"The heat was always there — the slow decay of the Earth's core, the magma rising beneath a young volcanic island. The engineers at Hengill did not make this energy. They drilled a channel and let the planet's own warmth pass through into light and heat for the people above."
— The Energy Codex · observation without ownership · thecodex.expert
Cluster 1 · What is it?
What Hellisheiði is — precisely
Hellisheiði is one of the largest geothermal power stations on Earth: a plant that turns naturally superheated underground steam into both electricity and hot water, sitting on the flank of an active volcanic system 25 kilometres from Reykjavík.
What is a geothermal plant, in plain English?
Iceland sits on a crack between two of the Earth's tectonic plates, where magma rises close to the surface. That heat boils underground water into steam. At Hellisheiði, engineers drill deep wells — over two kilometres down — and let that natural steam rush up. The steam spins turbines to make electricity, and the leftover heat warms fresh water that is piped to homes in Reykjavík. No fuel is burned. The "fuel" is simply the heat of the planet itself.
Iceland sits on a crack between two of the Earth's tectonic plates, where magma rises close to the surface. That heat boils underground water into steam. At Hellisheiði, engineers drill deep wells — over two kilometres down — and let that natural steam rush up. The steam spins turbines to make electricity, and the leftover heat warms fresh water that is piped to homes in Reykjavík. No fuel is burned. The "fuel" is simply the heat of the planet itself.
Consistent with: IRENA Geothermal
Technical classification: Hellisheiði is a high-temperature, flash-steam plus binary, combined heat-and-power (CHP) geothermal station.
High-temperature field — the Hengill reservoir runs around 270 °C, hot enough that water flashes directly to steam at the surface.
Flash-steam — pressurised geothermal fluid is "flashed" into steam that drives high- and low-pressure turbines.
Binary add-on — lower-temperature fluid heats a secondary working fluid through a heat exchanger to extract still more power.
Combined heat and power — the plant produces both electricity (~303 MWe) and district heating hot water (~200 MWth), making total energy use far more efficient than electricity alone.
High-temperature field — the Hengill reservoir runs around 270 °C, hot enough that water flashes directly to steam at the surface.
Flash-steam — pressurised geothermal fluid is "flashed" into steam that drives high- and low-pressure turbines.
Binary add-on — lower-temperature fluid heats a secondary working fluid through a heat exchanger to extract still more power.
Combined heat and power — the plant produces both electricity (~303 MWe) and district heating hot water (~200 MWth), making total energy use far more efficient than electricity alone.
Classification: ON Power · Orkustofnun
Hengill central-volcano geothermal system, Western Volcanic Zone, Iceland. Reservoir: fractured basaltic hyaloclastite and lava sequences, fluid enthalpy in the high-temperature class (>200 °C), measured reservoir temperatures ~240–320 °C with a working figure near 270 °C. Production wells drilled to ~2,000–3,000 m. Power cycle: double-flash high- and low-pressure steam turbines supplemented by binary units; reinjection of separated water and condensate to maintain reservoir pressure and manage dissolved gases. Installed: ~303 MWe + ~200 MWth across staged commissioning 2006–2011. Operator: ON Power (Orka náttúrunnar), subsidiary of Orkuveita Reykjavíkur. Co-located: CarbFix CO₂-to-basalt mineralisation and Climeworks Orca/Mammoth direct air capture.
~303 MWeElectrical capacity
~200 MWthDistrict-heating capacity
~270 °CReservoir temperature
2006–2011Staged commissioning
Cluster 2 · Where does the energy come from?
The heat source — a mid-ocean ridge on land
Most geothermal heat is hard to reach. Iceland is the rare place where a mid-ocean ridge rises above sea level, putting volcanic heat within drilling distance almost everywhere.
Iceland sits exactly on top of the Mid-Atlantic Ridge — the seam where the North American and Eurasian plates pull apart. Magma constantly rises into this gap. The Hengill volcano next to Hellisheiði is one of these hot centres. Rainwater and snowmelt sink into the cracked rock, get heated by the magma below, and turn into the steam the plant uses. The Earth quietly refills the supply.
