Degree Project in Heat and Power TechnologySecond Cycle, 30 ECTSStockholm, Sweden 2018

Introducing acentral receiversystem forindustrialhigh-temperatureprocess heatapplicationsA techno-economic casestudy of a large-scale CSTplant system in a SouthAfrican manganese sinterplantMaria HallbergElin Hallme

KTH ROYAL INSTITUTE OF TECHNOLOGYSUSTAINABLE ENERGY ENGINEERING

Title registration number

TRITA-ITM-EX 2019:89

Authors

Maria Hallberg Elin Hallme Sustainable Energy EngineeringKTH Royal Institute of Technology

Place for project

Stellenbosch, South AfricaStockholm, Sweden

Examiner

Dr. Björn LaumertHeat and Power TechnologyKTH Royal Institute of Technology

Supervisors

Dr. Rafael GuedezResearcher within Heat and Power TechnologyKTH Royal Institute of Technology

Dr. Matti LubkollResearch Group Coordinator at STERGStellenbosch University

Acknowledgements

First of all, we would like to thank Dr. Matti Lubkoll for giving us the unforgettableopportunity to do our thesis project at STERG in Stellenbosch, South Africa.You have supervised us with patience and positive energy, always eager to shareyour knowledge, regardless of the intelligence level of our questions. Your greatcommitment and interest in concentrating solar technologies is admirable and weare grateful for all your help and input in this thesis work.

We would also like thank Dr. Rafael Guedez, our supervisor at KTH. You inspiredus to write a thesis within the field of concentrating solar technologies and helpedus to actualize that idea. Thank you for your input and for keeping us on trackalong the way, as well as for arranging our presentation. A great thanks also toour examiner, Dr. Björn Laumert, for correcting our thesis and for enabling ourpresentation despite the circumstances.

Thank you Christoph Pan for your invaluable help and patience regarding MATLAB.Without your help, the monster would never have been tamed. Great thanks alsoto Matthew Meas for helping us with Tonatiuh in a very pedagogic way. A specialthanks also to Elias Basson, Simon Puteanus, Otto Sheffler and Jean-Gerard de laBat for your time, effort and strong arms during our field work.

Lastly, we would like to thank Vargöstiftelsen and Nils Ohlssons Stiftelse for thegenerous support, and Azelio for the interest in our thesis work and the valuableinput on our presentation.

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Abstract

The objective of this thesis was to investigate the potential for introducing aconcentrating solar thermal (CST) central receiver plant system based on flexibleheliostats - HelioPods - to provide high-temperature process heat in industrialapplications. A CST plant system was designed in MATLAB, optically simulatedfor three design days in the ray-tracing software Tonatiuh and further analyzed inMATLAB by interpolating the results for each hour of the year. A case study wasmade on introducing a CST plant system based on HelioPods in a South Africanmanganese sinter plant. The study included an investigation of the profitability ofup- and downsizing the heliostat field annually with fluctuating heat demand.

A circular heliostat field was modelled for the chosen location. The final field had aradius of 53 meters with the receiver located 60% from the field centre. The storagesize 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. Themarketing approach used for the following years was that the heat demand coveredby solar heat should never be below the share at the first year, despite the predictedfluctuations in demand. Thus, a minimum solar share of 88% was used as a strategyfor annual up- and downsizing of the fields throughout the investigated period of 25years. 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 MUSDover a period of 25 years and the LCOH was 35.39 USD/MWht. However, it wasfound that the profitability of the system was sensitive to the different scenarios forpredicted 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 asuitable solution to supply high-temperature process heat to industrial applications.It also shows that the HelioPods can unlock potential for flexibility with changingproduction patterns in the industry of implementation. The results from the studycan be used also for other industries with similar temperature range and heatdemand. Thus, it could be argued that the implementation of a HelioPod basedCST plant system also can be suitable for other industries located in high-DNIareas with dependency on conventional fuels and steady production throughout thewhole day.

Keywords

Solar energy, concentrating solar thermal, CST, central receiver system, CR,HelioPod, high-temperature process heat, manganese, business case

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Sammanfattning

Syftet med denna uppsats var att undersöka potentialen för implementering avkoncentrerad termisk solvärme (CST) från ett soltorn med ett heliostatfält baseratpå flexibla heliostater - HelioPods – för att generera högtempererad processvärme förindustriell tillämpning. Ett CST-system designades i MATLAB, simulerades för tredesigndagar i det optiska ray-tracingprogrammet Tonatiuh och analyserades sedanåter i MATLAB genom att interpolera de genererade resultaten för årets alla timmar.En fallstudie av ett CST-system baserat på HelioPods i ett sydafrikanskt sinterverkför mangan genomfördes därefter. Studien innehöll en undersökning av lönsamhetenav årlig ökning och minskning av heliostatfältet vid fluktuerande värmebehov.

Ett cirkulärt heliostatfält modellerades för den valda platsen. Det slutgiltiga fältethade en radie om 53 meter med mottagaren placerad 60% från fältets mittpunkt.Storleken på lagringsfaciliteten var 16 timmar av full tillförsel och antalet verkuppgick till 17. Resultaten visade att 88% av det årliga värmebehovet kunde försesmed solvärme under designåret. Marknadsstrategin för de resterande åren var attden procentuella andelen solvärme aldrig skulle vara lägre än under designåret,oberoende av fluktuationer i värmebehovet på grund av ändrad produktion. Såledessattes 88% solvärme som ett minimikrav och utgjorde strategin för den årligaökningen och minskningen av fältet för den undersökta perioden av 25 år. Detresulterade i en fältradie mellan 52 och 55 meter.

Återbetalningstiden för det slutgiltiga fältet var 4.35 år, nuvärdesberäkningenav det framtida kassaflödet var 54.22 miljoner USD över en 25-årsperiod ochproduktionskostnaden för värme (LCOH) var 35.39 USD/MWht. Dock varsystemets lönsamhet känslig för de olika prognoser av framtida dieselpriser somundersöktes, detta eftersom priset för solvärme sattes till 90% av dieselpriset.Resultaten i denna uppsats visar att ett CST-system baserat på HelioPods ären lämplig lösning för att generera högtempererad processvärme för industrielltillämpning. De visar även att HelioPods kan öka potentialen för flexibilitet vidförändringar i produktionsmönstret i vederbörande industri. Resultaten kan ävenanvändas i andra industrier med likartade temperaturer och värmebehov. Hävdaskan således att implementation av ett CST-system kan vara lämpligt även för andraindustrier belägna i områden med högt DNI som är beroende på konventionellaenergikällor och har jämn produktion dygnet runt.

Nyckelord

Solenergi, koncentrerad termisk solvärme, CST, soltorn, HelioPod, högtempereradprocessvärme, mangan, affärsmodell

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Nomenclature

Abbreviations

BMC - business model canvasCAPEX - capital expendituresCO2 - carbon dioxideCR - central receiverCRF - capital recovery factorCSP - concentrating solar powerCST - concentrating solar thermalDNI - direct normal irradianceDoE - South African Department of EnergyDSO - distribution system operatorEOR - enhanced oil recoveryEPC - engineering, procurement and constructionESCO - energy service companyHCFeMn - high-carbon ferromanganeseHPA - heat purchase agreementHTF - heat transfer fluidIPP - independent power producerIRP - integrated resource planIRR - internal rate of returnJDA - joint development agreementKPI - key performance indicatorLCOE - levelized cost of electricityLCOH - levelized cost of heatLFR - linear Fresnel reflectorMn - manganeseNPV - net present valueNREL - National Renewable Energy LaboratoryO&M - operation and maintenanceOPEX - operational expendituresPBP - payback periodPDC - parabolic dish collectorPPA - power purchase agreementPTC - parabolic trough collectorPV - photovoltaicREIPPPP - renewable energy independent power producer procurement programRSA - Republic of South AfricaSASEC - Southern African Solar Energy ConferenceSiMn - silicmanganeseSTERG - Solar Thermal Energy Research GroupTES - thermal energy storageTSO - transmission system operatorUSD - U.S. American dollarZAR - South African rand

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Variables

α - elevation angleδ - declination angleηSF - solar field efficiencyθ - sun half angleϕ - latitude angleω - hour angleASF - solar field areacc - carbon contentCflow - cash flowChelio - cost of heliostatChx - cost of heat exchangerCinv - investment costCrec - cost of receiverCtower - cost of solar towerCTES - cost of thermal energy storageCtransp - cost of transportCtss - cost of transport supply systemEgross - gross heat outputEnet - net heat outputEsold - sold heatFCO2 - specific carbon dioxide emissionskd - dept interest ratekins - insurance costQf - fuel burned annuallyQinput - thermal input onto receiverr - discount raterf - field radius

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Contents

1 Introduction 11.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1.1 Thesis structure and disposition . . . . . . . . . . . . . . . . 11.2 Objective and research questions . . . . . . . . . . . . . . . . 21.3 Research questions . . . . . . . . . . . . . . . . . . . . . . . . . 31.4 Division and focus among the authors . . . . . . . . . . . . 31.5 General investigation strategy . . . . . . . . . . . . . . . . . . 3

