Integrated Geothermal Energy Systems for Small-Scale Combined Heat and Power Production: Energy and Economic Investigation

Abstract

In recent years, an increasing interest in geothermal energy has been registered in both the scientific community and industry. The present work aims to analyse the energy performance and the economic viability of an innovative high-efficiency geothermal-driven integrated system for a combined heat and power (CHP) application. The system consists of a heat exchanger (HEX) and a transcritical organic Rankine cycle (ORC) that work in parallel to exploit a high-temperature geothermal source (230 °C) and satisfy the energy demand of a commercial centre located in Southern Italy. The ORC and HEX sub-units can operate at partial load to increase the system flexibility and to properly react to continuous changes in energy request. A lumped model was developed to find the proper operating conditions and to evaluate the energy production on an hourly basis over the whole year. In particular, a multi-variable optimisation was implemented to find the most suitable configuration and a 101.4 kWel ORC was selected while the HEX nominal power was 249.5 kWth. The economic viability of the integrated system was evaluated in terms of net present value and payback period and different operating strategies were compared: thermal-driven, electric-driven, and a mixed strategy. The latter turned out to be the best solution according to both energy and economic criteria, with electric and thermal self-consumptions larger than 90%, with no heat dumping and a payback time close to five years.

The Potential of Ecological Distributed Energy Generation Systems, Situation, and Perspective for Poland

“…According to the experts, small-scale geothermal energy systems could build ecological distributed powerplants in countries that are rich in geothermal sources. This point of view has also be seen in recent publications [56,57].…”

Integration of biodiesel internal combustion engines and transcritical organic Rankine cycles for waste‐heat recovery in small‐scale applications

“…The reference efficiencies for separate electric and thermal production are equal to 44.2% and 85%, 77 respectively, and the efficiency of the auxiliary boiler is set to 90%. 79 The lower heating values of the natural gas and biodiesel are 35.9 MJ/Sm 3 and 36.9 MJ/kg. The investment period is fixed to 20 years, and the interest rate is 3%.…”

Sensitivity Analysis of Transcritical CO2 Cycle Performance Regarding Isentropic Efficiencies of Turbomachinery for Low Temperature Heat Sources

“…The pinch point temperature differences (∆T pp ) in heat exchangers were all assumed at 5K [30,37]. The location of the pinch point in the heater was kept at its outlet or equivalently, the expander inlet, to obtain the theoretically highest expander inlet temperature (T 3 ) under the ∆T pp restriction [11,17,21,31]. η p and η e were initially set at 65% and will be gradually increased to 95% afterwards.…”

“…Steam-based power plants cannot efficiently utilize such low temperature heat sources due to the high evaporation temperature of water [8,12]. Organic Rankine cycles (ORC) have been widely adopted in geothermal fields and industrial waste heat recovery systems with low-to-medium temperature heat sources [11][12][13][14][15][16][17]. However, the inherent high global warming potential (GWP) of the organic fluids that are commonly used in existing ORCs (i.e., R134a, R245fa) have imposed uncertainties on their future development [2,18].…”