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Topping Unit at Þeistareykir

Part of the increased energy generation at Þeistareykir involves installing a so-called topping unit. The turbine makes it possible to improve utilisation of the geothermal fluid and reduce the carbon footprint without extracting additional raw material.

Utilising High Pressure

In general, steam pressure in geothermal areas is below 15 bar and decreases with long-term utilisation. Most geothermal power stations therefore use steam pressure of around 10 bar, as is the case at Þeistareykir Geothermal Station. The Þeistareykir area is a very hot energy production area. The temperature of the geothermal fluid from the wells is high, reaching up to 240°C at pressures of around and above 30 bar. The topping unit will utilise this high pressure.

Computer-generated image of the topping unit building
Computer-generated image of the topping unit building

The topping unit is one of Landsvirkjun’s most cost-effective power options. The production wells at Þeistareykir are operated at high pressure to help prevent mineral deposits from forming inside the wells. Until now, the steam pressure has been reduced through orifice plates near the wellheads, before it reaches Þeistareykir Geothermal Station. With the topping unit, the same pressure drop, from around 30 to 10 bar, will instead take place in the topping unit’s back-pressure turbine. By converting this pressure drop into useful power generation, the project increases the overall efficiency of the geothermal resource and enables more electricity to be produced from the same amount of steam, before the steam continues to the existing generating units at Þeistareykir Geothermal Station. The topping unit will also be able to utilise high-pressure steam from future production wells drilled as part of the planned expansion of the geothermal field.

To our knowledge, this is the first time in the worldwide that a turbine designed for such high pressure is installed as part of a geothermal power station.

Construction

In addition to construction of a power house, the project includes installation of the turbine itself, a steam separator next to the top-pressure turbine building, new high-pressure steam pipelines alongside the existing collection pipes, underground power cables from the turbine to Landsnet’s substation, and access roads.

  • Construction will begin in summer 2026.
  • Commissioning is planned towards the end of 2028.
The topping unit will be housed in a building located south of the existing separator station at Þeistareykir Geothermal Station.

Better utilisation and a smaller carbon footprint

With the installation of a top-pressure turbine we expect to achieve up to 28% better utilisation of the geothermal fluid. The turbine will reduce the carbon footprint per unit of energy without the need to extract more raw material.

Energy generation at Þeistareykir has been assessed as sustainable, as the geothermal area maintains its energy capacity despite current utilisation and the expansion planned in the near future. The project is therefore well aligned with Landsvirkjun´s policy of maximising the value of the resources entrusted to us.

Q&A

Below are the main questions and answers about the topping unit at Þeistareykir Geothermal Station.

General Information

  • The turbine differs from the condensing turbines already in operation at Þeistareykir Geothermal Station. It is a back-pressure turbine unit that generates electricity from the difference between the operating pressure of high-pressure wells and the steam supply pressure in the existing steam system.

  • The operating pressure of some wells at Þeistareykir is much higher than the steam supply pressure in the current system, which is effectively the pressure throughout Þeistareykir Geothermal Station.

    This is because the geothermal fluid has much higher enthalpy, or energy per unit of mass, than originally expected. One consequence of high temperature is a high concentration of dissolved silica in the geothermal fluid. To prevent silica scaling inside the wells, the pressure at the wellhead is kept much higher than the operating pressure of the system, including the steam supply, separators and turbines.

    Today, the pressure at the wellhead, 27 bar, is reduced to the operating pressure of 9,5 bar before the geothermal fluid enters the steam supply system and then the production process.

    When the topping unit is added to the system, the geothermal fluid will be directed to the turbine at high pressure. The pressure will then be reduced there, instead of at the wellhead. The turbine will use this pressure drop, which has not previously been utilised, to generate up to 25 MW, or 210 GWh, of electricity.

Constructions

  • Preparations for the installation of the topping unit began some time ago. Landsvirkjun’s construction preparation process has six phases: preliminary assessment, preliminary design, detailed design, tender design, tendering and construction.

    Construction will take place over three years, 2026, 2027 and 2028. Commissioning is planned towards the end of 2028.

  • The total number of people on site will range from 130 to 200, depending on the work being carried out at each stage. Workers’ accommodation will be built in the same area used during the construction of Þeistareykir Geothermal Station, where infrastructure is already in place.

  • It will be necessary to stop Þeistareykir Geothermal Station when the steam systems are connected. Efforts will be made to coordinate this work with scheduled maintenance shutdowns to minimise disruption to energy generation.

Resource and Utilisation

  • By adding a top-pressure turbine to the production process at Þeistareykir Geothermal Station, we expect to achieve up to 28% better utilisation of the geothermal fluid extracted from the ground.

    Disturbance and environmental and visual impacts will be kept to a minimum. The only visible works will be the topping unit building, a steam pipeline installed alongside the existing pipeline and an access road.

  • The additional energy generated by the topping unit will be sold to Landsvirkjun’s customers. Landsnet will handle transmission, as it does for other electricity generated at Þeistareykir Geothermal Station.

  • No. The turbine will only use the geothermal fluid that is already being extracted from the ground, while increasing its utilisation by up to 28%.

Environment and Community

  • The main environmental impacts will be on visual appearance and geological formations. These impacts have been assessed as insignificant. The National Planning Agency concluded that the project is not subject to environmental impact assessment.

    Local vegetation will be used when restoring disturbed areas, as was done during the construction of Þeistareykir Geothermal Station.

  • The main community impacts will be increased activity in the local economy, transport of people and goods, and a temporary increase in the number of people in the area.

  • Particular care was taken during the construction of Þeistareykir Geothermal Station, and the project has received international recognition for project management and its focus on sustainability, including positive economic, social and environmental impacts.

    The same approach will be used for the topping unit: active dialogue with stakeholders and cooperation with contractors, residents and landowners in the local community. Transport of people and materials will also be planned in consultation with municipalities and residents.