The impact of the ambient conditions and component’s part-load behaviour on the actual annual power output of CO2-Plume Geothermal (CPG) systems

Abstract

Subsurface reservoirs play an important role in decarbonizing the energy sector, be it through geothermal energy production or carbon capture and storage (CCS). In recent years, there has been an increasing interest in CO2-Plume Geothermal (CPG), which combines CCS with geothermal, using CO2 instead of water as a subsurface heat and pressure energy carrier. CO2 as a subsurface working fluid is more efficient as it has a higher mobility (inverse kinematic viscosity) and its large thermal expansion coefficient results in a thermosiphon effect that reduces the pumping power required. CO2 can also be directly utilized in a turbine for power generation. Furthermore, since CPG systems are added to full-scale CO2 Capture and Sequestration operations, all of the initially injected CO2 is ultimately stored. CPG therefore constitutes both CO2 Capture Utilization as well as Storage (i.e. CCUS). In recent years, CPG has experienced increasing interest from academia and industry. Several in-depth studies have assessed the impact of various parameters such as the geothermal gradient, wellbore diameter or reservoir permeability on the CPG performance. However, these studies have not evaluated the potentially significant impact of the varying ambient conditions on the CPG performance profile. The potential effect of the air temperature on the CPG performance has only been discussed in a paper by Adams and Kuehn (2012) and in a more recent work by van Brummen et al. (2022), but without considering the the off-design behaviour of the main components, such as the turbine or compressor. This contribution assesses and discusses how the CPG performance profile might vary across several geographical settings and how the design point of the CPG components affect their achievable net power outpt. Therefore, valuable insights regarding the most attractive settings for future CPG systems can be drawn.