Unlike a wind turbine in a back yard or a community solar PV farm, a geothermal energy plant is unlikely to be seen in local neighbourhoods in the foreseeable future.
But that doesn’t diminish the importance of geothermal as an energy source or its potential to contribute to growing renewable targets and the drive for carbon emissions reductions.
At a meeting in September organised by the Global Geothermal Alliance (GGA), governments committed to working together to accelerate geothermal energy development to achieve a 500% increase in the global installed capacity for power generation along with a 200% increase in geothermal heating by 2030.
The GGA comprises countries and development, industry and academic partners.
Geothermal energy potential
In principle, geothermal energy can be sourced from virtually anywhere. In practice, its capture has been limited to areas close to volcanic activity, such as the mid-Atlantic ridges, rift valleys and Pacific ‘Ring of Fire’ associated with the plate tectonic boundaries.
According to the International Renewable Energy Agency (IRENA) in a new review, in 2016 the installed geothermal power capacity was 12.7GW. The power generated (in 2015) was approximately 80.9TWh or about 0.3% of global electricity generation.
The leading countries are the United States with 2.5GW, Philippines with 1.9GW and Indonesia with 1.5GW. In Europe, the majority of the installed capacity is in Italy with 824MW and Iceland with 665MW, while Turkey has 821MW.
The attractiveness of geothermal energy is several-fold. When developed, it is a low cost resource without the intermittencies of wind and solar. The project costs - while site and technology sensitive - are dropping, and are expected to continue to do so through 2050, further improving the business case.
And in regions such as East Africa, which are prone to drought, it provides a stable alternative to hydropower.
IRENA estimates the levelised cost of energy for geothermal between $0.04-0.14/kWh – similar to that of fossil fuel power generation.
“Geothermal's vast potential is currently untapped,” commented Gian Luca Galletti, Minister of Environment in Italy, which hosted the Alliance meeting.
“We must develop new technologies and encourage new investments to ensure we cover this gap.”
The global potential for geothermal energy has been estimated conservatively around 200GW but may be up to ten times that figure.
According to the IRENA report, the main barrier to geothermal development is access to finance for exploration and drilling.
Deep drilling in Iceland
With ongoing technological developments geothermal energy may have an even more significant future.
Currently, geothermal well depths are anything up to around 3,000m but what about going deeper into the earth’s crust where it is hotter?
The Iceland Deep Drilling Project (IDDP), which was launched in 2000, is aimed to investigate the economic feasibility of extracting energy and chemicals from fluids under supercritical conditions (when the temperature and pressure is such that distinct gas and liquid phases cease to exist).
In this state, the liquid has much higher energy content than conventional high temperature geothermal steam, with the potential for highly efficient energy production.
Indicative of the challenges at these higher temperatures, the project’s initial targets were finally achieved in January of this year.
Starting from an existing 2,500m deep production well at the Reykjanes Peninsula geothermal field in the southwest of the country, drilling reached a depth of 4,659m and the presence of fluids at supercritical conditions. The measured temperature was 427oC and the pressure 340 bars.
According to the project report, the potential utilisation will not be known until the end of 2018 when further testing is completed, but the “first indications are positive”.
The report comments that if deep supercritical wells can produce more power than conventional geothermal wells, fewer wells would be needed to produce the same power output, leading to less environmental impact and improved economics.
Another option in this case would be to use the deep well for injection to enhance the performance of the overlying current production zone of the Reykjanes geothermal field.
“If the best outcome of the project is achieved, it would open new dimensions in geothermal utilisation,” states the report.