy budget will be strained to the maximum, IMHO.

Bill White · 2003-11-28 23:18:50

Bill, I must say I do admire your lateral thinking in combining two separate ideas, nuclear reactors and solar towers, into one.
Martian insolation is only about 43% of Earth's but, supplemented by the waste heat from a reactor, the solar heat accumulator at the base of a solar tower might function well and produce a very considerable updraught to power the turbines.
Nice one, Bill! :;):

Thank you Shaun. Nice words are always appreciated.

As for my mindset, I attempt to recall Frank Herbert's novel Dune and the Fremen obsession with assuring that no moisture is ever lost. Remember how Paul Atreides wept and the shedding of tears (waste of water) greatly moved the Fremen?

Apply that mentality to everything, especially energy, and that is how I believe settlements will survive on Mars. Every milli-watt will count, even with clusters of nuclear reactors. Lets attach generators to the exercise equipment!

Dune is supposedly patterned on Mars, right?

Josh Cryer · 2003-11-29 02:53:48

Ahh, Bill, now that's the kind of thinking I agree with. Not only would energy be conserved, so too would chemicals and materials, because it's arguably cheaper to recycle something than it is to rederive that something from the outside environment.

Rxke · 2003-11-29 02:57:55

Agree with that sentiment. We throw away too much usable stuff (and energy)

BTW: further in the novels, i recall the ressurected-cloned Duncan thinking the Fremen had lost it, because he saw wastedumps in their cities. Real Fremen recycled everything.

If only we Earthdwellers could be so wise....

Bill White: "Dune is supposedly patterned on Mars, right?"

IIRC Frank Herbert had, in each book a different 'thema' in mind: The first book about ecology, one about politics and so on...

GCNRevenger · 2003-11-29 20:31:47

I think you guys may underestimate just how much power a large nuclear reactor can deliver... a few megawatts lets say of power put out by a few reactors is a quite a bit for a small settlement. Even a 100KW reactor is a fair amount of power.

Also don't forget about the huge amount of radiation they put out. If you put a reactor in the middle of a chimney greenhouse without massive shielding, I guarantee you that nothing will grow and nobody could get anywhere near the place. You'd be lucky if the radiation didn't depolymerize what you would use to make the chimney skirt with. In any event, do not underestimate the danger of doing anything near a running nuclear reactor; without signifigant distance and/or heavy shielding (park in a crater, ring with meters of regolith), anything living or chemicly delicate would be fried.

The big problem with using any moving Martian air to produce power is that its so thin: less pressure, less force on the turbine blades... using the waste heat from a reactor to power it helps, but not that much. It would be better to use the waste heat from the reactor in place of things you would use electricity to do. The heat could be piped to the ISPP system used to make fuel instead of just electric heating or at the very least use the heat from the reactor to keep the habitat and greenhouses warm.

Recycling is a good idea for many things, but it is NOT inherintly cheaper or easier than simply making more of it. For instance, the hardware required in trying to integrate a colony heat management system to a large low power Sterling engine would probobly outweigh simply bringing a slightly bigger reactor, or instead haul another roll of polymer solar pannels.

To summerize, recycling is good for things that are hard to get ahold of, like nitrogen and rocket fuel, or things that easy to recycle like plastic bags and chicken dinner leftovers, but the more you recycle the more the machinery you will have to lug from Earth, machinery you will have to power, operate, and maintain. There is a such thing as too much recycling!

dicktice · 2003-11-30 09:41:01

When I first joined, I posted the idea of tent-roofing over a north/south ravine one mile deep say, piercing it with such a chimney containing multistage turbines for generating ac-power for the pressurized habitat enclosures beneath the ambient pressure anchored cover, and just allow nature to take its course as far as recirculation was concerned. No other energy source for the scheme. Whacko, or. . . ?

Bill White · 2003-11-30 14:05:38

GCNR writes:

Also don't forget about the huge amount of radiation they put out. If you put a reactor in the middle of a chimney greenhouse without massive shielding, I guarantee you that nothing will grow and nobody could get anywhere near the place. You'd be lucky if the radiation didn't depolymerize what you would use to make the chimney skirt with. In any event, do not underestimate the danger of doing anything near a running nuclear reactor; without signifigant distance and/or heavy shielding (park in a crater, ring with meters of regolith), anything living or chemicly delicate would be fried.

