Optimal concentration and temperatures of solar thermal power plants

Abstract

Publication informationEnergy Conversion and Management, Publisher Elsevier Item record/more information http://hdl.handle.net/10197/4904 Publisher's statementThis is the author's version of a work that was accepted for publication in Energy Conversion and Management. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Energy Conversion and Management (60, , (2012) Abstract:Using simple, finite-time, thermodynamic models of solar thermal power plants, the existence of an optimal solar receiver temperature has previously been demonstrated in literature. Scant attention has been paid, however, to the presence of an optimal level of solar concentration at which the conversion of incident sunlight to electricity (solar-to-electric efficiency) is maximized. This paper addresses that gap. The paper evaluates the impact, on the design of Rankine-cycle solar-trough and solar-tower power plants, of the existence of an optimal receiver temperature and an optimal level of solar concentration. Mathematical descriptions are derived describing the solar-to-electric efficiency of an idealized solar thermal plant in terms of its receiver temperature, ambient temperature, the receiver irradiance (radiation striking unit receiver area), solar receiver surface to working fluid conductance, condenser conductance, solar collector efficiency, convective loss coefficients and radiative loss coefficients. Using values from the literature appropriate to direct-steam and molten-salt plants, curves of optimal solar receiver temperature, and optimal solar-to-electric conversion efficiency, are generated as a function of receiver irradiance. The analysis shows that, as the thermal resistance of the solar receiver and condenser increases, the optimal receiver temperature increases whilst the optimal receiver irradiance decreases. The optimal level of receiver irradiance, for solar thermal plants employing a service fluid of molten salts, is found to occur within a range of values achievable using current solar tower technologies. The tradeoffs (in terms of solar-to-electric efficiency) involved in using molten salts rather than direct steam in the case of solar towers and solar troughs are investigated. The optimal receiver temperatures calculated with the model suggest the use of sub-critical Rankine cycles for solar trough plants, but super-critical Rankine cycles for solar tower plants, if the objective is to maximize solar-to-electric efficiency.

Thermodynamic analysis of an idealised solar tower thermal power plant

“…1000W/m ଶ , the heat transfer coefficients for each heat exchanger are same; according to the 170 suggested formula in previous literature [4], given that U ୌ ൌ U ൌ U ୖ ൌ U ൎ 171 15000W/m ଶ K, the above equation could be rewritten as: 172…”

“…Previous literature 162 [4] gave a rough formula to calculate the convection coefficient for solar tower, which is as 163 follows: 164…”

“…Despite of this, 47 the analysis of an idealised solar thermal power system is still beneficial because it could help 48 to gain knowledge about the influential parameters and the deviation between a real and ideal 49 systems. In the solar thermal application, Salah [2], Chen [3], Ronan [4], Sahin [5], Tamer 50…”

Thermo-Economic Optimization of an Idealized Solar Tower Power Plant Combined with MED System

“…Reference [18] gives the convection heat transfer coefficient of the tower power plant receiver to the environment:…”

Optimization of the deployment of utility scale solar plants

“…McGovern & Smith [4] note that because of global energy problems and the danger of fossil energy depletion, higher renewable energy utilization is needed to be developed and optimized, and the optimization parameters of solar plants are more challenging than those for fossil fuel plants.…”