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Aiming strategies for small central receiver systemsGrobler, Annemarie 03 1900 (has links)
Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Concentrating solar power as a sustainable energy technology is considered favourable
in South Africa due to the high solar resource and the integration possibilities with
the current electricity grid. Considering the various concentrating solar power
technologies, the central receiver system is thought to be one of the most promising
due to its high capacity factor and cost-efficient thermal storage capabilities.
These thermal systems are able to reach high temperatures (more than 1000°C
have been shown), and to obtain such temperatures, a high solar flux is required.
This is achievable by aiming all of the heliostats at the centre of the target. High flux
gradients over the receiver surface area and between the outer and inner surfaces
of the receiver material can exist. These thermal gradients account for differences
in temperatures on the receiver which result in thermal stresses leading to elastic
and potentially plastic deformation of the material.
To eradicate the thermal stresses, the aim points of the heliostats can be managed
such that the flux density distribution over the receiver aperture is decreased and
homogenised. The primary objective of this thesis is to develop an aiming strategy
specifically for small experimental heliostat fields. To reach this objective, a simulation
platform was developed to model any heliostat field and receiver, and an
analysis was conducted to compare analytical flux prediction methods to ray tracing.
At high incidence angles of between 30° and 60°, the standard deviations of the
circular Gaussian flux approximation methods were found to differ between approximately
10 % and 30 % from the ray traced results. A novel method, the Gaussian
mixture model, was suggested and deviated less than 4 % from the ray traced
results when considering the standard deviation of the flux profile.
Two basic aiming strategies were developed using the Tabu search and Genetic algorithm optimisation methods. These two strategies make use of approximate
method of flux prediction. Experiments were conducted to investigate static aiming
strategies on physical systems and to identify factors that could have an effect
on the experimental results. Finally a method of implementing the aiming strategy
on a dynamic system was proposed.
By implementing both optimisation methods to complement each other, a new
aiming strategy was developed that proved to provide better homogenisation of
the flux distribution than either of the two methods alone. The accuracy of the final
predicted flux distribution was improved by using the Gaussian mixture model as
the flux distribution approximation method. / AFRIKAANSE OPSOMMING: Gekonsentreerde sonenergie as ’n hernubare energie bron, word in Suid-Afrika as
uitvoerbaar beskou weens die hoë stralingsdigtheid asook die moontlikheid om
hierdie tegnologie te koppel aan die huidige energienetwerk. As die verskeie gekonsentreerde
sonenergie tegnologieë in ag geneem word, word sentrale ontvangerstelsels
beskou as die mees belowende sonenergie konsep as gevolg van die hoë
energie kapasiteit en die vermoë om termiese energie te stoor.
Hierdie termiese stelsels besit die vermoë om hoë temperature te bereik (meer as
1000°C is al opgemerk), en om hierdie temperature te verkry word ’n hoë termiese
vloed benodig. Dit is bereikbaar deur al die heliostate op die middel van die ontvanger
te rig. Hoë termiese vloedgradiënte oor die oppervlakte van die opvanger
en tussen die buite- en binne laag van die opvanger materiaal kan ontstaan. Termiese
vloedgradiënte kan verskille in temperatuur op die ontvanger veroorsaak
wat termiese spanning tot gevolg het kan lei tot elastiese en potensieel plastiese
vervorming van die materiaal.
Omvan die termiese spanning ontslae te raak kan die heliostate deur beheerstelsels
na ander dele van die ontvanger gerig word om sodoende ’n laer en meer egalige
termiese vloed oor die oppervlak van die ontvanger te verkry. Die hoofdoel van
hierdie tesis is die ontwikkeling van ’n mikstrategie, hoofsaaklik bedoel vir klein
eksperimentele heliostaatvelde. Om hierdie hoofdoel te bereik, was ’n simulasieplatform
ontwikkel waardeur heliostaatvelde en opvangerstelsels gemodelleer kan
word, en ’n analise is gedoen om die verskeidenheid benaderende analitiese metodes
te vergelyk met die straalopsporingsmetode.
By hoë invalshoeke tussen 30° en 60° is daar gevind dat die benaderende modelle
wat die termiese vloed as ’n normale Gaussiese verspreiding beskou, ’n afwyking van die straalopsporingsresultate toon van ongeveer 10 % tot 30 %. ’n Nuwe metode,
die Gaussiese mengsel model, was voorgestel en het minder as 4 % van die
straalopsporings resultate afgewyk, met die standaard afwyking van die termiese
vloed profiel in ag geneem.
Twee basiese mikstrategieë is ontwikkel deur gebruik te maak van die Tabu soek en
Genetiese algoritme optimeringsmetodes. Hierdie strategieë maak gebruik van die
benaderende metodes om termiese vloed te voorspel. Eksperimente is uitgevoer
om die implementering van statiese mikstrategieë op ’n fisiese stelsel te beskou en
die faktore wat ’n invloed op die eksperimentele resultate sal hê te identifiseer. Ten
laaste word ’n metode voorgestel vir die implementering van die mikstrategieë op
’n dinamiese stelsel.
