A pre-feasibility study of a concentrating solar power system to offset electricity consumption at the Spier Estate

Thesis (MScIng)--University of Stellenbosch, 2011.ENGLISH ABSTRACT: The Spier Estate - a wine estate in the Western Cape Province of South Africa - is engaged in a transition towards operating according to the principles of sustainable development. Besides changes in social and other environmental aspects, the company has set itself the goal to be carbon neutral by 2017. To this end, Spier is considering the on-site generation of electricity from renewable energy sources. This study was initiated to explore the technical and economic feasibility of a concentrating solar power plant for this purpose on the estate. The investigation was carried out to identify the most appropriate solar thermal energy technology and the dimensions of a system that fulfils the carbon-offset requirements of the estate. In particular, potential to offset the annual electricity consumption of the currently 5 570 MWh needed at Spier, using a concentrating solar power (CSP) system, was investigated. Due to rising utility-provided electricity prices, and the expected initial higher cost of the generated power, it is assumed that implemented efficiency measures would lead to a reduction in demand of 50% by 2017. However, sufficient suitable land was identified to allow electricity production exceeding today’s demand. The outcome of this study is the recommendation of a linear Fresnel collector field without additional heat storage and a saturated steam Rankine cycle power block with evaporative wet cooling. This decision was based on the system’s minimal impact on the sensitive environment in combination with the highest potential for local development. A simulation model was written to evaluate the plant performance, dimension and cost. The analysis was based on a literature review of prototype system behaviour and system simulations. The direct normal irradiation (DNI) data that was used is based on calibrated satellite data. The result of the study is a levelised cost of electricity (LCOE) of R2.741 per kWh, which is cost competitive to the power provided by diesel generators, but more expensive than current and predicted near-future utility rates. The system contains a 1.8 ha aperture area and a 2.0 MWe power block. Operating the plant as a research facility would provide significant potential for LCOE reduction with R2.01 per kWh or less (favourable funding conditions would allow for LCOE of R1.49 per kWh) appearing feasible, which results in cost competitiveness in comparison a photovoltaic (PV) solution. Depending on tariff development, Eskom rates are predicted to reach a similar level between 2017, the time of commissioning, and the year 2025. The downside is that the plant would not solely serve the purpose of electricity offsetting for Spier, which may result in a reduced amount of electricity that may be generated. Further studies are proposed to refine the full potential of cost reduction by local development and manufacturing as well as external funding. This includes identification of suitable technology vendors for plant construction. An EIA is required to be triggered at an early stage to compensate for its long preparation.AFRIKAANSE OPSOMMING: Die Spier wynlandgoed in die Wes-Kaap Provinsie van Suid-Afrika is tans in ‘n oorgangsfase tot besigheids-praktyke gebaseer op volhoubare ontwikkeling. Afgesien van die sosiale en omgewingsaspekte het die groep hom ook ten doel gestel om koolstof neutraal te wees teen 2017. Ten einde hierdie doel te bereik, moet die maatskappy sy algehele elektrisiteitsverbruik vervang met hernubare bronne. Hierdie studie is dus geloods om die tegniese en ekonomiese uitvoerbaarheid van 'n gekonsentreerde sonkragstasie op die landgoed te ondersoek. Hierdie ondersoek is gedoen om die mees toepaslike sontermiese tegnologie en die grootte van 'n termiese sonkragstelsel te bepaal, wat aan die koolstof vereistes van die landgoed voldoen. Die potensiaal om die jaarlikse elektrisiteitsverbruik van 5 570 MWh met 'n gekonsentreerde elektriese sonkragstelsel te vervang, is ondersoek. Weens die toename in die elektrisiteitsprys en die verwagte hoërkoste van opgewekte elektrisiteit word aanvaar dat die implementering van voorgestelde doeltreffendheidsverbeteringe, sal lei tot 'n afname in die aanvraag na elektrisiteit van tot 50% teen die jaar 2017. Voldoende beskikbare grond is geïdentifiseer om genoeg elektrisiteit te produseer om die huidige vraag na elektrisiteit te oorskry. Die uitkoms van die studie is die aanbeveling van 'n lineêre Fresnel kollektorveld sonder addisionele warmte storing, asook 'n versadigde stoom Rankine sikluskragblok met ‘n nat-verdamping verkoelingstelsel. Die besluit is gebaseer op die stelsel se minimale impak op die omgewing, tesame met die hoogste potensiaal vir plaaslike ontwikkeling. 'n Simulasie is ontwikkel om die aanleg se werkverrigting, grootte en koste te evalueer. Die analise is gebaseer op 'n literatuuroorsig van 'n prototipe stelsel gedrag en stelsel-simulasies. Die direkte normale sonstralings data wat gebruik is, is gebaseer op gekalibreerde satelliet data. Die bevinding van die studie is 'n gebalanseerd koste van elektrisiteit van R2.74 per kWh, wat mededingend is met die koste van elektrisiteit wat deur diesel kragopwekkers verskaf word, maar is aansienlik duurder as die huidige en toekomstige voorspellings van Eskom-tariewe. Die stelsel bevat 'n 1.8 ha son kollektor oppervlakte en 'n 2.0 MWe krag-blok. Daarbenewens, sal die gebruik van die aanleg as 'n navorsingsfasiliteit die potensiaal hê om die gebalanseerd koste van elektrisiteit te verminder na R2.01 per kWh of minder (gunstig befondsing voorwaardes sal gebalanseerd koste van elektrisiteit van R1.49 per kWh tot gevolg hê), wat mededingend is met die koste van 'n fotovoltaïese alternatief. Daar word voorspel dat Eskom-tariewe dieselfde sal bly vanaf 2017, die jaar van inbedryfstelling van die aanleg, tot en met die jaar 2025. Die nadeel is dat die aanleg nie noodwendig uitsluitlik vir die opwek van elektrisiteit vir Spier gebruik sal word nie, en daarom kan dit lei tot 'n vermindering in die hoeveelheid elektrisiteit wat deur die aanleg opgewek word. Daar word voorgestel dat verdere studies onderneem word om die moontlikheid van koste-besparings vir die aanleg te ondersoek deur gebruik te maak van plaaslike ontwikkeling en vervaardiging, asook eksterne befondsing. Dit sluit die identifisering van geskikte tegnologie verskaffers vir die aanleg-kostruksie in. 'n Omgewingsimpakstudie, volgens die EIA regulasies, moet ook so gou as moontlik gedoen word aangesien dit n langsame proses is

