solar power towers on mars - km-high vertical wind tunnel turbo-elec

MarsDog · 2004-12-04 08:43:53

For efficiency, modify the http://www.du.edu/~jcalvert/tech/fluids … htm]Pelton wheel for Martian air, put it up, at the top of the canyon or crater. The solar chimney would blow air onto the bucket; Looking like a ferris wheel.

If you have 1 km^2 collecting area;
Total power incoming from the Sun = 0.5X10^6 KW

Running from 300K to 200K, the the maximum engine efficiency is 1-(200/300)=33%

Minus other losses, 10^5 KW peak electrical power is possible ?

RobS · 2004-12-04 11:21:40

Martian windmills would probably have to be designed to run at higher speeds than those on Earth. All windmills have a stall speed, below which the wind can't turn them. It's usually 1-2 miles per hour (1 meter per second). But the amount of energy the wind provides increases by the square of the velocity. Slow winds have very little energy in them, so on Mars, with its thin air, there's no reason to design a windmill for low wind speeds.

I'd design Martian windmills to generate power in as wide a range of speeds as possible with the high end favored. On Earth it would be hard to design a windmill tower even to survive a gale-force wind. Not so on Mars; 200 mph/300 kmph/100 m/sec winds would be quite nice in terms of power production. You'd want to make the blades out of light-weight, high-strength materials like kevlar so they can start turning at a lower wind speed and can handle the centrifugal force of a high speed. You might even want to install a system of gears (like in a car) so that a wider range of windmill rotation speeds can produce a small range of rotation speeds in the generator. I doubt high-speed rotation in high winds is a structural problem; helicopter blades turn much faster.

-- RobS

RobS · 2004-12-04 11:46:46

Some additional thoughts about this solar power tower. I don't see warm greenhouses and such as necessarily a useful source of wind energy. If the greenhouses heated the Martian air above them, they'd quickly cool off to temperatures too low to be used as greenhouses. The thing that keep greenhouses warm is increasing the residence time of the heat inside, not increasing the total amount of heat escaping from them.

To increase the total heat available, you need to change the albedo. Right now, Mars has an albedo of something like 20% or 25% (I don't recall) meaning most of the sunlight is absorbed and only a quarter or fifth of it is reflected straight back to space. But covering a large area of the Martian surface with black plastic will radically decrease the albedo and will heat the Martian air above it. That could generate wind energy.

-- RobS

Euler · 2004-12-04 14:36:20

But the amount of energy the wind provides increases by the square of the velocity.

Actually, the amount of energy that the wind provides increases with the cube of the velocity.

I doubt high-speed rotation in high winds is a structural problem; helicopter blades turn much faster.

Helicopter blades are also a lot smaller than the blades of large windmills. If you increase the length of a rotor while keeping it spinning at the same rate, then the strength of the materials that you are using would have to increase proportionately to the square of the blade length.

High speed rotation is a problem for large windmills. It is the reason why modern large-scale windmills use carbon fiber or fiberglass blades. It is also one of the reasons why windmills must tilt their blades so that less power is produced in high winds.

dicktice · 2004-12-06 19:50:40

Right on, MarsDog! Using the canyon walls to support inflatable solar power towers, or chimneys, is brilliant. Shame on the rest of you, who treated this as a "windmill" scheme. You couldn't have read the Australian project report. RobS, the open-sided "greenhouse" canopy would be supported, tent-like, hundreds of feet above the canyon floor, perhaps sloping, to channel the incoming ambient air towards a circle of axial turbo-generators located at the base of the chimney. The canopy has to be transparent in the visible spectrum, and opaque in the thermal infrared, which (greenhouse-wise) warms up everything under the canopy, including the incoming air flowing past different kinds of habitat domes to converge on the generators, providing incidental warmth to the domes, in addition to what they get from the visible radiation that they get throufh the canopy. How about someone who can, adapting the Australian solar power tower calculations to canyons-on-Mars conditions, now, and see what we get?

GCNRevenger · 2004-12-06 19:57:34

I don't think you guys are really fathoming just how little energy the Martian atmosphere, even heated, will provide you. The tower idea is impractical for the same reasons as above stated, and no magic canyon wind tunnel will save it.

dicktice · 2004-12-07 21:29:55

Durn! I'd still like to see corresponding figures with respect to the Aussie ones, just for fun. God knows, we have little enough of that to write about, these days.

