introduction to concentrating solar power (csp)...

© Woodhead Publishing Limited, 2012

3

1Introduction to concentrating solar power

(CSP) technology

K. L OV E G R OV E, IT Power, Australia and W. S T E I N, CSIRO Energy Centre, Australia

Abstract: This introductory chapter begins by defi ning ‘concentrating solar power’ (CSP) and outlining the role of the book. It then introduces some of the historical background to the development of CSP systems and the present day context of a period of industry growth amid major changes to the world’s energy systems. It describes the key approaches of parabolic trough, central receiver, linear Fresnel, Fresnel lens and paraboloidal dish concentrator systems. The prospects for continued deployment growth and parallel cost reductions are discussed. Finally the organization of the overall book is outlined.

Key words: concentrating solar power, concentrating photovoltaics, dish, trough, tower, Fresnel lens, linear Fresnel refl ector, history, approaches to concentration, cost reduction, growth in deployment.

1.1 Introduction

Concentrating solar power (CSP) systems use combinations of mirrors or lenses to concentrate direct beam solar radiation to produce forms of useful energy such as heat, electricity or fuels by various downstream technologies. The term ‘concentrating solar power’ is often used synonymously with ‘concentrating solar thermal power’. In this book the term is used in a more general sense to include both concentrating solar thermal (CST) and con-centrating photovoltaic (CPV) energy conversion.

Whilst the primary commercial attention today and the emphasis in this book is on systems designed for generation of electric power, there are individual chapters that review the important market segment of process heat and also the concept of solar fuels production, which the editors suggest is likely to see a rapid rise in interest in the near future.

This book seeks to address multiple audiences, and chapters can be read selectively according to need.

• A reader with a background in science or engineering should fi nd a resource that introduces all the key principles and the state of the art of the CSP fi eld.

• Many of the chapters contain detailed review and presentation on various key aspects that should provide value to those experts already

4 Concentrating solar power technology


working in the fi eld and, given the pace of technological change, sug-gested resources for remaining up to date.

• At the same time, the book should provide value to readers without a technical background. Care has been taken to provide overviews and introductions of all key concepts in a manner targeted at the non-technical audience such as policy makers, for example.

This book seeks to provide comprehensive, complete and up-to-date cover-age of the CSP fi eld. A previous well-respected coverage of this nature was provided by Winter et al. (1991). There are a number of past and recent books that address broader solar energy topics and others with more techni-cal coverage of specifi c issues, which are referenced in various chapters where relevant.

1.1.1 History and context

Global investments in clean energy generation are continuing to increase with global energy producers (and users) now experiencing strong signals to develop a clean energy future. Over the last three decades, the world wind industry has grown at an average rate of approximately 30% per year to reach a total installed capacity of 239 GW by the end of 2011. This represents nearly 3% of total world electricity annual generation (WWEA, 2012) and wind capacity is now being installed at a faster annual rate than nuclear.

Over a shorter period, the solar photovoltaic (PV) industry has grown with comparable or higher rates of growth but from a lower base and in 2011 had a worldwide installed capacity of approximately 69 GW (EPIA, 2012). CSP technology saw a fi rst surge of commercial development between 1984 and 1995, but then no further commercial deployment until 2005, although in that time considerable research, development and demonstra-tion took place. Since then, commercial CSP deployment has recommenced and gained considerable momentum. Total installed capacity is, however, an order of magnitude smaller than PV, given that commercialization of the technology is a decade or so behind.

The concept of concentrating solar energy has been a technology of inter-est throughout history. For example:

• Archimedes described the idea of mirrored panels to concentrate the sun in around 200 BC;

• The Greek mathematician Diocles described the optical properties of a parabolic trough in the second century BC;

• The development of heliostat designs was described by Comte de Buffon in 1746;

• Augustin Mouchot demonstrated a dish driven steam engine system at the 1878 universal exhibition in Paris.

Introduction to concentrating solar power (CSP) technology 5


A more contemporary historical landmark was Frank Schuman’s successful parabolic trough driven pumping system built in Egypt in 1913. Experi-ments and prototypes were developed all through the twentieth century. The real birth of CSP as an industry came in California in the 1980s. Favour-able government policy settings lead to the construction of nine separate parabolic trough based ‘Solar Electric Generating Systems’ (SEGS), total-ling 354 MWe of installed capacity. These were based around steam turbines for power generation, and used oil as the heat transfer fl uid within the trough receivers.

These plants, with more than 2,000,000 m2 of mirror area, continue to operate under utility ownership after more than 20 years and have estab-lished the technology as commercially proven. The tenth plant was in the early stages of construction when the effect of lower oil prices and changes in government policy led to a loss of investment and subsequent demise of the company driving the development (LUZ). However, the technology was now on the map, and over that 1984–95 period, with just 354 MW deployed, the capital cost was successfully halved.

