CO2 Plume Geothermal (CPG) Systems for Combined Heat and Power: Opportunities and Challenges


Christopher SCHIFFLECHNER, Christoph WIELAND, Hartmut SPLIETHOFF, Martin O. SAAR

Key Words:

CO2 Plume Geothermal Systems, CPG, Deep Geothermal Energy, Combined Heat and Power Generation, CCUS


Stanford Geothermal Workshop




Emerging Technology



Paper Number:


File Size:

899 KB

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In recent years, there has been an increasing interest in CO2 Plume Geothermal (CPG) systems, which is an attractive approach to combine CCS with geothermal energy production. Applying CO2 as the heat carrier fluid can be more efficient than water since it displays higher mobility and a higher thermal expansion coefficient. While CPG systems are highly attractive for sole electric power generation in former oil and gas fields, they could also be applied in regions with higher population densities for combined heat and power generation (CHP). To increase public acceptance and support the decarbonization of the heating sector, CHP CPG systems might be an attractive concept for selected CPG sites. This work investigates the potential benefits and challenges of CPG systems for CHP applications compared to geothermal systems using water/brine as the subsurface heat carrier. Two different CPG CHP configurations are evaluated for a reference case with a depth of 4.5 km and a required district heating network supply temperature of 80°C. The application of a CHP system reduces the achievable net power output compared to a sole power generation system. While a thermosiphon system displays a net power reduction of 11 %, a significantly higher net power output decrease of around 32 % can be observed for a pumped CPG system. Comparing both investigated CHP options reveals the favorability of a CHP layout with heat extraction on an intermediated pressure level. Thus, despite the higher plant complexity, this option can result in significantly higher power output and achievable revenues. Furthermore, the required reservoir depths for both water and CO2 are evaluated concerning different district heating supply temperatures and heat demand as well as geothermal gradients. Depending on the assumed boundary conditions, a CPG system requires a higher reservoir depth between 800 and 1100 m compared to a system using water as a heat carrier. Thus, CPG CHP can only be applied to locations with promising geological settings in a sufficient depth.

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