Steam obscuring the Hengill geothermal area

Iceland: powered by the planet

Iceland leads the world in production of geothermal energy, with no fewer than six power stations generating electricity from Earth's natural heat. We take a tour to see what's keeping Iceland's lights on.

In his 1864 science fiction classic, 'A Journey to the Centre of the Earth', Jules Verne depicted Iceland as his imagined gateway into the planet's interior. Approaching Hellisheidi Geothermal Plant, only a 30-minute drive from the Icelandic capital of Reykjavik, Verne's idea seemed strikingly fitting. Vast plumes of thick grey vapour frothed into the sky almost completely obscuring the mass of pipes and funnels that make up the main power station building. Surrounding the site, smaller plumes spewed from the hillsides, which were streaked in places with vibrant mineral colours. The noise from the plumes was a constant visceral thunder and everywhere the hellish stench of sulphur was overwhelming. Strange geodesic dome structures scattered around the landscape lent the site the appearance of an eerie moon base.

Of course, Iceland does not provide an entrance into the Earth's interior as Verne imagined, but it is unmistakable that the innards of the planet are very close to the surface here. The country is pocked with more than 200 volcanoes, over 600 hot springs and at least 20 designated high-temperature areas that contain steam fields. The island is, after all, a small outcrop of porous basalt in the centre of the North Atlantic sitting directly over a crack in the planet's crust where the North American and Eurasian plates pull apart from each other at a rate of 2cm per year. New crust is constantly being formed to fill the gap, making Iceland one of the few places in the world where 'seafloor spreading' is visible on land. This intense geological activity, combined with large underground water reservoirs replenished by the country's high annual precipitation rates, makes Iceland extremely well-suited for producing geothermal energy.

Ever since the country's early settlement in the ninth century, geothermal energy in the form of hot springs has been used for bathing, laundry and sometimes cooking. But it wasn't until 1908 that the first larger-scale attempts to harness geothermal energy were made. Eventually, it was the 1970s oil crisis that prompted Iceland to seek a permanent alternative to its dependence on expensive imported fossil fuels and which subsequently sparked the birth of the country's geothermal industry.

Iceland is now considered to be a world leader in the exploitation of geothermal resources. With a small population of around 320,000 people, the country is currently the world's top producer of geothermal power per capita. According to Orkustofnun, the national energy authority of Iceland, the installed generation capacity of geothermal power plants in the country totalled 665MWe in 2013. The electricity production was 4,600GWh, or 24.5 per cent of the country's total electricity output.

Combined heat and power

Hellisheidi Geothermal Plant is the largest of Iceland's six geothermal power stations and one of the largest geothermal facilities in the world. Since reaching full production capacity in 2010, Hellisheidi has produced 303MWe of electricity per year (accounting for nearly half of Iceland's total geothermal production) and 133MWth of thermal energy annually in the form of hot water.

The power plant draws its energy from 57 geothermal wells spread across the local area. Each borehole is excavated using a 500-ton drill with a bit embedded with industrial diamonds to cut through layers of volcanic tuff. The boreholes extend some 3km into the bedrock to access water and steam at temperatures of up to 300°C. Each of the odd-looking geodesic dome structures scattered around the power station covers a well-head. Any excess steam from the borehole is released into the air from the domes but must first pass through a 'muffler' that lowers the pressure of the steam in increments. Otherwise the noise caused by the release of high-pressure steam would be 'at the threshold of pain'.

Hellisheidi is a flash steam combined heat and power plant. This is distinct from a binary geothermal plant which would utilise steam to heat a secondary fluid to drive turbines. Instead, at Hellisheidi, when the geothermal fluid is forced up the boreholes to the surface, liquid and steam are separated. The steam is processed to reduce its corrosive properties and used to drive seven 45MW high-pressure turbines and one 33MW low-pressure turbine for electricity production.

Meanwhile the liquid component of the geothermal fluid is too toxic to be used directly as hot water, so it is used to warm fresh cold water sourced from elsewhere. The fresh water is warmed to a temperature of 82°C and piped 27km above ground to Reykjavik. During the journey the water loses only a few degrees of temperature, therefore a proportion of the supply is artificially cooled for safety before it is piped directly into homes as hot water.