Deur beide optimeringsmetodes te implementeer sodat hul mekaar komplimenteer,
word ’n nuwe mikstrategie ontwikkel wat beter homogenisering van die termiese
vloed verspreiding bewys het as enige van die alleen staande metodes. Die
akkuraatheid van die finale voorgestelde termiese vloed verspreiding was verbeter
deur gebruik te maak van die Gaussiese mengsel model as die benaderende
metode van die termiese vloed verspreiding.
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A heliostat field control systemMalan, Karel Johan 04 1900 (has links)
Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The ability of concentrating solar power (CSP) to efficiently store large amounts of
energy sets it apart from other renewable energy technologies. However, cost
reduction and improved efficiency is required for it to become more economically
viable. Significant cost reduction opportunities exist, especially for central receiver
system (CRS) technology where the heliostat field makes up 40 to 50 per cent of the
total capital expenditure.
CRS plants use heliostats to reflect sunlight onto a central receiver. Heliostats with
high tracking accuracy are required to realize high solar concentration ratios. This
enables high working temperatures for efficient energy conversion. Tracking errors
occur mainly due to heliostat manufacturing-, installation- and alignment tolerances,
but high tolerance requirements generally increase cost. A way is therefore needed to
improve tracking accuracy without increasing tolerance requirements.
The primary objective of this project is to develop a heliostat field control system
within the context of a 5MWe CRS pilot plant. The control system has to govern the
tracking movement of all heliostats in the field and minimize errors over time. A
geometric model was developed to characterize four deterministic sources of heliostat
tracking errors.
A prototype system comprising 18 heliostats was constructed to function as a scaled
down subsection of the pilot plant heliostat field and to validate the chosen control
method and system architecture. Periodic measurements of individual heliostats’
tracking offsets were obtained using a camera and optical calibration target combined
with image processing techniques. Mathematical optimization was used to estimate
model coefficients to best fit the measured error offsets. Real-time tracking error
corrections were performed by each heliostat’s local controller unit to compensate for
a combination of error sources. Experimental tracking measurements were performed using the prototype system.
Daily open-loop RMS tracking errors below one milliradian were obtained, thereby
satisfying the project’s primary objective. The thesis concludes that high tracking
accuracy can be achieved using the control method proposed here. This could
potentially lead to a reduction in heliostat cost, thereby lowering the levelised cost of
electricity for CRS plants. / AFRIKAANSE OPSOMMING: Gekonsentreerde sonkrag se vermoë om groot hoeveelhede energie effektief te stoor
onderskei dit van ander hernubare energie tegnologieë. Kostebesparing en hoër
effektiwiteit word egter vereis om dit ekonomies meer lewensvatbaar te maak.
Beduidende kostebesparingsgeleenthede bestaan wel, spesifiek vir tegnologieë vir
sentraal-ontvangerstelsels (central receiver system (CRS)) waar die heliostaatveld 40
tot 50 persent van die totale kapitaalbestedings uitmaak.
CRS aanlegte gebruik heliostate om sonlig op ’n sentrale ontvanger te reflekteer.
Heliostate met ’n hoë volgingsakkuraatheid word vereis om hoë sonkragkonsentrasieverhoudings
te laat realiseer. Dit maak hoë werkstemperature moontlik vir effektiewe
energie-omsetting. Volgingsfoute kom hoofsaaklik voor a.g.v. die heliostaat se
vervaardigings-, installasie- en instellingstoleransies, maar hoë toleransie-vereistes
verhoog gewoonlik die koste. Daar is dus ’n manier nodig om volgingsakkuraatheid
te verbeter sonder om die toleransie-vereistes te verhoog.
Die primêre doel van hierdie projek is om ’n heliostaat aanleg kontrole-stelsel te
ontwikkel binne die konteks van ’n 5 MWe CRS toetsaanleg. Die kontrole-stelsel
moet die volgingsbeweging van al die heliostate in die aanleg bestuur en ook met
verloop van tyd volgingsfoute verminder. ’n Geometriese model is ontwikkel om die
vier bepalende bronne van heliostaat volgingsfoute te karakteriseer.
’n Prototipe stelsel met 18 heliostate is gebou om as ’n funksionele skaalmodel van
die toetsaanleg heliostaatveld te dien en om die gekose kontrole-metode en stelselargitektuur
geldig te verklaar. Periodieke metings van die individuele heliostate se
volgingsafwykings is verkry deur ’n kamera en optiese kalibrasie teiken te kombineer
met beeldprosesseringstegnieke. Wiskundige optimering is gebruik om die model se
koëffisiënte te skat om die beste passing te bepaal vir die gemete foutafwykings.
