Deakin Communicating Science 2016

EES 200/101

Into the Future: Energy Transformation [Revised]

The trouble with energy production—or rather, energy transformation—is that we often use “fossil fuels” (which are finite resources) to do it. Such processes involve nuclear fission (with uranium) or burning combustible materials (e.g. coal or oil). This leads to depleted levels of fossil fuels available, and creating too much pollution. It may be ‘cheaper’ to produce energy with fossil fuels, but it’s unsustainable for our future. What will we do with our nuclear power plants after we’ve exhausted uranium supplies? How can we fuel our future sustainably?

Challenges for Renewable Energy

You may think solar panels and wind farms are the way to go, but even these have problems: solar panels absorb less energy on cloudy days, and wind farms cannot generate electricity if there isn’t any wind. Even river turbines are prone to requiring optimal conditions. The future needs an efficient way to harness energy from an unlimited resource . . . Yet it may have been under our noses all along: Geothermal Energy.

Earth’s Temperature . . . Underground

Diagram showing some layers beneath the surface of the earth [Source: Stober I & Bucher K]

Diagram showing some layers beneath the surface of the earth [Source: Stober I & Bucher K]

The core of the earth is made of solid iron, and exceeds temperatures of 5000℃. The heat from this core is continuously being absorbed by the cooler layers which surround it. In general, for every 100 metres you dig underground, the crust temperature of the crust increases by an average of 3℃. The earth’s surface has an average temperature of 14℃, therefore a linear equation can predict the earth’s temperature at a given depth:

𝑦 = 30𝑥 + 14

Equation predicting earth’s temperature (𝑦, in ℃) based on the depth of the earth’s crust (𝑥, in kilometres) [Source: Stober I & Bucher K]

Using this equation, a depth of 5.5 kilometres into the earth would have a temperature of approximately 180℃. This temperature exceeds the boiling point of water, which evaporates into steam. Although steam is used in fossil fuel energy production, it’s also the primary technique for generating geothermal energy.

Introducing Geothermal Energy

Geothermal power plants use the earth’s natural geothermal energy to create steam, then the steam is used to generate electricity. This simplified diagram shows how this works:

Diagram showing the general means of converting geothermal energy into electricity [Source: James Kanjo]

Diagram showing the general means of converting geothermal energy into electricity [Source: James Kanjo]

In the above diagram, cold water is pumped down a pipe which extends as far as 5.5 kilometres into the earth. The geothermal temperature at these depths average at 180℃. The cold water absorbs the heat energy and becomes hot steam (albeit in liquid form, due to high pressure underground). This hot steam is pumped above the earth’s surface, and travels faster using Bernoulli’s principle (the piping widens above the surface and has lower pressure). The steam has enough energy to turn the steam turbine, and thus power the electricity generator. Then the steam cools down back into a cool liquid once more, and is pumped back into the earth to repeat the cycle. As the earth has an “unlimited” supply of geothermal energy (in terms of the continuing existence of humanity), this is a source of perpetual energy.

In a future of limited fuel resources for human consumption, the prospect of an eco-friendly perpetual energy source is highly desirable. As geothermal energy is present wherever land exists, its abundance will make electricity freely available for everybody, and is therefore ideal for a currency-less society.

Editor’s Amendment:

As reader Adam has commented, the “perpetual” nature of geothermal energy should be clarified. One prediction of the earth’s core’s cooling rate is a decrease of 100℃ every billion years. So it will cool to 0℃ in approximately 50 billion years. However, another prediction is in 1.1 billion years, the sun’s expansion will overheat the earth and evaporate our oceans (guaranteeing the extinction of life on earth). So essentially, we have 50 billion years of geothermal energy and less than 1 billion years to harness it (if indeed we can).

So Adam is right, it’s perpetual until the earth dies.

Of course, geothermal sites cool as we absorb the earth’s energy, but this can be overcome by digging deeper piping to be closer to our geothermal core (if our technology permits). I should also mention that (unfortunately), not all areas are good candidates for geothermal energy, as they can influence tectonic activity and cause earthquakes to surrounding areas.


Sources

Stober I & Bucher K, “Geothermal energy : from theoretical models to exploration and development”, Heidelberg : Springer, published 2013:

  • Image of “Internal structure of the Earth”, pp. 3
  • Average temperature of Earth’s surface, pp. 7
  • Gradient of Earth’s temperature vs. depth, pp. 8

Diagram “Converting geothermal energy into electricity”, created by James Kanjo, based on the following source:

  • Stober I, & Bucher K, “Geothermal energy : from theoretical models to exploration and development”, Heidelberg : Springer, pp. 57, published 2013.
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2 comments on “Into the Future: Energy Transformation [Revised]

  1. Adam
    April 21, 2016

    G’day James,

    Great work on this blog. I think you have a real knack for communication in general. 🙂

    I don’t have a lot to say because it is pretty good but some dots to think about include:

    – Provide some links that can help me look into things myself.
    – Re-read it and fix up some nit-picky grammar issues and remove some flowery/unnecessary words.
    – I am a skeptic at heart and when someone says ‘perpetual’ energy I immediately think about why it’s not. It’s perpetual until the world dies ;-).
    – A sentence or two explaining the difficulties/drawbacks of geothermal would be great. These could include resource use, location suitability or my favourite, inequitable distribution of power (in both senses of the word). the good thing about solar or wind is that it can be distributed and owned by normal people. Geothermal would centralise energy with big corps like energy production today.

    Great job, I enjoyed reading this and learnt some new things.

    Cheers,
    Adam

    Like

    • jkanjodeakin
      May 5, 2016

      Hi Adam!

      I’ve taken on your suggestions, and tried to simplify my floral sentences for clarity. In general, I’ve also simplified the details of some explanations too.

      Squashed some grammar rebels too 😉

      You make a good point about the “perpetual” nature of geothermal energy, and I’ve amended my blog post to account for that. I hope I’ve done justice in this regard. I also added a couple of disadvantages of geothermal energy production too, albeit, more as “after-thoughts”, but they’re in there now 😉

      Thanks again for your feedback, and thanks for reading my blog!

      Like

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This entry was posted on April 7, 2016 by in Burwood - Thursday 2pm.

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