Heat From The Earth

This week's energy topic is geothermal and this one's not making the news as much... yet. But keep an eye on it, folks. Over at NexGen, I start with the basics:

Since I'm a closet classicist, let's start by breaking down geothermal from the Greek, Gus Portokalos style:

Okay. Geothermal comes from the Greek word geo, meaning earth, and therme, meaning heat. So, what do you energize your house with? You see: Heat from the earth. Geothermal. There you go!

So the source of geothermal energy is heat below the Earth's surface. Steam and hot water generated there provide electricity and heat buildings. And since rain replenishes the water involved and heat is continuously produced...it's completely renewable! Direct use has no negative impact on our environment and geothermal plants gives off low emissions. Not bad, eh?

Read my full post getting into some of the science involved at the Sb energy blog...



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Worth noting is that geothermal energy will have direct impact on whatever energy sources are used to capture the energy. For instance, any of the geysers and related structures in Yellowstone would be destroyed if they were used to harness the associated geothermal energy. Think of a nearby hot springs which is used for tourism - it's modified the original source.

So the impact is there. It's local, and certainly less than most other sources of energy.

By David Bruggeman (not verified) on 10 Sep 2008 #permalink

Okay, except for one thing.

I get get a bad feeling when people move into exploiting a new resource and claim it is 'limitless'. Story was the fish were so thick near the mouth of certain east coast rivers in the 1700s that people had difficulty rowing ashore. The whales were thick off Nantucket. In both case it was assumed to be a virtually unlimited resource.

We have played this game with game species, mineral wealth, water and air. Virtually every time we do we jump in with both feet and ruin what was, if it was exploited in a conscientious and sustainable manner, a nice steady supply.

Perhaps geothermal energy is truly a limitless and inexhaustibly supply. If so it may be the only one.

On the other hand, if you extract enough heat to significantly lower the temperature of the magma your going to have problems. Less molten magma doesn't flow really well. And as it slows the earth would start to lose its magnetic field. Once the magnetic field is weak enough the solar wind can reach our atmosphere and start to strip it away.

Losing our atmosphere sounds like a significant problem to me. Humanity could live a lesser but still tolerable life on a slightly warmer planet. Liveing on earth as the atmosphere bleeds off into space could get messy.

Is this danger real? As I understand the outline based on unlimited extraction of heat energy, yes. How much energy could we extract before we run into problems I don't know. As I understand it there is some 'recharge rate', mainly from compression heating and nuclear decay, that might represent a line we might not want to cross. Perhaps the geologists and geophysicists will chime in and set me right.

But then again when people were paddling up to the east coast they saw a huge forest of great trees and declared that it represented more wood than we could ever use up. I doubt we would run into issues any time soon but humanity has a habit of expanding to exceed the capacity of all available resources and do so in shockingly short times.

One very big thing people often ignore when talking about "geothermal energy" is that geothermal energy is all around us.

It need not come from a deep well, a hot spring or the like.

Anyone who has ever been in a cave in the dead of winter or the heat of the summer knows that it stays at pretty much the same temperature year round (about 55F).

I'm not implying that we should all go live in caves, of course. In fact, below just a few feet, the ground around your house is considerably warmer than the outside air in winter and considerably cooler than the outside air in summer.

So, the ground can act as a heat sink in summer (for a cooling system) or a heat source in winter (for a heating system).

By dark tent (not verified) on 10 Sep 2008 #permalink

In certain respects, it makes little difference if, by some magic or miracle of technology, we were able tomorrow to tap a vast, unlimited supply of energy--although this might provide some immediate respite. All growth is ultimately unsustainable. And I know of no known example in the long trajectory of human prehistory or history in which an increase in energy production and consumption led to a decrease in the growth of human population or a decrease in the intensification or resource exploitation.

Sustainability, as used in the current vernacular, is a myth. This is why even arguments to forestall global warming fall flat, since they almost all imply "substitution" technologies that ignore almost all other aspects of growth, including the elephant in the room--the size of the human population.

I am weary of all the talk and hype about new energy technologies, although they warm the heart of the scientific community. At the moment, all of them combined amount to a hill of beans compared to the immense nature of our current fossil fuel dependence. Any number of projections suggest that an energy crisis will come to a head before many of these substitution technologies are in a position to make the slightest difference.

This notion has not gone unnoticed even by the general public, who are with good reason primarily concerned with the here and now of economic survival. Thus, as I have predicted, concerns about energy cost and availability are beginning to trump concerns about global warming in the public sphere and in political debate.

Here, in the United States, we still are relatively insulated against the cost and availability of fossil-fuel driven transportation and electrical generation. That is not true in many other parts of the world. And China is terrified that their recent growth and industrialization might be curtailed by insufficient hydrocarbons, and are making agressive inroads into acquiring those resources. The possibility of global resource wars should not be dismissed, and a good argument can be made that they already have begun.

Thus, I believe even the scientific community is shortsighted and I do not believe they understand the deep anthropology of our current predicament, nor do they have the motivation or expertise to evaluate the connection between energy and the evolution of human societies.

A popular, if flawed, version of the anthropology can be found in Daniel Quinn's "Ishmael" and in Thom Hartmann's "The Last Hour of Ancient Sunlight." Yet their message resonates.

What is the solution? Probably not in any way connected to traditional ideas of solutions. Nothing less than a total restructuring of human social organization. This is unlikely to happen by choice, just as no major development in the history of human culture has been a matter of choice or conscious action.

It will simply happen.

By Eric the Leaf (not verified) on 10 Sep 2008 #permalink

The use of deep-down Earth heat to drive heat engines at the surface is not renewable for the same reason the heat is there to begin with: it diffuses slowly in rock.

So what people would accomplish, if they were to build any large amount of geothermal power plants, would be heat mining. The heat within a few metres of the wells they dig gets mined, and more cannot be mined except they dig new wells.

Since it is low-grade heat, most of it is rejected by the heat engine. One Kalina-cycle project, for example, takes 90 L/s from a 120°C hot spring and drives a 1.8-MW dynamo and discharges the water at 80°C, so converting 0.12 of the heat to electricity.