Life cycle inventory of a flash geothermal combined heat and power plant located in Iceland

This paper presents a life cycle inventory (LCI) describing the material and energy demands for constructing and operating a geothermal combined heat and power (GCHP) plant as well as direct emissions of gases, waste water, and waste heat. The data are based on a newly constructed GCHP plant in Iceland, representing the design of both single flash (SF) and double flash (DF) power plants that currently produce the majority of electricity from geothermal plants worldwide.

Primary data were collected for the construction, operation, and maintenance of a GCHP plant. As the design and operation of geothermal flash power plants is site-specific due to the different nature of geothermal resources, a method of scaling data to a site specific parameter is proposed to make the LCI available as representative secondary data for such plants. These parameters along with other data identified as site-specific serve as the minimum data to be collected for adjusting the presented data to represent other flash power plants with or without combined heat production.

The construction stage dominates the material burdens for the electricity and heat production. For the life cycle of electricity, it includes 80 % of diesel fuel use (whereof 96 % originates from well drilling), while 99 % of groundwater is used during the operational stage. The use and composition of geothermal fluid is site-specific but accounts for all direct emissions from the electricity production. The main materials in terms of mass used for the construction of the GCHP plant are water, diesel, steel, cement, asphalt, bentonite, and silica flour. Mineral wool and aluminum were also among the main material contributors. Material and energy burdens per functional unit are generally higher for a SF plant compared with DF plants. For heat production, 1.7 MJ of waste heat from power generation is used to produce 1 MJ of usable heat.

By presenting LCI data scaled with site-specific parameters, the flexibility of its use is increased as secondary data. However, the collection of primary data for the composition of geothermal fluid and values for site specific parameters is always required to represent local conditions. Thus, the LCI for Hellisheiði GCHP can be regarded as representative data for electricity and heat from geothermal flash power plants.