Impingement heat transfer with pressure recovery

A conventional impinging jet is effective at transferring a large heat flux. However a significant pressure loss is also experienced by the free jet of a jet impingement heat transfer device due to rapid expansion because it does not incorporate effective pressure recovery. A novel high-flux impingement heat transfer device, called the Tadpole, is developed to improve the heat transfer and pressure loss (performance) characteristics of the conventional impingement domain by incorporating pressure recovery with a diffuser. The Tadpole is scrutinized through an experimental comparison with a conventional jet impinging on the inner wall of a hemisphere under the turbulent flow regime. The Tadpole demonstrates promising capability by exceeding the performance characteristics of the impinging jet by up to 7.3% for the heat transfer coefficient while reducing the pressure loss by 13%. Multiple dimensional degrees of freedom in the Tadpole’s flow domain can be manipulated for an enhanced heat transfer coefficient, a reduced total pressure loss or a favourable combination of both metrics. A Computational Fluid Dynamics (CFD) model is developed, the Four-Equation Transition SST turbulence model demonstrates satisfactory experimental validation with a deviation of < 5% for the heat transfer coefficient and < 23% for the total pressure loss. The Tadpole is a promising heat transfer device for high-flux applications and is recommended for further work incorporating design improvements and multidimensional optimization.The Solar Thermal Energy Research Group (STERG) at Stellenbosch University.https://link.springer.com/journal/231hj2023Mechanical and Aeronautical Engineerin

