Getting Energy from the Moon's Extreme Temperatures

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jewish_scientist
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Getting Energy from the Moon's Extreme Temperatures

Postby jewish_scientist » Mon May 04, 2015 8:21 am UTC

Every power-plant on Earth basically works like this: 1) stuff 2) make steam 3) put steam through a turbine that has a magnet attached to it 4) repeat. Some power-plants use steam while it is in liquid form a.k.a. water.

The temperature on the Moon ranges from about -150 C to 100 C.* There must be some way to get energy from a 250 temperature difference. A really simple idea for one: Build slanted turbine that has a pipe connecting its top and base. Fill it with excess water. During the day, the water rapidly evaporates, forcing its way through the turbine. During the night, the water rapidly condenses, flowing down the tubes to the base of the turbine. Maybe we could also put a turbine in there. The turbine will need to be insulated so the change in temperature is never too fast. If hypothetical people near the power-plant need some extra water, they just wait until night, enter a pressurized chamber and cut ice blocks out. This is also a great way to sterilize and distill grey water. It does have a fairly major down side. The turbine only spins then it crosses the terminator, which would be once every 15 days. A farm of these generators will never be able to power a base, but it could offer regular surplus power.

So, what do you thing about my design? Can you think of a better design? Is there a substance besides H2O what will generate power more efficiently in this?

*NASA, the best source for anything ever ( http://www.nasa.gov/mission_pages/LRO/m ... rpole.html )

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Re: Getting Energy from the Moon's Extreme Temperatures

Postby Neil_Boekend » Mon May 04, 2015 8:37 am UTC

You could use the expansion of the rock and an invar rod to generate movement. Couple that with a generator and be happy.

Problem is the efficiency as in kW per kg. Getting materials to the moon is expensive. Getting a 100 ton thermal generator to the moon to generate the same power a 10 ton solar plant would generate is not efficient.
Now I don't know the numbers but the cycle time of 1 month seems to decrease the practical energy output significantly.
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Re: Getting Energy from the Moon's Extreme Temperatures

Postby peregrine_crow » Mon May 04, 2015 8:41 am UTC

Wouldn't it be better to just use a bunch of solar panels instead? Your using the same power source, but you don't have the extra step of waiting for the moon to turn to get to the next step of your condensation/evaporation cycle.

Your suggestion is probably cheaper in terms of base materials, but I imagine weight is more relevant than costs if we have to drag everything to the moon first.
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Re: Getting Energy from the Moon's Extreme Temperatures

Postby Ingolifs » Mon May 04, 2015 8:50 am UTC

How efficient would a stirling engine be?
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Re: Getting Energy from the Moon's Extreme Temperatures

Postby KarenRei » Mon May 04, 2015 10:02 am UTC

jewish_scientist wrote:Every power-plant on Earth basically works like this: 1) stuff 2) make steam 3) put steam through a turbine that has a magnet attached to it 4) repeat.


Every steam-driven thermal plant does, but not every power plant. Solar cells don't do this, wind turbines don't do this, hydroelectric plants don't do this, and non-steam-cooled (for example, very low temperature or very high temperature) thermal plants don't do this.

Also, not all steam plants are turbine-driven.

The temperature on the Moon ranges from about -150 C to 100 C.* There must be some way to get energy from a 250 temperature difference.


Yes, there are - for example:

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

Among many others :)

A really simple idea for one: Build slanted turbine that has a pipe connecting its top and base. Fill it with excess water. During the day, the water rapidly evaporates, forcing its way through the turbine. During the night, the water rapidly condenses, flowing down the tubes to the base of the turbine. Maybe we could also put a turbine in there. The turbine will need to be insulated so the change in temperature is never too fast.


I don't get your "slanting" - and where is "excess" water supposed to come from on the moon? Anyway, any large, heavy construct on the moon is going to be a non-starter for a very long time; basically, anything with big water reservoirs with huge sun-exposed surfaces and the like is not practical versus say sending solar panels or a pre-built small nuclear reactor from Earth. If you want to propose something to be used in the next century it's going to need to be small and light.

The moon of course already does capture a day-night temperature difference in the regolith at differing depths, no reservoirs of water needed, so you may be able to make a more practical version of day-night energy storage just with boreholes a couple dozen meters deep that then turn horizontal. Still probably easier just to send solar panels, though.

Also note that not only are there different gradients at different depths, but also different locations. For example, there are peaks of eternal light sitting next to permanently shadowed craters.

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Re: Getting Energy from the Moon's Extreme Temperatures

Postby Izawwlgood » Mon May 04, 2015 12:46 pm UTC

The moon has a 28d day night cycle.

