I have yet to get my mind around the idea that Earth’s inner core is dense iron and nickel, surrounded by boiling liquid like the stuff that comes out of volcanos. Nevertheless I find the potential power of it awesome, although it does remind me how transient life is on earth. The ancient Greeks were not far off when they believed everything – including you and me – is a composite of the classical elements of earth, water, air, and fire.
It would be absurd to speculate how hot the Earth’s core is. The temperature would read off any human scale. What is more important is the geothermal energy potential this represents. From time to time, the molten lava wells up through a crack or fissure. If it encounters water, it makes it warm or instantly vaporises it as steam.
The Oldest Known Hot Spring Pool
This water carries beneficial mineral properties with it. Hence, the earliest uses of geothermal power were therapeutic baths. The dip pool in the image dates from the third century BC and is in China. Archaeologists rediscovered it when they excavated a 3,000-year-old holiday resort of the Emperors in the 1980’s.
When water superheats, as it does in kettles and in geothermal vents, it expands into hot steam at up to 1,700 times the original volume. It shoots out of vents like Old Faithful Geyser in Yellowstone National Park, Wyoming, United States. The first working steam engine saw the light of day in 1712. Since then, engineers have built a variety of steam devices for turning pressure into motive power.
Emergence of Steam Engines
Almost all electricity comes from turning an armature inside a magnetic field, with the exception of solar power. The earliest power stations were hydro. In 1862, Thomas Edison built the first steam power station in London, England. Since then, superheated steam has been the main driving force for the electricity we use in industry, and in our homes.
The traditional energy source to heat the water continues to be fossil fuel, or a controlled nuclear reaction. Coal continues to accelerate global warming. Unfortunately it has the advantage of being relatively cheap, and able to provide consistent power around the clock, unlike solar, wind, and tidal. The current global generation mix is 31% coal, 27% oil, 23% natural gas, renewables 14%, nuclear 5%. The 81% non-renewables are steadily suffocating our planet.
Drum Roll for Geothermal, Please
There is nothing wrong in principle with the rotor in the picture. It is an inanimate object and a thing of great beauty in engineering eyes. The problem is the non-renewable nature of the energy source that drives it. I think it is time to call a drum roll for geothermal energy. It is waiting deep down in the heart of the earth, and I believe promising to be our sustainable solution.
The first thermal power station energised five light bulbs in 1904, using thermal steam emerging from the ground in the Larderello Valley. This evolved into a commercial venture others copied in California and Japan. The first large-scale enterprise appeared in 1958 in New Zealand, where it still produces 13% of the nation’s electricity. Nowadays there are geothermal power stations in most places where there is a reliable supply of naturally boiling water.
The Extent of Global Geothermal Power
The World Energy Council reports that geothermal power could meet up to 8.3% of global energy needs. All things being equal, this would reduce reliance of coal by 25%, which would be a good start. Leading electricity beneficiaries are the United States, Italy, the Philippines, Indonesia, and Mexico. The largest direct users for heating and cooling are China, the USA, and Sweden. The Geothermal Energy Association thinks we have tapped less than seven percent of the potential.
There are currently three ways to generate electricity using geothermal power once we have taken it in pipes to a generating station:
• In dry steam power stations, geothermal steam of 150 °C or higher is sufficient to turn turbines and make electricity
• Flash steam stations pull high pressure water at 180 °C plus into lower-pressure tanks where it super-expands
• In binary stations, water as low as 57 °C passes through a secondary fluid with a lower boiling point that drives the turbine
The ‘Best’ is Not Good Enough for Me
I reject the World Energy Council’s estimate of limited geothermal potential. If we can frack the earth in order to release natural gas, why can we not drill a hole and release more heat for geothermal steam. Iceland is drilling a five-kilometre hole into molten magma. It thinks that this could generate supercritical steam ten times more powerful than traditional geothermal wells.
That is news I want to hear!