Intydse volgingsfoutregstellings is deur elke heliostaat se plaaslike beheereenheid
gedoen om te vergoed vir ’n kombinasie van foutbronne. Eksperimentele volgingsmetings is uitgevoer met die prototipestelsel. Daaglikse ooplus
RMS volgingsfoute onder een milliradiaan is verkry, en sodoende is die projek se
primêre doel behaal. Die tesis maak die gevolgtrekking dat hoë volgingsakkuraatheid
behaal kan word deur die gebruik van die beheer-metode soos hier voorgestel. Dit
kan potensieel bydra tot kostebesparing in die heliostaatveld van CRS aanlegte om
sodoende die geykte koste van elektrisiteit te verminder.
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Heliostat field layout optimization for a central receiverLutchman, Shanley Lawrence 12 1900 (has links)
Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: There are two methods generally used for heliostat field layout optimization:
the field growth method and the pattern method. A third, less
commonly used method also exists: the free variable method. Each of
these three methods offers its own set of advantages and disadvantages.
The purpose of this study is to explore the subject of heliostat field layout
optimization and to examine the free variable method. In order to
achieve this objective, optimization was conducted using the free variable
method. To perform optimization, a technical model of the heliostat field
was constructed using approximating functions from literature and geometric
analysis. Results of this study indicated that the free variable method
is possible using a gradient-based optimization algorithm. The free variable
method was applied to redesign the field of a commercial plant, PS10,
located in Spain. The original plant was improved by 1.2% in annual intercepted
energy. The study has demonstrated some of the characteristics,
advantages and pitfalls of the free variable method and has proved useful
in contributing to the understanding of heliostat field layout optimization.
The free variable method requires more research and development before it may be used commercially. / AFRIKAANSE OPSOMMING: Daar word oor die algemeen twee metodes gebruik om 'n heliostaatveld se
uitleg te optimeer: die terreinvermeerderingsmetode (field growth) en die
patroonmetode (pattern). 'n Derde, minder algemeen gebruikte metode
bestaan ook: die vrye veranderlike metode (free variable). Elkeen van hierdie
drie metodes bied sy eie voordele en nadele. Die doel van hierdie studie
is om die onderwerp van heliostaat veld uitleg optimalisering te verken en
die vrye veranderlike metode te ondersoek. Ten einde te hierdie oogmerk
te bereik, is die optimalisering uitgevoer met gebruik van die vrye veranderlike
metode. Om optimalisering uit te voer, is 'n tegniese model van
die heliostaat veld gebou met behulp van benader funksies van letterkunde
en geometriese analise. Resultate van hierdie studie het aangedui dat die
vrye veranderlike metode moontlik is deur gebruik te maak van 'n gradientbebaseerde
optimeeringslagoritme. Die vrye veranderlike metode is ook
aangewend om die terrien van 'n kommersiele aanleg, PS10 in Spanje, te
herontwerp. Die oorspronklike aanleg is in jaarlikse onderskep energie verbeter
met 1.2%. Die studie het sommige van die eienskappe, voordele en
slaggate van die vrye veranderlike metode getoon en het nuttige bewys
om by te dra tot die begrip van heliostaat veld uitleg optimalisering. Die
vrye veranderlike metode vereis meer navorsing en ontwikkeling voordat dit
kommersieel gebruik kan word.
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The Hybrid Pressurized Air Receiver (HPAR) for combined cycle solar thermal power plantsKretzschmar, Holger 04 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Concentrating solar power technology is a modern power generation technology
in which central receiver systems play a significant role. For this technology a
field of heliostats is used to reflect solar irradiation to the receiver located on
top of the tower. An extensive review has shown that contemporary receiver
designs face geometric complexities, lack of thermal efficiency as well as issues
with durability and cost. The purpose of this study is to develop a new receiver
concept that can potentially reduce these issues. A parametric analysis
was used to identify potential means of improvement based on an energy balance
approach including sensitivities involved with convection and radiation
heat transfer. Design criteria such as the use of headers to minimize pressure
drop was also investigated. Based on these findings the hybrid pressurized
air receiver was developed which is a combination of tubular and volumetric
receiver technologies. The fundamental idea of the receiver was investigated
by simulating the ray-tracing and coupled natural convection and radiation
heat transfer. The ray-tracing results have shown that the use of quartz glass
is a prospective solution to higher allowable flux densities, but with reflection
losses in the order of 7 %. The coupled natural convection heat transfer
simulation further revealed that the receiver concept effectively eliminates the
escape of buoyant plumes and radiative heat losses are minimized. Empirical
data was gathered from a medium flux concentrator and good agreement with
the numerical results was obtained. The thesis therefore concludes that the
research outcomes were met. Ongoing research aims to optimise the receiver
concept for a 5MW pilot plant. / AFRIKAANSE OPSOMMING: Gekonsentreerde sonkrag tegnologie is ’n moderne kragopwekkingstegnologie
waar sentrale ontvangersisteme ’n beduidende rol speel. Vir hierdie tegnologie
word ’n veld heliostate gebruik om sonstraling na die ontvanger wat aan
die bopunt van die toring geleë is te reflekteer. ’n Omvattende hersiening
het daarop gewys dat kontemporêre ontwerpe van die ontvangers ’n aantal
geometriese kompleksiteite, ’n tekort aan termiese doeltreffendheid sowel as
probleme in terme van duursaamheid en koste in die gesig staar. Die doel van
die studie is om ’n nuwe ontvangerskonsep te ontwikkel wat moontlik hierdie
probleme kan verminder. ’n Parametriese analise is gebruik om potensiële
maniere van verbetering aan te dui wat gebaseer is op ’n energiebalans benadering;
insluitend sensitiwiteite betrokke by konvektiewe en stralingswarmteoordrag.
