Exclusive interview with Exergy: discover the new Gemini dual-flow radial outflow turbine, the first single-unit ORC solution for 30–60 MW geothermal projects, offering up to 30 % lower costs and 99 % availability.
By: Robert Buluma.
An interview with Luca Pozzoni - Deputy CEO | Group CFO - Exergy International and the Exergy Team
1. Can you walk us through the key design innovations in your new Gemini turbine and how it differs from previous models?
The major innovation of the Gemini turbine lies in the dual-flow configuration: unlike conventional radial outflow turbines which are equipped with a single bladed overhung rotor disk, the Gemini features a double-side bladed rotor disk mounted in a between-bearing configuration. This enables the efficient processing of significantly larger volumes of fluid, leading to higher power output having basically two radial outflow turbines in a single machine with enhanced operational stability and simplified maintenance.
2. What operating conditions and working fluids enable the performance metrics you’ve announced for the Gemini turbine?
The optimal operating conditions for the Gemini Turbine are medium enthalpy drop with large amount of resource, which means high volumetric flow rate. Generally, these conditions are reachable with different hydrocarbons, but also refrigerants are sometimes used for these applications.
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3. How do you handle variable geothermal conditions, such as fluctuating temperatures or two-phase flows, in the ORC cycle?
Exergy is specialized in supplying tailor-made plants to maximize the power output based on the available resource, whatever it is full brine, full steam or brine and steam applications. The flexibility of the plant in operation is ensured by the centralized control system, which manages the control valves and the machines optimizing the plant operation based on the actual resource and ambient conditions within the safety limits.
In addition, the Radial Outflow turbine ensures stable efficiency even in off-design conditions.
With this approach, the efficiency of the plant can be always maximized.
4. What measures have you taken to ensure turbine durability, reliability, and minimal maintenance requirements?
Exergy portfolio is now composed by around 60 plants and almost 600MW of capacity, most of which are under maintenance agreements: this allowed us to develop a deep understanding of our equipment, giving us a robust base for new projects requirements.
That is one of the reason why we are proud to claim an availability greater than 99% for our plants.
5. How does the Gemini turbine scale in terms of modularity, and what size of geothermal resource can it now efficiently serve?
In terms of modularity, the Gemini Turbine can be scaled depending on the operating conditions. The size that it can efficiently serve is in the 30-60 MW range, but it has the space to increase even more.
6. How does the cost per MWh and overall economic profile of the Gemini turbine compared to your previous ORC models and competing technologies?
Compared to a standard parallel configuration, the Gemini solution offers up to a 30% reduction in turbine costs. Additionally, it simplifies the overall plant layout, reduces the total footprint, and leads to potential cost savings in plant construction. For instance, the use of a single generator contributes to these savings. These advantages hold true even when compared to competing technologies.
7. How do you ensure environmental sustainability in your ORC plants, including water use and reinjection of geothermal fluids?
ORC plants are environmentally friendly as they work through a closed-loop system that fully reinjects geothermal fluids back into the reservoir, thereby preventing any atmospheric emissions. Additionally, by employing air-cooled condensing systems, we can eliminate the need for water consumption entirely. Geothermal power plants also offer the smallest land footprint for energy produced among renewable energy sources. For example, while solar photovoltaic requires approximately 16.08 km²/TWh and wind 9.21 km²/TWh, ORC geothermal plants stand out with just 0.20 km²/TWh (source: TEHA – Ambrosetti).
8. Do you have pilot or test installations planned for the Gemini turbine, and how will performance be validated before full-scale deployment?
We are currently evaluating more than five applications with our customers where the Gemini can be the best solution. Since the technology behind the Gemini is well known for us, being conceptually identical to our consolidated aerodynamic design, the same references of the standard ROT can be applied also to the Gemini.
9.Beyond Gemini, what are Exergy’s next R&D priorities or innovations in ORC technology?
Our R&D priorities will focus, on the one hand, on continuing to improve the efficiency and competitiveness of our ORC solutions, both in cycle design and turbomachinery. It’s important to note that Exergy has a dedicated department fully committed to the continuous enhancement of our proprietary technology. On the other hand, Exergy we are investing in the development of new clean energy technologies by leveraging our know-how and experience. In line with this strategy, last year we launched the Exergy X-Heat® series of industrial heat pumps, , designed for applications in the industrial sector, and in geothermal field, for district heating projects.
10.How do you see ORC technology evolving in the next 5–10 years, particularly for geothermal and industrial waste heat applications?
ORC technology has established itself as the preferred solution for geothermal development over the past decade, thanks to its sustainability, flexibility, and efficiency in harnessing low- to medium-high enthalpy geothermal resources. Over the next 5–10 years, we expect this growth trajectory to continue, with increasing opportunities for power generation in regions such as North America, East Africa, and Asia-Pacific, as well as for geothermal heating applications in Europe.
For industrial waste heat recovery, the adoption of ORC technology will be more context-driven. Project development in WHR is strongly influenced by government incentives - today completely absent in many markets - supportive regulatory frameworks, and electricity prices, which remain key drivers for investment within the industrial sector.
11. What markets or regions do you see as the most strategic for deploying Gemini turbines, and how do you address adoption barriers?
There is no single most strategic market for deploying Gemini turbines; rather, any project requiring large-scale geothermal power generation with an output from 25-30 MW up can benefit from the advantages offered by a single high-capacity Gemini unit. The technology is particularly well-suited to next generation Enhanced Geothermal Systems (EGS) and Advanced Geothermal Systems (AGS), where scale and efficiency are critical.
We do not see significant barriers to adoption, as Gemini is based on the proven Radial Outflow Turbine design, with over 500 MWe already installed globally. It delivers multiple benefits, including cost reductions, a smaller footprint, and performance equivalent to multiple smaller units—all within a reliable and well-established technological framework.
12. How does Exergy balance technological innovation, profitability, and sustainable development in emerging geothermal markets?
Exergy balances technological innovation, profitability, and sustainable development by adopting an integrated approach that starts with the design of its plants and extends to business models. On one hand, we continuously invest in research and development to improve the efficiency of ORC cycles, focusing on reducing operating costs to make geothermal plant development competitive. On the other hand, we have also developed modular and flexible solutions that enable greater bankability of projects and faster implementation, facilitating the start of operations and the profitability of investments.
At the same time, sustainability remains a fundamental pillar: our plants operate in a closed loop, fully reinject geothermal fluids, and can be combined with air-cooled condensation systems to avoid water use. This allows us to offer technologies that not only generate economic value but also support responsible energy growth, respectful of the environment and aligned with the ecological transition goals of the countries where we operate.
Related: Exergy Unveils the Gemini Turbine: A Giant Leap for Large-Scale Geothermal Power Generation
As a guarantee of our high standards of quality and sustainability, our company has adopted an Integrated Management System compliant with UNI EN ISO 9001:2015, UNI EN ISO 14001:2015, and UNI ISO 45001:2018.
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