Thermal performance characteristics of a tessellated-impinging central receiver

Current central receiver Concentrating Solar Power plants using molten salt as a heat transfer fluid add heat at around 565 °C in a power plant. Adding heat at a higher temperature can improve the thermodynamic performance and may reduce the cost of power. One way to achieve this is by using pressurized air solar receivers. Current receivers have achieved thermal efficiencies of around 80% at an outlet temperature of 800 °C. This paper investigates a novel central receiver technology that makes use of a tessellated array of heat transfer units. The units employ impingement heat transfer within a concave surface. The receiver can be scaled for a desired thermal rating by the number of heat transfer units. The convolution-projection flux modelling approach is used to model and project an incoming flux distribution on the receiver’s surface. This flux distribution is interpreted by a Computational Fluid Dynamics model as a volumetric heat source. Radiative and convective heat losses are considered. An initial performance outlook estimates that an outlet temperature of 801 °C can be reached at a thermal efficiency of 59% and an exterior surface temperature of 1142 °C for an aperture flux of 635 kW/m2. A limitation is an insufficient exterior surface area to absorb the incoming flux which causes a high surface temperature and thermal losses. Similar thermal performance is estimated at high and low pressures, with increased pumping losses at low pressures. The efficiency may be improved by taking advantage of a larger surface area relative to the aperture area.An Erasmus+ mobility grant awarded by Alliance4Universities which made a collaboration at UC3M possible.http://www.elsevier.com/locate/atehj2023Mechanical and Aeronautical Engineerin

Performance characteristics of a spiky central receiver air pre-heater (SCRAP)