Ontwerpkriteria soos die gebruik van spruitstukke om drukverliese
te minimaliseer is ook ondersoek. Gebaseer op hierdie bevindinge is die hibriede
saamgepersde-lug ontvanger ontwikkel. Laasgenoemde is ’n kombinasie
van buis- en volumetriese ontvangertegnologie. Die fundamentele idee van die
ontvanger is ondersoek deur straalberekening asook die gelyktydige natuurlike
konveksie en stralingswarmteoordrag te simuleer. Die straalberekeningsresultate
het getoon dat die gebruik van kwarts glas ’n moontlike oplossing is om
hoër stralingsintensiteit te bereik, maar met refleksieverliese in die orde van
7 %. Die gelyktydige natuurlike konveksie en stralingswarmteoordrag simulasie
het verder aan die lig gebring dat die ontvangerkonsep die ontsnapping
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Rock bed thermal storage for concentrating solar power plantsAllen, Kenneth Guy 04 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Concentrating solar power plants are a promising means of generating electricity. However, they are dependent on the sun as a source of energy, and require thermal storage to supply power on demand. At present thermal storage – usually molten salt – although functional, is expensive, and a cheaper solution is desired. It is proposed that sensible heat storage in a packed bed of rock, with air as heat transfer medium, is suitable at temperatures of 500 – 600 °C. To determine if this concept is technically feasible and economically competitive with existing storage, rock properties, packed bed pressure drop and thermal characteristics must be understood. This work addresses these topics.
No previously published data is available on thermal cycling resistance of South African rock, and there is limited data from other countries in the proposed temperature range for long-term thermal cycling, so samples were thermally cycled. There is rock which is suitable for thermal storage applications at temperatures of 500 – 600 °C. New maps of South Africa showing where potentially suitable rock is available were produced. Dolerite, found extensively in the Karoo, is particularly suitable.
Friction factors were measured for beds of different particles to determine the importance of roughness, shape, and packing arrangement. Five sets of rock were also tested, giving a combined dataset broader than published in any previous study. Limitations of existing correlations are shown. The friction factor is highly dependent on particle shape and, in the case of asymmetric particles, packing method. The friction factor varied by up to 70 % for crushed rock depending on the direction in which it was poured into the test section, probably caused by the orientation of the asymmetric rock relative to the air flow direction. This has not been reported before for rock beds. New isothermal correlations using the volume equivalent particle diameter are given: they are within 15 % of the measurements. This work will allow a techno-economic evaluation of crushed rock beds using more accurate predictions of pumping power than could previously be made.
Thermal tests below 80 °C show that bed heat transfer is insensitive to particle shape or type. A heat transfer correlation for air in terms of the volume equivalent diameter was formulated and combined with the E-NTU method. The predicted bed outlet temperatures are within 5 °C of the measurements for tests at 530 °C, showing that the influence of thermal conduction and radiation can be reasonably negligible for a single charge/discharge cycle at mass fluxes around 0.2 kg/m2s.
A novel method for finding the optimum particle size and bed length is given: The Biot number is fixed, and the net income (income less bed cost) from a steam cycle supplied by heat from the bed is calculated. A simplified calculation using the method shows that the optimum particle size is approximately 20 mm for bed lengths of 6 – 7 m. Depending on the containment design and cost, the capital cost could be an order of magnitude lower than a nitrate salt system. / AFRIKAANSE OPSOMMING: Gekonsentreerde son-energie kragstasies is n belowende manier om elektrisiteit op te wek, maar hulle is afhanklik van die son as n bron van energie. Om drywing op aanvraag te voorsien moet hulle energie stoor. Tans is termiese stoor – gewoonlik gesmelte sout – hoewel funksioneel, duur, en n goedkoper oplossing word gesoek. Daar word voorgestel dat stoor van voelbare warmte-energie in n gepakte rotsbed met lug as warmteoordrag medium geskik is by temperature van 500 – 600 °C. Om te bepaal of dié konsep tegnies gangbaar en ekonomies mededingend met bestaande stoorstelsels is, moet rotseienskappe, gepakte bed drukval en hitteoordrag verstaan word. Hierdie werk spreek hierdie aspekte aan.