2 Literature review 52.1 Concentrating solar power . . . . . . . . . . . . . . . . . . . . 5

2.1.1 Direct normal irradiance . . . . . . . . . . . . . . . . . . . . . 52.1.2 Concentrating solar collectors . . . . . . . . . . . . . . . . . . 62.1.3 Critical components in CR systems . . . . . . . . . . . . . . . 102.1.4 Current CR setups . . . . . . . . . . . . . . . . . . . . . . . . 12

2.2 Energy situation in South Africa . . . . . . . . . . . . . . . . 142.2.1 Electricity market . . . . . . . . . . . . . . . . . . . . . . . . 152.2.2 South African industry . . . . . . . . . . . . . . . . . . . . . . 172.2.3 CSP in South Africa . . . . . . . . . . . . . . . . . . . . . . . 182.2.4 Current market outlook . . . . . . . . . . . . . . . . . . . . . 202.2.5 Value chain and project structure . . . . . . . . . . . . . . . . 24

2.3 Components in a HelioPod based system . . . . . . . . . . 252.3.1 Development of the HelioPod . . . . . . . . . . . . . . . . . . 252.3.2 Target applications . . . . . . . . . . . . . . . . . . . . . . . . 272.3.3 Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292.3.4 Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302.3.5 Control system . . . . . . . . . . . . . . . . . . . . . . . . . . 302.3.6 Power generation . . . . . . . . . . . . . . . . . . . . . . . . . 312.3.7 Process heat . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

2.4 Concentrating solar thermal . . . . . . . . . . . . . . . . . . . 312.4.1 Examples of CST plants . . . . . . . . . . . . . . . . . . . . . 322.4.2 Current business models and markets . . . . . . . . . . . . . 342.4.3 Business opportunities . . . . . . . . . . . . . . . . . . . . . . 342.4.4 Industrial CST applications . . . . . . . . . . . . . . . . . . . 35

3 Methodology 413.1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413.2 Description of software . . . . . . . . . . . . . . . . . . . . . . . 41

3.2.1 Tonatiuh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

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3.3 Key performance indicators . . . . . . . . . . . . . . . . . . . 433.3.1 Net heat output . . . . . . . . . . . . . . . . . . . . . . . . . 433.3.2 Net heat sold . . . . . . . . . . . . . . . . . . . . . . . . . . . 433.3.3 The Specific CO2 Emissions . . . . . . . . . . . . . . . . . . . 433.3.4 The Capital Expenditures (CAPEX) . . . . . . . . . . . . . . 433.3.5 The Operational Expenditures (OPEX) . . . . . . . . . . . . 443.3.6 The Levelized Cost of Heat (LCOH) . . . . . . . . . . . . . . 443.3.7 The Net Present Value (NPV) . . . . . . . . . . . . . . . . . 443.3.8 Internal rate of return (IRR) . . . . . . . . . . . . . . . . . . 453.3.9 Payback period (PBP) . . . . . . . . . . . . . . . . . . . . . . 45

4 Simulation modeling 464.1 Model description . . . . . . . . . . . . . . . . . . . . . . . . . . 46

4.1.1 Sun angles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464.1.2 Heliostat field . . . . . . . . . . . . . . . . . . . . . . . . . . . 474.1.3 Optical simulation in Tonatiuh . . . . . . . . . . . . . . . . . 504.1.4 Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 504.1.5 Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 504.1.6 Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

4.2 Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514.3 Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

4.3.1 Cost assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 524.3.2 Choice of approach . . . . . . . . . . . . . . . . . . . . . . . . 524.3.3 Number of plants . . . . . . . . . . . . . . . . . . . . . . . . . 534.3.4 Storage size . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534.3.5 Interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

5 Economic and logistic business model 555.1 Business model . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

5.1.1 Target customer segments . . . . . . . . . . . . . . . . . . . . 565.1.2 Value propositions . . . . . . . . . . . . . . . . . . . . . . . . 565.1.3 Distribution channels . . . . . . . . . . . . . . . . . . . . . . 575.1.4 Customer relationships . . . . . . . . . . . . . . . . . . . . . . 585.1.5 Revenue streams . . . . . . . . . . . . . . . . . . . . . . . . . 585.1.6 Key activities . . . . . . . . . . . . . . . . . . . . . . . . . . . 585.1.7 Key resources . . . . . . . . . . . . . . . . . . . . . . . . . . . 585.1.8 Key partners . . . . . . . . . . . . . . . . . . . . . . . . . . . 595.1.9 Cost structure . . . . . . . . . . . . . . . . . . . . . . . . . . 59

5.2 Logistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

6 Modeling results and discussion 606.1 Plant system design . . . . . . . . . . . . . . . . . . . . . . . . . 606.2 Logistical results . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

6.2.1 Field study . . . . . . . . . . . . . . . . . . . . . . . . . . . . 646.2.2 Up- and downsizing of heliostat field . . . . . . . . . . . . . . 676.2.3 Cash flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 706.2.4 The dynamics between several CST plant systems . . . . . . 70

6.3 Sensitivity analysis . . . . . . . . . . . . . . . . . . . . . . . . . 71

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6.3.1 Heliostat cost . . . . . . . . . . . . . . . . . . . . . . . . . . . 716.3.2 Resilience to changes in diesel price . . . . . . . . . . . . . . . 716.3.3 Labour costs . . . . . . . . . . . . . . . . . . . . . . . . . . . 726.3.4 Output to process . . . . . . . . . . . . . . . . . . . . . . . . 73

6.4 Evaluation of CST plant . . . . . . . . . . . . . . . . . . . . . . 746.4.1 Business model . . . . . . . . . . . . . . . . . . . . . . . . . . 746.4.2 Analysis through Hughes’ concepts . . . . . . . . . . . . . . . 74

6.5 SWOT analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

7 Conclusion 787.1 Future work and recommendations . . . . . . . . . . . . . . 79

7.1.1 Pilot plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . 797.1.2 Transportation of particles . . . . . . . . . . . . . . . . . . . 797.1.3 Technical design of the HelioPod . . . . . . . . . . . . . . . . 797.1.4 Plonkable tower . . . . . . . . . . . . . . . . . . . . . . . . . 797.1.5 Integration of PV . . . . . . . . . . . . . . . . . . . . . . . . . 807.1.6 Market and legislation analysis . . . . . . . . . . . . . . . . . 80

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Chapter 1

Introduction

1.1 Overview

Concentrating solar technologies with thermal energy storage (TES) have thepotential to generate renewable energy 24 hours per day. Such technologies canbe subdivided into two main groups; concentrating solar power (CSP) for electricitygeneration and concentrating solar thermal (CST) for heat generation. The onlylarge difference in the plant design is the power block that is excluded in a CSTplant.

In this thesis, the implementation of CST in industrial high-temperature applicationswas investigated. Furthermore, a case study was made on introducing a CST centralreceiver (CR) system with the purpose of supplying high-temperature process heatto the manganese industry in South Africa. Thus, a CR plant was modelled andsized to fit the current heat demand of the Kalagadi Manganese sinter plant. Asthe annual production rate of manganese is fluctuating, a case study was madefor the thermal output from the plant to fit the annual heat demand. To do so,an investigation on changing the plant size by adding and removing heliostats wasdone. This was possible due to the fact that the studied heliostat systems - theHelioPods - developed by the Solar Thermal Energy Research Group (STERG) atStellenbosch University are easily assemblied and disassemblied. Based on this, thehypothesis was that it could be shown that the introduction of a CST system inthe South African manganese industry can be profitable, as well as that it would bepossible to create a profitable dynamic business case in which the CST plant systemcould be adapted to the sinter production rate on an annual basis.

1.1.1 Thesis structure and disposition

The thesis is divided into seven chapters. They are presented briefly below to givethe reader an overview of the thesis disposition.

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Table 1.1: The seven chapters.

Chapter Content1 A brief overview, the research questions and the

hypothesis

2 The general background information from a literaturereview

3 The methodology, softwares and equations used

4 The developed simulation model

5 The business model for the investigated case study

6 Quantitative results from the developed model andresults from field study, as well as a discussion

7 Conclusion of the findings in the thesis work andpresentation of suggestions of future directions ofresearch and improvements

1.2 Objective and research questions

The purpose of this study was to investigate the potential for introducing CSTbased on flexible heliostats - HelioPods - to provide high-temperature process heatin industrial applications. A case study was made on introducing a CST plantsystem based on HelioPods in a manganese sinter plant. Firstly, the investigationwas made based on a steady manganese production. Secondly, a business case anda dynamic model were created to evaluate the potential for up- and downsizing thesystem to fit the annual fluctuations in manganese production from an ESCO’s pontof view.

CR systems with a heliostat field for generating thermal heat is the technologystudied in this thesis. Hereafter, when referring to a CST plant, that is the typeof technology being considered, excluding consideration of other concentrating solartechnologies unless specified explicitly.

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1.3 Research questions

This thesis provides a framework for how solar heat from a CST plant systembased on HelioPods can be introduced in high-temperature industrial applications.By preforming a case study of a manganese sinter plant in South Africa, realisticproduction rates were used in the model.

Q.1 Is a CST plant system based on HelioPods a suitable solution to supplyhigh-temperature process heat to industrial applications?

Q.1.1 Which are the benefits of introducing a CST plant system basedon HelioPods to supply high-temperature process heat to industrialapplications?

