Nesjavellir Combined Heat and Power Plant

The Nesjavellir geothermal field is a high-enthalpy geothermal system within the Hengill area of SW-Iceland.  The plant is a combined geothermal heat and power plant (CHP) wherein it generates electricity and hot water for district heating. Construction of the geothermal power plant began in 1987 and the first stage of the thermal plant was commissioned in 1990, following an intensive drilling and testing phase in the 1980s. The last 30 MWe turbine generator unit was commissioned in 2005.

Mannvit Services:  

  • Project management
  • Assistance during contract negotiation
  • Pre-feasibility study
  • Site supervision
  • Feasibility study
  • Site engineering
  • EIA and report
  • Supervision for turbine and cold end installation
  • Design management
  • Steam gathering system
  • Overall power plant design
  • Technical supervision
  • Detailed mechanical design of the plant
  • Electrical work supervision
  • Control system supervision
  • Civil work supervision
  • Geotechnical design
  • Mechanical work supervision
  • Electrical design
  • Commissioning work and start-up
  • Design of control systems
  • Acceptance testing
  • Process- and system design
  • Training of operators
  • Design of steam gathering systems
  • Groundwater modelling
  • Well design
  • Drilling bid documents and procurement
  • Reservoir engineering
  • Drilling work supervision and
  • Design of HVAC systems
  • Project planning report
  • Review of manufacturing design
  • Supervision for drilling operations
  • Procurement management
  • Inspections
  • Bid documents preparation and evaluation
  • Supervision of construction work
  • Document control



The plant itself is a combined cycle plant, wherein a mixture of steam and geothermal brine is transported from the wells to a central separation station at 200° C and 14 bars. From there the fluid (steam and liquid) goes into a steam separator and the two phases are separated. Moisture is removed from the steam, which is then sent through the turbine after which it is condensed in a condenser.  Within the condenser fresh water is preheated.  The preheated fresh water is then run through a system of heat exchangers, which utilize the heat from the liquid part of the brine after the steam separator.  The fresh water is heated to the required temperature and sent through de-areators, which remove the bulk of the oxygen. Then finally a small amount of geothermal steam containing acidic gases (hydrogen sulfide) is injected into the water to remove any remaining oxygen, thereby preventing corrosion and scaling.  

This hot water is then pumped to a large storage tank at an elevation of 406 meters.  From there, the hot water flows by gravity to two smaller storage tanks on the outskirts of Reykjavik to be used for heating and hot tap water.

Plant details

Combined Heat and Power cycle geothermal plant

  • Electricity generation: 120 MWe, developed in three phases
  • District heating supply: 300 MWth
  • 25 boreholes were drilled, from 1,000-2,200 meters


Mannvit handled overall plant design, construction management, commissioning, and supervision for all phases along with associated consultants, Verkís. The two firms managed the procurement for equipment, tender documents for contractors, and assistance in negotiation.

120 MW 
Installed power
300 MW 
Installed heating capacity

Nesjavellir Combined Heat and Power Plant