Combined use of volumetric expanders and Scheffler receivers to improve the efficiency of a novel direct steam solar power plant

Abstract

This research proposes an innovative solar thermal plant able to generate mechanical power through an optimized system of heliostats with Scheffler-type solar receivers coupled with screw-type steam expanders. Scheffler receivers appear to perform better than parabolic trough collectors due to the high compactness of the focal receiver, which minimizes convective and radiative heat losses even at high vaporization temperatures. At the same time, steam screw expanders are volumetric machines that can be used to produce mechanical power with satisfactory efficiency also by admitting two-phase mixtures and with further advantages compared to steam turbines: low working fluid velocities, low operating pressures, and avoidance of overheating. This study establishes a mathematical model to assess the energetic advantages of the planned solar thermal power system by evaluating the solar-to-electricity efficiency for different off-

Numerical Optimization and Energetic Advantages of an Innovative Solar Power System Based on Scheffler Receiver Coupled with Volumetric Expanders

“…5) which prevail over increasing Rankine cycle efficiencies η SRC . 20 For this reason, it is essential to detect optimum working conditions of the planned solar power plant for each level of solar irradiance. The parametric analysis of the polynomial functions shown in Fig.…”

“…It is evident that the heat collector efficiency η SOL , which compares the net thermal power Q av to the solar radiation I d •A ap,ref arriving on the receiver, always decreases with increasing evaporation temperature. 20 To exhibit the energetic benefits of the solar receivers under investigation, the solar power collection efficiencies η SOL of SC receivers (shown in Fig. 5) are then compared with those of ordinary PTC receivers for the same ranges of solar beam intensity and vaporization temperature, as shown in Fig.…”

“…(19). 20 The convection heat transfer coefficient, h e x t , c a v, comprises both forced and natural convection coefficients, as indicated in Eq. (20).…”

“…1). 19,20 The energy balance in the receiver is described in Eq. (1), where the net heat available to transfer at the working fluid, Q av , is evaluated as the difference between the heat gathered in the cavity, Q rec , and all heat losses Q loss comprising convection, conduction, and radiation losses.…”

Performance Evaluation of a Photovoltaic-Thermal Collector Coupled Stepped Solar Still for Indian Climatic Conditions

“…In this study, a novel direct steam solar power plant based on an SRC is proposed. Water is used as the working fluid and heat transfer medium, while Scheffler solar receivers are used as the thermal source and work-producing machinery, respectively [24].…”