lehpron
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Geothermal Power, Perpetual?

Wed Jan 11, 2006 5:55 pm

My thermodynamics professor refered to the atmosphere for all practical purposes as a TER, a thermal energy resevoir, such that any energy dumped into it would not vary the total much. I.e. the hot exhausts from a jet engine to the air isn't going to render the weather warmer tomorrow.

Even if the entire planet harnessed the heat from the Earth to generate electricity (closed cycle, heated underground), it could take maybe millions of years to cause any change in then temperature down there.

Could it be technically perpetual considering it within human memory, unlike fossil or biofuels, or solar or nuclear? I do not think there would be any shortages or short-term environmental side effects. But then this question did pop in my mind like an hour ago.  Smile

What could we do to make this happen?
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oly720man
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RE: Geothermal Power, Perpetual?

Wed Jan 11, 2006 6:49 pm

If geothermal power is used then eventually all the power that was converted below ground will appear as energy above ground.

Would this heat up the world? Possibly. In comparison with the amount of incoming solar irradiation (about 2 kw/m sq) geothermal will probably be minor. Also, energy does radiate from the earth.

The environmental impact would probably be the construction of all the power lines to get the power from the geothermal plants to where the energy is needed.
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eilennaei
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RE: Geothermal Power, Perpetual?

Wed Jan 11, 2006 8:54 pm

Quoting Oly720man (Reply 1):
the geothermal plants

What geothermal plants? Here you just drill a 100 meters deep hole in the granite and you have the heating/cooling for your house or two.
 
Pyrex
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RE: Geothermal Power, Perpetual?

Wed Jan 11, 2006 10:03 pm

Quoting Oly720man (Reply 1):
The environmental impact would probably be the construction of all the power lines to get the power from the geothermal plants to where the energy is needed.

Actually that is a myth about geothermal energy, that it has no environmental impact. When you harness the heat of the earth for your own needs you basically have to release a lot of gases that should not be released (some of those can be nasty stuff, lots of sulphur). Geothermal power may be renewable, as it is not foreseeable that we could exhaust it in the medium term, but it certainly isn't "free energy", environmentaly speaking.
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Klaus
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RE: Geothermal Power, Perpetual?

Wed Jan 11, 2006 10:07 pm

Quoting Pyrex (Reply 3):
When you harness the heat of the earth for your own needs you basically have to release a lot of gases that should not be released

Not necessarily. When you're using heat exchangers no gases will be released to the surface. This will be a factor only in regions with high volcanic activity with large amounts of heated gases close to the surface.
 
mt99
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RE: Geothermal Power, Perpetual?

Wed Jan 11, 2006 11:44 pm

Quoting Klaus (Reply 4):
Not necessarily. When you're using heat exchangers no gases will be released to the surface. This will be a factor only in regions with high volcanic activity with large amounts of heated gases close to the surface.

You are talking about 2 different things. Geothermal Heating - which, is just like you say a heat exchanger (same as heating water using the sun), and Geothermal Electricity.

Geothermal Electricity is nothing but a steam plant. The Steam is produced by underground water heated by the earth which moves a turbine. When this steam cools it becomes water which contains sulphur and other kinds of not so great stuff. Some plants re-inyect this water back into the ground so it can be resused - at least some of it.

I still think that pumped storgage hydro-electric plants are the way to go.
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jwenting
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RE: Geothermal Power, Perpetual?

Thu Jan 12, 2006 12:09 am

I wonder what the longterm consequences on the planet itself (not the atmosphere) would be from really large scale use.
You're extracting energy from the planet after all, that can only mean that either the planet (probably starting with the mantle) cools down or that energy is reabsorbed from somewhere else (which can only be the atmosphere).

Yes, on the current scale the impact is likely so minimal that it can't be detected.
But the current scale is similar to what wind power was 20 years ago when the climate changes (change in wind and rain patterns and temperature gradients in their vicinity as well as noise and dead birds) produced by large arrays of wind generators had not been observed.
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Klaus
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RE: Geothermal Power, Perpetual?

Thu Jan 12, 2006 6:04 am

Quoting Mt99 (Reply 5):
You are talking about 2 different things. Geothermal Heating - which, is just like you say a heat exchanger (same as heating water using the sun), and Geothermal Electricity.

No, I don't. I'm just talking about two separate ways of extracting energy, not about the target energy form. You can use the heat exchanger method for generation of electricity as well.

Quoting Jwenting (Reply 6):
I wonder what the longterm consequences on the planet itself (not the atmosphere) would be from really large scale use.
You're extracting energy from the planet after all, that can only mean that either the planet (probably starting with the mantle) cools down or that energy is reabsorbed from somewhere else (which can only be the atmosphere).

Quite right. It is not entirely inconceivable, for instance, that large-scale localized heat extraction could lead to a local cooldown which might change magma flow patterns below and possibly have an impact on eruptions or earthquakes.

Plus it is not a renewable energy source, it is simply a very large one.
 
777236ER
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RE: Geothermal Power, Perpetual?

Thu Jan 12, 2006 6:07 am

Quoting Klaus (Reply 7):

Plus it is not a renewable energy source, it is simply a very large one.