However, the largest component in the direct use of geothermal energy within Iceland is space heating. In 2011, the total use of geothermal energy was 42.2PJ, with space heating accounting for 45 per cent. It is estimated that 89 per cent of households in Iceland use geothermal resources for space heating and hot water, and the number is rising. In addition, 138 of the 169 recreational swimming pools in the country use geothermal heat. But perhaps the most telling indication of Iceland's wealth of heating resources is the fact that 1420TJ of geothermal energy per year is used in snow-melting systems under pavements, car parks and driveways. Such systems had already been laid under a combined area of 920,000m2 by 2008, with at least a further 50,000m2 later added in the capital.

The numbers are large, but domestic and residential consumption of energy is far outweighed by industrial use. Some geothermal energy (up to 740TJ per year) is used by Iceland's greenhouse sector and in fish farming, but in 2013 the aluminium industry alone used 70 per cent of all electricity produced, compared with just 4.6 per cent residential consumption.

Many in Iceland hope that the country's abundance of cheap and relatively clean geothermally produced electricity will attract larger aluminium smelters and other power-hungry industries. Others have set their sights on the potentially lucrative export market. For a country still fighting to recover from economic collapse, it is easy to see why selling its excess energy to the 500 million consumers of the European Union for at least double the price it could fetch domestically would be an attractive prospect.

Export potential

In 2012 the UK and Iceland signed an agreement to investigate the possibility of establishing a high voltage direct current (HVDC) cable between the two countries, specifically for the export of electricity produced from renewable resources.

The submarine cable would be 1000km long, which is nearly twice the length of the world's current longest subsea HVDC cable between Norway and the Netherlands. The engineering challenges are obvious but if successful, the cable will have a capacity of 1.2GW, compared with NorNed's 700MW.

Iceland's President, Olafur Ragnar Grimsson, is a vocal supporter of the project, saying that it 'would enable us [Iceland] to get more profit out of what we have already created.' But not everyone agrees. A group of 11 environmental organisations have been warning of the enormous environmental impact the plan would have through the construction of new power plants and overhead power lines.

Popular blogger Lara Hanna Einarsdottir sums up the feeling against the cable, writing that Icelanders 'should supply ourselves and coming generations' rather than 'building more and more plants so that we can provide electricity to towns in Scotland.'

Fears of over-exploitation

Already, Icelandic national papers regularly carry stories about the hazards of excessive exploitation of geothermal resources. The fears focus on the risk that although geothermal sites are capable of providing heat for many decades, eventually specific locations may cool down, particularly if overused. If the energy of a well is tapped in large enough quantities, without allowing enough time for the bedrock to replenish its heat, a hot-spot can go cold.

Arni Finnsson, head of Iceland's Nature Conservation Association, claims that tapping geothermal resources too quickly could result in the underground hot water reservoirs that are necessary for power production running dry within 70 years. He warns that geothermal energy is 'not renewable if you use it to an extreme.'

Other local experts have estimated that a geothermal plant running on full capacity could deplete its heat source in as little as 50 years. Stefan Arnorsson, a geologist at the University of Iceland, adds further reason for caution. 'If you use energy at this capacity and it runs out in 50 years it won't replenish itself again in 50 years, or in one century or even two centuries,' he warns. 'It could take 1,000 years before that geothermal system becomes a resource again.'

Orkuveita Reykjavikur, operator of the Hellisheidi Geothermal Plant, has resolutely defended the 'renewable energy' status of geothermal power. It contends that by reinjecting used geothermal fluid and steam back into the bedrock it is ensuring a sustainable system. But even OR concedes in official material that 'excessive production from a geothermal field can only be maintained for a relatively short time'. It is the prospect of 'excessive production' that has the Reykjavik public concerned.

The disagreement over sustainable use of geothermal resources in Iceland has been exacerbated by controversial projects that aim to pioneer new techniques for exploiting geothermal energy: methods that could potentially increase production by an order of ten.

In 2000 a consortium of Icelandic energy companies, alongside Orkustofnun, launched the Iceland Deep Drilling Project (IDDP) to investigate the potential of tapping into geothermal resources at higher temperatures, deeper within the bedrock.

It is well known that pressure and temperature increase with depth in geothermal areas and that at a critical point the liquid and steam phases of water merge to produce a fluid called 'supercritical water'. By decompressing this supercritical water, it was proposed that it could be brought to the surface through boreholes as superheated steam at temperatures of up to 600°C at sub-critical pressures of less than 220 bar. Where a conventional borehole accessing geothermal fluid at 300°C typically yields a power equivalent of 5MWe, it was predicted that a borehole accessing fluid at supercritical conditions would yield a tenfold increase in power. However, accessing supercritical conditions would mean drilling much deeper than has ever been achieved before.