The Hengill system is a triple junction where the Reykjanes Peninsula rift, the Western Volcanic Zone, and the South Iceland Seismic Zone meet. This makes it one of the most geologically active and heat-rich areas in Iceland. Meteoric water percolates kilometres deep, is heated convectively by shallow magma intrusions, and rises again — a natural circulation that the plant taps and then partly reinjects to keep stable.
Hengill is a Holocene central volcano with associated fissure swarms; the geothermal system is convection-dominated, recharged by meteoric water with deep circulation along permeable fault and fracture networks. Heat source is inferred shallow magmatic intrusion. The basaltic host rock is central to the co-located CarbFix process: fresh basalt is rich in calcium, magnesium and iron that react with dissolved CO₂ to form stable carbonate minerals.
Cluster 3 · How does it work?
From steam to socket
Wells bring up a mix of steam and hot water. The plant separates them, spins turbines with the steam, harvests heat from the water, and sends both electricity and hot water out to the capital region.
Steam rushes up the wells and is separated from hot water. The steam spins big turbines connected to generators — that makes the electricity. The hot water left over isn't wasted: it heats clean fresh water that flows through insulated pipes all the way to Reykjavík's taps and radiators. Used geothermal fluid is pumped back underground so the reservoir doesn't run dry.
Production wells deliver a two-phase fluid to steam separators. High-pressure steam drives the HP turbine; flashing the separated brine again yields low-pressure steam for additional generation. Exhaust steam is condensed, and its heat — together with the separated geothermal brine — is transferred via heat exchangers to a clean freshwater district-heating loop. Condensate and spent brine are reinjected. Non-condensable gases (mainly CO₂ and H₂S) are captured for the CarbFix process rather than vented.
Double-flash steam cycle with HP/LP turbine stages plus binary bottoming units; surface condensers with cooling provided by cold groundwater. District-heating production uses plate heat exchangers transferring thermal energy to a closed freshwater loop delivered to the OR distribution network. Gas abatement: H₂S and CO₂ scrubbed into water and reinjected (the SulFix/CarbFix approach), reducing both emissions and odour. Reinjection wells maintain reservoir pressure and mitigate subsidence.
Cluster 4 · Who runs it?
ON Power and Reykjavík Energy
Hellisheiði is owned and operated by ON Power (Orka náttúrunnar), the renewable-energy arm of Reykjavík Energy, the utility serving Iceland's capital region.
The plant is run by ON Power, part of Reykjavík Energy — the public utility owned mainly by the City of Reykjavík and neighbouring towns. So the plant belongs, in effect, to the people it serves. ON Power also runs a visitor centre at the plant, the Geothermal Exhibition, where the public can see the turbines and learn how it works.
Orka náttúrunnar (ON Power) is a subsidiary of Orkuveita Reykjavíkur (Reykjavík Energy / OR), a utility owned by the City of Reykjavík and partner municipalities. OR's group also covers water, wastewater and fibre. ON Power operates Hellisheiði and the nearby Nesjavellir geothermal plant, and partners with CarbFix and Climeworks on carbon removal at the site.
Ownership chain: City of Reykjavík (majority) and partner municipalities → Orkuveita Reykjavíkur → Orka náttúrunnar (ON Power) → Hellisheiði and Nesjavellir power stations. CarbFix became a standalone subsidiary of OR to commercialise mineral carbon storage; Climeworks operates the co-located Orca (2021) and Mammoth (2024) DAC plants under offtake and storage arrangements with CarbFix.
Cluster 5 · What makes it special
CarbFix — turning CO₂ into stone
Hellisheiði is famous beyond power generation because it hosts CarbFix: a process that dissolves carbon dioxide in water and injects it into basalt, where it turns to solid rock within about two years.
