What is geothermal energy, what makes it unique and what are the benefits and challenges to using this ancient form of renewable energy to power our modern world?
The sun beneath our feet
Derived from the Greek words geo (earth) and therme (heat), ‘geothermal’ refers to drawing heat from the earth’s core. The molten core of the earth is toasty, roughly as hot as the sun at a sizzling 6,000 degrees Celsius. This heat is consistently replenished by the decay of naturally occurring radioactive elements within the earth’s crust. Humans have been taking advantage of this natural and consistent source of heat for thousands of years.
Modern day use
While paleolithic humans lounged in hot springs after a hard day of hunting, our use of geothermal energy today has grown in sophistication and variety. We now use geothermal energy to heat buildings (including entire towns), grow plants in greenhouses, dry agricultural products (such as berries, tea, coffee or rice), heat water at fish farms, and support certain industrial processes such as pasteurising milk. We even pipe geothermal water under roads to melt snow.
A major use of geothermal energy today is to generate electricity, via geothermal power plants. These plants come in three different designs: dry steam, flash steam and binary cycle. Dry steam, the oldest type of power plant, draws steam directly from fractures in the ground to drive a turbine, which in turn generates electricity. Flash steam plants draw high pressure water from underground and mix it with cooler, low pressure water to create steam, which in turn drives a turbine to generate electricity. Binary cycle power plants – the most popular today and considered the way of the future – use hot water passed through a secondary liquid that has a lower boiling point than water. This secondary fluid transforms to vapour, which in turn drives a turbine to generate electricity.
Advantages of geothermal energy
As a renewable energy source, geothermal energy has huge potential to power our world in a sustainable, reliable and environmentally friendly way. Producing just one-sixth of the carbon dioxide emitted by a clean natural-gas power plant, geothermal energy is a sensible choice for a world looking to reduce its carbon emissions. Unlike other renewable energy sources like the sun and the wind, geothermal energy does not fluctuate – it is consistently available. This ‘round the clock’ reliability makes it the perfect complement to other renewable energy sources as it can fill in the gaps when the sun isn’t shining and the wind isn’t blowing, ensuring a stable power grid.
Due to being underground, geothermal energy is resilient to most weather and man-made disasters, offering further stability. We also don’t need to worry about it running out any time soon. As noted by National Geographic: ‘geothermal energy isn't entirely renewable – it will run out when the earth does. In about five billion years.’
Challenges of geothermal energy
While there are many advantages to be gained from geothermal energy, there are significant challenges holding it back from widespread use today. A key challenge is that it is location specific: geothermal plants are limited to areas near tectonic plate boundaries, in order to access the heat from deep underground. Geothermal power plants can run the risk of triggering earthquakes, as they force water into the earth’s crust to open up fissures, which in turn alters the stability of the earth’s structure. However, most geothermal plants are located away from populous areas to mitigate this risk. This is probably a good thing on another account, as geothermal plants may release hydrogen sulphide, a gas that smells like rotten eggs.
There are also environmental impacts to consider: greenhouse gases stored beneath the earth’s surface are released into the atmosphere during digging. While the emissions rate is much lower than that associated with fossil fuels, it is still important to consider. Geothermal energy is also an expensive resource to tap into, with power plants costing millions of dollars and home geothermal pump systems setting you back as much as $30,000, depending on where you live.
Geothermal energy around the world
The United States is currently the world’s largest producer of geothermal energy. In 2020, there were geothermal power plants in seven states, producing around 17 billion kilowatt hours and comprising 0.4 per cent of the nation’s total utility-scale electricity generation. The United States is also home to the largest geothermal development in the world – Geysers Geothermal Complex – which is made up of 22 power plants spread across several kilometres north of San Francisco, with a capacity of 900 megawatts.
In terms of geothermal energy use per capita, Iceland leads the world, sourcing 25 per cent of its total electricity generation from geothermal sources. With 25 active volcanoes and 600 hot springs, it is well placed to do so. Elsewhere, Indonesia and the Philippines are currently developing some of the largest geothermal projects in the world.
Geothermal energy in Australia
While Australia has excellent geothermal resources, the industry is still emerging – as yet there is no commercial production of geothermal energy in the country. However, exploration is currently being conducted in all states and the Northern Territory, with several companies in the advanced stages of exploration. Current drilling technology reaches a maximum depth of five kilometres, restricting companies to focus on elevated temperatures at five kilometres deep or less. That said, tapping into just one per cent of Australia’s estimated geothermal energy shallower than five kilometres and hotter than 150 degrees Celsius could supply Australia’s total energy requirements for 26,000 years.
Commercial-scale geothermal technology in the residential sector is currently being developed (a first in Australia) by Frasers Property Group, who have installed geothermal heat pumps at a Fairwater development in Blacktown, New South Wales. Due for completion in 2023, the project will provide over 14,000 kilowatts of geothermal heating and cooling to all 850 homes on-site, making it the largest geothermal community in the southern hemisphere.