Q.1.2 Can the HelioPods unlock the potential for flexibility withchanging production patterns?

Q.1.3 Is annual up- and downsizing of the CST plant system based onHelioPods profitable as a business case with changing manganese sinterproduction?

Q.1.3.1 What is the internal rate of return (IRR) of a CSTplant system based on HelioPods introduced in a manganese sinterplant?

1.4 Division and focus among the authors

In this thesis the authors have been working closely together for the main part ofthe project, but with different focus areas. Maria Hallberg has mainly been focusingon the plant modeling, due to her specialization in solar energy. Her experience insimilar softwares was of great importance for the quantitative outcome. Elin Hallmehas mainly been focusing on the business case and the economic modeling, due to herspecialization in transformation of energy systems. Hallme has also studied businessadministration which brought additional value to the economic evaluation.

1.5 General investigation strategy

The research made in this thesis is quantitative as it was based on the analysis ofmeasured and calculated data and analyzed through numeric comparisons. Firstly,a literature review was made. As a start, the current system set-ups and thecharacteristics of the technology were investigated. By evaluating impacts such asthe plant size, operating strategies and standard performance, the previous researchbecame the base to the first approach of a plant model. To design a convenient plant,the purpose of the plant had to be defined. In this thesis, the aim was to investigatethe convenience of introducing CST in high-temperature industries, exemplified bymodelling a system to provide the manganese industry with an alternative heatingsupply for the preheating of manganese ore. Once the purpose and the location of

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the plant were fixed the modeling began. By optimizing the field size according tothe limitations of the designated receiver and always striving to achieve the highestpossible field efficiency, the optimal field size was found.

The following step was to investigate the optical performance of the plant. Thesoftware Tonatiuh uses a Monte Carlo ray tracer for the optical simulation of solarconcentrating systems and was used to simulate the optical performance. Threedesign days were simulated. The obtained flux onto the receiver was then analyzedin MATLAB. The interpolation in between the design days resulted in an hourlyenergy flux over the entire year, providing hourly results. As the aim of the studywas not limited to an evaluation of a plant but to put it into a context, a businesscase was created. The heating demand from a manganese sinter plant was introducedto investigate how large share of the demand a CST plant system could coverthroughout a year. Figure 1.5.1 illustrates a flowchart of the methodology.

Figure 1.5.1: Flowchart of the methodology.

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Chapter 2

Literature review

In this chapter, an introduction to the discussed technologies as well as the currentmarket are presented.

2.1 Concentrating solar power

The interest in CSP has grown stronger over the last decades as a result of thetransition towards a sustainable energy sector around the globe, where renewableenergy technology plays an important role. The growing attention for CSP is mainlydue to the fact that it is one of few renewable energy technologies applicable witha cost-effective energy storage [1]. The first commercial plants started operating inthe mid 80’s and since 2006, several plants have been commercially introduced -initially in Spain and the US and now globally. In 2010 the total capacity of CSPapproached 1 GW and with all ongoing projects worldwide the expected installedcapacity in 2020 is 11 GW [2][3]. Today CSP is mainly used to generate electricity,however, it can also be used for thermal heat generated directly, CST. This type ofapplications are not as common commercially and to better explain the technologyand current set-ups, the following sections are mostly focused on CSP.

2.1.1 Direct normal irradiance

The energy input source for CSP is sunlight. The sunlight reaching the Earth’ssurface is either direct or indirect. On a clear day the direct irradiance can reachup to 90% of all the solar energy. The weather is one of the sources that affects theshare of direct sunlight. If it is cloudy or foggy the direct sunlight can be almostnon-existing. In a CSP design the direct solar irradiance is crucial in order to reachthe high temperatures desired in the system. By using mirrors or lenses the sunlightis being directed to a small area, the receiver, that collects the heat. To achieve highefficiency of the system it is important to choose a suitable location for the plant bymeasuring the direct normal irradiance (DNI). The DNI can also provide the firstapproximation of the output potential of the CSP plant. The rule of thumb is to

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have a bottom threshold of DNI around 2000 kWh/m2 for cost-effective deployment[2].

The weather is not the only factor determining the magnitude of DNI at a specificlocation. The composition of the atmosphere is another aspect that must be takeninto consideration. Areas with a high DNI are usually found on latitudes from 15°to 40° North or South of the equator with a relatively dry climate. Areas withlatitudes lower than 15° are characterized by a more cloudy atmosphere and wetsummers while in latitudes higher than 40° the weather is often too cloudy for CSP.However, the DNI increases with higher altitudes since the absorption and scatteringof sunlight is lower. Figure 2.1.1 below shows how the DNI varies around the globe[2].

Figure 2.1.1: World map of the distribution of direct normal irradiation [4].

The annual amount of solar energy reaching the Earth’s surface is close to 885 millionTWh, making it the most important energy source available. However, there aresome disadvantages when using the sun as a main energy source. The intermittenceand variability of the sun cannot be disregarded. The sun rises and sets every day,creating intermittence. The variability is strongly connected to the weather and theatmospheric conditions. Even so, the variability is significantly lower than for othercomparable renewable energy sources such as wind. As a result of the disadvantages,it is common to include a storage facility in the design of a CSP plant in order todecrease the consequences caused by intermittence [5].

2.1.2 Concentrating solar collectors

The technology behind CSP is different to a photovoltaic (PV) system. The maindifference is that CSP systems use the sun as a thermal energy source instead ofphoton energy for immediate electricity generation. As previously mentioned, theCSP technology uses mirrors or lenses to concentrate a large area of sunlight ontothe receiver [6]. After the sunlight reaches the receiver it will either be directeddirectly to the power block (steam turbines) or stay in storage tanks where the heat

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can be stored and used when needed. The storage possibility is one of the uniquecharacteristic of a CSP plant [3]. In Figure 2.1.2 below a typical plant schematic isshown.

Figure 2.1.2: Layout of a CR plant with molten salt storage [3].

Independent of collector technology used, the heat collected in the receiver can thenbe used as thermal energy or for generating electricity, typically through a steamturbine cycle that is connected to an electrical power generator [6]. Figure 2.1.3below illustrates how solar radiation is transformed to either electricity, or thermaland mechanical energy.

Figure 2.1.3: Flow diagram of energy transformation in CSP systems.

To convert solar energy to power or thermal heat, the radiation from the sun isconcentrated on a point or on a line where thermal energy is transferred to a heattransfer fluid (HTF). There are currently two primary categories for concentratingsolar technologies; the line-focused and the point-focused solar concentrators. Theline-focused concentrators reflect the solar radiation onto a linear receiver, achievinga concentration ratio between 30 and 80 in commercially available plants whereas thepoint-focused concentrators reflect the solar radiation onto a point receiver, reachingconcentration ratios of 800 for heliostat fields and 2000 for dish collectors [5]. Thefour main CSP technologies are shown in Figure 2.1.4; parabolic trough collectors(PTC), parabolic dish collectors (PDC), central receiver (CR) systems and linearFresnel reflectors (LFR) [7].

Parabolic trough collectors

Parabolic trough collectors (PTC) are line-focused and is the most deployedtechnology used in most commercial solar power plants [8]. A plant typically consistsof a group of mirrors, most commonly silvered acrylic with a parabolic shape. Theyare curved in one dimension to best focus the sunlight onto an absorber tube thatis located in the focal line of the parabola. The absorber tube is a type of heatcollector that usually consists of a metal tube covered by glass. In order to reduceconvective heat losses there is either air or vacuum between the two materials. Bothcomponents move together and track the sun’s position throughout the day. Thereflectors are connected in parallel and are referred to as the solar field. The most

7

Figure 2.1.4: The four types of concentrated solar power plants. (A) Parabolic trough collector(PTC); (B) Parabolic dish collector (PDC); (C) Central receiver (CR); (D) Linear Fresnel reflector(LFR) [6].

common HTF used in these systems are thermal fluids that can transfer heat to asteam cycle and further on to a Rankine power cycle. Another configuration it touse molten salts as a HTF or even the use of a steam generation system directly[7].

Linear Fresnel reflectors

Linear Fresnel reflectors (LFR) are line-focused and consist of long rows of slightlycurved or flat mirrors to reflect the sunlight onto a linear receiver. As a fixedcomponent, the receiver is mounted on a tower above or along the linear reflectors.The reflectors can track the movement of the sun on either a single or a dual axis.The main advantage of this system is the simplicity and the flexibility of the designthat allows for lower investment costs. It can facilitate direct steam generationmeaning that it can eliminate the need of HTF and heat exchangers. The maindrawbacks of LFR is that is less efficient and more difficult to incorporate storagecapacity into the system. However, new discoveries suggest two parallel receiversfor each row of mirrors, resulting in a smaller land area needed, to achieve the sameoutput [7].

Parabolic dish collectors

Parabolic dish collectors (PDC) are point-focused and concentrate the rays on afocus point above the center of the dish. Due to tracking, the entire system canfollow the movement of the sun [9]. One unique feature with this design is theelimination of HTF and cooling water. It also offers the highest transformationefficiency of any CSP system. However, it is a rather expensive technology and has alow compatibility with thermal storage and hybridization. Some claim that it couldbe a more compatible technology once the dishes could be mass-produced. Eachparabolic dish transfers heat independently and since the dishes have low capacities,

8

hundreds or thousands of them are needed to install a large-scale power plant. Thereis only one current operational plant, Maricopa Solar Project, in Arizona, USA.Theplant has a net capacity of 1.5 MW [7].