Normally, carbon dioxide stored underground is a gas that might slowly leak back out. CarbFix does something cleverer: it mixes the CO₂ into water — like making soda water — and pumps it into Iceland's basalt rock. The rock reacts with the fizzy water and the carbon literally turns into stone. Once it's stone, it can't escape. The Climeworks machines next door pull CO₂ straight from the air, and CarbFix turns it to rock.
CarbFix dissolves CO₂ (and H₂S) into water and injects the solution into reactive basaltic rock. Calcium, magnesium and iron leached from the basalt react with the dissolved carbon to precipitate stable carbonate minerals. Field results showed the majority of injected CO₂ mineralised within roughly two years — far faster than once assumed. Operating at the site since 2012, CarbFix turned the plant's own geothermal CO₂ emissions into a storage feedstock, and now also stores CO₂ captured from air by Climeworks.
Mineral carbonation pathway: CO₂(aq) → carbonic acid → dissolution of divalent cations (Ca²⁺, Mg²⁺, Fe²⁺) from basalt → precipitation of carbonate minerals (calcite, magnesite, siderite, and ankerite-series). Peer-reviewed monitoring at Hellisheiði reported that ~95% of injected carbon mineralised within ~2 years using isotopically traced CO₂. Co-located DAC: Climeworks Orca (~4,000 t CO₂/yr nominal, 2021) and Mammoth (larger modular plant, 2024) provide atmospheric CO₂ for permanent mineral storage by CarbFix.
Cluster 6 · India connection
What Hellisheiði means for India
India has no high-temperature volcanic geothermal like Iceland's, but Hellisheiði matters to India in two ways: as a model for carbon mineralisation in basalt, and as a benchmark for using waste heat.
India can't easily copy Iceland's volcano power — India's geology is different. But India has something important in common: the vast Deccan Traps in western India are made of the same basalt rock that CarbFix uses to turn CO₂ into stone. That makes the Hellisheiði carbon-storage idea directly relevant to India's climate plans. India's own geothermal potential is in moderate-heat springs in places like Ladakh and the Himalayas.
The Deccan Traps basalt province of Maharashtra, Gujarat and Madhya Pradesh is one of the world's largest basalt formations — geologically suited to CarbFix-style mineral carbon storage, a subject of active Indian research interest. On the power side, India's geothermal resources are low-to-medium enthalpy (Puga and Chumathang in Ladakh, Tattapani in Chhattisgarh), better suited to direct heat use and binary plants than to Hellisheiði-scale flash generation.
India's geothermal provinces (GSI mapping): Himalayan (Puga, Chumathang — Ladakh), West Coast, SONATA (Tattapani), Godavari and Cambay. Resource is predominantly <150 °C, favouring binary/ORC and direct-use applications. Strategic relevance of Hellisheiді: the Deccan basalt offers a candidate host for mineral carbonation analogous to CarbFix, linking India's CCS research to the proven Hellisheiði pathway.
Cluster 7 · What it gave the world
Proof that geothermal can scale — cleanly
Hellisheiði showed that a single geothermal site can power and heat a capital region while also becoming the world's reference site for permanent carbon mineral storage.
Hellisheiði helped make Iceland a country that runs almost entirely on clean energy. It also became the place where two big climate ideas were proven for real: pulling CO₂ from the air, and turning that CO₂ into stone. Scientists and officials from around the world visit to see whether it can work in their countries too.
The plant anchors Iceland's near-100%-renewable electricity and district heating, and demonstrated combined heat-and-power efficiency at large scale. Through CarbFix and Climeworks, it became the world's leading demonstration of mineral CO₂ storage plus direct air capture co-located with a power plant — a template now studied for replication in other basaltic regions.
Contribution: validated high-temperature flash+binary CHP at ~303 MWe/200 MWth; field-proven basalt mineral carbonation (CarbFix, since 2012); first commercial DAC-to-permanent-storage coupling (Climeworks Orca 2021, Mammoth 2024). Collectively these establish a measurable, monitored, permanent carbon-removal pathway — distinct from gaseous geological storage — that informs IPCC and IEA assessments of carbon-dioxide removal.
