Geothermal wells
This picture shows a vertical slice (cross-section) through the earth. The yellow zone represents the Kingia Sandstone, which is known to be a good reservoir.
Petroleum companies try to find areas where gas has become trapped in pore spaces within the rock formation. In most areas there is no gas trapped and the pore space is full of hot water.
For a geothermal development, wells are drilled into the hot water zone away from any gas. Hot water is pumped to the surface where the heat energy is extracted and used to make electricity. After extracting the heat, the water is returned to the original reservoir via an injection well.
The re-injected water will absorb more heat from the surrounding rock and eventually be produced again.
Power generation
Power will be generated using a binary Organic Rankine Cycle (ORC) plant. Geothermally heated water is pumped up a production well and passed through a heat exchanger where it vaporises a secondary (organic) fluid. The organic vapour then drives a turbine which is used to generate electricity. The vapour is cooled, condensed, and recycled. The cooler water is re-injected back into the same subsurface rock formation via an injection well.
Since the produced water has no direct exposure to the atmosphere at the surface there are no emissions and the water is completely isolated from the secondary fluid - only the heat energy is transferred.
Binary ORC technology is a well-established and reliable means of converting heat energy into electricity. It is proven technology, with plants operating in 21 countries worldwide.
Existing plant example
This photo shows the Velika Ciglena binary ORC geothermal power plant in Croatia. It has a capacity of 17.5 MW and is the same type of facility envisioned for this project.
Geothermal plants have a very small footprint compared to solar PV arrays of similar capacity.
In addition, geothermal plants can produce power 24/7.