Engineers Work to Cut Costs and Emissions in Geothermal Power

Geothermal energy is a promising method of producing heat and electricity, since it is renewable and can provide constant power.  According to Iceland's National Energy Authority, 85 percent of the country's energy comes from renewable sources.  Geothermal power provides 66 percent of Iceland's energy and a quarter of the country's electricity.

However, the technology has high upfront costs, finding adequate geothermal resources can be a risky investment, and some instances of geothermal power emit greenhouse gases.  In parts of the world, geothermal energy can emit more carbon dioxide than coal.

The CarbFix project at Hellisheiði tackles the emissions side of geothermal energy.  The plant produces 303 megawatts of electricity and 133 MW of hot water, and in 2012, engineers began reinjecting carbon dioxide and hydrogen sulfide into geothermal wells at wellheads covered with geodesic domes instead of allowing these gases into the air.

The goal was to get basalt rocks rich in calcium and magnesium to react with the injected gases to form calcium carbonate limestone, permanently locking emissions away.  In nature, this process can take thousands of years, but engineers set out to create conditions that would make it happen in five.

The results showed the mineralization was even faster.

"What I really like about the CarbFix solution is using the natural processes," said Edda Sif Pind Aradóttir, project manager for CarbFix at Reykjavik Energy.  "After two years, it's just rock, and it stays that way."

Aradóttir and her team published their findings last month in the journal Science.  The project started out injecting 250 tons of carbon dioxide in 2012 and ramped up to 5,000 tons in 2014.

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