Ijen’s Blind Geothermal System vs. Zanskar’s AI-Discovered Resources: Two Models for Finding Hidden Heat The geothermal industry is entering a new phase in which the most valuable resources may no longer be the fields marked by obvious hot springs, geysers, fumaroles, or steaming ground. Increasingly, developers are targeting “blind” or hidden geothermal systems,reservoirs that lack clear surface expressions but can still contain the temperature, permeability, and fluid needed for commercial power generation. Two examples illustrate how different parts of the industry are approaching this challenge. In Indonesia, the Blawan-Ijen geothermal field in East Java was developed through geological interpretation, magnetotelluric imaging, conceptual modelling, and drilling. The project is now operating commercially, with its first phase delivering approximately 35 MW to the Java grid under a 30-year power purchase agreement. In the United States, Zanskar Geothermal & Minerals is using...
From Waste Heat to Power: Indonesia’s Lahendong Breakthrough and the Future of Geothermal Efficiency
Yet even within geothermal, a quiet inefficiency has persisted for decades: waste heat.
Now, Indonesia is rewriting that narrative.
A landmark agreement between
Pertamina Geothermal Energy (PGE), PLN Indonesia Power, and Perusahaan Listrik Negara (PLN) signals a pivotal shift—not just for Indonesia, but for the global geothermal sector. The trio has finalized electricity tariff terms for the Lahendong Bottoming Unit, a 15 MW geothermal expansion project that transforms previously wasted heat into usable electricity.
This is not just another power plant.
It is a statement.
The Lahendong Opportunity: Reinventing an Existing Giant
Located in Tomohon, within Indonesia’s geothermal-rich region of North Sulawesi, the Lahendong geothermal field is no newcomer. It has long been one of the pioneers of geothermal development in Eastern Indonesia.
The existing PLTP Lahendong consists of four generating units with a combined capacity of approximately 80 MW. For years, it has supplied clean, baseload electricity to the Sulawesi grid, supporting both industrial growth and community electrification.
But like most geothermal plants worldwide, Lahendong has been leaving energy on the table.
After high-temperature steam drives the primary turbines, a significant portion of residual heat remains unused. Historically, this “low-grade heat” has been considered uneconomical to capture. That assumption is now being challenged.
Understanding the Bottoming Cycle: Turning Losses into Gains
At the heart of this transformation lies bottoming cycle technology—a system designed to extract additional energy from waste heat streams.
Instead of discarding the remaining thermal energy after primary power generation, the bottoming cycle captures it and channels it into a secondary system. Typically, this involves a binary cycle process, where a secondary fluid with a lower boiling point is vaporized using the residual heat, driving an additional turbine to produce electricity.
The result?
- Higher overall plant efficiency
- Increased power output without additional drilling
- Reduced environmental footprint per unit of electricity generated
In Lahendong’s case, this innovation is expected to add 15 MW of capacity, all derived from energy that would otherwise be lost.
This is not just efficiency—it is optimization at its finest.
From Agreement to Execution: What Happens Next
With tariff agreements now in place, the project enters its next critical phases:
1. Joint Venture Formation
PGE and PLN Indonesia Power are expected to establish a dedicated joint venture entity to oversee development, financing, and operations.
2. EPCC Process
The project will proceed through Engineering, Procurement, Construction, and Commissioning (EPCC)—a critical phase that ensures technical precision, cost control, and timely delivery.
3. Power Purchase Agreement (PPA)
A formal PPA will define long-term electricity sales to PLN, ensuring revenue stability and investment security.
These steps are not mere formalities—they are the backbone of bankable, scalable energy infrastructure.
Ulubelu: A Parallel Success Story in Motion
Lahendong is not an isolated case.
In December 2025, PGE and PLN Indonesia Power also finalized tariff agreements for another bottoming cycle project: the Ulubelu Bottoming Unit, a 30 MW expansion linked to the larger 220 MW Ulubelu geothermal field in Lampung.
Together, these projects represent a growing realization: the future of geothermal is not just about new fields—it’s about maximizing existing ones.
A Strategic Alliance: The Power of State-Owned Synergy
One of the most compelling aspects of these developments is the collaboration between two Indonesian energy giants:
- Pertamina Group, through PGE
- PLN Group, through PLN and PLN Indonesia Power
This synergy reflects a broader national strategy: leveraging state-owned enterprises to accelerate the energy transition.
