Potential, Location and Exploration
Geothermal energy flows from the center of the Earth to the surface with a power rate of 75 TW – twice as much as the entire energy consumption rate of humanity. How much of this is actually extractable with current technology and where are these geothermal resources located in the World?
There are basically two main categories in how we harness geothermal energy:
- Geothermal heat pumps for residential and commercial situations.
- Industrial electricity generation with geothermal steam turbine power plants.
When it comes to generating electricity and hot water production with geothermal energy, there are three different types of geothermal reservoirs we use:
Hot Spring Reservoirs
These are the ideal reservoirs that are easiest and cheapest to harness energy from. Unfortunately, they are only located near tectonic plate boundaries. As you can see on the map below, there is a boundary going straight through Iceland. No wonder why this country generates as much as one third of electricity from geothermal energy.
The second best pick when it comes to geothermal reservoirs are hot aquifers. An injection well is drilled into the aquifer and hot water/steam flows up to the surface.
Hot Dry Rocks
The last reservoir types we have the technology to harness are hot dry rocks. Developing these resources is called enhanced geothermal systems (EGS). We use an approach called hydrofracturing, which involves drilling wells into the reservoir, and sending high-pressure water into it to fracture the rock, creating thousands of tiny pathways where water can flow (hydrofracturing).
Enhanced geothermal systems push the potential of geothermal energy to practically unlimited. Vastly more resources are available to us by hydrofracturing. Read more about this technique in How Enhanced Geothermal Systems (EGS) Work.
Exploration of new geothermal resources requires a combination of technical and scientific expertise. Highly specialized equipment and sophisticated computer systems are also required. Test drilling is required to figure out how the reservoir, which often is several hundred feet below the surface, really looks like. Geothermal exploration is associated with as much as 42% of the total expenses.
The bottom line is that we have all the geothermal resources we need. However, further developing all these resources is not affordable. Most geothermal resources are not able to able to produce cost-competitive electric power and hot water production.