Concentrating solar power in South Africa - a comparison of parabolic trough and central receiver technologies with molten salt as heat transfer fluid.

Poole, Ian Vincent (2017-03)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: The most common type of concentrating solar power (CSP) plant in operation today is the parabolic trough plant. In recent years molten salt power tower plants have demonstrated the benefit of using molten salt as heat transfer fluid and a storage medium. New research has shown that molten salt can be used in parabolic trough technology in a similar manner. This thesis documents an investigation into both technologies in order to compare them on a qualitative and quantitative basis. South Africa has become a hotspot for the development of CSP thanks to the abundant solar resource and the implementation of the Renewable Energy Independent Power Producer Procurement Program (REIPPPP) in the country. South Africa therefore provides a realistic backdrop for the comparison of the two CSP technologies. Parabolic trough and a power tower simulation models are constructed for the comparison of the two technologies. Meteorological data for six selected sites in South Africa are used to simulate the performance of both of the technologies, while operating under a flat feed in tariff and a two-tiered feed in tariff. Results of plant simulations show that molten salt can be used effectively as heat transfer fluid in parabolic trough technology. Parabolic troughs are shown to have higher annual optical efficiency compared to power towers. The main drawback of the parabolic trough technology is the thermal losses experienced in the field during overnight recirculation of the hot molten salt. Parabolic trough solar fields show a large seasonal variation in efficiency while power tower plants are shown to benefit from relatively consistent solar field efficiency throughout the year. The seasonal variation in solar field efficiency results in substantially higher thermal energy being available in the summer than in the winter, thereby resulting in storages being filled and the subsequent dumping of solar energy in parabolic trough plants. A simple cost model is built to compare the financial performance of the two technologies and allow for the optimization of the plants according to levelized cost of electricity (LCOE). At a site near Springbok in the Northern Cape Province optimization of both plant types resulted in an estimated LCOE of 0.127 USD/kWhe and 0.129 USD/kWhe for parabolic trough and power tower plants respectively. This study demonstrates that both parabolic trough and power tower plants require careful consideration when selecting the most appropriate CSP technology for a given location. Depending on the available solar resource and the tariff structure under implementation, this thesis finds that both parabolic trough and power tower plants can offer competitive CSP solutions with their own set of strengths and weaknesses.

Die mees algemene vorm van ‘n gekonsentreerde sonkrag (GSK) aanleg in hedendaagse bedryf is die paraboliese trog aanleg. In die afgeloope jare het gesmelte sout krag toring tegnologie voordeel getoon in die gebruik van gesmelte sout as hitte-oordrag vloeistof en as 'n stoor medium. Onlangse navorsing het getoon dat die gesmelte sout in paraboliese trog tegnologie op 'n soortgelyke wyse gebruik kan word. Hierdie tesis dokumenteer 'n ondersoek van altwee tegnologieë ten einde hulle te vergelyk op 'n kwalitatiewe en kwantitatiewe basis. Suid-Afrika het gewild geword vir GSK ontwikkeling te danke aan die oorvloed van son hulpbron en die implementering van die Hernubare Energie Onafhanklike Krag Aankoop Program in die land. Suid-Afrika bied dus 'n realistiese agtergrond vir die vergelyking tussen die twee GSK tegnologieë. Paraboliese trog en 'n krag toring modelle is gebou vir die vergelyking van die twee tegnologieë. Meteorologiese data vir ses gekiesde liggings in Suid-Afrika word gebruik om die optrede van beide tegnologieë te simuleer, terwyl dit bedryf word onder 'n vaste koers invoer tarief en 'n twee-vlak invoer tarief. Resultate van aanleg simulasies toon dat gesmelte sout effektief as hitte-oordrag vloeistof in paraboliese trog tegnologie gebruik kan word. Paraboliese trôe vertoon ‘n hoër jaarlikse optiese doeltreffendheid in vergelyking met krag torings. Die mees kenmerkende nadeel van die paraboliese trog tegnologie is die termiese verliese in die veld tydens oornag hersirkulasie van die warm gesmelte sout. Paraboliese trog sonvelde wys ‘n groot seisoenale verskil in doeltreffendheid terwyl die krag toring aanlegte wys ‘n konstante sonveld doeltreffendheid deur die jaar. Die seisoenale verskil in die sonveld doeltreffendheid beteeken dat meer termiese energie beskikbaar in die sommer in verlgelyking met die winter maande, daarvoor word die stoortenke vol en die daaropvolgende storting van sonenergie in paraboliese trog aanlegte. 'n Eenvoudige kostemodel is gebou om die finansiële prestasie van die twee tegnologieë te vergelyk en voorsiening te maak vir die optimering van die aanlegte volgens gelyke koste van elektrisiteit (GKVE). Op 'n ligging naby Springbok in die Noord-Kaap het optimering van beide aanlegsoorte gelei tot 'n geskatte GKVE van 0.127 USD/kWhe en 0.129 USD/kWhe vir paraboliese trog en krag toring aanlegte onderskeidelik Hierdie studie toon dat beide tegnologieë deeglike oorweging vereis vir die keuse van die mees geskikte GSK tegnologie vir 'n gegewe ligging. Afhangende van die beskikbare sonkrag hulpbron en die tariefstruktuur onder implementering, bevind hierdie tesis dat beide paraboliese trog en krag toring aanlegte mededingende GSK oplossings met hul eie stel sterk- en swakpunte kan bied.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101228
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