Hellisheidi Geothermal Power Plant

Hellisheidi geothermal power plant is a flash steam, combined heat and power plant (CHP) located in SW-Iceland, on one of the largest geothermal systems (high-enthalpy) in Iceland.  The plant's purpose is to meet increasing demand for electricity and hot water for space heating.  The development plan was an incremental expansion from 2006 to 2018 to an output of 303 MWe and 200 MWth, making it the largest geothermal combined heat and power plant in Iceland and one of the world's largest geothermal power plants. The installed heat capacity is planned to be 400 MWt as demand for heating increases in the Reykjavik capital area. Overall, 61 wells were drilled, from 1,000-2,200 meters, 44 production and 17 reinjection wells. The plant owner is ON (formerly Orkuveita Reykjavíkur). 

Gufuveita Hellisheiðarvirkjun

Mannvit services

  • Project management
  • Mechanical design
  • Overall plant design
  • Document control
  • Environmental Impact Assessment
  • HVAC systems
  • Design management
  • Site supervision
  • Technical supervision
  • Supervision for turbine and cold end installation
  • Well design
  • Steam gathering system supervision
  • Drilling bid preparation and tender evaluation
  • Electrical work supervision
  • Inspection of rigs, equipment, materials
  • Control system supervision
  • Supervision for drilling operations
  • Civil work supervision
  • Process and system design
  • Mechanical work supervision
  • Detailed plant design
  • Supervision of construction work
  • Construction drawings
  • Commissioning work and start-up
  • Preparation of bid documents
  • Acceptance testing
  • Bid evaluation
  • Training of operators
  • Design of control systems




Plant details

Phase 1: 2006, 2 x 45 MWe - high pressure turbines.

Phase 2: 2007, 33 MWe - low pressure turbine (bottoming plant).

Phase 3: 2008, 2 x 45 MWe - high pressure turbines

Phase 4: 2010, 133 MWth - thermal power plant

Phase 5: 2011, 2 x 45 MWe - high pressure turbines

Phase 6: 2015, connection of four production wells

Phase 7: 2018, expansion of the heating plant to 200 MWth

Phase 8: 2030 (planned) - 133MWth



Geothermal fluid from production wells is gathered in central separation stations.  The separated water is flashed and the steam is used in the low pressure turbine but the water is used in heat exchangers to heat the preheated water up to the required temperature.  Electricity is generated with condensing steam turbines, six high pressure turbines and one low pressure turbine.  The condensers from four turbines are used to preheat fresh water.  The heated water is treated in de-aerators to suit the requirements of the distribution system. The separated water is diluted with condensate and then pumped into re‐injection wells.  Co-generation of electric and thermal power is thus utilized in the most economical way possible.


Transmission of energy

Electric energy is transmitted to the substation which is directly connected to the national grid. The line voltage from each unit is 220 kV. The hot water is pumped from the plant to a tank at the highest point of the transmission pipe. From there the water flows by gravity to the storage tanks of the district heating system from where it is distributed to the consumers in Reykjavik. 


Mannvit played a leading role in the preparation, drilling, design, project management and construction of the entire project in an integrated team with the plant owner ON. The latest expansion (phase 6) adding 12 km of pipelines both steam and separated water from Hverahlid area to the plant was installed in 2015. Mannvit, Verkís, Tark Architects and Landslag Architects shared supervision, detailed piping, electrical and control design for all phases.

303 MW 
Installed power
200 MW 
Installed heating capacity
Production and injection wells

Hellisheidi power plant is one of the world's largest geothermal energy plants. In 2014 cleaning of NGC and reinjection of H2S and CO2 into the bedrock began.


Hellisheidi Geothermal Power Plant