Central receiver system

Central receiver (CR) systems are point-focused and use a field of heliostat collectors,meaning a field of sun-tracking reflectors, to reflect sunlight to a focus point on topof a tower [9]. Heliostats are mirrors with a flat or slightly concave shape that cantrack the sun in dual axes. The heat is absorbed by a HTF in the central receiverand transfers the heat to heat exchangers that can power a steam cycle. Very hightemperatures can be achieved which increases the efficiency of the output [7]. Thistechnology is known for its flexibility due to its variety of heliostat fields, the differentdesigns of solar receivers, and the range of HTF:s [9].

Historically, one of the main reasons for the slow adoption of CR systems comparedto PV has been the difficulty to scale the plant modularly, this due to an inverserelationship between energy cost and plant size due to thermo-economic reasons.The ability to up- and down-scale is a clear advantage of PV, enabling businesses ina wide range of markets. Several studies have shown that there is a great potentialin using small heliostats, but there is a lack of results regarding the advantages inoperation and maintenance when the number of heliostats is large [10].

Comparison of CSP collectors

As previously mentioned, PTC plants are by far the most commonly used CSPtechnology in commercially operating plats. When comparing the costs of plantdevelopment, the two most expensive systems are CR and PDC. Predictions offuture costs assume that CR systems will be the cheapest CSP technology by 2020.CR systems and LFR require less use of land compared to PTC when producinga given output. However, PDC requires the smallest area of land among the fourstudied collectors. The next comparable category is the different water requirementsfor the cooling and condensing processes. PTC and LFR need around 3000 L/MWwhich can be compared to the water requirements of a nuclear reactor per MW. CRsystems require less water, approximately 1500 L/MW, and the PDC technologyrequires no water since the dishes are cooled by the surrounding air. However, PDCare more expensive and reduce the efficiency of the plant. The above mentionedrequirements should be compared to the water requirement of 2000 L/MW for acoal-fired power plant [7].

The concentration ratio of sun is a measurement to describe the intensity of energyconcentration achieved by a given receiver. A high ratio enables the possibilityto achieve better thermodynamic efficiency and that results in higher workingtemperatures. For the CR technology a large amount of irradiation is focused on asingle receiver reaching capacities of 200 to 1000 kW/m2. This results in minimalheat losses and simplifies heat transport and thus reduces costs [7]. To conclude, the

9

Table 2.1: Comparison of the different collector types[7][9][11].

Capacity[MW]

Operating temp.range [℃]

Solar conc.ratio [-]

Cooling water[L/MWht]

Storageintegration

PTC 10-200 20-400 15-45 3000 Possible

LFR 10-20 50-300 10-40 3000 Possible

CRS 10-150 300->1000 150-1500 1500 Highly possible

PDC 0.01-0.4 120-1500 100-1000 0 Difficult

CR technology is showing a promising outlook for future development. Table 2.1shows a comparison between the different described technologies.

Figure 2.1.5 shows how the global installed capacity has increased since the beginningof year 2000. Figure 2.1.6 shows the technological trends for CSP. Currently, PTCis the most common CSP technology but the predictions show a shift in technologytowards CR systems in the future.

Figure 2.1.5: The global installed CSPcapacity [12]. Figure 2.1.6: CSP technology trends [12].

Opportunities for CR systems

As previously mentioned, CR systems are interesting to study further due to thehigh operating temperatures of the system, the high solar concentration ratio andthe fact that it possesses very promising possibilities for storage integration. Onereason why this technology has not yet been widely deployed are the high costs.The lack of system maturity leads to higher risks, higher costs and higher LCOE.However, research has shown great opportunities for this technology, both for powerand thermal heat purposes.

2.1.3 Critical components in CR systems

In addition to the solar collectors described in Section 2.1.2, the receiver and thestorage unit are two critical components in a CR system.

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The receiver

The receiver is the component that absorbs the reflected energy from the heliostatfield. A HTF is pumped up the tower and into the receiver. Usually up to 95%of the reflected energy can be absorbed into the working fluid. The heated fluid(or steam) returns down the tower and can be used as to further generate electricalpower or as industrial process heat. The difference between a central receiver conceptcompared to the alternatives, trough or dish, is that the collected solar energy isbeing transmitted optically to a small area instead of being piped along a field. Thisgives this system the characteristic by large power levels (up to 500 MW) and hightemperatures (540 to 840 ℃) [13].

Thermal Storage Systems

All of the different collector types have the possibility to store heat, some better thanothers. Today most storage systems are using a mixture of molten salts as storagemedium. The concept behind thermal storage is quite straightforward. During theday when the sun is shining, excess heat is stored in the storage medium. By theevening when the sun sets, the stored heat can be introduced to the system and theplant can still generate electricity or heat. Figure 2.1.7 illustrates the DNI and theflows from the solar field to the turbine and the storage facility. Due to the rapid costreductions of PV-systems, a CSP plant without storage is almost irrelevant makingthis component of a plant ever so important. By introducing thermal storage to aCSP plant an increase capacity factor and a reduction of LCOE can be obtained[14].

Figure 2.1.7: Use of storage for shifting production to cover evening peaks.[14].

One of the advantages with the CR systems is the compatibility with storage systems.The TES systems can be categorized as active or passive according to the heattransfer in between the storage medium and the HTF. The active system refersto when the TES medium circulates through a heat exchanger during both thecharging and discharging processes. It is common to use one or two insulated tanksas containers for the TES medium. Active systems are usually classified as direct orindirect depending on if the media used in HTF and TES are the same. The mostcommon medium used in the two-tank active concept is molten salts. Passive TESsystems usually consist of a dual medium TES system, meaning that the HTF passesthough the TES material in order to charge or discharge it. The TES medium itself

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does not circulate. It is common to use a solid media such as concrete or solid phasechange materials. However, the main draw-back of that is the low conductivitywhich affects the charge and discharge rates [3].

2.1.4 Current CR setups

According to the National Renewable Energy Laboratory (NREL) there arecurrently 35 existing CR plants worldwide. The following sections describe twoof these setups and two planned setup more in detail[15].

Gemasolar

Torresol Energy in Seville, Spain, was the first company to build a commercial CRplant with a molten salt storage system. The plant has a 120 MW solar receiver anda storage unit that can reach up to 565°C. This was a milestone within the field ofCSP technologies. The project opened up new possibilities for the CR technologyas a large-scale application [16].

The plant consists of 2 650 heliostats requiring an area of 185 hectares. The plantcan generate 100 GWh/year and supply electricity to 25 000 homes. Each heliostathas an aperture area of 120 m2. The storage size is big enough to operate withoutsun radiation for 15 hours and contains 8 500 tons of salts. The plant is owned 60percent of the technology group SENER Grupo de Ingeniería and MASDAR, andAbu Dhabi Future Energy Company, controls the remaining 40%. The approximatecost of the plant is 230 million EUR [16][17].

Ivanpah

The world’s largest solar thermal power plant project is found in the desert ofCalifornia, USA. It is owned by BrightSource and has been in operation sinceFebruary 2014. The Ivanpah plant produces a gross total of 392 MW solar powerat full capacity. It consists of three solar towers of 137 meters each and a total of173 500 heliostats. The heliostats are placed onto metal pylons that are individuallydriven into the ground [18][19]. Each heliostat consists of two mirrors and has anaperture area of 15 m2. That results in a heliostat field of 2,600,000 m2 aperturearea and covers an area of 3 500 acres [20].

The plant is a joint effort between NRG Energy, Google and BrightSource Energyand the project received a 1.6 billion loan guarantee from the US Departmentof Energy. They estimate to pay 650 million USD in salaries for construction,and the operation is expected to have a payback period of 30 years [18]. Today,BrightSource’s Ivanpah plant accounts for close to 30% of all solar thermal energyin the whole country. The project has employed nearly 3 000 site workers andtogether they have completed more than 8 million labor hours [18] [19]. However,this plant does not have any thermal storage. The estimation of the total cost for theplant is approximately 2,2 USD billion [20]. A study made by Tharp and Anderson

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[21] suggest that Ivanpah have a real LCOE of 110.9 USD/MWh and an internalrate of return (IRR) of 12.59%.

247Solar

247Solar is a U.S. American company mainly focusing on medium-scale CR setupsbased on a low-pressure Brayton cycle to generate electricity via a turbine incombination with a dry TES consisting of ceramics or firebrick. The so-calledModular Baseload Brayton Power Tower consists of a 30 to 40 meter tall tower, aheliostat field with dualaxis tracking mirrors and an air-heating solar receiver with ahigh-temperature heat exchanger transferring the heat to compressed air to power aturbine. The system is applicable both on- and off-grid. According to the company,a 247Solar plant offers lower building cost per kWh than a PV plant as well as lowCAPEX and O&M costs and minimal custom engineering. The LCOE is estimatedto less than 0.09 USD/kWh. Currently, it also has a configuration for combinedheat and power for which the 300 kWe basic model produces 300 kWh power and440 kW usable heat per hour with an efficiency of 75% [22]. In November 2016,247Solar announced an agreement with the South African company Stellenergy tocollaborate and build a plant in Southern Africa [23].

