Thermo-economic assessment of a micro CHP system fuelled by geothermal and solar energy

A micro combined heat and power (CHP) plant operating through an Organic Rankine Cycle (ORC) using renewable energy is analysed. The reference system is designed to produce 50 kWe. The heat sources of the system are geothermal energy at low temperature (80e100 C) and solar energy. The system uses a solar field composed only by evacuated solar collectors, and work is produced by a single turbine. Different working fluids (e.g. R134a, R236fa, R245fa) are considered in the analysis. The aim of this paper is to assess the cost of the proposed CHP plant and to determine the most convenient working fluid through a thermo-economic analysis. The system is sized in base of the weather data of a city in the centre of Italy in three different months (January, March, July), and the main characteristics of the system (i.e. heat exchanger surface, solar collector area) are presented. The results of the thermo-economic analysis show that R245fa allows the lowest price of electricity production and the lowest overall cost of the CHP plant.