The lead role in renewable energy development was grasped around that time by countries in north-western Europe, led by Denmark and then Germany. The emphasis was on pursuing wind power given the favourable wind and less favourable solar resources in those countries. Though wind turbines today are of the order of 3–5 MW per unit, at that time they were in the small hundreds of kW, and even though the specifi c capital cost was similar to or higher than CSP, the smaller modules provided a much easier investment path. Led by government incentives, PVs have moved from high cost space/satellite and small remote off-grid applications to residential applications and more recently large multi-MW installations. The renew-able energy agenda has spread around the globe and overall market demand for renewable electricity continues to grow exponentially, though the ‘new’ renewables such as wind and PV still account for only a few percent of the world’s electricity demand.

A past and continuing challenge for CSP is its dependence on the econo-mies of scale afforded by large steam turbines, leading to large levels of risk capital per project for a relatively new technology. However, now that the size of new renewable projects has grown, there is more appetite for making the necessary investments.

Concern over human induced climate change has emerged to dominate the political agenda around energy supply. There has been a resurgence of CSP development since 2005, led partly by the recognition that it is a technology which could make large greenhouse gas emission cuts quickly, and offer the signifi cant benefi t of distributable solar power through integrated thermal storage. This growth has been led predominantly by Spain through specifi c and targeted feed-in tariff incentives that have



proven highly successful for the technology. Approximately 2,400 MW is approved for operation by 2014 with half of that already operating. The sun belt of the south-west USA has also been targeted for CSP through tax credits and loan guarantees with approximately 1.8 GW expected to be in operation by the end of 2013. Importantly, the majority of new instal-lations now incorporate thermal storage, usually of the order of 6 hours or so.

Other countries with CSP projects announced or under construction include North Africa (Algeria, Morocco) and the Middle East (Egypt, Israel), China, India, Australia, South Africa, Portugal, Italy, Greece, Malta and Cyprus. In 2010, India took a major initiative with the establishment of the Jawaharlal Nehru National Solar Mission, with a target of 20 GWe of combined PV and CSP capacity to be installed by 2022. China has a target of 1 GW of CSP by 2015. This activity has combined to give a rate of growth from 2005 to 2012 of approximately 40% per year. This is similar to the rate of growth for wind power during its fi rst decade of modern commercial deployment, which began in approximately 1990, and faster than that for PVs when it began to accelerate commercial deployment in about 1992. Whilst the industry is still in its early stages and vulnerable to sudden policy changes in key countries, continued strong growth in global installed capac-ity is predicted.

Due to the 15-year hiatus in commercial CSP deployments, installed PV capacity grew to be some ten times greater than CSP, and as a result PV has seen signifi cant cost reduction over recent years, whilst CSP is at an early stage of its cost reduction path. In 2012, PV is lower cost than CSP for non-dispatchable electricity production under most applications. Under these circumstances, greater attention is turning to CSP’s potential benefi ts of built-in thermal energy storage and dispatchability, as well as other non-electrical applications such as fuels.

Whilst the issue of climate change is dominating the future energy agenda, the idea that demand for oil may have now passed the level of supply from conventional sources is well accepted and, despite large levels of fl uctuation, the overall trend is to increasing prices. This could prove to be a very major driver for technology change both increasing demand for solar electricity and encouraging developments such as solar fuels.

1.2 Approaches to concentrating solar power (CSP)

CSP systems capture the direct beam component of solar radiation. Unlike fl at plate photovoltaics (PV), they are not able to use radiation that has been diffused by clouds or dust or other factors. This makes them best suited to areas with a high percentage of clear sky days, in locations that do not have smog or dust.



The confi gurations that are currently used commercially in order of deployment level are:

• parabolic trough• central receiver tower• linear Fresnel• Fresnel lenses (for CPV)• paraboloidal dishes.

Each technology boasts particular advantages and in some cases particular market segments. Project and technology developers are actively pursuing all types of CSP technologies. In addition to these concepts that are applied commercially, a solar furnace arrangement is widely used as a tool for research projects. A solar furnace typically consists of a paraboloidal dish mounted in a fi xed orientation in a laboratory building, with one or more external heliostats directing solar radiation to it at a fi xed angle.

1.2.1 Parabolic trough

Parabolic trough-shaped mirrors produce a linear focus on a receiver tube along the parabola’s focal line as illustrated in Fig. 1.1. The complete assem-bly of mirrors plus receiver is mounted on a frame that tracks the daily movement of the sun on one axis. Relative seasonal movements of the sun in the other axis result in lateral movements of the line focus, which remains on the receiver but can have some spill at the row ends.

1.1 Parabolic trough collector: tracks the sun on one axis (background picture, Nevada Solar 1 plant, R. Dunn).



Trough systems using thermal energy collection via evacuated tube receivers are currently the most widely deployed CSP technology. In this confi guration, an oil heat transfer fl uid is usually used to collect the heat from the receiver tubes and transport it to a central power block. Chapter 7 examines trough systems in detail.

