As the world moves toward cleaner and more resilient energy systems, geothermal energy stands out as one of the most stable and sustainable sources of power. Unlike solar and wind, which depend on weather conditions, geothermal energy draws from the constant heat of the Earth’s interior—a virtually inexhaustible resource that can provide reliable electricity around the clock.
Found beneath the surface in reservoirs of hot water and steam, geothermal energy offers a low-carbon, high-efficiency alternative to fossil fuels. Today, advancements in technology are making geothermal energy production and storage more accessible and cost-effective, opening new pathways for countries to meet their sustainability targets.
What is geothermal energy?
Geothermal energy is the heat produced naturally within the Earth’s core. The term originates from the Greek words geo (earth) and therme (heat), reflecting its deep, geological origins.
This energy is considered renewable because the Earth’s interior constantly generates heat through naturally occurring radioactive elements, such as potassium-40 and thorium-232. The result is a steady flow of thermal energy radiating outward through rock formations and subterranean fluids.
Reservoirs of hot water and steam form at various depths beneath the surface. These geothermal resources are what power plants use to produce clean, dependable electricity.
How geothermal energy works
How is geothermal energy generated? Geothermal power plants convert the heat energy drawn from underground reservoirs into electricity.
To generate power from geothermal systems, three natural elements are needed:
- Heat – naturally occurring deep within the Earth’s crust
- Fluid – usually water, which absorbs and transports heat to the surface
- Permeability – fractures or porous pathways that allow the fluid to flow through hot rock formations
Given the presence of these three elements, how then does geothermal energy work? The electricity generation process generally follows these steps:
- Tapping the reservoir: Wells, ranging from a few feet to several miles deep, are drilled into the underground reservoirs to access steam and very hot water.
- Drawing heat to the surface: The fluid flows through the hot rocks, absorbing heat. This heated material (steam or hot liquid) is drawn up through the wells to the Earth’s surface.
- Driving the turbine: Once at the surface, the heat energy is used to create steam or vapor. This steam or vapor then drives a turbine, which is connected to a generator that produces electricity.
- Reinjection: After use, the spent steam or liquid is frequently reinjected back into the underground reservoir.
This closed-loop system minimizes waste, conserves water, and enables geothermal plants to operate with remarkable efficiency for decades.
The advantages of geothermal energy
The generation and storage of geothermal energy offers several advantages that position it as one of the most strategic renewable energy sources in the transition to a Net Zero future.
Reliable, round-the-clock power
Unlike intermittent solar and wind farms, geothermal plants can operate continuously. This reliability makes it an ideal source of power, capable of stabilizing electricity grids and complementing other renewable sources.
Sustainable and replenishable
Because geothermal heat originates from the Earth’s interior, replenished naturally by the elements, it is virtually inexhaustible.
Low-carbon and clean
Modern geothermal systems emit minimal greenhouse gases. Life-cycle emissions from geothermal energy are far lower than solar, wind, or fossil fuels, making it a leading choice for clean power generation.
Compact and land-efficient
Geothermal power plants require less land per unit of energy produced than coal, wind, or solar photovoltaic installations, minimizing ecological disturbance and maximizing land use efficiency.
Water-conscious
Geothermal facilities use closed-loop systems that recycle water, consuming significantly less over their lifetime compared to traditional power plants.
Energy security
As a domestic resource, geothermal energy reduces dependence on imported fuels, bolstering energy independence and resilience for developing nations.
Types of geothermal power plants
Different technologies are used to generate geothermal energy into electricity, depending on the temperature and type of underground resource.
Dry steam power plants
These systems use steam drawn directly from natural underground sources to turn turbines.
Flash steam power plants
Flash steam systems use high-pressure hot water from deep reservoirs (over 182°C). When the fluid reaches the surface, the pressure drops, causing it to turn into steam that drives a turbine.
Binary-cycle power plants
Binary-cycle systems use moderately hot geothermal fluids (typically below 182°C) that transfer heat to a secondary working fluid with a lower boiling point. The vaporized secondary fluid powers the turbine.