Cluster 8 · History
A plant built in stages
Hellisheiði came online in phases between 2006 and 2011, expanding generation and adding heat production and carbon storage over time.
The plant didn't appear all at once. The first turbines started around 2006. More were added over the next few years, and a big hot-water heating station was added so it could warm homes too. In 2012 the CarbFix carbon-to-stone experiment began. In 2021 and 2024 the Climeworks air-capture machines were switched on next door.
Key milestones: first power ~2006; staged turbine additions through ~2008–2011 bringing electrical capacity to ~303 MWe; district-heating station (~133–200 MWth) added to supply the capital region; CarbFix pilot injection 2012, scaling thereafter; Climeworks Orca DAC 2021; Climeworks Mammoth DAC 2024.
Commissioning sequence reflects OR's staged development of the Hengill resource to match demand growth in the Reykjavík capital region and to supply power-intensive industry. Reinjection strategy and gas-abatement (SulFix/CarbFix) were progressively integrated to address induced-seismicity concerns and H₂S emissions as capacity rose.
Cluster 9 · Risks & controversies
The honest difficulties
Geothermal at this scale is clean but not free of problems: induced earthquakes, hydrogen-sulphide gas, and the challenge of keeping the reservoir productive.
Pumping water back underground can trigger small earthquakes — Hellisheiði's reinjection has caused tremors that residents nearby have felt. The plant also releases hydrogen sulphide, the gas that smells like rotten eggs, which had to be cleaned up. And like any geothermal field, if you take heat out faster than the Earth refills it, the wells slowly cool. Engineers manage all three carefully, but they are real trade-offs.
Induced seismicity from fluid reinjection has produced felt earthquakes near Hellisheiði, prompting adjusted reinjection management. H₂S emissions raised air-quality concerns in the capital region, addressed via the SulFix gas-abatement programme that scrubs and reinjects sulphur. Reservoir pressure decline and thermal drawdown require active reinjection and well management to sustain output.
Documented challenges: reinjection-induced microseismicity (felt events correlated with injection rates), mitigated by distributing injection and rate control; H₂S abatement via SulFix mineralisation; pressure support and enthalpy maintenance through optimised reinjection; make-up well drilling to offset decline. These are standard high-temperature geothermal management issues rather than unique failures.
Cluster 10 · Future
Where it goes from here
Hellisheiді's future is increasingly tied to carbon removal: scaling CarbFix and Climeworks to store ever more CO₂, while sustaining stable power and heat.
The plant will keep making power and heat, but its most-watched future is carbon removal. Climeworks' newer Mammoth machine is far bigger than the first, and CarbFix plans to store much more CO₂ in the basalt. If it works at large scale and low cost, the Hellisheiði model could spread to other volcanic and basalt regions worldwide.
Direction of travel: expansion of DAC-to-mineralisation capacity (Mammoth, 2024, and beyond), CarbFix's "Coda Terminal" concept for importing CO₂ to mineralise in Icelandic basalt, and continued optimisation of the geothermal reservoir. The site is positioning as a global carbon-removal hub rather than only a power station.
Pipeline: Climeworks Mammoth modular scale-up; CarbFix Coda Terminal (proposed large-scale mineral storage receiving shipped CO₂); ongoing reservoir management for capacity sustainability. Key uncertainties are DAC energy cost, mineralisation monitoring at scale, and public acceptance of expanded injection given seismicity history.
People also ask
Common questions about Hellisheiði
Is Hellisheiði the largest geothermal plant in the world?