Excellent point! Okay, I was wrong, it happens.

More and bigger nukes.

After my original post, I found links to David Poston's work including this one:

ABSTRACT
Ambitious solar system exploration missions in the near future will require robust power sources in the range of 10 to 200 kWe. Fission systems are well suited to provide safe, reliable, and economic power within this range. The Heatpipe Power System (HPS) is one possible approach for producing near-term, low-cost, space fission power. The goal of the HPS project is to devise an attractive space fission system that can be developed quickly and affordably. The primary ways of doing this are by using existing technology and by designing the system for inexpensive testing. If the system can be designed to allow highly prototypic testing with electrical heating, then an exhaustive test program can be carried out quickly and inexpensively, and thorough testing of the actual flight unit can be performed?which is a major benefit to reliability. Over the past 4 years, three small HPS proof-of-concept technology demonstrations have been conducted, and each has been highly successful. The Safe Affordable Fission Engine (SAFE) is an HPS reactor designed for producing electricity in space. The SAFE-400 is a 400-kWt reactor that has been designed to couple with a 100-kWe Brayton power system. The SAFE-400 contains 127 identical molybdenum (Mo) modules. A Mo/sodium heatpipe is at the center of each module, surrounded by three Mo tubes that each contain a rhenium-clad uranium-nitride fuel pin. Fission energy is conducted from the fuel pins to the heatpipes, which then carry the heat to a heatpipe-to-gas heat exchanger. This paper describes the design and analysis of the current SAFE-400 reactor design. ?2002 American Institute of Physics.

Does this say Poston believes he can get 25% efficiency from the SAFE 400? Do I read that right? If he can do that, or better than that, then I agree with GCNRevenger. Look at my original post. RobS was talking about 5% efficiencies.

Here is a great list of links for anyone with access to the appropriate library.

As for recycling, I agree absolutely that "it depends" - - 5% efficiency from your nukes and maybe we had better be damn frugal with our power. If we achieve much higher efficiencies? Launch another reactor.

= = =

As an aside, I believe David Poston is coming up with these ideas more as a matter of personal interest and this research is not getting any significant funding. But maybe I am wrong again. ???

Bill White · 2003-11-30 14:15:28

When I first joined, I posted the idea of tent-roofing over a north/south ravine one mile deep say, piercing it with such a chimney containing multistage turbines for generating ac-power for the pressurized habitat enclosures beneath the ambient pressure anchored cover, and just allow nature to take its course as far as recirculation was concerned. No other energy source for the scheme. Whacko, or. . . ?

These discussions do tend to go in circles. I do remember your proposal.

However, I personally do not believe we can generate sufficient electricity without nuclear power. Maybe I am wrong about that and I am neither a scientist nor an engineer, but that is my opinion.

RobS · 2003-11-30 16:44:07

GCNRevenger is right about low power densities of the thin Martian atmosphere. As I noted somewhere recently, I think one needs a windmill with 100 meter diameter blades spinning at 25 mph/40 kmph to make a mere 5 kilowatts of power. The way to calculate this (and here's the revised calculation!) is to start with a windmill described on the web with 46 foot (15 meter) in diameter blades that can make 25 kw in a 25 mph wind. The Martian atmosphere is about 1/130 as dense and thus would make 25/130 = 1/5 kw for the same size blade and windspeed. But power increases by the square of the blade diameter, so a 100 meter diameter blade would make 100/15 = 6.6666 squared = 44.4 times as much power, times 1/5 kw = 8.8 kw. Most of the time you don't have 25 mph winds; other times you have faster winds, though.

So a solar chimney with a 25 mph wind in it, making a steady 8.9 kw, has to be 100 meters in diameter, unless you can get the air going faster; double the wind speed and you quadruple the power output.

Rather than build a solar chimney a mile high up a side canyon of Marineris, it would probably be more efficient to use the same resources to build dozens of windmills. You'd get more power and have less problems with maintaining the chimney.