Geen voorheen gepubliseerde data is beskikbaar oor die termiese siklus weerstand van Suid-Afrikaanse rots nie, en daar is beperkte data van ander lande in die voorgestelde temperatuurbereik, dus is monsters onderwerp aan termiese siklusse. Daar bestaan rots wat geskik is vir termiese stoor toepassings by temperature van 500 – 600 °C. Nuwe kaarte van Suid-Afrika is opgestel om te wys waar potensieel geskikte rots beskikbaar is. Doleriet, wat wyd in die Karoo voor kom, blyk om veral geskik te wees.
Wrywingsfaktore is gemeet vir beddens van verskillende partikels om die belangrikheid van grofheid, vorm en pak-rangskikking te bepaal. Vyf rotsstelle is ook getoets, wat n saamgestelde datastel gee wyer as in enige gepubliseerde studie. Beperkings van bestaande korrelasies word aangetoon. Die wrywingsfaktor is hoogs sensitief vir partikelvorm en, in die geval van asimmetriese partikels, pakkings metode. Die wrywingsfaktor het met tot 70 % gevarieer vir gebreekte rots, afhanklik van die rigting waarin dit in die toetsseksie neergelê is. Dit is waarskynlik veroorsaak deur die oriëntasie van die asimmetriese rots relatief tot die lugvloei rigting, en is nie voorheen vir rotsbeddens gerapporteer nie. Nuwe isotermiese korrelasies wat gebruik maak van die volume-ekwivalente partikel deursnee word gegee: hulle voorspel binne 15 % van die gemete waardes. Hierdie werk sal n tegno-ekonomiese studie van rotsbeddens toelaat wat meer akkurate voorspellings van pompdrywing gebruik as voorheen moontlik was.
Termiese toetse onder 80 °C wys dat die warmteoordrag nie baie sensitief is vir partikelvorm en -tipe nie. n Warmte-oordragskorrelasie vir lug in terme van die volume-ekwivalente deursnee is ontwikkel en met die E-NTU-metode gekombineer. Die voorspelde lug uitlaat temperatuur is binne 5 °C van die meting vir toetse by 530 °C. Dit wys dat termiese geleiding en straling redelikerwys buite rekening gelaat kan word vir n enkele laai/ontlaai siklus by massa vloeitempos van omtrent 0.2 kg/m2s.
n Oorspronklike metode vir die bepaling van die optimum partikelgrootte en bedlengte word gegee: Die Biot-getal is vas, en die netto inkomste (die inkomste minus die bed omkoste) van n stoomsiklus voorsien met warmte van die bed
word bereken. n Vereenvoudigde berekening wat die metode gebruik wys dat die optimum grootte en lengte ongeveer 20 mm en 6-7 m is. Afhangende van die behoueringsontwerp en koste, kan die kapitale koste n orde kleiner wees as dié van n gesmelte nitraatsout stelsel
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Identifying the optimum storage capacity for a 100-MWe concentrating solar power plant in South AfricaMadaly, Kamalahasen 04 1900 (has links)
Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Central receiver power plants generate renewable electricity by exploiting the
energy provided by the sun. The conditions experienced in the Northern Cape
region of South Africa provide the ideal conditions for the development of these
plants. Without a storage medium these plants have capacity factors in the range
of 25-30%. The inclusion of a thermal energy storage medium provides the ability
to increase the capacity factors of these plants. Although storage increases the
costs, it results in better utilisation of the power block and a decrease in the
levelised electricity cost (LEC). Eskom intends building a 100MWe central
receiver dry cooled power plant in the Upington region. This research identifies
the appropriate storage medium and ideal storage capacity to achieve the lowest
LEC.
A literature survey was performed to identify the different methods of storage that
are available. The different storage methods were evaluated and the best storage
medium for a central receiver power plant based on the developments of the
various storage technologies was identified.
To determine the costs associated with a central receiver power plant, data
published by NREL was used. Different plant parameters were required to
evaluate the costs. A power plant model based on efficiencies and energy balances
was created to determine the required plant parameters. It provided the ability to
determine the effect of changing different plant parameters on the LEC and
estimate the plant output. The power block parameters were initially varied to
determine the most efficient power block configuration. Once the most efficient
power block configuration was identified the solar field and storage parameters
were varied to determine the plant configuration which resulted in the lowest
LEC.
