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Geothermal energy: a large increase in utilisation in recent years and an enhanced utilisation ratio for electricity generation

13.12.2010

Geothermal utilisation has increased significantly in recent years with the establishment of new geothermal power plants.  At the same time, the utilisation ratio of primary energy for electricity generation has increased considerably.

In 2008, the total primary energy use of geothermal was 144.2 PJ, out of which geothermal power plants accounted for 114.5 PJ and district heating utilities in low-temperature areas for 25.2 PJ.  The primary energy use of geothermal power plants increased by 237% between 1998 and 2008, while the use by district heating utilities in low-temperature areas increased by 21%.

The utilisation ratio of primary energy in Icelandic geothermal power plants for electricity generation has increased steadily over the years, and was about 12% in 2008.  For comparison the value was 7% in 1998.  The main reasons for this increase can be attributed to the following: 

primaryenergy_report_2010

1.  The Svartsengi and Nesjavellir CHP plants were originally designed with the purpose of hot water production for district heating.  This resulted in a considerable portion of produced high enthalpy fluids on a country-wide scale not being used for electricity generation.  Over time, the ratio of high enthalpy fluid used directly for electricity production has increased steadily and today hot water for district heating from these CHP plants is primarily produced from waste heat from the electricity generation process. 

2.  The average enthalpy of geothermal fluid for electricity generation in Iceland has been on the rise over the last few decades. Thus, the average enthalpy of produced geothermal fluid was 1150 kJ/kg in 1970, but had increased to 1577 kJ/kg in 2008.  Greater efficiency can be expected in the thermal electricity generation process with higher fluid enthalpy. 

3.  The conversion efficiency of the electricity generation process of new power plants is higher than that of older plants due to technological progress and improved management of geothermal fluids.  Losses have been cut by increasing the number of separators and separation steps, thereby enhancing efficiency.

 

The information described above appears in a report recently published by the National Energy Authority, titled: "Primary energy use of geothermal power plants and district heating utilities in Iceland until 2009". The report is only available in Icelandic.