GREENHOUSE GAS EMISSIONS FROM NEW ZEALAND GEOTHERMAL POWER GENERATION IN CONTEXT

Abstract

Conventional geothermal systems are complex natural features, usually comprising a deep heat source such as a magma chamber, and above this a convecting system of hot water/steam. There are often natural features at the surface indicating the presence of these geothermal systems underground, including fumaroles, hot springs, geysers and steaming ground. There are many geothermal fields in New Zealand, mostly associated with volcanism within the extensional Taupo Volcanic Zone of the North Island.
From these geothermal surface features, there is a significant natural flux of CO2 and methane (CH4) through the ground surface and into the atmosphere. These gases are transported to the surface by hot geothermal fluids, though the original source of the gases is not yet known and is the subject of current research by GNS. When geothermal fields are developed for electricity generation, CO2 and methane are released during the power generation process, while the natural flux of these gases is thought to diminish.
CO2 and methane emissions data during plant operation (combined as CO2-equivalent) are presented for the major geothermal plants in New Zealand. There is a focus on the most recent emissions for the calendar year 2018, followed by a review of how these emissions have changed over the period 2010-2018. The tendency of geothermal emissions intensity to decrease over time is shown, as well as the effect of plant/operational changes. The geothermal emissions intensity is compared to typical values for other clean energy sources, and also to fossil fuels.