Deep drilling is both expensive and difficult. The world's deepest well is 12km, but in most geothermal areas accessing supercritical water would require drilling to 13km or more. Fortunately Iceland has an unusually high geothermal gradient and the consortium estimated that given a carefully selected site, supercritical conditions might be reached within as little as 5km of the surface.

Hitting magma

Drilling began on IDDP-1 at a site near the Krafla Geothermal Plant in northeast Iceland in 2009. The plan was to drill to depths of 4.5km but excavation came to an abrupt halt when the borehole penetrated magma at a depth of 2.1km. 'When we drilled into the magma the project was nearly over,' describes Guomundur Frioleifsson, head geologist at HS Orka, a member of the IDDP consortium. 'Fortunately, the project managers wanted to continue research to assess the feasibility of utilising the geothermal steam just above the magma pocket which reaches a temperature of 900°C.'

At the time there had only been one other recorded incident of drilling into magma. It occurred in Hawaii and the response had been to immediately plug the well with concrete. In Iceland, project managers decided to line the well with steel casing and concrete, adding a perforated section nearest the magma.

As steam began to flow through the well, engineers had to design new equipment and techniques to deal with the unprecedented high levels of pressure, temperature and corrosive chemical composition. But by 2012 the well-head temperature had risen to 450°C at pressures greater than 140 bar. This is the highest recorded well-head temperature in the world, making IDDP-1 the hottest geothermal well in history. With flow rates sufficient to produce 36MW of electricity (more than half the installed electrical capacity of the nearby Krafla Geothermal Plant), the project announced that it had created the very first Magma Enhanced Geothermal System. 'We are on the precipice of a new age in energy generation,' says Frioleifsson, with obvious excitement.

But not everyone was overjoyed by this unexpected scientific serendipity. One of the techniques employed in establishing the IDDP-1 geothermal well was to pump cold water into the borehole, which fractured the hot, dry rock close to the magma by cooling it. The breaking up of the rock increased permeability, which is typically low at such high temperatures.

Elsewhere in the world too, particularly in the US, Australia and Japan, attempts to create Enhanced Geothermal Systems (EGS) have involved pumping cold water into hot dry rock at depth before retrieving it as heated water and steam through nearby boreholes. The process is usually accompanied by the injection of high-pressure water to break up the rock. This increases permeability, allowing greater circulation of the water and thereby, better results. Known as hydro-fracking (or sometimes geothermal fracking), it is a method borrowed from the oil and gas industry.

Given the publicity that surrounds fracking, it is perhaps unsurprising that questions are being raised as to whether hydro-fracking is subject to the same risks and hazards as those alleged to be concomitant with fracking for natural gas and oil. In particular, there are fears that an EGS using such methods could induce greater seismic activity in geothermal areas.

Microseismicity

A research group within the Earthquake Engineering Research Centre of the University of Iceland in Selfoss has been investigating links between the exploitation of geothermal resources and seismic activity. They found that ever since operations at the Hellisheidi Geothermal Plant began in 2006, the reinjections of geothermal fluid, hot water and steam back into the geothermal reservoir have been accompanied by increased microseismicity. Furthermore, the sequence of induced seismic activity culminated in two ML3.8 earthquakes on 15 October 2011. These were severe enough to be widely felt in the neighbouring town of Hveragerdi, 12km away.

A more recent study conducted by the University of California in 2013 also found a strong correlation between seismic activity and operations for production of geothermal power in southern California that involve pumping water into and out of an underground reservoir.

This is in addition to the bizarre case of Markus Haring, a geologist based in Basel, Switzerland, who was charged with causing $9m worth of damage to buildings in 2006 when seismic analysis of a local earthquake revealed that the tremors centred on his EGS drilling project.

More research is being carried out to further quantify the connection between EGS and induced seismic activity.

Meanwhile, the potential energy gains of EGS continue to spark excitement in Iceland. Despite the distraction of the Magma-EGS at Krafla, the IDDP consortium has not abandoned its original aim of exploring the power generation possibilities of supercritical conditions. Preparatory work for the drilling of well IDDP-2 is scheduled to begin later this year at a site on the Reykjanes Peninsula in south-west Iceland. The plan is to bore down 5km to access the extensive Reykjanes geothermal system where supercritical conditions are believed to exist. Proposals are also under way for well IDDP-3 at a site within the Hengill geothermal area close to the Hellisheidi Power Plant.

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