-- RobS

Shaun Barrett · 2003-12-01 08:06:58

I'm under the impression that the expansive umbrella-like 'solar catcher' at the base of a solar chimney is designed to trap and heat large volumes of air, which are funneled inward and increasingly upward to the central chimney.
As I understand it, the updraught in the chimney reaches very high speeds. I can't remember the figures (if I ever saw them! ) but I have a mental impression of cyclonic wind speeds inside the chimney.

Is it not possible to shield a reactor sufficiently to eliminate most nuclear radiation, while still allowing heat to escape?
I'm still trying to save Bill's neat idea! :;):

Bill White · 2003-12-01 09:46:52

I'm under the impression that the expansive umbrella-like 'solar catcher' at the base of a solar chimney is designed to trap and heat large volumes of air, which are funneled inward and increasingly upward to the central chimney.
As I understand it, the updraught in the chimney reaches very high speeds. I can't remember the figures (if I ever saw them! ) but I have a mental impression of cyclonic wind speeds inside the chimney.
Is it not possible to shield a reactor sufficiently to eliminate most nuclear radiation, while still allowing heat to escape?
I'm still trying to save Bill's neat idea! :;):

I hope they actually go ahead and build one of these things near Los Angeles - - see the earlier link - - but it will probably mess up bird migration or something. :;):

Whether this will work for Mars will depend on the numbers. Without waste heat from a nuclear reactor, its a much harder to be certain the numbers work.

If David Poston and others can develop higher efficiency reactors, then urgency is reduced.

clark · 2003-12-02 08:35:11

Hmmm....

What would be the power production of a theoritcal Solar Power Sat in Mars orbit that transmits the power via microwaves?

Where would they get these things?

Why the moon of course! Afterall, there are some upstarts that talk about building them for Earth, so someone thinks it's possible...

So if it is possible, then why not ship some of those sats to Mars for power? I don't know much about ISP or delta V, but others keep saying it's cheaper to send something to Mars from the Moon, than say Earth, right?

Nuclear reactors are a neccessity, of course. Saftey and redundancy being the major factor. And all the power counts, out here in So Cal, we have power outs and we bake in the heat- space, well, you just plain ol die. I hope no one in space is playing it close to "2% reserve" like here in CA.

RobS · 2003-12-03 02:04:47

It migh be even easier putting the "powersat" on one of the moons of Mars. Then there are no orbital maintenance issues. Phobos goes around Mars 3 times a day, from the point of view of the surface, so it could provide power to any place except the polar regions on a regular basis. This is very helpful if you want to beam power to remote expeditions that could be anywhere on the surface.

-- RobS

GCNRevenger · 2003-12-03 14:38:41

Mmmm though it might eventually be practical for power on Earth, where reliability and availability are less of a concern (since we won't die in hours without power), it is for any space ship or base. Solar satelites are unproven technology, space reactors are. Solar satelites cannot provide power continuously, which nessesitates the need for batteries or fuel cells, so you might as well bring another reactor instead. Also, the collection station for the microwave beam will have to be rather large... on the order of hundreds of square meters or even square kilometers for a large one, clearly much more difficult to build and service than a reactor. Solar panels will also suffer micrometeor and solar flare damage over time but will more importantly would be far too hard to keep clean with the micro-fine dust environment on Mars, while a reactor will not. A large reactor, designed to be refueled, would obviously be the best choice for a Mars colony, and considering the energy density of Uranium, would also be competitive for a Moon base.

Bill White · 2003-12-03 14:50:23

Mmmm though it might eventually be practical for power on Earth, where reliability and availability are less of a concern (since we won't die in hours without power), it is for any space ship or base. Solar satelites are unproven technology, space reactors are. Solar satelites cannot provide power continuously, which nessesitates the need for batteries or fuel cells, so you might as well bring another reactor instead. Also, the collection station for the microwave beam will have to be rather large... on the order of hundreds of square meters or even square kilometers for a large one, clearly much more difficult to build and service than a reactor. Solar panels will also suffer micrometeor and solar flare damage over time but will more importantly would be far too hard to keep clean with the micro-fine dust environment on Mars, while a reactor will not. A large reactor, designed to be refueled, would obviously be the best choice for a Mars colony, and considering the energy density of Uranium, would also be competitive for a Moon base.

GCNR, what is your opinion of these papers and the work of David Poston?

