Cumulative energy, emissions, and water consumption for geothermal electric power production

Abstract

A life cycle analysis has been conducted on geothermal electricity generation. The technologies covered in the study include flash, binary, enhanced geothermal systems (EGS), and coproduced gas and electricity plants. The life cycle performance metrics quantified in the study include materials, water, and energy use, and greenhouse gas (GHG) emissions. The life cycle stages taken into account were the plant and fuel cycle stages, the latter of which includes fuel production and fuel use (operational). The plant cycle includes the construction of the plant, wells, and above ground piping and the production of the materials that comprise those systems. With the exception of geothermal flash plants, GHG emissions from the plant cycle are generally small and the only such emissions from geothermal plants. Some operational GHGs arise from flash plants, and though substantial when compared to other geothermal power plants, these are nonetheless considerably smaller than those emitted from fossil fuel fired plants. For operational geothermal emissions, an emission rate (g/kW h) distribution function vs. cumulative capacity was developed using California plant data. Substantial GHG emissions arise from coproduced facilities and two other "renewable" power plants, but these are almost totally due to the production and use of natural gas and biofuels. Nonetheless, those GHGs are still much less than those from fossil fuel fired plants. Though significant amounts of water are consumed for plant and well construction, especially for well field stimulation of EGS plants, they are small in comparison to estimated water consumed during plant operation. This also applies to air cooled plants, which nominally should consume no water during operation. Considering that geothermal operational water use data are scarce, our estimates show the lowest water consumption for flash and coproduced plants and the highest for EGS, though the latter must be considered provisional due to the absence of field data. The EGS estimate was based on binary plant data. V C 2013 American Institute of Physics. [http://dx.

Life cycle greenhouse gas emissions from geothermal electricity production

“…5,14,15 Briefly, when comparing different power generating technologies during the operational stage of a plant, it is customary to consider only fossil fuel consumption. e fc is generally substantial for fossil (including nuclear) plants, zero for renewable power technologies, and intermediate for hybrid plants, which are a combination of renewable and fossil technologies.…”

“…In a study of U.S. plants, Bloomfield et al 3 reported a weighted average emission rate of 91 g/kWh for CO 2 . However, to account for all relevant GHGs, Sullivan et al 5 computed the effect of methane (CH 4 ) emissions also reported in the Bloomfield study, and revised their CO 2 emission rate up to 105 g/kWh of CO 2 equivalent (CO 2 e) GHGs. Further, because Bloomfield et al 3 values are capacity weighted averages that include binary plants (14% of total capacity) which they rightfully assumed have no GHG emissions, Sullivan et al 5 further revised GHG value up to 127 g/kWh for CO 2 e (106 g/kWh for CO 2 only).…”

“…Unfortunately, with the exception of California, there are few publicly available data sets for GHG emissions from U.S. geothermal power plants. In a previous study, 5 we reported for California geothermal power production preliminary values of geothermal power GHG emissions including a running capacity weighted average (98 g/kWh) and an emission rate vs. cumulative running capacity distribution function (CDF). The data employed were taken from California Environmental Protection Agency's (CEPA) website 8 and the Energy Information Agency.…”

A simplified model for the estimation of life-cycle greenhouse gas emissions of enhanced geothermal systems

“…-The case study presented by Sullivan et al (2013) proposes a 20 MW EGS power plant equipped with 10 boreholes. Such characteristics are not considered in our variability ranges since the upper boundaries are set to 3.5 MW and three wells.…”

“…The functional unit is the net energy produced over the life cycle, which means that the results will be expressed in terms of grams of CO 2 equivalent per electrical kWh delivered to the grid. EGS power plants, being binary systems, do not generate direct GHG emissions related to the energy production unlike their hydrothermal flash and dry steam counterparts (Sullivan et al 2013). Life cycle emissions are principally caused by the construction phase.…”