Carbon Negative Geothermal: advanced energy cycle featuring geothermal with bioenergy and carbon capture and storage

Abstract

Geothermal energy has proven to be a reliable baseload resource with much lower emissions intensities on average (~122 gCO2/kWh) than fossil fuel plants. However, the majority of global geothermal resources are classified as low enthalpy systems with reservoir temperatures less than 160°C, which are often not well suited for electricity generation. The combination of geothermal energy with bioenergy and carbon capture and storage (BECCS) could address this challenge by boosting renewable power output from geothermal resources, including for lower enthalpy systems. In addition, this energy cycle results in net negative carbon emissions, which could be a valuable pathway for emissions reduction in the energy sector. In this work, we classify what constitutes geothermal-BECCS and quantify its potential for electricity production and decarbonisation in accordance with global climate targets.

BECCS technologies are prominently featured in cost-effective emissions reductions pathways. Pairing geothermal energy with BECCS could limit energy loads and costs for feedwater preheating, with reinjection wells serving as cost effective sequestration apparatus. Here, we present results from a systems model that characterizes key thermodynamic phenomena for four potential geothermal-BECCS configurations. This model allows us to quantify conversion efficiency, sequestration potential, and provide a preliminary estimate of likely costs.

For low enthalpy geothermal systems, geothermal-BECCS can improve power production by over 17 times that of conventional flash and binary plants. Additionally, geothermal-BECCS plants could exhibit operational emissions intensities between -191 gCO2/kWh to -711 gCO2/kWh, offsetting between 45% to 172% of the emissions from a standard natural gas plant.