Thermodynamic and economic evaluation of a small-scale organic Rankine cycle integrated with a concentrating solar collector

Recently, distributed power systems especially with renewable sources have shown an increasing demand all over the world and have been a technical viable solution to demand growth for electricity. Among these, solar-thermal power plants show a trustworthy source for electricity generation especially for rural areas where small-scale plants are needed. Organic Rankine cycle (ORC) is a suitable power cycle for electricity generation from low-grade heat and has shown a good compatibility with parabolic trough solar collectors (PTCs). In this study, a PTC integrated with an ORC is being studied thermodynamically and economically for small-scale electricity generation up to 100 kW electricity. Four schematics of the cycle including the recuperation and superheating are examined. Effect of superheating and recuperating was investigated on the thermal efficiency and costs of the system. A parametric study shows the effect of key parameters such as turbine inlet temperature and pressure on the characteristics of the system such as net work, thermal efficiency, oil temperature, overall heat transfer coefficient and heat transfer area of shell-and-tube heat exchangers and also on costs of the system. Results show the dependence of the system efficiency and system costs on the operating pressure of heat exchangers. Existence of the Recuperator seems quite effective on increasing the cycle efficiency and, in some cases, lowering the total costs due to lowering the condenser load. A comparison of different working fluids including benzene, butane, pentane, isopentane, R123 and R245fa have been done to cover a wide range of operating pressures and temperatures. Results show that benzene has the best thermodynamic performance among other fluids followed by pentane, isopentane, R123, R245fa and butane. Also, benzene has the highest total cost among other fluids followed by pentane, isopentane, butane, R123 and R245fa. This paper helps to evaluate a solar ORC power plant both thermodynamically and economically.

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