Copiapó

SolarReserve is a global developer of large-scale solar power projects. The companyhas selected the mining industry as a key customer segment and are now involved inprojects in mining regions all over the world. The opportunity within this sector isthe need for reliable energy supply each hour during the year, the lack of grid serviceand the increasing energy cost. By offering a base-load of solar supply the mines canenable a more cost-effective energy usage. SolarReserve has an ongoing project inthe Atacama Desert, Copiapó, which is a PV-CSP project. The plant configurationis with 2 CSP plants, with a net capacity of 130 MW each, in combination witha 150 MW PV park. With a molten salt TES system for 14 hours, the plant canprovide a base load every day throughout the year [24][25]. The project is expectedto cost around 2 billion USDS [26]. In Figure 2.1.8 the expected annual output fromthe mine is shown.

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Figure 2.1.8: Output in Copiapó on a monthly basis [25].

2.2 Energy situation in South Africa

The Republic of South Africa (RSA) is classified as a low- and middle-incomecountry and is approaching several issues to grow economically. Old and insufficientinfrastructure, inefficient administrative processes for international, national andlocal investments, a poorly structured governmental coordination and energychallenges such as blackouts, high tariffs and energy poverty in low-incomehouseholds due to underinvestments in the electricity sector are some of the mainissues [27].

Figure 2.2.1: Electricity sources in the South African power sector in 2016 [28].

South Africa is estimated to be the seventh largest coal producer worldwide andaccounts for the highest rate of greenhouse gas emissions per capita in Africa. Over77% of the country’s required energy is supplied from coal and 85.7% of the generatedelectricity, see Figure 2.2.1 above, and it is estimated that 45% of the carbon dioxideemissions origin from the power sector [27][28][29]. As the distribution infrastructurelacks, there are several areas - mainly rural - without access to the grid. Only 55%of rural households have access to electricity, compared to 88% of the urban. Sinceaccess to electricity is crucial for both social and economic development, lackingareas are far behind in industrial development, educational level, job opportunities

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and life quality. With large potential for renewables, mainly for solar and wind,there are great opportunities to change the energy situation. On average, SouthAfrica has 2 500 hours of sun per year and a radiation level between 4.5 to 6.6kWh/m2. Many regions in the country have an average of 8 to 10 hours of sun perday [29].

Several factors influence the implementation of renewables in the South Africanenergy system. The political situation with lacking policy certainty may affectinternational potential stakeholders’ willingness to invest, and there are uncertaintiesin which direction the government is leading the energy strategy. For instance,discussions to build a second nuclear power plant were held between the years of2006 and 2017. Furthermore, the reliability of the grid is inferior. The criticism onEskom’s grid maintenance is widespread and grid improvements - both in assetmanagement and grid extensions - are requested. There is also a lack in localtechnical skills, both in development and implementations of renewables. However,increasing research around the country is contributing to the knowledge base onrenewable energy technology, policy and other related matters, often on world-class level, and there is an institutional support which influences policies and fundresearch. In addition to that, the cost of renewable energy technologies is decreasing[29].

2.2.1 Electricity market

South Africa has been described as a technology colony due to the high dependenceon foreign technology. Historically, South African research has been limited andconcentrated to research institutions and few technologies have been finalized asproducts. Instead, the flow of imported products has been large from high-incomecountries and most business activities within the country have been carried outin the last steps of the product life-cycle. As for concentrated solar technologies,world-class research is now being done in South Africa and with a technologicalbreakthrough with respect also to the economic competitiveness, the investigatedtechnology could possibly be applied in several various areas of use, in different sizesand for both electricity and heat purposes, either separately or in combination withconventional energy technologies[30].

Eskom

Historically, the structure of the South African energy market has been centralized toEskom as a sole state-owned electric utility with a monopoly on the transmission anddistribution grid. As an independent power producer (IPP), the generated electricityhad to be sold to Eskom which sold and distributed it to customers. Since recently,IPP:s are permitted to generate and supply electricity, but currently, approximately95% of the electricity used in South Africa, including the industrial, commercial,agricultural and residential sectors, is generated by Eskom. Furthermore, thecompany generates 45% of the electricity used in Africa in total. However,

15

distribution has started to occur on municipality level and this trend is expectedto expand exponentially [31][32].

The Integrated Resource Plan (IRP)

The Integrated Resource Plan (IRP) was established by the South AfricanDepartment of Energy (DoE) in 2010 with the objective to obtain a sustainableand demand balanced energy sector. The plan contains generating capacity, type,timing and cost and considers economic, social and environmental deliberations andis a living plan, meaning that it is under continuous development. Over the next20 years, the GDP growth forecast is 4.6% in average, meaning that an increasein capacity of 52 248 MW is required. Furthermore, the projection is a continuousbeneficiation of local natural resources [33].

The six main categories for the IRP are affordability, reduction of carbon dioxideemissions, uncertainties of new technologies, use of water, job creation and energysecurity. This includes the following as in Table 2.2, cited from the DoE [33]:

Table 2.2: The six main categories for the IRP [33].

Categories1. How to increase the contribution of solar energy beyond the 600 MW in

the proposed scenario, and if possible commence with it earlier than theproposed 2014, in light of the potentially large economic multiplier

2. Viable opportunities and targets for biofuels and biogas and theincorporation of them earlier than 2020, for the same reason

3. Measures to ensure that the generation capacity anticipated in the IRP 2010is achieved as efficiently and timeously as possible, with the best possibleoutcomes in terms of economic growth, development and employment

4. Measures to minimise the impact of electricity pricing decisions on poorhouseholds, labour-absorbing sectors and industrial competitiveness

5. Measures to drive local production and supplier development of relevanttechnologies

6. The required reduction in the energy intensity of the economy and a costingof demand-side management measures

The Renewable Energy Independent Power Producer ProcurementProgramme (REIPPPP)

A competitive auction for IPP renewable energy projects was introduced in2011 by the DoE. The so-called Renewable Energy Independent Power ProducerProcurement Programme (REIPPPP) holds responsibility to dispense capacity fordifferent renewable energy technologies for which the IPPs bid for plants that theyplan to build [34]. The initial IRP plan has allocated 1100 MW to CSP technologiesuntil 2030 [10]. In 2017, 92 IPPs were allocated to introduce more than 6 300 MWrenewable power into the grid, mainly from solar and wind [29].

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2.2.2 South African industry

Ever since South Africa became a democracy in 1994 the country has gone throughchanges and the economic structure is no exception. By 2012 the GDP had increasedby 77% compared to 1994. However, the pace of the economic growth is still unstableand strongly linked to the performance of the global economy. In 2012 the strongestsectors in the industrial sector of South Africa’s GDP were: manufacturing (12.4%),mining and quarrying (9.3%) and agriculture (2.6%). The manufacturing sector isdominated by chemicals, metals and machinery as well as the food and beveragesectors. However, the contribution of the manufacturing to the overall GDP andemployment has declined in the past four decades [35].

The mining industry

The mining sector has become increasingly diverse since the 1980’s where themain share of the mining was gold. In 2012 the mining included several metalsand minerals, where coal was the biggest share. This is a result of the domesticand international power generation requirements. The mining sector plays aninvaluable role in the South African economy, especially due to the value additionand employment. The expenditures of the sector in the local economy benefitsother sectors in the country such as machinery and equipment, electricity, water,construction and civil engineering [35].

In 2017 the South African mining sector experienced a challenging year due toa global decline in demand and it continued facing major challenges locally. Ona domestic scale most challenges were connected to the structural nature of themining industry, such as costs associated with deep-level mining (mostly gold andplatinum) but also the increased pressured to address the environmental damageresulting from many decades of mining activities. The overall mining production in2017 increased by 4 % compared to the previous year and the manganese sub-sectorrecorded the highest growth rate at almost 31 % in 2017 [36]. Table 2.3. shows themost important minerals and metals mined in South Africa [37].

Energy demand

Close to 45 % of South Africa’s final energy demand is heat. A share of 67 % of theheat demand is used for industrial proposes. The most common fuel in the country isby far coal which stands for 57 % of the heating fuel, see Figure 2.2.3. However, coalis mainly used in the industrial sector where it accounts for 71 %. South Africa, likeother fossil dependent countries, are currently suffering from the rapid increasingcosts for fossil fuel. Even though coal is the most affordable energy source, the costshave increased on average 8.8 % on an annual basis over the last 20 years. Carbontaxing is currently being discussed on a governmental level in South Africa whichwould increase the prices even more and according to DoE, South Africa has about50 years left of coal supply. Thus, it is more important than ever to investigate otheralternatives for the mining sector to create a stable and sustainable industry in thecountry [38].

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Table 2.3: South Africa’s role in world mineral reserves, production and exports, 2012 (latestavailable data) – by mineral[37].

Commodity South Africa’sreserves

Worldranking

Location of majorreserves

Chromium 3 100 Mt 1 1. South Africa2. Kazakhstan3. Zimbabwe

Coal 30 156 Mt 8 1. USA2. Russia3. China

Copper 11 000 kt 11 1. Chile2. Peru3. Australia

Gold (metal) 6 000 t 2 1. Australia2. South Africa3. Russia

Manganese 150 Mt 1 1. South Africa(metal) 2. Ukraine

3. Brazil

Platinum 63 kt 1 1. South Africagroup metals 2. North America

3. Russia

46%

29%

14%

8%3% IndustrialTransport

Residential

CommercialAgricultural

Figure 2.2.2: Final energy demand inSouth Africa[35].