The most efficient power block configuration of 0.4206 was found for a system
comprising of six feedwater heaters with the feedwater temperature of 230°C,
main steam pressure 140 bar and an exit steam generator salt temperature of
290°C. A solar multiple of 3.0 with 16 hours of storage resulted in a LEC of
R1.41/kWh with no system constraints. A capacity factor constraint of 60%
resulted in a solar multiple of 1.8 with 8 hours of storage and a LEC of
R1.78/kWh. / AFRIKAANSE OPSOMMING: Sonkragaanlegte met sentrale ontvangers wek hernubare elektrisiteit op deur
sonenergie te ontgin. Die klimaat in die Noord Kaap-streek van Suid-Afrika is
ideaal vir die oprigting van hierdie aanlegte. Sonder ’n bergingsmedium is die
kapasiteitsfaktore van sulke aanlegte ongeveer 25-30%. Met die insluiting van ’n
bergingsmedium vir termiese energie kan die kapasiteitsfaktore egter verhoog
word. Hoewel berging aanlegkoste verhoog, lei dit terselfdertyd tot beter
aanwending van die kragblok en ’n afname in die konstante eenheidskoste van
elektrisiteit (LEC). Eskom beplan om ’n droogverkoelde kragaanleg van 100 MW
met ’n sentrale ontvanger in die Upington-streek op te rig. Hierdie navorsing was
dus daarop toegespits om die mees geskikte bergingsmedium en ideale
bergingskapasiteit te bepaal om die laagste moontlike LEC uit die aanleg te
verkry.
’n Literatuurstudie is onderneem om die verskeie beskikbare bergingsmetodes te
bestudeer. Die verskillende metodes is beoordeel, waarna die beste
bergingsmedium vir ’n kragaanleg met ’n sentrale ontvanger op grond van die
ontwikkelings in die verskillende bergingstegnologieë bepaal is.
Om die koste van ’n kragaanleg met ’n sentrale ontvanger te bepaal, is
gepubliseerde data van die Amerikaanse Nasionale Laboratorium vir Hernubare
Energie (NREL) gebruik. Verskillende aanlegparameters was egter nodig om die
koste te beoordeel. Dié parameters is gevolglik bepaal deur ’n kragaanlegmodel
op grond van doeltreffendheidsfaktore en energiebalanse te skep. Sodoende kon
vasgestel word watter uitwerking veranderinge in die verskillende parameters op
die LEC sou hê, en kon die aanleguitset geraam word. Die kragblokparameters is
aanvanklik afgewissel om die doeltreffendste kragbloksamestel te bepaal. Nadat
dít bepaal is, is die sonenergieveld en bergingsparameters weer afgewissel om vas
te stel watter aanlegsamestel die laagste LEC tot gevolg sou hê. Die beste termiese benuttingsgraad is behaal vir ʼn stoom siklus met ses water
verhitters en ʼn water temperatuur van 230 °C by die ketel se inlaat, ʼn stoom druk
van 140 bar, en sout uitlaat temperatuur van 290 °C. ʼn Vermenigvuldigingsfaktor
van drie vir die heliostaat veld, en 16 uur termiese energie storing gee ʼn
opwekkingskoste van R 1.41/kW/h indien daar geen beperkings op die grootte of
koste van die stelsel geplaas word nie. Indien die kapitaal uitgawe ʼn perk van
60 % op die kapasitiet van die stelsel plaas, verander die optimale ontwerpspunt
na ʼn vermenigvuldigingsfaktor van 1.8, en die termiese stoorkapasitiet verlaag na
8 uur. In hierdie geval is die opwekkingskoste R 1.78/kWh.
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Heliostat Design / HeliostatkonstruktionerBjörkman, Nils January 2014 (has links)
A heliostat is a motorized mirror used in a Solar Power Tower plant. The technology has been around since the 1970’s, and involves hundreds or thousands of heliostats reflecting the sun’s rays to the top of a high tower, where the incident solar energy is converted to heat energy, which in turn is used to drive steam turbines and produce electricity. Demonstration plants have been built in the U.S.A. and Spain, and a number of new facilities have been added since 2005. To achieve a commercial breakthrough, the technology must be made more efficient so that electricity can be produced at prices comparable with other options such as wind, photovoltaic, nuclear and coal. A critical component in the economics of the Solar Power Tower plant is the cost of the heliostat, which is estimated to account for approximately 50 % of the investment cost of the total plant. This report deals with the heliostat from a multifaceted perspective. Different design approaches are explained. First, mirror geometries, with manufacturing dimensions, for a rotation-symmetric paraboloid-shaped mirror-assembly are obtained for mirrors with different sizes with a Matlab code. Investigating wind loads are among the most important tasks in a heliostat development project, as large wind loads radically complicates the design work. A wind load calculation-method based on previous work by Sandia National Laboratories and finite element method (FEM) is used in this work to design heliostats to withstand expected wind loading. The design of the geometry and the structure to withstand wind loading is illustrated with two azimuth elevation heliostats (25 m 2 and 49 m2). Finally, a number of innovative technical solutions are suggested. These are a new mirror facet mounting technique, sliding bearings, elevation drive, and a very unique azimuth motor module, which uses steel wires as belts with an integrated brake. It is hoped that the results and designs presented in this thesis will be a good foundation for further research in the heliostat structures