Thesis (D.Phil)--Stellenbosch University, 2017.ENGLISH SUMMARY: A combined cycle concentrating solar power (CSP) plant provides significant potential to achieve an efficiency increase and an electricity cost reduction compared to current single-cycle plants. A combined cycle CSP system requires a receiver technology capable of effectively transferring heat from concentrated solar irradiation to a pressurized air stream in a gas turbine. The novel spiky central receiver air pre-heater (SCRAP) technology is proposed to provide such a receiver and overcome barriers experienced by developments to date. The SCRAP receiver is a novel metallic receiver technology aimed at preheating an air stream to about 800◦C, either prior to a combustion chamber or alternatively a cascaded secondary non-metallic receiver system, capable of achieving elevated temperatures. The SCRAP receiver is distinguished in shape and functioning from receiver concepts presented to date for the application in Brayton or combined cycles. The receiver is predicted to perform at solar-thermal efficiencies exceeding 80%. The geometric design of the receiver achieves a relatively low radiative heat loss, predicted at about 4% – 5%, whereas the relatively large surface results in vulnerability to convective heat losses. The pressure drop was found to be dependent on the geometries selected but relatively low, compared to existing alternative receiver designs, with system pressure drops below 40mbar achievable. A ray-tracing analysis showed that the flux impinging on the absorber assemblies is in its spatial distribution dependent on the solar field, more specific, the heliostat size and design. A thermodynamic model was developed to investigate the performance characteristics of the SCRAP receiver. The developed thermodynamic computer model was verified against an experimental test setup designed and built at the heat transfer laboratory at Stellenbosch University. Tests with steam heating at nominally 100◦C show good agreement between the experimental results and the modeled predictions, at various air flow rates. Further work on the SCRAP receiver technology is recommended. On the modelingsideworkisproposedondevelopingsolutionsforjetimpingementheat transfer on the spike tip to improve heat transfer while reducing pressure drop. Furtherworkonhelicallyswirledfinsissuggestedtocontributetoincreasedheat transfer characteristics. The receiver showed vulnerability towards convective heat losses; further work to better predict and mitigate these is required. Experiments under solar flux or simulated solar flux should further improve understanding of the technology. Cost effective manufacturing processes need to be developed to satisfy economic suitability of the receiver technology.AFRIKAANS OPSOMMING: ’n Saamgestelde siklus gekonsentreerde sonkrag (GS) aanleg bied aansienlike potensiaal vir ’n toename in doeltreffendheid en ’n vermindering in elektrisiteitskoste in vergelyking met huidige enkel-siklus aanlegte. ’n Saamgestelde siklus GS aanleg vereis ’n ontvangertegnologie wat in staat is om warmte doeltreffend oor te dra vanaf sonstraling na ’n saamgedrukte lugstroom binne ’n gasturbine. Die nuwe Puntige Sentrale Ontvanger Lug-Voorverwarmer (PSOLV) tegnologie word voorgestel as so ’n ontvanger om hindernisse te oorkom wat tot dusver deur ontwikkelaars ervaar is. Die PSOLV ontvanger is ’n nuwe, metaal-ontvanger tegnologie wat daarop gemik is om ’n lugstroom tot sowat 800◦C voor ’n verbrandingskamer te verhit, of alternatiewelik in ’n kaskade met ’n sekondêre nie-metaal ontvangerstelsel, wat in staat is om verhoogde temperature te bereik. Die PSOLV ontvanger word onderskei in vorm en funksionering van ontvanger konsepte tot op datum voorgestel vir toepassing in Brayton- of saamgestelde kringlope. Die voorspelling is dat die ontvanger son-termiese doeltreffendhede van 80% sal oorskry. Die geometriese ontwerp van die ontvanger bereik ’n relatief lae voorspelde stralingswarmteverlies van sowat 4% – 5%. Die relatief groot oppervlakte toon daarteenoor ’n kwesbaarheid vir konveksie warmteverliese. Daar is bevind dat die PSOLV drukval afhanklik is van die geselekteerde geometrieë, maar relatief laag is in vergelyking met bestaande alternatiewe ontvangers, met stelsel drukvalle onder 40mbar bereikbaar. ’n Straalspoor analise het getoon dat die ruimtelike verdeling van die vloed wat inval op die ontvangersamestelling afhang van die sonversamelveld, en meer spesifiek van die heliostaat grootte en ontwerp. ’n Termodinamiese model is ontwikkel om die gedragskenmerke van die PSOLV ontvanger te ondersoek. Die ontwikkelde rekenaar model is geverifieer teen ’n eksperimentele toetsopstelling, ontwerp en gebou in die warmteoordrag laboratorium by Stellenbosch Universiteit. Toetse met stoomverwarming by nominaal 100◦C toon goeie ooreenkoms tussen eksperimentele resultate en model voorspellings, by verskeie lugvloeitempo’s. Verdere werk op die PSOLV ontvanger tegnologie word aanbeveel. Op die modelleringskant word werk voorgestel op die ontwikkeling van oplossings vir straalbotsing-warmteoordrag binne die die stekelpunt om warmteoordrag te verbeter, terwyl drukval verminder word. Verdere werk op heliese vinne word anbeveel om by te dra tot verhoogde warmte-oordrag eienskappe. Die ontvanger het kwesbaarheid teenoor konvektiewe warmteverliese getoon; verdere werk word vereis om dit beter te voorspel en te beperk. Eksperimente onder direkte of gesimuleerde sonvloede behoort begrip van die tegnologie verder te verbeter. Koste-effektiewe produksieprosesse behoort ontwikkel te word om ekonomiese toepaslikheid van die ontvanger tegnologie te bevredig

A pre-feasibility study of a concentrating solar power system to offset electricity consumption at the Spier Estate

