A Technical and economic assessment of molten salt parabolic trough power plants and operating strategies in Southern Africa.
Date
2020-12
Authors
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Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT: Parabolic trough power plants (PTPP) using thermal oils as heat transfer fluid (HTF) are currently still state-of-the-art. Using molten salts as HTF instead enables higher operating temperature differences and therefore higher cycle efficiencies. Nevertheless, the use of molten salts is linked to several engineering and operational challenges that require special consideration to be placed on improved operating strategies and power plant configurations. This can, for example, be achieved through a technical and economic assessment,where design variables and operational parameters can be determined that lead
to an optimised financial feasibility of molten salt PTPPs for various operating objectives.For this purpose, a two-dimensional dynamic parabolic trough solar collec-tor model using molten as HTF was developed and validated with measure-ment data obtained from the Archimede Solar Energy demonstration plant formolten salt receiver tubes in Massa Martana, Italy. An empirical heat loss equation based on the outer surface temperature of the absorber tube was introduced to the model in order to improve simulation efficiency. The finite volume method was applied to discretise the receiver into control volumes,whereby the effect of decreasing levels of discretisation on the model accuracy is analyzed. The relative error of the loop outlet temperature is 0.69 % for the most detailed model and 0.99 % when one control volume per solar collector array is used. A division into five control volumes is recommended as a trade-off between model accuracy and simulation time.
A location-tailored economic model for South Africa and Namibia was implemented and validated with financial data of two existing concentrating solar power plants in South Africa, leading to a maximum error of−5 % for the levelised cost of electricity (LCOE). A sensitivity analysis was carried out to identify the key technical and financial design parameters that lead to the best potential improvements in terms of power plant efficiency and profitability. In order to combine the cost reduction potentials of all key design parameters identified in the sensitivity analysis, a multi-objective optimisation was carried out, simultaneously minimising the investment costs and maximising the internal rate of return. The results show that Solar Salt offers the lowest LCOE out of three investigated HTFs and a freeze protection system using thermal energy from the hot tank enables a significant reduction of the LCOE in comparison to the baseline approach of relying on electric freeze protection only.
Based on the optimisation results, a range of power plant configurations and operational parameter set points are recommended for base load and two-tier tariff structures. For base load power plants, the minimum required bidding tariff is 119.4 $/MWh in South Africa and 115.8 $/MWh in Namibia under cur-rent financial boundary conditions. A projection of the LCOE until 2050 showsthat an LCOE of 49.6 $/MWh is expected for South Africa and 49.3 $/MWhfor Namibia with a technology learning rate of 20 %. However, assuming reduced financing costs, tariffs as low as 50.4 $/MWh can already be financially feasible today and a spot market participation of molten salt PTPPs is possible with LCOEs between 58.9 $/MWh and 65.6 $/MWh.
AFRIKAANSE OPSOMMING: Raadpleeg teks vir opsomming
AFRIKAANSE OPSOMMING: Raadpleeg teks vir opsomming
Description
Thesis (PhD)--Stellenbosch University, 2020.
Keywords
Molten salt, Dynamic performance simulation, UCTD, Parabolic trough collector