SpaceNut · 2015-08-12 21:58:55

This topic starts out looking like its supplimental from recapture of a nuclear plant exhaust heat stack but its way more than that.
Fixed shifting issue all but for the post by Josh.

My initial thoughts are to place a chimeny above the nuclear stack which also is augmented with a rotor blade generator to make use of the stacks up draft and then to make use of it once more on the solar chimenty as well.

The blade information from Rob is another possible path to power creation....

Antius · 2015-10-30 10:10:41

I like this idea, but would argue that it isn't neccesary on Mars, nor would it really work in such a thin atmosphere. But something similar would. At typical Martian temperatures you can liquefy CO2 from the atmosphere with very little compressive work as temperatures are close to the triple point of CO2. You can then 'boil' the CO2 using solar or nuclear heat and generate power from the expanding vapour. Nothing like that would work on Earth, so we have to build huge chimneys to exploit tiny density differences in the gas phase.

In many ways, Mars offers advantages to a civilisation that do not exist here on Earth. For example, without seas or oceans, it will ultimately be easy to transport anything across the planet using rail, roads and pipelines. No need for tankers or aeroplanes as the entire planet has a passable solid surface. The air itself provides a feedstock of oxygen, carbon, nitrogen and hydrogen that is easy to extract and process by compression. Again, this does not apply in the same way on Earth. The atmosphere is thin enough that it does not contribute to heat transfer in a big way, but thick enough to shield out solar flares. The dry Martian environment allows the use of unbaked soils as structural components without damage from damp. That is a major plus when it comes to building structures. In many ways, Mars as is is a very habitable environment and in some ways more habitable than Earth.

SpaceNut · 2018-12-20 21:20:33

Bump for solar co2 collection

louis · 2018-12-21 04:38:34

I like this post. It's something I've mentioned elsewhere on other occasions - Mars has many advantages when it comes to civilisation building but just four drawbacks: extreme (and low) temperature range, a thin atmosphere, occasional dust storms and a significant radiation risk. But the thin atmosphere means you don't get extreme weather events apart from the (low power) dust storms and the low temperature means you have a firm surface for transport and construction nearly everywhere.

So could we simply transport solid CO2 from the poles in well insulated (robot) rovers that travel by night. and otherwise sit in the shade. Then when the rovers reach the temperate zone where our settlements are, we sublimate the CO2 (using solar power) in high pressure chambers and drive turbines?

Antius wrote:

I like this idea, but would argue that it isn't neccesary on Mars, nor would it really work in such a thin atmosphere. But something similar would. At typical Martian temperatures you can liquefy CO2 from the atmosphere with very little compressive work as temperatures are close to the triple point of CO2. You can then 'boil' the CO2 using solar or nuclear heat and generate power from the expanding vapour. Nothing like that would work on Earth, so we have to build huge chimneys to exploit tiny density differences in the gas phase.
In many ways, Mars offers advantages to a civilisation that do not exist here on Earth. For example, without seas or oceans, it will ultimately be easy to transport anything across the planet using rail, roads and pipelines. No need for tankers or aeroplanes as the entire planet has a passable solid surface. The air itself provides a feedstock of oxygen, carbon, nitrogen and hydrogen that is easy to extract and process by compression. Again, this does not apply in the same way on Earth. The atmosphere is thin enough that it does not contribute to heat transfer in a big way, but thick enough to shield out solar flares. The dry Martian environment allows the use of unbaked soils as structural components without damage from damp. That is a major plus when it comes to building structures. In many ways, Mars as is is a very habitable environment and in some ways more habitable than Earth.

SpaceNut · 2018-12-21 17:30:46

Not entirely so as a rover got stuck in the sand...

Using heat concentrating to make dry ice expand will rise the pressure that it has. Then after a few cycles you end up with more with the least amount of power used. So it becomes a question of what period of time to make use of for gathering co2 versus how much time is it going to take to convert it into LCH2 and LOX based on the amount of fuel we need.

We have seen that we can make pulliung co2 out of the air to make fuel using waste heat so its reasonable to think that its also possible for mars just done in a different manner.