Thesis (MScIng)--University of Stellenbosch, 2011.ENGLISH ABSTRACT: The Spier Estate - a wine estate in the Western Cape Province of South Africa - is engaged in a transition towards operating according to the principles of sustainable development. Besides changes in social and other environmental aspects, the company has set itself the goal to be carbon neutral by 2017. To this end, Spier is considering the on-site generation of electricity from renewable energy sources. This study was initiated to explore the technical and economic feasibility of a concentrating solar power plant for this purpose on the estate. The investigation was carried out to identify the most appropriate solar thermal energy technology and the dimensions of a system that fulfils the carbon-offset requirements of the estate. In particular, potential to offset the annual electricity consumption of the currently 5 570 MWh needed at Spier, using a concentrating solar power (CSP) system, was investigated. Due to rising utility-provided electricity prices, and the expected initial higher cost of the generated power, it is assumed that implemented efficiency measures would lead to a reduction in demand of 50% by 2017. However, sufficient suitable land was identified to allow electricity production exceeding today’s demand. The outcome of this study is the recommendation of a linear Fresnel collector field without additional heat storage and a saturated steam Rankine cycle power block with evaporative wet cooling. This decision was based on the system’s minimal impact on the sensitive environment in combination with the highest potential for local development. A simulation model was written to evaluate the plant performance, dimension and cost. The analysis was based on a literature review of prototype system behaviour and system simulations. The direct normal irradiation (DNI) data that was used is based on calibrated satellite data. The result of the study is a levelised cost of electricity (LCOE) of R2.741 per kWh, which is cost competitive to the power provided by diesel generators, but more expensive than current and predicted near-future utility rates. The system contains a 1.8 ha aperture area and a 2.0 MWe power block. Operating the plant as a research facility would provide significant potential for LCOE reduction with R2.01 per kWh or less (favourable funding conditions would allow for LCOE of R1.49 per kWh) appearing feasible, which results in cost competitiveness in comparison a photovoltaic (PV) solution. Depending on tariff development, Eskom rates are predicted to reach a similar level between 2017, the time of commissioning, and the year 2025. The downside is that the plant would not solely serve the purpose of electricity offsetting for Spier, which may result in a reduced amount of electricity that may be generated. Further studies are proposed to refine the full potential of cost reduction by local development and manufacturing as well as external funding. This includes identification of suitable technology vendors for plant construction. An EIA is required to be triggered at an early stage to compensate for its long preparation.AFRIKAANSE OPSOMMING: Die Spier wynlandgoed in die Wes-Kaap Provinsie van Suid-Afrika is tans in ‘n oorgangsfase tot besigheids-praktyke gebaseer op volhoubare ontwikkeling. Afgesien van die sosiale en omgewingsaspekte het die groep hom ook ten doel gestel om koolstof neutraal te wees teen 2017. Ten einde hierdie doel te bereik, moet die maatskappy sy algehele elektrisiteitsverbruik vervang met hernubare bronne. Hierdie studie is dus geloods om die tegniese en ekonomiese uitvoerbaarheid van 'n gekonsentreerde sonkragstasie op die landgoed te ondersoek. Hierdie ondersoek is gedoen om die mees toepaslike sontermiese tegnologie en die grootte van 'n termiese sonkragstelsel te bepaal, wat aan die koolstof vereistes van die landgoed voldoen. Die potensiaal om die jaarlikse elektrisiteitsverbruik van 5 570 MWh met 'n gekonsentreerde elektriese sonkragstelsel te vervang, is ondersoek. Weens die toename in die elektrisiteitsprys en die verwagte hoërkoste van opgewekte elektrisiteit word aanvaar dat die implementering van voorgestelde doeltreffendheidsverbeteringe, sal lei tot 'n afname in die aanvraag na elektrisiteit van tot 50% teen die jaar 2017. Voldoende beskikbare grond is geïdentifiseer om genoeg elektrisiteit te produseer om die huidige vraag na elektrisiteit te oorskry. Die uitkoms van die studie is die aanbeveling van 'n lineêre Fresnel kollektorveld sonder addisionele warmte storing, asook 'n versadigde stoom Rankine sikluskragblok met ‘n nat-verdamping verkoelingstelsel. Die besluit is gebaseer op die stelsel se minimale impak op die omgewing, tesame met die hoogste potensiaal vir plaaslike ontwikkeling. 'n Simulasie is ontwikkel om die aanleg se werkverrigting, grootte en koste te evalueer. Die analise is gebaseer op 'n literatuuroorsig van 'n prototipe stelsel gedrag en stelsel-simulasies. Die direkte normale sonstralings data wat gebruik is, is gebaseer op gekalibreerde satelliet data. Die bevinding van die studie is 'n gebalanseerd koste van elektrisiteit van R2.74 per kWh, wat mededingend is met die koste van elektrisiteit wat deur diesel kragopwekkers verskaf word, maar is aansienlik duurder as die huidige en toekomstige voorspellings van Eskom-tariewe. Die stelsel bevat 'n 1.8 ha son kollektor oppervlakte en 'n 2.0 MWe krag-blok. Daarbenewens, sal die gebruik van die aanleg as 'n navorsingsfasiliteit die potensiaal hê om die gebalanseerd koste van elektrisiteit te verminder na R2.01 per kWh of minder (gunstig befondsing voorwaardes sal gebalanseerd koste van elektrisiteit van R1.49 per kWh tot gevolg hê), wat mededingend is met die koste van 'n fotovoltaïese alternatief. Daar word voorspel dat Eskom-tariewe dieselfde sal bly vanaf 2017, die jaar van inbedryfstelling van die aanleg, tot en met die jaar 2025. Die nadeel is dat die aanleg nie noodwendig uitsluitlik vir die opwek van elektrisiteit vir Spier gebruik sal word nie, en daarom kan dit lei tot 'n vermindering in die hoeveelheid elektrisiteit wat deur die aanleg opgewek word. Daar word voorgestel dat verdere studies onderneem word om die moontlikheid van koste-besparings vir die aanleg te ondersoek deur gebruik te maak van plaaslike ontwikkeling en vervaardiging, asook eksterne befondsing. Dit sluit die identifisering van geskikte tegnologie verskaffers vir die aanleg-kostruksie in. 'n Omgewingsimpakstudie, volgens die EIA regulasies, moet ook so gou as moontlik gedoen word aangesien dit n langsame proses is