GCNRevenger · 2004-12-07 22:19:12

Lets see... 1/115th times the air pressure and 38% of the gravity, since it is after all gravity powerd, would give you around 00.33% of the energy as a comperable tower on Earth.

MarsDog · 2004-12-08 03:04:14

Assume 1 km^2 collecting area, 500 watts/ m^2, creating 300k, exhausting to 200k

You have to calculate the weight of CO2 that has to flow to transport the 0.5 X 10^9 Watts incoming.

http://www.fluidmech.net/jscalc/gp-calc03.htm]reference 1

http://www.uigi.com/carbondioxide.html]reference 2

ideal gas rough approximation

1 m^3 = 44 moles at STP (1000 liters / 22.414 liter/mole)
Mars pressure is about 0.75% of the average on Earth = 0.33 moles/m^3

So 1 m^ of CO2 on Mars, mass = .33*44 = 14.5 grams at 300k
22 grams at 200k

---------------
Heat capacity per gram CO2 j/g °K = 0.85

so 1 m^3 =14.5 g * 0.85 * 100 degrees =1233 joules
total flow = 0.5x10^9/1233 = 4x10^5 m^3/sec ? (74 meter cube of CO2)

Assume pipe cross section area of 1,000 m^2;
The gas velocity becomes 400 meters/second = 895 mph

somebody please check and calculate pipe and turbine

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http://wire0.ises.org/wire/independents … ment]Spain Version

http://www.globalwarmingsolutions.co.uk … htm]making it more efficient

http://www.lerc.nasa.gov/WWW/K-12/airpl … ml]Martian atmosphere java applet to check and compare with earth

http://www.science.org.au/nova/037/037print.htm#box 3]Wind Power Basics

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http://www.memagazine.org/supparch/mepo … ds.html]On Earth, wind needs to blow at about 10 meters, or 33 feet, per second to operate a wind turbine, Flynn said. On Mars, it has to blow at about 30 meters, or 98 feet, per second because the planet's atmosphere is extremely thin.

dicktice · 2004-12-09 16:52:42

Gosh, I'm impressed, with both CGNR and MarsDog. What impressed me the most, was the additional contribution, in the true spirit of brainstorming, offered by MarsDog. How about adding (presumed) geothermal heat, to the heat exchanger, from pipes driven from the floor horizontally into the canyon walls? I'm concerned that the possibilities those deep canyon floors and high canyon walls aren't being addressed, for whatever reason, the power chimney being just a side issue. I see Mars as an underground living space for human habitats, from the word go.

MarsDog · 2004-12-09 18:14:04

All kinds of possibilities;

The pipes into the canyon wall to store energy, to be used during dust storms.

2 pressurized greenhouses, at different elevations, connected with hot and cold air pipes. The bottom one acting as a collector of heat, the top one as a radiator, running a turbine.

Turbocharge the heat pipe, just like a car engine ?

Austin Stanley · 2004-12-11 02:33:18

Gosh, I'm impressed, with both CGNR and MarsDog. What impressed me the most, was the additional contribution, in the true spirit of brainstorming, offered by MarsDog. How about adding (presumed) geothermal heat, to the heat exchanger, from pipes driven from the floor horizontally into the canyon walls? I'm concerned that the possibilities those deep canyon floors and high canyon walls aren't being addressed, for whatever reason, the power chimney being just a side issue. I see Mars as an underground living space for human habitats, from the word go.

If you have geo-thermal heat, why bother with a kilometer tall tower in the first place? Just use that to power your turbine in the first place.

Again it's not so much an issue as to if you might be able to use it to generate power. There are a LOT of ways to generate electricity and heat, you could put out a realy long anttenna and gather radio waves for example. The issue is not all of these methods are practicle, and building a kilometer plus tower on Mars certianly qualifies as impracticle, IMO.

Michael Bloxham · 2004-12-12 16:04:20

The issue is not all of these methods are practicle, and building a kilometer plus tower on Mars certianly qualifies as impracticle, IMO.