Nothing is a renewable energy source. There's finite energy in the universe.
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Newark777
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RE: Geothermal Power, Perpetual?

Thu Jan 12, 2006 6:09 am

Quoting Mt99 (Reply 5):

Geothermal Electricity is nothing but a steam plant. The Steam is produced by underground water heated by the earth which moves a turbine. When this steam cools it becomes water which contains sulphur and other kinds of not so great stuff. Some plants re-inyect this water back into the ground so it can be resused - at least some of it.

Who says you must use the water from below ground? You would simply use the heat exchangers to heat the clean water on the surface, which would turn the turbines.

Same with a nuclear power plant, the water and steam that spins the turbines never comes in contact with nuclear material.

Harry
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mt99
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RE: Geothermal Power, Perpetual?

Thu Jan 12, 2006 6:09 am

Quoting Klaus (Reply 7):
heat exchanger method for generation of electricity as well

How?
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jafa39
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RE: Geothermal Power, Perpetual?

Thu Jan 12, 2006 6:11 am

The geothermal plants in Rotorua have to be very carefully managed as the hot water used in the process has to be put back in the ground to heat up again, this causes a gradual reduction in the size and temp of the geothermal field and also problems with subsidence.

There are many lgoistical and physical problems associated with it, also the enviromental impact on the energy source itself.

Far better that all men have dynamos attached to their arses so that having sex produces energy which keeps the house powered....could change our lives forever  Smile so if the missus wanted to watch Shortland Street, she'd have to put out first!!
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Klaus
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RE: Geothermal Power, Perpetual?

Thu Jan 12, 2006 6:16 am

Quoting Mt99 (Reply 10):
How?

The same way it's done in any nuclear power plant: By generating steam in the heat exchanger which drives a turbine, is re-condensed and then re-used in a closed system.

For lower temperature differentials a Stirling engine can be more efficient than a turbine.

Peltier elements can achieve a direct conversion to electricity, but they are relatively inefficient.

[Edited 2006-01-11 22:19:08]
 
mt99
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RE: Geothermal Power, Perpetual?

Thu Jan 12, 2006 6:18 am

Quoting Newark777 (Reply 9):
You would simply use the heat exchangers to heat the clean water on the surface, which would turn the turbines.

How would you build it? to have clean water out, it would not have to touch the ground. Meaning you would have to run the water through a pipe or something. How do you build a pipe at very very temperatures thousands of feet under ground?
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mt99
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RE: Geothermal Power, Perpetual?

Thu Jan 12, 2006 6:22 am

Quoting Klaus (Reply 12):
The same way it's done in any nuclear power plant: By generating steam in the heat exchanger which drives a turbine, is re-condensed and then re-used in a closed system.

Sure, but can it be built?

Nuclear power plants arent "fired up" until everything is built. The earth is hot already.

[Edited 2006-01-11 22:25:16]
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Newark777
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RE: Geothermal Power, Perpetual?

Thu Jan 12, 2006 6:22 am

Quoting Mt99 (Reply 13):
How would you build it? to have clean water out, it would not have to touch the ground. Meaning you would have to run the water through a pipe or something. How do you build a pipe at very very temperatures thousands of feet under ground?

Not sure about the execution, I'm just speaking in theoreticals.

Harry
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Birdwatching
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RE: Geothermal Power, Perpetual?

Thu Jan 12, 2006 6:24 am

Quoting Jafa39 (Reply 11):
Far better that all men have dynamos attached to their arses so that having sex produces energy which keeps the house powered....could change our lives forever Smile

That is the single most funny thing I've ever read in this forum! RR +1
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mt99
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RE: Geothermal Power, Perpetual?

Thu Jan 12, 2006 6:33 am

Quoting Newark777 (Reply 15):
Not sure about the execution, I'm just speaking in theoreticals.

Its ok. Being in the Consulting business i am used to thinking about all aspects of a project feasibility.

Some great ideas only work in the Lab
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Klaus
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RE: Geothermal Power, Perpetual?

Thu Jan 12, 2006 7:07 am

Quoting Mt99 (Reply 14):
Sure, but can it be built?

Probably - but whether it would be cost-effective is another point entirely...
 
mt99
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RE: Geothermal Power, Perpetual?

Thu Jan 12, 2006 7:20 am

Quoting Klaus (Reply 18):
Probably - but whether it would be cost-effective is another point entirely...

It only takes time and money.. right?  Smile
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Klaus
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RE: Geothermal Power, Perpetual?

Thu Jan 12, 2006 7:23 am

Quoting Mt99 (Reply 19):
It only takes time and money.. right?

Pretty much (ahem)! Big grin
 
eilennaei
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RE: Geothermal Power, Perpetual?

Thu Jan 12, 2006 8:01 am

Quoting 777236ER (Reply 8):
There's finite energy in the universe.

That's right, since there's been observed a leak into another universe. What we typically call energy is just a side effect of the universe's mass being converted into radiation. The radiation has no capability to recreate the missing mass, so we're lost.
 
eilennaei
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RE: Geothermal Power, Perpetual?

Thu Jan 12, 2006 8:52 am

Quoting Eilennaei (Reply 21):
That's right, since there's been observed a leak into another universe

Oops you'll be advised to read that as ".. there's _never_ been..."

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