Capability of a novel impingement heat transfer device for application in future solar thermal receivers

CSP receivers are designed to permit higher outlet temperatures in order to enable higher theoretical efficiencies of the associated thermodynamic cycles. For pressurized air receivers, it is attempted to increase the operating temperature of metallic pre-heaters to then achieve high air outlet temperatures with cascaded ceramic receivers. Two limitations of metallic pressurized air receivers are cost and material creep at elevated temperatures and pressures. Therefore, it is necessary to maximize heat transfer from the receiver surface to the working fluid while minimizing the material surface temperature. Current research has demonstrated that jet impingement heat transfer devices are appropriate for application in thermal receivers because of the associated desirable heat transfer characteristics. However, it is shown that significant pressure losses are caused by such impinging jets because of the sudden expansion phenomenon. A novel enhanced impingement heat transfer device is presented in this paper. Experimental testing was conducted to investigate the domain comparatively with impinging jet configurations. The device is shown to be capable of delivering an enhanced surface heat transfer coefficient while affecting a lower total pressure loss around the domain when compared with similar impinging jet configurations. The geometry of the device can also be chosen to achieve a favorable combination of heat transfer and pressure loss characteristics. The device is applicable within the SCRAP concept and may be implementable within the SOLHYCO and SOLUGAS receivers. The device may also find an application in a parabolic dish collector. Finally, a novel receiver concept that incorporates the device in a tessellated structure is introduced – the SUNflower.https://aip.scitation.org/journal/apcpm2021Mechanical and Aeronautical Engineerin