- Yeah, but so is manufacturing photovoltaic cells, nuclear power plants, burning petrofied martian microbes...
Your concentrating too much on terrestrial efficiency; whats more important is that a chimney thingy could be manufactured easily from native materials, and constructed with basic tools.

GCNRevenger · 2004-12-12 16:38:32

The issue is not all of these methods are practicle, and building a kilometer plus tower on Mars certianly qualifies as impracticle, IMO.
- Yeah, but so is manufacturing photovoltaic cells, nuclear power plants, burning petrofied martian microbes...
Your concentrating too much on terrestrial efficiency; whats more important is that a chimney thingy could be manufactured easily from native materials, and constructed with basic tools.

The limitations of lower gravity and lower air pressure simply make the whole idea impractical. You are talking about only producing 1/300th of the energy of a comperable tower on Earth! This just won't work! Earth has a dense atmosphere and tripple the gravity, which is what is relied on to make it work here. Mars doesn't have either, so it won't work.

Trying to take terrestrial power generation technology and applying it to Mars just doesn't always translate... Furthermore, you have no concrete to build your tower with, since this requires water which you don't have in abundance enough to waste on building materials. Plus you need heavy machinery, which you also won't have, and some method for making refined metals which is also not that easy and very highly energy intensive. No bulk polymers either, since hydrogen to make them with will be at a premium.

Austin Stanley · 2004-12-13 03:02:37

- Yeah, but so is manufacturing photovoltaic cells, nuclear power plants, burning petrofied martian microbes...
Your concentrating too much on terrestrial efficiency; whats more important is that a chimney thingy could be manufactured easily from native materials, and constructed with basic tools.

I disagree. Nuclear, photovoltaic, and solar thermal are all far more practicle on mars then building kilometer tall towers (that wouldn't work).

Nuclear - at first you do have to import a rather large reactor from earth, as building one on mars will always be kind of tricky. However, after you have one there all you need is the fuel, which is a rather small componet and can last you a very long time. Some reactors (those mediated with heavy water, such as the CANDU IIRC) can even run on unrefined nuclear fuel, which could found and processed on mars without to much difficulty.

Photovoltaic - the manufacture of photovolatics is actualy not as complicated as you might think, at least for ones that are only marginaly efficent. After a martian base/colony has heavy metal refining down I expect this to be the next thing they try and tackel.

Solar Thermal - the best home grown power solution IMO. Focus some mirrors to heat some water and turn a turbine. Could be built with some fairly simple and cheap parts, perhaps even salavaged from no longer functional components.

All of these options are immensily more practicle than the multi-kilometer tall chimney (if you scale it up to necessary Martian sizes). Despite the fact that the materials might theoreticaly be easily avaliable on mars, assembling them into a tower of some extream proportions is still extreamly difficult. I mean we haven't even built any towers that tall here on earth!

GraemeSkinner · 2004-12-13 03:29:42

Solar Thermal - the best home grown power solution IMO. Focus some mirrors to heat some water and turn a turbine. Could be built with some fairly simple and cheap parts, perhaps even salavaged from no longer functional components.

Solar thermal is very simple technology, and I can well imagine its use on Mars as there is very little to go wrong on a basic setup.

Graeme

MarsDog · 2004-12-13 07:23:52

The difference in mass for 200°K to 300°K is 7.5 grams/m^3. (22-14.5)

Adjusting for 3/8 Mars gravity;
You would only get around 3 grams lift per cubic meter.
3 kilograms/meter^2 for 1 kilometer total height.

Assume pipe cross section area of 1,000 m^2 (36 meter diameter) Total upward = 3,000 kg earth equivalent.

There is enough to turn a very large turbine with low pressure, high speed gas.

ERRORIST · 2004-12-13 08:09:02

http://www.spacedaily.com/news/chip-tech-04zt.html

GCNRevenger · 2004-12-13 08:58:51

The difference in mass for 200°K to 300°K is 7.5 grams/m^3. (22-14.5)
Adjusting for 3/8 Mars gravity;
You would only get around 3 grams lift per cubic meter.
3 kilograms/meter^2 for 1 kilometer total height.
Assume pipe cross section area of 1,000 m^2 (36 meter diameter) Total upward = 3,000 kg earth equivalent.
There is enough to turn a very large turbine with low pressure, high speed gas.