Rather than working in silos, these institutions are aligning resources, expertise, and capital to unlock latent geothermal potential across 19 existing projects.
This model offers valuable lessons for other countries—especially those with fragmented energy sectors.
The Scale of Impact: Numbers That Matter
To understand the significance of these projects, one must look at the broader footprint of PGE:
- 15 geothermal working areas under management
- 1,932 MW total installed capacity
- 727 MW directly operated by PGE
- 1,205 MW under joint operation schemes
- Approximately 70% of Indonesia’s total geothermal capacity
Perhaps most importantly, these operations contribute to an estimated 10 million tons of CO₂ emissions reduction annually.
This is not incremental change.
This is systemic impact.
Why Bottoming Cycles Matter More Than Ever
In a world increasingly constrained by capital, land, and environmental limits, the ability to extract more value from existing infrastructure is invaluable.
Bottoming cycle technology offers several strategic advantages:
1. Capital Efficiency
No need for new drilling campaigns, which are often the most expensive and risky components of geothermal development.
2. Faster Deployment
Projects can be integrated into existing facilities, reducing development timelines.
3. Lower Environmental Impact
Minimal additional land use and reduced emissions per megawatt generated.
4. Grid Stability
Additional baseload capacity strengthens energy security without introducing intermittency.
For countries like Kenya, Iceland, and the Philippines—where geothermal resources are already in use—this approach could unlock significant untapped potential.
Global Implications: A Blueprint for the Geothermal World
Indonesia’s move is not just a national milestone—it is a global signal.
For decades, geothermal innovation has focused on exploration technologies, drilling techniques, and reservoir management. While these remain critical, the Lahendong and Ulubelu projects highlight a different frontier: efficiency optimization.
This shift has profound implications:
- Mature geothermal fields worldwide can be retrofitted for higher output
- Investors gain new opportunities with lower risk profiles
- Policymakers can accelerate clean energy targets without new land acquisition
In essence, the industry is moving from expansion to intensification.
Challenges Ahead: Not Without Complexity
Despite its promise, bottoming cycle deployment is not without hurdles:
Technical Integration
Retrofitting existing plants requires careful engineering to ensure compatibility and reliability.
Economic Viability
While cheaper than new drilling, bottoming units still require significant upfront investment.
Regulatory Frameworks
Tariff structures must reflect the unique nature of these projects to attract investors.
Operational Expertise
Managing dual-cycle systems demands advanced technical capabilities.
Indonesia’s success will depend on how effectively these challenges are addressed.
The African Perspective: Lessons for Kenya and Beyond
For a country like Kenya—home to world-class geothermal resources in the Rift Valley—the implications are immediate and compelling.
Kenya has already established itself as a geothermal leader in Africa, with major developments in Olkaria and beyond. However, like Lahendong, many of these plants may still be discarding valuable residual heat.
Imagine:
- Retrofitting existing plants with bottoming cycles
- Adding tens of megawatts without drilling a single new well
- Increasing efficiency while lowering costs
This is not a distant vision. It is a practical, proven pathway.
For companies like Alphaxioms, this represents a strategic opportunity to lead in geothermal optimization technologies, bridging global innovation with local expertise.
A Turning Point for Energy Transition
The Lahendong Bottoming Unit is more than a 15 MW project.
It is a redefinition of what efficiency means in the energy sector.
It challenges long-held assumptions about waste, value, and potential. It demonstrates that innovation does not always require new frontiers—sometimes, it requires looking deeper into what we already have.
As the world accelerates toward net-zero targets, such innovations will be indispensable.
Not every country has untapped geothermal fields.
But many have untapped geothermal efficiency.
Conclusion: The Silent Revolution Beneath Our Feet
In the grand narrative of energy transition, breakthroughs are often associated with new technologies—fusion reactors, hydrogen economies, or next-generation batteries.
Yet, the Lahendong project reminds us of a quieter, equally powerful truth:
Sometimes, the future of energy lies not in discovering new resources, but in better using the ones we already have.
By turning waste heat into power, Indonesia is not just generating electricity—it is setting a precedent.
See also: From Energy Poverty to Power Independence: Enfield’s Geothermal Revolution
A precedent that says efficiency is innovation.
A precedent that says sustainability is optimization.
And a precedent that the geothermal sector—long considered mature—still has untapped potential waiting to be unleashed.
The question now is not whether the world will follow.
It is how fast.
Source: Katada
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