57%

16%

15%

9%3% Coal

Wood and bagasse

Electricity

Gas

Oil based

Figure 2.2.3: Fuels used for heatingpurposes in South Africa [35].

2.2.3 CSP in South Africa

South Africa has exceptional conditions for renewable energy systems such as windand solar. This results in a unique opportunity to generate energy at a low cost.Figure 2.2.4 shows the DNI map of South Africa. It is clear to see that the country isvery suitable for CSP due to the high levels of DNI in large parts of the country.

As previously mentioned, the main energy source in South Africa is coal. In 2012, itwas reported that some coal powered plants in the country had reached over 300%of their deign lifetime. As a results of the aging energy system, many power stationswill be decommissioned in the next decades [40]. In 2017, South Africa was theonly country to begin new commercial operations on CSP plants. Spain and theU.S. accounted for 80% of the global CSP capacity in 2017 while South Africa hadthe third highest CSP capacity installed. The global capacity is expected to growsignificantly in the upcoming years with several CSP projects in development allover the world. Even though South Africa is moving in a direction towards CSP,it should be stated that the country has strict requirements in regards to foreigninvestors and their use of local content [41]. Table 2.4 shows the current large-scaleCSP projects in South Africa. Two of them are CR plants, whereof one of them is

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Figure 2.2.4: DNI map of South Africa[39].

still under development[42][43].

Table 2.4: Current CSP plants in South Africa [42][43].

Bookport Ilanga I KathuSolarPark

KaXuSolar One

Khi SolarOne

Redstone XinaSolarOne

Location Groblershoop Upington Kathu Poffader Upington Postmasburg Pofadder

Owner ACWAPowerSolafricaBokpoortCSP PowerPlant (Pty)Ltd

N/A Kathu So-lar ParkConsor-tium

AbengoaSolar andIDC

AbengoaSolar andIDC

ACWA AbengoaSolar

Technology PTC PTC PTC PTC CR CR PTC

Storagecapacity[h]

9.3 4.5 4.5 2.5 2 12 5.5

Storagemedium

Molten salt Moltensalt

Molten salt Molten salt Saturatedsteam

Molten salt Moltensalt

Turbinenetcapacity[MW]

50 100 100 100 50 100 100

Generatedelectricity[GWh/yr]

230 N/A N/A 330 180 480 N/A

Approx.cost [USD]

565 N/A N/A 860 N/A N/A 880

PPA [yr] 20 20 20 N/A 20 N/A N/A

Projecttype

Commercial Commercial Commercial Commercial Commercial Commercial N/A

Status Operational Underdevelop-ment

Operational Operational Operational Under de-velopment

Operational

Start year 2016 2020 2018 2015 2016 2018 2017

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2.2.4 Current market outlook

The world of renewable energy technologies is under rapid development and aspreviously mentioned, CSP maintains a unique value on the market due to itscost-effective energy storage. In April 2018, 23 countries with a total global CSPcapacity of 9.95 GWh was installed or under development, whereof 5.21 GWh isalready in operation[44]. However, the CSP plants are not as cost competitivecompared to other renewable technologies and the conventional technologies [12].This is a result of high investment costs which can vary from 4000 USD/kW to9000 USD/kW depending on the solar resource and the capacity factor. Costs wereexpected to decrease as the deployment of CSP advanced and followed a learningrate of 10 percent, defined as the unit cost decrease by a constant percentage foreach doubling of experience[14][45]. Due to a decrease of market opportunities forCSP plants it is possible to see that the cost of materials has in fact increased,particularly the more mature part of the system such as power blocks. As forthe operations and maintenance (OM), a plant of 50 MW usually requires about30 employees for operation of the plant and about 10 additional employees forfield maintenance. Estimations show that O&M costs of 50 USD/MWh are to beexpected, see Figure 2.2.5 [14].

Figure 2.2.5: O&M costs for PTC and CR[46].

In 2014, the estimated cost of a PTC or CR plant with 4 to 8 hours TES was typically6 800 to 12 800 USD/kW, based on available cost data for existing plants. The costsare broken down in shares in Figure 2.2.6 where it can be seen that in a CR systemsin South Africa the heliostat field contributes to the largest cost, followed by otherdevelopment costs, total power block and engineering (including site preparations).Overall for the four South African projects included in this graph (three PTC andone CR), the total CAPEX was similar – USD 914 for PTC and USD 978 for CR[46].

In 2017, the estimated total installed cost of a PTC or CR plant with up to fourhours of TES was typically USD 3 500 to 9 000/kW, based on available cost data

20

Figure 2.2.6: Indicative breakdown of CSP plants per technology and storage size in 2014 [46].

for existing plants. Between 2013 and 2015, plants with four to eight hours ofTES costed USD 6 050 to 12 600/kW and plants with more than eight hours ofTES ranged between USD 7 300 and 11 300/kW. In 2017, a higher capacity of CRplants were under construction or development than PTC plants, see Figure 2.2.7.Regarding PTC, the main HTF is synthetic oil and for CR systems with molten saltholds the largest share (

LCOE of about 0.07 USD/kWh. CSP is estimated to supply a LCOE of about 0.12USD/kWh and for PV it has decreased to only 0.04 USD/kWh due to the currentlyrapid growth over the last decade [12]. However, it is important to state that eventhough this is an important key indicator, it does not represent the entire economicbalance of a CSP plant. Still, there is no doubt that the biggest barrier for theCSP-technology is the large initial investment costs [14].

Future outlook

The CR technology is expected to grow in the coming years and ultimately be thebiggest utility scale CSP technology. Figure 2.2.8 shows that the cumulative CSPcapacity is predicted to double between 2020 and 2030, followed by a reduction incost of installation of 25%. In 2050, 95 GW CSP is expected to be installed globally[49]. However, one bottleneck for this technology is the current costs where theheliostat field accounts for up to 40% of the total capital costs. Today, innovativedesign improvements can decrease that cost for which South Africa is responsible forseveral innovative solutions. By designing smaller heliostats one could decrease thecost of transportation and due to a less robust structure it would also result in lowermaterial costs. By optimizing the control system it is possible to reduce associatedcosts and the electrical system of the independent mirror driver can diminish theauxiliary power requirement [50].

Figure 2.2.8: Forecast of the global cost of CSP, cumulative capacity and annual installed capacity[49].

Another important component is the receiver, and by increasing the outlettemperature it is possible to increase the efficiency and decrease the thermal losseswhich could reduce costs up to 45%. Another aspect is the standardization whichwill come as the technology gets more mature. This creates a decline in building andoperating costs and enables cheaper manufacturing costs due to greater volumes. Allthese factors can generate a drop in LCOE by 50% between 2013 and 2020. Theestimation is that CSP will become 40 to 50% cheaper in South Africa over the nextdecade [50].

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South Africa is one of the emerging economies that has the manufacturing andtechnological innovation capability to become a competitive manufacturer of large-scale solar technologies. Estimations show that 70 to 85% of the capital cost for autility scale CR plant could be spent on domestically produced products in thefuture. This is a result of local technology pioneers that have developed newtechnologies including patented innovative control systems and new heliostat fieldconfigurations, potentially creating over 13 000 manufacturing and construction jobsby the mid 2020’s [50].

Benefits

A CSP plant with thermal storage has the opportunity to follow economic dispatchand provide other auxiliary services such as frequency responsive and regulatingreserves. Including a storage unit combines the operational flexibility with highcapacity value. In a study by Denholm and Hummon (2012) the process of howdispatched energy from CSP with thermal storage can benefit the system is shown.Figure 2.2.9 below shows the production from a CSP plant, with and without thermalstorage from a period of 3 days in Colorado, USA. The selected time period is duringwinter with a cloudy weather [51].

Figure 2.2.9: CSP with thermal energy storage dispatched against simulated January 22-24 energyprices in Colorado [51].

The system marginal price, usually the fuel cost or market price for fossil fuels, tomeet the demand is illustrated by the green line. The units of the system marginalprice (USD/MWh) are located on the right hand y-axis. The remaining two linesshow the generation of CSP with storage (blue) and without storage (red). It isclear that the generation from CSP without storage takes place mostly in the lowestprice intervals, following the typical PV generation. On the contrary, the blue lineshows that the generation from CSP with storage can maximize the energy benefitsby shifting energy to the highest price intervals. To conclude, the average valueof the energy generated in a CSP plant with storage is higher than the alternative[51].

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2.2.5 Value chain and project structure

The development phase of a new CSP plant involves four main phases: a proposalpreparation phase, a financing phase, a construction phase and an operationalphase. Projects are usually based on that competitive bid tenders decide on a PowerPurchase Agreement (PPA) between the power producer and the electricity buyersuch as utility companies or state-owned entities. The design of a public tenderoften includes a pre-qualification process in which the developers are assessed ontheir previous experience. Furthermore, a feasibility study including technological,environmental, socio-economic and political aspects is carried out in advance. Therequest for proposals may limit the proposed plant to a certain design. Once theseproposals are made public, the preparations of the power plant proposal are carriedout, including an evaluation of the available solar resource and a preliminary plantlayout of the main blocks as well as a review of the key performance indicators (KPI)for the bidding process [3].

