Hellisheidi Geothermal Energy Plant, Iceland

Renewable energy: heat, power, and circular economy in one

About

Challenge

Reykjavik and the greater capital area needed to increase the heating capacity to accommodate the growing city and meet an increase in electricity demand.

Solution

ON Power decided to harness a large geothermal energy resource just outside Reykjavik and build a modern geothermal flash steam combined heat and power plant (CHP). The Hellisheidi Geothermal Power Plant was built in phases, the first one commissioned in 2006 and the latest in 2018. The present output of the plant is 303 MWe and 200 MWth, making it the largest geothermal CHP plant in Iceland and the fourth largest geothermal power plant in the world.

Value

The plant is designed to have an installed heat capacity of 400 MWth. The plant will therefore meet the demand for space heating in the Reykjavik capital area for years to come in a sustainable manner by producing green electricity for the energy transition.

Specifications

Plant capacity

A 303 MW electrical and 200 MW heating capacity

Power plant

Fourth largest geothermal power plant in the world. 66 production wells and injection wells at depths ranging from 1,000 metres to more than 3,000 metres.

Location

Reykjavik

Period

2002–ongoing

Country

Iceland

Partners

ON power (owner), Verkís, Tark Architects and Landslag Architects

Services

Project management; EIA; overall and detailed plant design; design management; process, mechanical and system design; well design; preparation of bid documents and bid evaluation; site supervision; inspection of rigs, equipment & materials; supervision of drilling operations, steam collection system, civil works, mechanical work, turbine and cold end installation, control system & electrical work; commissioning work and start-up; acceptance testing; and training of operators.

This water is up for a ride

At Hellisheidi Geothermal Power Plant, the heating process happens through a complex process. First, the two-phase geothermal fluid from the production wells is piped to a central separation station where steam is separated from the water at a pressure of about 10 bar. The steam is piped to power stations where electricity is generated in condensing steam turbines, six high-pressure turbines and one low-pressure turbine. The condensers from the four turbines are then used to preheat fresh water. The separated water is flashed at lower pressure, and the steam generated is used in the low-pressure turbine, whereas the water is used in heat exchangers to heat the water – preheated in the condensers – to the required temperature for the district heating system in Reykjavik.

The hot water is deaerated and piped to Reykjavik. The cooled separated water is diluted with condensate and then pumped into re‐injection wells. Co-generation of electric and thermal power is thus utilised in the most efficient way possible. Associated with the geothermal fluid are incondensable gases such as carbon dioxide (CO₂) and hydrogen sulphide (H₂S). These gases are cleaned from the power plant exhaust, dissolved in the reinjection water and injected into the geothermal reservoir in what is called CarbFix and SulFix processes.

"To provide the necessary geothermal fluid for the power plant in time, up to three drill rigs were operating simultaneously. This is quite rare in geothermal projects."

Kristinn Ingason, Head of Section, Geothermal Energy, Iceland

Transmission of energy – benefitting the locals

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 pipeline. From there, the water gravitates to the storage tanks of the district heating system close to Reykjavik from where it is distributed to the consumers in Reykjavik and the neighbouring municipalities.

Circular economy at its finest

Next to the power plant, the plant owner and operator, ON Power, owns Jarðhitagarður (Geothermal Park). The Geothermal Park encompasses a wide range of operations by third-party operators that utilise the resources of the geothermal plant. This way, the use of the energy resource is maximised, and waste is minimised to benefit the environment and create value from resources that would otherwise be discarded. The resources available are electricity, cold water, hot water, steam and carbon dioxide from the adjacent geothermal plant.

The park is a prime example of a circular economy where CarbFix and Climeworks capture CO₂ and store it by pumping it underground where it mineralises. VAXA Impact Nutrition’s algae cultivation production facility converts clean energy into food, producing the most sustainable crop in the world: microalgae rich in Omega-3 and protein. GeoSilica produces a 100% natural silica mineral supplement from geothermal fluids used in the power plant.