This technology enables geothermal power generation in areas with lower-temperature resources, making geothermal energy more accessible and versatile across diverse terrains.
By combining these technologies, geothermal plants can harness heat from a wide range of underground conditions. This flexibility strengthens energy resilience and broadens renewable generation potential. But how can this geothermal energy be stored?
Storing geothermal energy
Beyond generation, geothermal systems can also store geothermal energy underground, offering an efficient form of large-scale energy management.
How is geothermal energy stored? Through Geothermal Energy Storage (GES) or Aquifer Thermal Energy Storage (ATES), energy is stored in subsurface groundwater. The system uses two wells—one for cold water and one for warm water—linked to an aquifer.
- In summer, excess heat from buildings is transferred to the warm water well.
- During the cold season, this stored heat is retrieved to warm indoor spaces.
This cyclical process provides an innovative and sustainable way to manage energy demand, reduce heating and cooling costs, and further stabilize renewable energy systems.
Applications of geothermal energy
Geothermal energy can be applied in several ways, offering both large-scale and direct-use benefits:
Electricity generation
By tapping deep geothermal reservoirs, utilities can produce renewable electricity that delivers consistent baseload power.
Heating and cooling
Geothermal heat pumps (GHPs) use stable underground temperatures to heat and cool buildings efficiently. In cold weather, the ground serves as a heat source; in warm weather, it acts as a heat sink.
District heating systems
Entire neighborhoods, campuses, or industrial zones can be powered through centralized geothermal systems that provide heat and cooling across multiple buildings.
Direct industrial use
Hot geothermal water can directly support industrial applications, including:
- Heating greenhouses and fish farms
- Drying lumber and crops
- Processing food and paper products
Co-produced geothermal power
Hot water generated as a byproduct of oil and gas operations can also be captured to produce electricity, maximizing energy efficiency and reducing waste.
Geothermal energy leadership in the Philippines
The Philippines is one of the world’s leaders in geothermal energy generation due to its location along the Pacific Ring of Fire—a tectonically active zone marked by volcanoes and geothermal fields. This strategic geography provides vast potential for clean, stable, and renewable baseload power.
As of 2025, the Philippines is the third-largest producer of geothermal energy globally, following the United States and Indonesia. With an estimated 4,064 megawatts (MW) of potential capacity, over 1,900 MW has already been developed and connected to the grid—supplying around 14% of the country’s total electricity generation.
The Philippines’ geothermal potential presents a powerful opportunity to reinforce national energy security, diversify renewable generation, and accelerate the transition toward a fully sustainable future.
Pioneering the future of clean power
Through strategic partnerships, ACEN is also a geothermal energy company with key projects in the Philippines and Indonesia. The company’s geothermal projects contribute to firm, flexible energy systems that sustain both economic growth and environmental stewardship.
One of ACEN’s landmark geothermal energy generation assets is the 32 MW Maibarara Geothermal power plant in Batangas, a project in joint venture with PetroGreen Energy Corporation (PGEC) and PNOC Renewables Corporation (PNOC). The facility demonstrates consistent performance, supplying stable, weather-resilient power to the Luzon grid. As the first geothermal project developed under the Philippines’ Renewable Energy Act of 2009, Maibarara Geothermal symbolizes ACEN’s commitment to advancing clean power solutions that balance energy security with environmental responsibility.
In Indonesia, ACEN, through a consortium with Star Energy and Electricity Generating Public Company Limited, also operates the 271 MW Darajat and 377 MW Salak geothermal plants in West Java. These facilities, which began commercial operations in the 1990s, also support reforestation and community livelihood programs.Ap
Geothermal energy generation and storage exemplify the kind of progress the world needs—sustainable, stable, and deeply rooted in natural systems. As ACEN moves toward Net Zero by 2050, the company’s commitment to developing renewable solutions such as geothermal power ensures that communities across Asia and beyond can access clean energy for generations to come. By harnessing the Earth’s heat, ACEN powers a future defined by innovation, balance, and enduring progress.
Learn more about ACEN’s renewable energy projects in the Philippines and other markets.
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