Carbon Dioxide Emissions from Geothermal Power Plants

Abstract Geothermal is commonly considered to be a clean, green energy source but it does produce some greenhouse gas emissions, particularly CO2. The amount of CO2 is usually measured as an emission intensity of kg of CO2 emitted per MWh of electricity produced. However, the quantity that is measured for the calculation of emission intensity is the waste CO2 in the separated steam that feeds the power plant. In terms of total CO2 emissions this is only part of the picture as there is a natural outflow of CO2 into the atmosphere at most geothermal systems and this natural outflow is affected by the operation of a power plant. The correct measure of CO2 emissions is the extra CO2 output resulting from the operation of the power plant. Here we discuss a computer modelling study of the Ohaaki (New Zealand) geothermal project and show that during the lifetime of the project extra CO2 is emitted but after the project is shut down the emission of CO2 is reduced below its natural level and viewed over a long time period (300 years) there is no extra CO2 emitted as a result of the operation of the Ohaaki power plant.