| Title | Greenhouse Gas Emissions from New Zealand Geothermal: Power Generation and Industrial Direct Use |
|---|---|
| Authors | K. McLean, I. Richardson, J. Quinao, T. Clark, L. Owens |
| Year | 2020 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Carbon dioxide, methane, greenhouse gas, geothermal, emissions, direct use |
| Abstract | Greenhouse gas emissions for geothermal power stations in New Zealand are reported annually under current regulations. The CO2 and CH4 emissions data are combined and reported as one CO2-equivalent (CO2e) emissions factor. In combination with the amount of steam used each year, and the MWh (net) of electricity generated that year, the overall geothermal emissions intensity for each power station can be calculated as gCO2e/kWh(net). A recent study presented the emissions intensity for the 12 major geothermal power stations in New Zealand focusing on the calendar year 2018, with data back to 2010 for some stations. In this paper the emissions intensity is presented for the calendar year 2019, and compared with trends from previous years. In New Zealand the emissions intensity for geothermal power generation is on average an order of magnitude lower than for fossil fuels. In most cases the geothermal emissions intensity numbers are calculated assuming that all of the CO2 and CH4 present in the steam entering the power station are released to the atmosphere during the power generation process. However in some geothermal plant designs a fraction of the gases are retained in the condensates, which are reinjected back into the reservoir. Accounting for the gases in the condensates results in a more accurate calculation of the actual emissions intensity. Another nuance of the emissions intensity for geothermal is that the numbers do not account for the benefits of geothermal fluids for direct use applications such as industrial process heat. Direct use projects utilise energy directly, as thermal energy, which is not accounted for in the emissions intensity data which only deals with electrical energy. Nevertheless the benefits of geothermal direct use are a very real, if invisible, part of the geothermal emissions intensity story, and examples are given. |