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.
Highlights
Combined heat and power (CHP) generation presents several advantages in terms of lower costs, emissions, fuel consumption, and higher decentralised generation share as compared to conventional separate electric and thermal production [1,2,3]
The system consists of an organic Rankine cycle (ORC) for the electric production and a heat exchanger (HEX) able to provide the thermal energy
The two components work in parallel and simultaneously and the total geothermal mass flow rate can be arranged between the ORC and HEX units according to the user energy demand
Summary
Combined heat and power (CHP) generation presents several advantages in terms of lower costs, emissions, fuel consumption, and higher decentralised generation share as compared to conventional separate electric and thermal production [1,2,3]. During the last few years, the research community and the industry have been focusing increased attention on renewable sources, sustainability and global efficiency [4,5,6]. In this framework, geothermal energy represents an interesting resource and, due to its not intermittent availability, an attractive solution for lowering fossil-fuel dependence and their environmental impact [7,8,9]. Sci. 2020, 10, 6639 direct (e.g., heat production for industrial and domestic users) and indirect applications (i.e., electricity generation at large, medium and small scales)
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