COMBINED HEAT AND POWER GENERATION BY ENHANCED GEOTEHRMAL SYSTEMS: COMPARISON OF DIRECT AND INDIRECT CONCEPTS FOR WATER AND SUPERCRITICAL CO2 AS HEAT CARRIERS

Enhanced Geothermal Systems (EGS) contain a tremendous technical potential without major regional restrictions. Over the last years, several studies proposed the application of supercritical CO2 (sCO2) as a heat carrier for the utilization of geothermal resources as a promising alternative to the usage of water. The existing studies focus only on sole power generation projects. However, the current development of the geothermal sector in Europe increasingly emphasizes the combined heat and power production. Consequently, the annual available heat flow for power generation might differ significantly due to the varying heat demand. Thus, an assessment of the potential different power plant types for EGS should consider the part load characteristic of the different concepts. This work compares a thermosiphon with direct utilization of sCO2 for power generation and a pumped brine system with power generation by an Organic Rankine Cycle. The comparison is carried out for defined reservoir conditions of 180°C and 49 MPa. The power generation through an ORC with R245fa displays the highest amount of produced net power during one year. For the ORC with R245fa the annual amount of net electricity is 10 % higher than for the ORC with R1233zd(E) and 11 % higher than for the sCO2 case. The net power of the sCO2 plant displays a significantly higher sensitivity to changes of the heat demand in comparison to brine systems with ORCs. The comparison of the ORC with R1233zd(E) and the sCO2 thermosiphon shows a varying advantageousness depending on the current heat demand. During winter days the net power of sCO2 is 6 % higher than for the R1233zd(E) ORC, whereas during periods with low heating demand the achievable net power is 4 % lower.     «

Enhanced Geothermal Systems (EGS) contain a tremendous technical potential without major regional restrictions. Over the last years, several studies proposed the application of supercritical CO2 (sCO2) as a heat carrier for the utilization of geothermal resources as a promising alternative to the usage of water. The existing studies focus only on sole power generation projects. However, the current development of the geothermal sector in Europe increasingly emphasizes the combined heat and power...     »