and heliostat controls at the Robotics lab in IISc and elsewhere. Keywords: Solar Power, Heliostat, Thermal solar power, Solar Power Tower, Central Receiver System / En heliostat är en motordriven spegel som används i tornsolkraftverk, kända som Solar Power Tower, även kallade Central Receiver system. Tekniken har funnits sedan 1970-talet och går ut på att hundratals eller tusentals heliostater speglar solstrålarna till toppen av ett högt torn, där stålningsenergin omvandlas till värmeenergi, som t.ex. kan användas till att driva ångturbiner och producera elektricitet. Demonstrationsanläggningar har byggts i bland annat USA och Spanien, och ett flertal nya installationer har tillkommit sedan år 2005. För att verkligen nå ett kommersiellt genombrott måste tekniken göras billigare så att solelen kan produceras till minst lika bra pris som andra alternativ, så som t.ex. solceller, kärnkraft och kolkraft. En kritisk komponent för tornsolkraftverkens ekonomi är kostnaden för heliostaterna, som beräknas stå för ungefär 50 % av anläggningens totala investeringskostnad. Den här rapporten avhandlar heliostaten ur ett mångfacetterat perspektiv där olika konstruktionsspår förklaras. Vidare behandlar rapporten spegelgeometrier, och en Matlab-kod som genererar tillverkningsmått för en rotationssymmetrisk paraboloidformad spegelyta finns bifogad. Att undersöka vindlaster är bland det viktigaste i ett heliostatutvecklingsprojekt, eftersom dessa är de dimensionerande lasterna för designarbetet. Här används en vindlastberäkningsmetod utgiven av Sandia National Laboratories, som kortfattat går ut på att man multiplicerar det dynamiska vindtrycket med en korrigeringsfaktor som baserats på emiriska studier av heliostatmodeller i vindtunnel. En dimensioneringsprocess för heliostater föreslås och utvecklingsgången för två Azimut-Elevation heliostater i storlek 25 m 2 resp. 49 m2 demonstreras. FEM-mjukvara nyttjas som det främsta verktyget för att dimensionera heliostatkonstruktioner som kan stå emot vindlasterna. Slutligen ges förslag på innovativa tekniska lösningar för spegelmontering, glidlager, montering av elevation-motorerna, och en unik azimut-motormodul, vilken använder stålvajrar som remmar och har en integrerad broms. Med all denna information bör Robotics Lab på IISc ha en god grund att stå på inför vidare forskning inom konstruktion och styrning av heliostater. Nyckelord: Solenergi, Heliostat, Termisk solenergi, Solar Power Tower, Tornsolkraftverk
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Conception optimale de centrales solaires à concentration : application aux centrales à tour et aux installations "beam down" / Optimal design of solar thermal power plants : application to solar power tower and "beam down" concentratorsFarges, Olivier 05 June 2014 (has links)
Depuis les années quarante, la consommation énergétique mondiale n'a cessé d'augmenter. Cette énergie étant majoritairement d'origine fossile, il en résulte une augmentation globale de température terrestre. De ce fait, il est devenu urgent de réduire les émissions de gaz à effet de serre pour stopper le changement climatique. Dans ce contexte, le développement de la production d'électricité à partir d'énergie solaire concentrée par voie thermodynamique est une solution prometteuse. Les efforts de recherche visent à rendre cette technologie plus efficace et plus compétitive économiquement. Dans ce but, ce manuscrit présente une méthode de conception optimale pour les centrales solaires à récepteur central. Elle tire parti des méthodes développées depuis de nombreuses années par le groupe de recherche StaRWest, regroupant notamment des chercheurs des laboratoires RAPSODEE (Albi), LAPLACE (Toulouse) et PROMES (Odeillo). Couplant des algorithmes de Monte Carlo à hautes performances et des algorithmes stochastiques d'optimisation, le code de calcul implémentant cette méthode permet la conception et l'optimisation d'installations solaires. Il est utilisé pour mettre en évidence les potentialités d'un type de centrales à récepteur central peu répandu : les centrales à réflecteur secondaire, également appelées centrales de type "beam down". / Since the early 40's, world energy consumption has grown steadly. While this energy mainly came from fossil fuel, its use has included an increase in temperatures. It has become urgent to reduce greenhouse gas emissions to halt climate change. In this context, the development of concentrated solar power (CSP) is a promising solution. The scientific community related to this topic has to focus on efficiency enhancement and economic competitiveness of CSP technologies. To this end, this thesis aims at providing an optimal design method applied to central receiver power plants. It takes advantage of methods developed over many years by the research group StaRWest. Both RAPSODEE (Albi), LAPLACE (Toulouse) and PROMES (Odeillo) researchers take an active part in this group. Coupling high performance Monte Carlo algorithms and stochastic optimization methods, the code we developed allows an optimal design of concentrated solar systems. This code is used to highlight the potential of an uncommon type of central receiver plants: reflective towers, also called "beam down" central receiver systems.
