Geothermal energy

Traditionally, there are three primary power plant technologies used to convert the energy in geothermal resources to electricity: (i) dry steam, (ii) flash steam and (iii) the binary cycle. Most legacy geothermal energy plants in operation for electricity generation are dry steam or flash plants that harness geothermal resources at temperatures of more than 150°C. However, medium temperature resources are increasingly being developed for electricity generation or combined heat and electricity, using binary cycle technology.

More recently, technological advancements over the past decade have created closed loop system developments to deal with low temperature reservoirs and any lack of permeability. In a closed loop system, the working fluid is contained in a closed loop that transports heat from the reservoir to the surface, an emission-free operation that does not require permeability of hot rocks. These systems, which have been proven, have significant industry backing and are in early commercialization stages in North America, Europe, and Asia, leverage exponential improvements in drilling, completion and power generation technologies to provide significant advantages that can complement or displace existing solutions.

Closed loop geothermal energy power plants are suitable for low to medium temperature ranging from 80ºC to 180ºC.

Key advantages of closed loop systems include:

• Access to heat in impermeable or “low flow” rocks, potentially unlocking the vast bulk of the earth’s geothermal resources (only ~2% are estimated to reside in permeable rocks)
• Operate in a broad range of temperatures and rock compositions, ranging from relatively low temperature sedimentary zones to hot, dry rock formations
• Low or no surface water/process water usage, and no withdrawal of subsurface fluids (aquifers)
• No fracking, no injection, and no fluid withdrawal and therefore no induced seismicity
• Provides both electricity and thermal energy

Geothermal energy is modular and scalable, allowing decentralised power generation that has many applications in Australia. In contrast, historic geothermal energy projects in Australia focused on high temperature reservoirs above 200°C which exist only in remote and deep formations.

The temperature of the geothermal resource dictates the most appropriate use. Historically temperatures of more than 150°C were required to produce electricity; however, technological advancements can now see power being generated from temperatures as low as 70°C. Advances in heat exchangers, drilling techniques, closed-loop materials and systems management are all driving efficiencies and applicability.