You could put rails around the moon using a material that expands as its heats sufficiently to slowly push a giant object, and have that object drive a turbine. I doubt the slow rotational period of the moon would allow this to work.

Or just use solar panels. Whichever.
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Re: Getting Energy from the Moon's Extreme Temperatures

Postby jewish_scientist » Mon May 04, 2015 3:56 pm UTC

Lets say your base gets its normal, daily energy supply from solar panels. The problem is that in order to run the super-awesome-amazing-science-stuff you need a lot more energy than the panels can generate. In this situation, my turbine may be useful. The people/robots will know exactly when a huge boost in power will happen, and only run the SAASS at those times.

The pipes are slanted in such a way that the water goes down the pipe instead of the turbine, and steam will go up the turbine instead of the pipes.

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Re: Getting Energy from the Moon's Extreme Temperatures

Postby Izawwlgood » Mon May 04, 2015 4:44 pm UTC

jewish_scientist wrote:Lets say your base gets its normal, daily energy supply from solar panels. The problem is that in order to run the super-awesome-amazing-science-stuff you need a lot more energy than the panels can generate. In this situation, my turbine may be useful.
What are you basing this on? You're proposing building science fiction level turbines, but ignoring the amount of solar energy that is present.

For all you know, solar panels may provide more than sufficient energy for the 'super-awesome-amazing-science-stuff'.
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Re: Getting Energy from the Moon's Extreme Temperatures

Postby jewish_scientist » Tue May 05, 2015 5:00 am UTC

I am speaking more on a hypothetical level than on a science-fiction level. Think of a hypothetical situation where the SAASS needs a large amount of power, but it is not constintly turned on. To send solar panels to provide the normal amount of power plus soler panels that will power the SAASS needs is wasteful. Panels sent up to power the SAASS will be generating a huge surplus of power on the days when they SAASS is not being run. The purpose of my turbine is to produce power for SAASS without producing excess power that would just have to be thrown away once all batteries are charged.

Also, by excess water I meant water that the astronauts do not currently need; the idea being that stored water that is still working for you. When you factor in that some kind of infrastructure and water are going to be needed on the Moon even without the turbines, the formula for power to mass ratio changes. Instead of (energy generated/mass), the formula is (energy generated/(mass of turbine - mass of standard structure)). I doubt that the turbine looks as ineffective when you use the second formula.

You may not want to think about it too hard, but this would be a very effective way to sterilize and distill grey water.

The general purpose of my question is not, "Do you thing these turbines could work." What I want to know is how could we create energy from the changes in the Moon's temperature. My turbines were just a really simple example that I came up with. The main reason why I don't like the answer, 'we could just use solar panels' is a) solar panels derive energy from sunlight, not the Moon's surface temperature; and b) until we think about and analyze 'crazy' idea, we cannot dismiss them as being unpractical and inefficient. The only way to be sure that an idea will not work is by examining it.

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Re: Getting Energy from the Moon's Extreme Temperatures

Postby scarecrovv » Tue May 05, 2015 5:34 am UTC

Izawwlgood wrote:You could put rails around the moon using a material that expands as its heats sufficiently to slowly push a giant object, and have that object drive a turbine. I doubt the slow rotational period of the moon would allow this to work.

Sounds like someone's been reading 2312. For those who haven't, there's a city on Mercury which always stays out of the sun by doing exactly this. Until, you know, something goes wrong. Good book.

I agree with those who think solar panels are probably the most efficient solution. I'd be interested in being proven wrong though.

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Re: Getting Energy from the Moon's Extreme Temperatures

Postby billy joule » Tue May 05, 2015 6:21 am UTC

Without a convenient cold sink (atmosphere, river) a thermal plant is a non-starter. The available temperature doesn't matter if the heat transfer is so poor you need many square kms of heat transfer area.

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Re: Getting Energy from the Moon's Extreme Temperatures

Postby Izawwlgood » Tue May 05, 2015 12:18 pm UTC

scarecrovv wrote:
Izawwlgood wrote:You could put rails around the moon using a material that expands as its heats sufficiently to slowly push a giant object, and have that object drive a turbine. I doubt the slow rotational period of the moon would allow this to work.

Sounds like someone's been reading 2312. For those who haven't, there's a city on Mercury which always stays out of the sun by doing exactly this. Until, you know, something goes wrong. Good book.

I agree with those who think solar panels are probably the most efficient solution. I'd be interested in being proven wrong though.

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jewish_scientist wrote:I am speaking more on a hypothetical level than on a science-fiction level.
Not really. You're proposing an enormous construction project to take advantage of a moon wide thermal gradient, and you're ignoring how much easier it would be to just collect solar radiation.
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