Are you adjusting for the two-orders-of-magnetude lower air pressure?

I don't think that even if you could get it to turn that it would produce much power, certainly almost none for the amount of materials & work invested.

MarsDog · 2004-12-13 18:50:53

http://searchsmallbizit.techtarget.com/ … 0.html]The density of air at STP is approximately 1.29 kilogram per meter cubed (1.29 kg/m3). This fact comes as a surprise to many people; a cubic meter of air weighs nearly three pounds!

CO2 weighs more by a factor of (44/29)

Pressure on Mars is 0.75% earth

The gravity on the surface of Mars is 3.72 m/s²

Mass of Cubic meter on Mars
1.29 (kg/m^3) X (44/29) X 0.0075 = 0.0147 kg @ 273.16°K
(273.16/200) X .0147 = 0.02 kg @ 200°K

That is a 20g-14.7g = 5.3g/cubic meter difference for the two temperatures

To get force F=m*g 0.0053kg x 3.72 m/s² = 0.0197 Newtons (lift for 1 m^3)

.... etc.

==================================

The high velocity would make up for the low density.
The usefullness of the thermal chimney is its ability to use low temperature differences. It could be an integral part of a canyon wall, multy level habitation complex.

For dusty weather periods; Heat could be stored in a geeenhouse enclosed lake below.

RobS · 2004-12-13 19:26:02

Why multiply pressure by 44/29? The pressure already has the mass of the CO2 included in it, right?

-- RobS

MarsDog · 2004-12-13 20:24:37

Why multiply pressure by 44/29? The pressure already has the mass of the CO2 included in it, right?

RobS is correct.

Pressure is the force per unit area from gravity acting on the the mass above.
However, all ideal gasses have same pressure at given temperature; although density varies from gas to gas.

The original assumption starts with 0.75% Earth pressure.

At STP
One http://www.digitalfire.ab.ca/cermat/edu … .html]mole of ideal gas occupies 22.4 liters
The weight of 22.4 liters is molecular weight in grams

22.4 liters of air weighs 29 grams
22.4 liters CO2 weighs 12 + 2x16=44 grams

At same pressure and temperature, ideal gas law PV=NRT
weight ratio of identical volumes is 44/29 times heavier for CO2 than Air.

============================================

Some Mars/Earth ratios

Specific heat per mass CO2/Air = 0.85/1.06 (kJ/kg °K)

Pressure 0.0075/1 atmosphere

Weight for indentical number of molecules = 44/29

Acceleration due gravity 3.72/9.8

=========================================

The big design differences deal with 133 times the volume of gas,
and 3/8 of total uplift force due lower gravity.

To get the same total force on the turbine blades as on Earth, at equal wind speed,
increase pipe cross section area by

(133 * (8/3 * 29/44)) = 234 times; pipe radius by sqrt(234) = 15.2 times

However, specific heat is different and given for weight units, so temperature difference, for same gas flow, is greater by factor of (1.06/0.85 * 44/29) = 1.89 times, to carry away all the heat incoming. The temperature difference increase uplift etc ... I cannot think of a closed form solution.

===============

http://www.visionengineer.com/env/solar … efficiency increases with the height of the chimney, exponentially

http://wire0.ises.org/wire/Publications … on.pdf]The output achieved is proportional to the product of volume flow per time unit and the fall in pressure at the turbine

SpaceNut · 2015-08-05 22:43:47

Another shifting topic fixed...

I am wondering what needs to be brought to allow a solar chimney to be built from insitu materials.

The carbon from the atmosphere would be a byproduct that we could make use of to create the temperature difference once we create the glass to make the chimney possible. All that needs to be brought is the ability to make the blades and a motor generator for power creation once it is spinning.

SpaceNut · 2018-12-09 18:37:33

Ah hah wind pwer energy from solar up draft.. aka solar chimney but in either case power from a windmill can also be garnered as we now know how fast mars winds are.

SpaceNut · 2019-11-18 16:49:53

nice calculation for wind on page 1

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Re: solar power towers on mars - km-high vertical wind tunnel turbo-elec

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