Title:

Greenhouse Gas Emissions from Geothermal Power Production

Authors:

Thrainn FRIDRIKSSON, Almudena MATEOS, Yasemin ORUCU, Pierre AUDINET

Key Words:

geothermal greenhouse gas emissions, GHG, World Bank, natural processes affecting GHG emissions, effects of production on GHG emission, knowledge gaps, ex ante estimation guidelines

Conference:

Stanford Geothermal Workshop

Year:

2017

Session:

General

Language:

English

Paper Number:

Fridriksson

File Size:

1030 KB

View File:

Abstract:

Geothermal power production may result in significant greenhouse gas (GHG) emissions. GHG emissions from geothermal power production, mostly in the form of CO2, are generally low in comparison to traditional base load thermal energy power generation. However, as the geothermal sector has expanded, a wider range of geothermal resources have been brought into exploitation, including geothermal systems with relatively high GHG concentrations in the reservoir fluid. Recent data from Italy (Mt. Amiata) and a number of sites in Turkey show that GHG emissions from geothermal power plants can be higher than 500 g/kWh and in some cases higher than 1000 g/kWh or on par with or higher than emissions from coal fired power plants. The best estimate for a global average CO2 emission factor from geothermal plants is 122 g/kWh from Bertani and Thain (2002). Recent CO2 emission factors for Iceland (2012), California (2014), New Zealand (2012), and Italy (2013) were 34, 107, 104 and 330 gCO2/kWh, respectively. Data to calculate the contribution of CH4 to geothermal GHG emissions are only available for New Zealand, where this amounts to 18.3 gCO2e/kWh. These national (and state-wide) average emission factors are all lower than typical emission factors for natural gas power plants (around 450 g/kWh) illustrating that, on average, geothermal plants emit significantly less GHG compared to fossil fuel fired thermal plants. A number of processes can affect the amount of GHGs released from geothermal power plants over time. These can be natural processes, such as when magmatic events cause temporary influx of CO2 into a geothermal reservoir resulting in increased GHG emission factors. In other cases, production from the reservoirs may result in changes in GHG emission factors from geothermal power plants. This can result in decreased emissions with time, such as when return of gas-free reinjection fluid dilutes the pristine geothermal fluid or when progressive boiling of the same fluid results in gradual degassing. On the other hand, formation of a steam cap at shallow levels in geothermal reservoirs may result in temporary increase in gas content of steam produced from shallow levels and causing an increase in GHG emission factors for the power plant. More project data are needed to allow better understanding of how GHG emissions from geothermal power plants evolve with time. The effects of geothermal power production on diffuse CO2 emissions through soil are still not fully understood and may vary drastically in different types of geothermal systems. In Reykjanes, Iceland, diffuse CO2 emissions have increased fourfold from the commissioning of a 100 MW geothermal power plant in the field in 2006. Historical heat flow measurements from Wairakei, New Zealand, suggest that power production also resulted in increased CO2 emission through the soil in that field. In Larderello, Italy, the opposite occurred, i.e. geothermal power production has resulted in significant reduction of surface activity and thus GHG emissions through fumaroles and soil. It is vital for the geothermal sector to have as complete understanding of the environmental impacts of geothermal power production as possible. This includes not only measuring GHG emission factors at the commissioning of power plants, but also understanding how GHG emission factors change over time and how power production affects GHG emissions through soil. The World Bank and other Multilateral Development Banks are increasingly paying attention to these issues. The World Bank has recently developed a scheme to estimate, ex ante, GHG emission factors from geothermal power projects financed by the institution. The World Bank is encouraging developers that benefit from World Bank financing to collect project data that will allow improved understanding of these issues. The geothermal sector, as a whole, is encouraged to collect and publish more data that will improve the collective understanding of GHG emissions from geothermal power production and the underlying processes.


ec2-54-163-200-109.compute-1.amazonaws.com, you have accessed 0 records today.

Press the Back button in your browser, or search again.

Copyright 2017, Stanford Geothermal Program: Readers who download papers from this site should honor the copyright of the original authors and may not copy or distribute the work further without the permission of the original publisher.


Attend the nwxt Stanford Geothermal Workshop, click here for details.

Accessed by: ec2-54-163-200-109.compute-1.amazonaws.com (54.163.200.109)
Accessed: Thursday 28th of March 2024 12:51:38 PM