Exergy’s Gemini turbine: insights from the engineering team

In a follow-up to Exergy’s announcement of the Gemini radial outflow turbine, we published earlier, ThinkGeoEnergy spoke with Giorgia Ruffato, Turbine Engineer at Exergy International, to learn more about the engineering behind the new design and how it responds to changing demands in the geothermal power market.

Exergy’s turbines are based on its proprietary radial outflow turbine (ROT) technology, widely applied in Organic Rankine Cycle (ORC) systems for geothermal and industrial waste heat recovery. With more than 550 MW of installed capacity worldwide, Exergy has established itself as one of the leading suppliers in the geothermal binary segment.

The Gemini turbine builds on this experience. It integrates two mirrored turbine stages into a single 60 MW unit, using a dual-inlet configuration that enables very high volumetric flow rates—above 50 cubic metres per second—while maintaining isentropic efficiency above 90 percent, equivalent to two separate turbines operating in parallel.

“The Gemini concept lets us achieve greater output while simplifying the plant,” Ruffato explained. “With one turbine and one generator, operators benefit from lower equipment needs, a smaller footprint, and easier maintenance.”

The turbine was developed to meet growing demand for larger power systems, especially those using Enhanced and Advanced Geothermal Systems (EGS/AGS). These new geothermal approaches, now gaining momentum in the United States and Europe, require turbines capable of handling higher mass flow rates and larger enthalpy drops. According to Ruffato, the Gemini turbine bridges the gap between traditional geothermal plants and the new generation of engineered reservoirs.

For conventional plants up to 30 MW, Exergy’s standard multi-stage ROT turbines continue to serve as a reliable solution, particularly in established geothermal markets such as Turkey and the Philippines. The Gemini extends this portfolio to serve plants in the 30–60 MW range, where efficiency and cost benefits from single-unit systems become decisive.

Among the main technical advantages of the Gemini are improved mechanical stability and simplified maintenance. The turbine adopts a between-bearings rotor support, which enhances rotor stability and increases reliability. Its compact structure shortens installation time and simplifies plant layout, contributing to up to 30 percent lower project costs compared with dual-turbine configurations.

Beyond its work on turbines, Exergy is also expanding into industrial-scale heat pumps through its X-Heat® Industrial Heat Pump product line, introduced in late 2024. The systems are based on similar thermodynamic principles as the company’s ORC technology and benefit from shared materials, components, and design knowledge. Ruffato highlighted that the synergy between power and heating applications allows Exergy to leverage its engineering strengths across both markets.

With the Gemini turbine and its growing focus on industrial heat pumps, Exergy is positioning itself as a key technology provider for the evolving geothermal and clean-heat sectors. By extending the reach of its proprietary turbine technology to single-unit systems up to 60 MW, the company aims to support the next generation of large-scale geothermal developments worldwide.