In the midst of a raging blizzard, the superheated mudpots of Hverir spit and bubble with relentless energy. The snowladen air is filled with the sulphurous stench of rotten eggs, while the lifeless ground boasts a garish array of mineral salts. As Iceland’s otherworldly landscapes go, this geothermal hotspot in the country’s northeast is one of the strangest and most primeval.
It was around 24 million years ago that Iceland first rose from the ocean as a collection of volcanoes spewing lava and gas. Perched atop the rift between the divergent North American and Eurasian tectonic plates, this north Atlantic island of fire and ice is still shaped by hugely powerful subterranean forces. Eruptions, earthquakes, mud pools, fumaroles and spouting geysers are all part of daily Icelandic life.
Given the vast amounts of energy flowing just below the ground, it’s little wonder that Iceland is now pushing the boundaries of geothermal technology and resource use. While naturally hot water has long been harnessed by Iceland’s inhabitants, it wasn’t until the oil and gas price hikes of the 1970s that the island began to use it to produce electricity. Four decades later, geothermal resources now generate a quarter of Iceland’s electrical power (the rest coming from hydropower), as well as meeting the heating and hot water needs of almost every building in the country.
On the face of it, Iceland appears to be sitting pretty with regard to renewable energy supplies. However, the country’s geothermal resources aren’t quite as clean, green or limitless as you might imagine. As geothermal technology continues to develop and Icelandic companies look to further tap the country’s tectonic maelstrom, a growing number of Icelanders are viewing geothermal energy with a jaundiced eye.
Hot spot Iceland’s abundant geothermal resources are a result of its unique geology and geography. Sitting above a shallow plume of molten material, the island is home to around 130 extremely active volcanoes that have been responsible for a third of the total global lava output over the past 500 years.
With so much magma lying close to the surface, Iceland’s geothermal gradient is unusually high. While the Earth’s average gradient is around 35°C per kilometre, in some parts of Iceland it can exceed 200°C per kilometre. This means that huge subterranean reservoirs of water – continually refilled by high levels of precipitation – are heated to more than 400°C. It’s this energy that’s tapped to generate electricity and to provide heat for commercial and residential building.
Iceland’s geothermal areas are divided into high- and low-temperature reservoirs. With temperatures of at least 150°C at a depth of one kilometre, high-temperature reservoirs are only found close to the plate boundary, which runs from the southwest to the northeast of the island.
Most of these reservoirs are laden with concentrated gases and minerals, rendering them unsuitable for heating and bathing. However, the steam and superheated water they contain can be brought to the surface and used to drive the turbines of electrical generators.
Iceland currently has five major geothermal power plants with a combined installed capacity of about 575 megawatts. The largest of these (indeed, the world’s largest) is at Hellisheidi, in the southwest. Operated by the publicly-owned Reykjavik Energy, it started electricity generation in 2006 and today lies at the heart of a complex debate over Iceland’s geothermal future. Out of steam Although Hellisheidi had a capacity of 303 MW when construction was completed in 2011, its electricity generating capacity is already declining. By last year, it had dropped to 276 MW, and scientists estimate that will continue to fall at a rate of 6 MW per year unless further boreholes are drilled.
‘Hellisheidi was built in a reckless way,’ says Árni Finnsson, chairman of the Iceland Nature Conservation Association. ‘The period leading up to the financial crisis in 2008 was one of great hubris for Iceland’s geothermal industry. Plants that came online were over-committed to providing electricity to aluminium smelters – they over-exploited the geothermal resources on hand and now they’re paying the price.’
The Hellisheidi situation neatly illustrates what can happen when too much energy is removed from a geothermal system. ‘The long-term commercial viability of geothermal power generation depends on the ability to extract heat in a thermally sustainable manner,’ Finnsson explains. ‘Studies have shown that the overuse of geothermal resources degrades reservoirs permanently, or for significant lengths of time. This is what has happened at Hellisheidi.’
Reykjavik Energy contends that the decrease in output was, in fact, predictable. ‘Drawdown at the Hellisheidi site has been as expected and within official permits,’ says the company’s head of communications, Eiríkur Hjálmarsson. ‘The productive area proved narrower than modelling had previously shown. To pursue sustainable operations, more steam will now be gathered farther away from the plant, from very promising boreholes drilled in 2008 and 2009.’
However, not everyone is convinced that this is the way forward. ‘Compared to the geological time scale of oil regeneration, geothermal energy is relatively renewable,’ says Miriam Rose, a geologist at Reykjavik-based NGO Saving Iceland. ‘But geothermal energy can’t truly be called a renewable energy source and boreholes need to be decommissioned after a few decades. Using geothermal energy to power large-scale industry, such as aluminium smelters that require hundreds of megawatts of energy, is certainly not sustainable or renewable.’
44 | October 2014