Figure 2.2.10: The structure of the development phase of a CSP plant [3].

The criteria for the evaluation of the proposals include environmental, technical,and risk analyses and the winning consortium is selected by the public entity incharge of the tender. From that on, the PPA discussions begin. The financialpart of a CSP project is often based on large amounts of funding. Financialinstitutions are involved in the negotiations to set the framework and conditionssuch as equity-to-dept ratio and loans. Additionally, it happens that public entitiesbecome part-owners and in the case of international agreements, global organizationsand governments are sometimes involved in financing. When the financial closure isreached by being accepted of all involved parties, the investors assess and evaluatethe risks of the project and once the technology is fundraised, the project can beconsidered bankable [3].

Soon after the financial closure, the construction of the plant starts once theengineering, procurement and construction (EPC) company and the developer have

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agreed on their responsibilities for the project. The EPC company is responsiblefor the required equipment and for the construction within a pre-defined time forwhich the costs are usually presented in the preliminary budget which was part ofthe initial proposal. Additionally, a further specification of the technical propertiesis delivered. Once the whole plant is commissioned it has to be proven to meet thespecified operation requirements. When this has been approved, the company incharge of operation takes over the responsibility for operating the plant until it isdecommissioned. However, if the PPA is shorter than the lifetime of the plant, theownership or operator may change one or several times. In addition, transmissionsystem operators (TSOs) and distribution system operators (DSOs) are involved inthe operating phase [3].

2.3 Components in a HelioPod based system

For CR plants approximately 40% of the CAPEX lies in the heliostat field.Traditionally the heliostats are designed to achieve a large individual aperture area.Currently, research is focusing on this specific component in order to optimize thesize, shape and drive systems for different applications to reduce the cost [52].

2.3.1 Development of the HelioPod

As a starting point, researchers at Stellenbosch University chose to focus on theimprovements of the foundation of the system. Looking beyond the traditionalsystem, new innovative solutions with free-standing heliostats known as pod systemswere investigated. The different system layouts are typically triangular pods,rectangular ganged heliostats and trapezoidal pods. The largest advantage of apod system is the reduction in cost due to reduced ground and civil work as wellas a decrease in material costs [52]. The HelioPod is a result of years of researchat Stellenbosch University funded by the Technology Innovation Agency. The SolarThermal Energy Research Group (STERG) was founded in 2010 at StellenboschUniversity to continue the study and development of heliostats for CR systems[53].

Helio1

One year after the formation of STERG the first solar roof laboratory was launchedand the Helio1 heliostat prototype was developed. However, this prototype wasfunctioning below expectations but it triggered an interest in the technology. Apipeline of projects started developing and got supported by the laboratory. Theproject got outstanding equipment for optical analysis such as software to processimages, that was of great support in the upcoming prototypes [53].

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Helio18

In order to create an excellent control system the Helio18 became a test-mule. Itwas brought into operation in 2012 and consisted of six small mirrors on a sharedmutual pedestal. The system had a total of three identical pedestals, resulting in atotal of 18 mirrors, explaining the name Helio18. It was the first heliostat technologyutilizing the shared pod structures that STERG are still developing and improving[53].

Helio40

After the progress in Helio18, STERG received funding from SASOL to develop a 40m2 rooftop-based heliostat system. The facility was built in 2013 but was officiallyopened during 2014 STERG symposium. The Helio40 consisted of a number ofindividual heliostats that was mounted on the control rooms roof and STERG’sSunTower was used. The research of the Helio40 was mainly focused to the controlsystems and receiver technology [53].

A team of engineers and students collaborated in the development phase of Helio40.The team gained more detailed knowledge on optics, control systems, costs,integration and operation. Simultaneously as the team worked on the prototype,funding by the Technology Innovation Agency was received to develop the nextgeneration of heliostats, the HelioPod [53].

Helio100

The Helio100 was initiated in 2015 in order to further develop the HelioPodtechnology. The project did not only turn out successfully, but it also disruptedthe heliostat market on a global scale. Today the results and development from theHelio100 project are globally recognized and keep contributing to new innovativefeatures such as improvements of the HelioPod [53]. The Helio100 test facility islocated in Stellenbosch, South Africa and consists of 20 triangular pods, in Table 2.5the specifications of the site and the heliostats are provided and Figure 2.3.1 showsthe visualization of the HelioPod [52].

Figure 2.3.1: The outline of a triangular pod [52].

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Table 2.5: The characteristics of Helio100 [52].

Helio100Site location Stellenbosch, South Africa

Tower height 12.2 m

Triangular Heliopod TU 4.1

Triangle side 6 m

Heliostat width 1.83 m

Heliostat height 1.22 m

Optical height 1.5 m

Nr. of Heliopods 20

As seen in Table 2.5 the heliostats are significantly smaller than in most commercialCST setups. The smaller size of the heliostats is strongly connected to importantcost reductions. A smaller heliostat is not exposed to the same weather forces asa heliostat with the size up to 100 m2. Thus, there is no need for the same robuststructure in the case of smaller heliostats. Instead, it is possible to make costreductions on a simple structure, with no on-site welding [52].

The changes in the structure of the pod frame implies new optical approaches. Thecommon method of dead reckoning using accurate survaed and aligned heliostatscannot be applied in this set-up. In the Helio100 project, a combination of micro-electromechanical systems and optical sensors are the main components of the opticalsystem. Together with a machine learning approach, this simple application couldgive mean errors of less than 1 milliradian [54][55].

With the HelioPod structure, the need for skilled labor is significantly reduced. Witha structure simple to assemble and disassemble, there is no need for formal skillsfor the employee to handle the assembly. This enables a wide range of possibletechnicians in the set-up process, which is of high value in a country like SouthAfrica where the unemployment rate is at 27.2% [56]. The simple structure alsogenerates a re-usability of the plant, making it is possible to remove the solar fieldfrom the plant and assemble it elsewhere.

2.3.2 Target applications

Large-scale CSP applications in the 50 to 100 MWe range typically operate witha concentrated flux on the receiver below 1.0 MW/m2, in many cases even below0.8 MW/m2. The advantage with a small-scale application like the HelioPod is thateven though it is developed for applications of a few MW, the solar flux requirementseasily exceeds 1.0 MW/m2. The HelioPod can be used for both electricity generationvia a micro gas turbine or high-temperature process heat applications [53].

The HelioPods can focus the light onto a receiver with high optical performance,achieving temperature in the range of 600°C to 1000°C. The high concentrated solarflux is essential to maintain high receiver efficiency. The unique features of theHelioPod technology is suitable for applications that require low cost heliostats for

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high temperature and high flux applications at a moderate scale [53].

Figure 2.3.2: Target applications of the HelioPod technology [53].

Cost predictions with industrialization of HelioPod

The goal of the HelioPod technology is to achieve a significant cost reduction withthe objective to reach 85 USD/m2. Figure 2.3.3 below illustrates the cost reductionover time with an increasing production volume. In order to reach the target thelearning rate must be between 12 and 17.5%. The green and blue curves represent azone in which the technology development must pull the heliostat costs on order toreach the goal. The pink and red curves indicate the production volumes assumedin order to reduce manufacturing costs [53].

Figure 2.3.3: Cost predictions with industrialization and development of HelioPod system [53].

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2.3.3 Receiver

The excellent optical performance of the HelioPod enables collaborations withrecognized companies. In high temperature applications the HelioPod is a suitablechoice of heliostat technology due to its low cost and high optical performance.One of the limiting factors of such a plant is the receiver. However, by usingDLR’s CentRec particle receiver technology (Figure 2.3.4) it is possible to achievetemperatures above 1000 °C [54].

It is based on an insulated metallic cylinder which is rotating as cold particles arefed from an inlet above, pressing them against the inner wall due to centrifugalacceleration, forming a stable, thin and optically closed layer of particles along thechamber wall. By gravity, the particle film moves downwards, being collected in aring around the aperture at the bottom of the cylinder and further transported alongthe subsequent particle transport to a storage facility after being heated. Thus, theheat is directly stored in the solid particles which is a great advantage to avoid heatlosses from thermal barriers. By adjusting the velocity of the rotation the particlefilm can be maintained for different particle flow rates, most commonly around3 kg/s. The particles consist of bauxite (Saint Gobain proppants 16/30 sinteredbauxite) and have a great inherent storage capability with a heat capacity of above1200 J/kgK at 800°C as well as appropriate properties for a large temperature rangebetween hot and cold and do not freeze, therefore no trace heating is required.The particles are suitable for temperatures up to 1000°C and are available inlarge quantities. In addition, the costs for particles are comparable with saltused in molten salt TES and the direct absorption of solar radiation leads to highreceiver efficiency. Nevertheless, the commercial availability for high temperaturecomponents is still limited [54][57][58].

Figure 2.3.4: The CentRec hot particle receiver [59].