It is among the largest by installed capacity (~303 MWe). Depending on how capacity is counted, it ranks alongside complexes such as The Geysers (USA) and large Indonesian and Philippine fields. It is widely cited as one of the world's biggest single geothermal stations. Source: ThinkGeoEnergy
It is among the largest by installed capacity (~303 MWe). Depending on how capacity is counted, it ranks alongside complexes such as The Geysers (USA) and large Indonesian and Philippine fields. It is widely cited as one of the world's biggest single geothermal stations. Source: ThinkGeoEnergy
What is CarbFix and why is it at Hellisheiði?
CarbFix dissolves CO₂ in water and injects it into basalt, where it mineralises into rock within roughly two years. It is located at Hellisheiði because the plant supplies CO₂, water and reactive basalt all in one place. Source: CarbFix
CarbFix dissolves CO₂ in water and injects it into basalt, where it mineralises into rock within roughly two years. It is located at Hellisheiði because the plant supplies CO₂, water and reactive basalt all in one place. Source: CarbFix
Who owns Hellisheiði?
It is owned and operated by ON Power (Orka náttúrunnar), a subsidiary of Reykjavík Energy, which is owned mainly by the City of Reykjavík. Source: ON Power
It is owned and operated by ON Power (Orka náttúrunnar), a subsidiary of Reykjavík Energy, which is owned mainly by the City of Reykjavík. Source: ON Power
Does the plant cause earthquakes?
Reinjecting water underground has triggered small, sometimes felt, earthquakes near the plant. Operators manage injection rates to reduce this. Source: Icelandic Met Office
Reinjecting water underground has triggered small, sometimes felt, earthquakes near the plant. Operators manage injection rates to reduce this. Source: Icelandic Met Office
Can the Hellisheiði model work in India?
India lacks Iceland's volcanic heat, but its vast Deccan basalt is geologically suited to CarbFix-style carbon mineralisation, making the storage concept relevant even though the power model is not directly transferable. Source: GSI
India lacks Iceland's volcanic heat, but its vast Deccan basalt is geologically suited to CarbFix-style carbon mineralisation, making the storage concept relevant even though the power model is not directly transferable. Source: GSI
Does Hellisheiði burn any fuel?
No. It generates electricity and heat from naturally superheated geothermal fluid. Its only significant gas emissions are naturally dissolved CO₂ and H₂S, much of which is now captured and mineralised on site. Source: Orkuveita Reykjavíkur
No. It generates electricity and heat from naturally superheated geothermal fluid. Its only significant gas emissions are naturally dissolved CO₂ and H₂S, much of which is now captured and mineralised on site. Source: Orkuveita Reykjavíkur
Connected to
Where this sits in the codex
Hellisheiді connects to the wider geothermal story, to carbon capture, and to Iceland's energy profile.
Sources
Every source used on this page
All figures on this page are documented from the named institutional sources below. Where sources differ, the page says so.
- ON Power (Orka náttúrunnar) — operator; capacity, technology, visitor information
- Orkuveita Reykjavíkur (Reykjavík Energy) — ownership, district heating, gas abatement
- CarbFix — mineral carbon storage process and results
- Climeworks — Orca and Mammoth direct air capture
- Orkustofnun (National Energy Authority of Iceland) — resource and regulatory data
- IRENA — geothermal technology context
- IEA — energy and CCUS context
- Icelandic Met Office — seismicity
- MNRE India & GSI — India geothermal and basalt context
Capacity figures (~303 MWe / ~200 MWth) and reservoir temperature (~270 °C) are as documented by ON Power and Orkuveita Reykjavíkur. CarbFix mineralisation timescales reflect peer-reviewed field results reported by CarbFix. Production-level details that operators do not publish are described as estimates.
Provenance
How this page was made
This page documents what named institutional sources record about Hellisheiði. It is a record of documentation, not a recommendation. Figures are rounded and were last verified June 2026. Energy data changes — always confirm at the linked primary source before relying on any number.
Entry type: asset · Confidence: high · Last reviewed: 2026-06-29 · Publisher: The Codex, Mumbai, India · Contact: hello@thecodex.expert