C02 Fluxes from Geothermal Systems: Assessing the Effects of Exploitation, and the Carbon Tax Implications

Abstract

The total flow of CO2 from geothermal systems to the atmosphere has rarely been measured, and probably never directly assessed. The natural fluxes from fields need to be measured, or otherwise assessed, and the effects of exploitation on these fluxes quantified, if fair and defensible carbon tax liabilities are to be imposed. The exploitation of geothermal energy releases greenhouse gases and causes disturbances to the natural flows, but these need to be quantified, both during the term of the exploitation and in the longer term. In 1992, attempts were made to measure the flows from three sites above geothermal systems in the Taupo Volcanic Zone. The data obtained gives important information on the range of fluxes at different sites, and on the variability of the flows in response to atmospheric variables and biological activity in the soils. The range of fluxes ascribable to geothermal C02 emissions ranged from 0.5 to 3 g/mí at Wairakei and Tauhara and up to 15-25 g/m2 at a hot site Reporoa. These values are higher than has been obtained elsewhere. The implications of these measurements and observed changes in heat and steam fluxes from exploited geothermal systems are that the induced increase in greenhouse gas releases to the atmosphere is very much underestimated.