The thermal efficiency of the receiver

For the acceleration of the particles to 43.5 rpm, the theoretical power needed isbelow 20 W. According to DLR, the predicted thermal efficiency of the CentRec is

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>90% at 800 to 900◦Cparticle outlet temperature [59][60]. It can be discussed thata thermal efficiency of 90% is high. However, particle receivers generally have higherefficiencies and temperature ranges than conventional receivers and the efficiency ishighly dependent on the particle flow rate and irradiance [61], which are both highin the CentRec, justifying a high efficiency. Nevertheless, a sensitivity analysis wasmade on different thermal efficiencies of the receiver, see Appendix C.

2.3.4 Storage

The solar heat produced by the plant will either be used directly or stored to thestorage unit. There are several commercially available TES systems for CR systemsavailable on the market that can be integrated easily [3]. The generated solar heat tothe process is delivered via hot air from heat exchanges that use the thermal energyin the hot particles. The large temperature range in the system results in a compactand cheap storage system. The storage system has a direct two-tank configurationwith high and low temperature storage on the ground. The transport system forthe hot particles used in the model is a truck transporting the particles in insulatedvessels in between the tower and the larger storage vessel, which is located close tothe industrial application, where the hot air is needed. The location of the storageunit for the hot particles is above the heat exchanger and the cold storage. Thisallows for gravity flow of the particles. The hot storage is supplied with the heatedparticles using a lift system transporting the insulated vessels to the top of the unit[62].

2.3.5 Control system

The HelioPod has a unique control system based on open loop tracking and errorcorrection. The kinematic model of the heliostat is designed to use two linearactuators with fixed axes in horizontal orientation. The control system is createdwith a modular architecture divided into three levels where the heliostats are groupedinto self-sufficient clusters for scalability. This results in a minimal effect on real-timeprocessing overhead. Figure 2.3.5 shows the layout of the control system architectureof the HelioPod [53].

The architecture for the control system and the distributed processing allows forlow-cost hardware. This is a critical component for the overall economic feasibilityof the HelioPods. The programmable logic receiver controller, system controller,field controller and cluster controllers communicate using TCP/IP over Ethernet orWLAN. The system controller is in charge of the monitoring of the solar receiver andthe overall system state transitions to maintain a safe operation. The field controlleris responsible for all solar array tasks, such as calibration and tracking of theheliostats to follow the sun. Each heliostat cluster has an individual communicationchannel, permitting all clusters to communicate simultaneously. The channels canbe either wired or wireless. To avoid additional costs such as cabling and trenching,the wireless option is recommended [53].

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Figure 2.3.5: Control system architecture [53].

2.3.6 Power generation

The HelioPod technology is designed for modular gas-turbine CSP. It is based onBrayton cycle solarized micro gas turbines. As such turbines require a high inlettemperature, up to 1000°C, a high optical performance as can be achieved by theHelioPod technology is required [53].

2.3.7 Process heat

The need for high-temperature heat is common in several industrial applications.Traditionally, a process heat application is a plant that the customer can integrate totheir process. The HelioPod field in combination with a volumetric open-air receiverand a low-cost storage offers an alternative process heat source, see Figure 2.3.6 forhow such a system might look [53].

Figure 2.3.6: Process heat application in a factory [53].

2.4 Concentrating solar thermal

Concentrating solar thermal (CST) is a promising energy technology for both powergeneration (CSP) and for industrial and thermo-chemical process heat due to hightemperatures, reliability and suitable storage possibilities that can deliver renewable

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energy upon demand [63]. CST can easily be implemented in industrial applicationsfor process heating, cooling and desalination. In South Africa the iron, steel, miningand metal industries together account for 59% of the energy consumed by theindustrial sector [50]. Regarding CSP, the technology is often compared to PVfor which the costs have decreased rapidly in the last years. Nevertheless, PVis more feasible for direct supply due to expensive and limited electricity storageoptions. Thus, the higher costs for CSP should be put in relation to the flexibilityof supplying power not only on sun hours. Furthermore, the construction phase canbe done with a large share of local equipment and labour compared to PV, makingit especially feasible for developing countries. As the general setup is the same forCST, excluding the power block, the advantages are the same as for CSP [63].

Currently, CST is commercially used in enhanced oil recovery (EOR) by heatingsteam to reach the last oil in wells. Except for that, only laboratory researchand pilot projects have been done for CR for heat supply integrated in industries.In addition to the metal and chemical industries, research has been made onfuel production such as syngas and hydrogen [10]. There is a large potential forimplementing CST in industrial and thermo-chemical processes designed for highworking temperatures that are currently based on fossil fuel burners. This can beachieved by replacing the burner with a solar receiver without changing the rest ofthe industry chain [63]. Currently, the use of process heat from CST is often limitedto temperatures below 400°C and the potential for achieving higher temperatureranges has previously been considered difficult. For CR, limitations in the materialcharacteristics of the receiver have been a limiting factor when approaching highertemperatures. Nevertheless, temperature ranges up to 1000°C can be achieved withhigh concentration ratios when using a rotating central particle receiver in which theparticles can be used as a medium for heat transfer as well as for thermal storage.In a case study made by S. A. C. Hockaday et. al., the potential for introducing theCST technology in the manganese sintering process was investigated. In addition tothe technical barrier of a thermal storage resistant to fluctuations in solar resourcesand high capital costs, there is a lack of pilot scale demonstrations of this concept[64]. By conducting more business cases based on real and simulated data, moreindustries may be interested in corporations that can enable more demonstrationsof the feasibility of this technology concept.

2.4.1 Examples of CST plants

A selection of three CST plants are described below; one in the U.S., one in Omanand one in Mexico.

Coalinga

In 2011, a demonstration facility for a CST-EOR pilot project was built in Coalinga,California. The facility was a 29 MWt solar-to-steam plant with the purpose tosupport the enhanced oil recovery at an oil field owned by Chevron between theyears 2011 and 2014. According to SBI Energy, conventional methods for recovering

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oil only enables extraction of 10 to 30% of the original oil in heavy-oil reserves suchas the one in Coalinga and this project was a successful demonstration of how itcould be improved with CST [65].

Figure 2.4.1: Schematics of the principle of CST oil recovery in Coalinga [66].

The number of heliostats was 3 822, all of them with two mirrors each. Theywere placed within an area of 0.4 km2 in front of a 100 m high tower. Thesteam production of 29 MW thermal equals approximately 13 MW electric andthe pilot project showed that CST can be used successfully for EOR applications[65], [66].

Miraah

In 2011, GlassPoint built a 7 MWt solar EOR pilot project in to prove theperformance and market competitiveness of their technology. This led to the 1GWt solar EOR project Miraah in Oman that started operating in 2017. The plantproduces 6 000 tons of steam daily, reducing the use of natural gas for the heavy oilproduction with up to 80%. The plant is based on the PTC technology and consistsof 36 blocks of troughs enclosed in a greenhouse glass to avoid sand and wind[67].GlassPoint is now planning to build a 850 MWt PTC project at the Belridge oil fieldin Bakersfield, California [68].

La Parrena

One of the top-producing mining companies, Peñoles, has introduced solar thermaltechnology to one of their copper mines in Mexico, La Parrena. The heat demand ishigh and heat is included in various processes in the mine. The solar collector fieldintroduced to the mines was at 6,270 m2, each collector with a size of around 14m42. The storage has a size of 660 m3. This CST-plant resulted in a 58% coverage

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of process heat from solar energy annually. The payback period is low, close to 4years, and a lifetime of at least 25 years [69].

2.4.2 Current business models and markets

Solar heat in industrial applications is a niche market with great potential inthe current energy market. Solar heat can be introduced in many applicationssuch as services, cooking, dairy thermal applications, automotive sector andhigh-temperature applications. To enable up-scaling of the deployment of CSTtechnologies, the awareness and acceptance for CST must increase. Secondly, theindustry must begin to invest in market development and RD initiatives. Lastly,mass production is required to decrease the cost per unit [70].

2.4.3 Business opportunities

The energy sector is currently undergoing a tremendous change by increasing theimplementation of renewable energy sources. One common issue regarding renewableenergy technologies is the high initial investment cost. Regarding thermal heat,the current market is centralized to energy suppliers where customers buy heator fuel instead of generating heat in an own plant [53]. In a country like SouthAfrica where the industry sector represents a large share of the energy use (36 to46%) and half of the country’s energy use is for heat applications, there is a largepotential for introducing new business models for thermal heat in the industry sector[71]. With CST applications growing in interest, a new market for energy servicecompanies (ESCOs) who would get the opportunity to invest in heat applicationsmore sustainable for their customers would be possible. However, the life-time of aplant is exceeding 20 years but the energy demand for certain projects is often inthe span of 3 to 5 years. This mismatch in time makes it difficult to create desirablebusiness cases for new upcoming technologies [53].

By introducing the HelioPod technology to CST plants, the customer could producecheap and clean heat generated from the plant, either directly or stored. With littleor no requirement of ground work and the ability for rapid assembly and disassembly,this technology could create a new market for CST for which the set-up is no longerrestricted to one location throughout its life-time. The mobility of the technologyenables a shorter contract periods where HelioPods could easily be moved to otherplants and costumers [53]. Thereby, there is no need for customers to plan long-term,opening up for business models of a more independent character. Furthermore, itwould be possible for smaller industries to share one plant, or to transport storedheat to different customers from one plant. The modularity, easy assembly andsimple structure of the plant al