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Introducing a central receiver system for industrial high-temperature process heat applications : A techno-economic case study of a large-scale CST plant system in a South African manganese sinter plantHallberg, Maria, Hallme, Elin January 2019 (has links)
The objective of this thesis was to investigate the potential for introducing a concentrating solar thermal (CST) central receiver plant system based on flexible heliostats - HelioPods - to provide high-temperature process heat in industrial applications. A CST plant system was designed in MATLAB, optically simulated for three design days in the ray-tracing software Tonatiuh and further analyzed in MATLAB by interpolating the results for each hour of the year. A case study was made on introducing a CST plant system based on HelioPods in a South African manganese sinter plant. The study included an investigation of the profitability of up- and downsizing the heliostat field annually with fluctuating heat demand. A circular heliostat field was modelled for the chosen location. The final field had a radius of 53 meters with the receiver located 60% from the field centre. The storage size was 16 demand hours and 17 plants were required. The results showed that 88% of the annual heat demand could be covered by solar heat in the design year. The marketing approach used for the following years was that the heat demand covered by solar heat should never be below the share at the first year, despite the predicted fluctuations in demand. Thus, a minimum solar share of 88% was used as a strategy for annual up- and downsizing of the fields throughout the investigated period of 25 years. That resulted in a field radius differing between 52 and 55 meters. The payback period of the final system was 4.35 years, the NPV was 54.33 MUSD over a period of 25 years and the LCOH was 35.39 USD/MWht. However, it was found that the profitability of the system was sensitive to the different scenarios for predicted future diesel prices, this since the pricing of the solar heat was set to 90% of the diesel price. The results in this thesis show that a CST plant system based on HelioPods is a suitable solution to supply high-temperature process heat to industrial applications. It also shows that the HelioPods can unlock potential for flexibility with changing production patterns in the industry of implementation. The results from the study can be used also for other industries with similar temperature range and heat demand. Thus, it could be argued that the implementation of a HelioPod based CST plant system also can be suitable for other industries located in high-DNI areas with dependency on conventional fuels and steady production throughout the whole day. / Syftet med denna uppsats var att undersöka potentialen för implementering av koncentrerad termisk solvärme (CST) från ett soltorn med ett heliostatfält baserat på flexibla heliostater - HelioPods – för att generera högtempererad processvärme för industriell tillämpning. Ett CST-system designades i MATLAB, simulerades för tre designdagar i det optiska ray-tracingprogrammet Tonatiuh och analyserades sedan åter i MATLAB genom att interpolera de genererade resultaten för årets alla timmar. En fallstudie av ett CST-system baserat på HelioPods i ett sydafrikanskt sinterverk för mangan genomfördes därefter. Studien innehöll en undersökning av lönsamheten av årlig ökning och minskning av heliostatfältet vid fluktuerande värmebehov. Ett cirkulärt heliostatfält modellerades för den valda platsen. Det slutgiltiga fältet hade en radie om 53 meter med mottagaren placerad 60% från fältets mittpunkt. Storleken på lagringsfaciliteten var 16 timmar av full tillförsel och antalet verk uppgick till 17. Resultaten visade att 88% av det årliga värmebehovet kunde förses med solvärme under designåret. Marknadsstrategin för de resterande åren var att den procentuella andelen solvärme aldrig skulle vara lägre än under designåret, oberoende av fluktuationer i värmebehovet på grund av ändrad produktion. Således sattes 88% solvärme som ett minimikrav och utgjorde strategin för den årliga ökningen och minskningen av fältet för den undersökta perioden av 25 år. Det resulterade i en fältradie mellan 52 och 55 meter. Återbetalningstiden för det slutgiltiga fältet var 4.35 år, nuvärdesberäkningen av det framtida kassaflödet var 54.22 miljoner USD över en 25-årsperiod och produktionskostnaden för värme (LCOH) var 35.39 USD/MWht. Dock var systemets lönsamhet känslig för de olika prognoser av framtida dieselpriser som undersöktes, detta eftersom priset för solvärme sattes till 90% av dieselpriset. Resultaten i denna uppsats visar att ett CST-system baserat på HelioPods är en lämplig lösning för att generera högtempererad processvärme för industriell tillämpning. De visar även att HelioPods kan öka potentialen för flexibilitet vid förändringar i produktionsmönstret i vederbörande industri. Resultaten kan även användas i andra industrier med likartade temperaturer och värmebehov. Hävdas kan således att implementation av ett CST-system kan vara lämpligt även för andra industrier belägna i områden med högt DNI som är beroende på konventionella energikällor och har jämn produktion dygnet runt.
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