SpaceNut · 2018-12-21 18:11:04

Here is the Earth version of co2 to fuel and its a powered system

As indicated 150 tons are what the plant targets in a year. On mars we have 2 to get it done. so out of earths co2 at 14.7 psi and only 0.04% content versus the mars psi at 96% co2 we can now compare apples to apples for a simular system to get the volume or tonms of co2 that we need.

louis · 2018-12-21 18:11:26

You mean the weather event caused an accumulation of sand? Maybe but the rovers concerned are puny things - not like the 20Kw-50kw power rovers that would be undertaking exploration once we were established on Mars.

JoshNH4H · 2018-12-21 19:00:34

Hey Louis,

I briefly discussed the possibility of bringing CO2 from the poles to the temperate equatorial regions as fuel in this post

I wrote:

It's certainly conceivable that mining dry ice at the poles could be economical, but it's hard (for me) to imagine that it would actually make sense unless the end user is actually at the poles.
You used coal as an analogy, and it's a pretty decent one. However, rather than showing the potential value of CO2 mining I believe it shows why it probably won't be worthwhile.
I believe the appropriate comparison is the system we were discussing before: a refrigeration system that uses energy to freeze CO2 out of the atmosphere. Here are the costs and benefits of such a system:
Costs:
Requires industrial equipment
Consumes energy
System has not been designed fully yet
Benefits:
Generates ~1 kg per kWh of inert gas (primarily Nitrogen and Argon)
Works equally well anywhere on Mars
Now, by comparison, here are the costs and benefits of pole-mining:
Costs:
Requires an ongoing supply of human labor (All mining does)
Consumes energy
Requires shipment over thousands of kilometers
Requires industrial equipment
System for mining a substance that sublimes at 195 K has never been built and would require some tweaks to existing techniques
Benefits:
Will produce water as a byproduct
In my view, the question is: Is more labor and thousands of km of shipping worth saving yourself 150 kJ/kg? In my opinion, it is not. It's good to compare this to coal: Coal on Earth has an energy content of 30 MJ/kg, 200 times greater than the energy you save. Because the energy content is so high, it really is worth pulling out out of the ground and shipping it to the point of use (or at least it was in times past). I question whether mining CO2 from the poles would save any energy at all.

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#1 2003-11-28 14:03:03

Re: Solar chimeys - Feasible?

#2 2003-11-28 20:18:10

Re: Solar chimeys - Feasible?

#3 2003-11-28 23:11:02

Re: Solar chimeys - Feasible?

#4 2003-11-28 23:18:50

Re: Solar chimeys - Feasible?

#5 2003-11-29 02:53:48

Re: Solar chimeys - Feasible?

#6 2003-11-29 02:57:55

Re: Solar chimeys - Feasible?

#7 2003-11-29 20:31:47

Re: Solar chimeys - Feasible?

#8 2003-11-30 09:41:01

Re: Solar chimeys - Feasible?

#9 2003-11-30 14:05:38

Re: Solar chimeys - Feasible?

#10 2003-11-30 14:15:28

Re: Solar chimeys - Feasible?

#11 2003-11-30 16:44:07

Re: Solar chimeys - Feasible?

#12 2003-12-01 08:06:58

Re: Solar chimeys - Feasible?

#13 2003-12-01 09:46:52

Re: Solar chimeys - Feasible?

#14 2003-12-02 08:35:11

Re: Solar chimeys - Feasible?

#15 2003-12-03 02:04:47

Re: Solar chimeys - Feasible?

#16 2003-12-03 14:38:41

Re: Solar chimeys - Feasible?

#17 2003-12-03 14:50:23

Re: Solar chimeys - Feasible?

#18 2015-08-12 21:58:55

Re: Solar chimeys - Feasible?

#19 2015-10-30 10:10:41

Re: Solar chimeys - Feasible?

#20 2018-12-20 21:20:33

Re: Solar chimeys - Feasible?

#21 2018-12-21 04:38:34

Re: Solar chimeys - Feasible?

#22 2018-12-21 17:30:46

Re: Solar chimeys - Feasible?

#23 2018-12-21 18:11:04

Re: Solar chimeys - Feasible?

#24 2018-12-21 18:11:26

Re: Solar chimeys - Feasible?

#25 2018-12-21 19:00:34

Re: Solar chimeys - Feasible?

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