1.2.2 Central receiver tower

A central receiver tower system involves an array of heliostats (large mirrors with two axis tracking) that concentrate the sunlight onto a fi xed receiver mounted at the top of a tower, as illustrated in Fig. 1.2. This allows sophisticated high effi ciency energy conversion at a single large receiver point. Higher concentration ratios are achieved compared to linear focusing systems and this allows thermal receivers to operate at higher temperatures with reduced losses. A range of system and heliostat sizes have been dem-onstrated. Chapter 8 examines tower systems in detail.

1.2.3 Linear Fresnel refl ectors

Linear Fresnel refl ector (LFR) systems produce a linear focus on a down-ward facing fi xed receiver mounted on a series of small towers as shown in Fig. 1.3. Long rows of fl at or slightly curved mirrors move independently on one axis to refl ect the sun’s rays onto the stationary receiver. For thermal

1.2 Central receiver tower plant: multiple heliostats move on two axes to focus the sun to a fi xed tower mounted receiver (background picture, Gemasolar plant, owned by Torresol Energy, © Torresol Energy).



systems, the fi xed receiver not only avoids the need for rotary joints for the heat transfer fl uid, but can also help to reduce convection losses from a thermal receiver because it has a permanently down-facing cavity.

The proponents of the LFR approach argue that its simple design with near fl at mirrors and less supporting structure, which is closer to the ground, outweighs the lower overall optical and (for CST) thermal effi ciency. To increase optical and ground-use effi ciency, compact linear Fresnel refl ectors (CLFRs) use multiple receivers for each set of mirrors so that adjacent mirrors have different inclinations in order to target different receivers. This allows higher packing density of mirrors which increases optical effi ciency and minimizes land use. Chapter 6 examines linear Fresnel systems in detail.

1.2.4 Fresnel lens

A conventional lens is expensive and impractical to manufacture on a large scale. The Fresnel lens overcomes these diffi culties and has been employed extensively for CPV systems. A Fresnel lens is made as a series of concentric small steps, each having a surface shape matching that which would be found on a standard lens but with all the steps kept within a small thickness. A plastic material is usually used and arrays of multiple lens units are typi-cally mounted on a heliostat structure as shown in Fig. 1.4. This is also a

1.3 Linear Fresnel refl ector: multiple mirrors move on one axis to focus the sun to a fi xed linear receiver (background picture, Kimberlina LFR plant, Bakersfi eld California, image courtesy of AREVA Solar).



point focus approach requiring accurate sun tracking in two axes. Chapter 10 examines various CPV systems in detail.

1.2.5 Parabolic dishes

Dish systems, like troughs, exploit the geometric properties of a parabola, but as a three-dimensional paraboloid as shown in Fig. 1.5. The refl ected direct beam radiation is concentrated to a point focus receiver and in CST systems can heat this to operating temperatures of over 1,000ºC, similar to tower systems.

Dish systems offer the highest potential solar conversion effi ciencies of all the CSP technologies, because they always present their full aperture directly towards the sun and avoid the ‘cosine loss effect’ that the other approaches experience. They are, however, the least commercially mature. Dishes up to 24 m diameter have been demonstrated.

As well as thermal conversion, CPV conversion on dishes is well estab-lished, it is also applied with ‘micro dishes’ with diameters of just several centimetres. Chapter 9 examines dish systems in detail.

1.3 Future growth, cost and value

CSP systems produce renewable electricity that ultimately must compete with other forms of electricity generation in the marketplace. Thus the cost

Fresnellens

Target(singlecell)

1.4 Fresnel lens-based CPV: multiple small units on a heliostat (background picture, River Mountains, USA, Amonix).



of CSP energy is the main preoccupation of the technology developers and research and development practitioners within the CSP community. With no fuel costs, the cost of CSP energy is dominated by the amortization of the high initial capital cost investment over the life of the plant.

CSP is a proven technology that is at an early stage of its cost reduction curve. A period of rapid growth in installed capacity, together with a rapid decay in cost of energy produced is confi dently predicted by the industry. The trend of cost reduction as installed capacity increases is logically linked to:

• technical improvements, as lessons are learned from installed plants and parallel R&D efforts identify performance improvements,

• scaling to larger installed plant size, which allows for more effi cient and more cost-effective large turbines and other components to be used, and

• volume production that allows fi xed costs of investments in production effi ciency to be spread over larger production runs.

Empirically these practical effects lead to a commonly observed trend for a new technology of a reduction in cost of an approximately fi xed fraction for every doubling of deployed capacity.

An analysis of various comprehensive studies investigating feasible cost reduction paths for CSP was carried out in a study for the Global Environ-ment Facility for the World Bank in 2006 (World Bank 2006). One compre-hensive scenario predicted a pathway to install 5 GW by 2015.

1.5 Paraboloidal dish concentrator: tracks the sun in two axes (background picture, Australian National University, 500 m2 dish).



A recent roadmap published by the International Energy Agency (IEA) for CSP technology presents a highly credible summary of the global situ-ation and way forward (IEA 2010). Cost of energy reductions to around 25% of 2010 values are predicted by 2050. AT Kearney (2010) was commis-sioned by European and Spanish CST industry associations to produce a study of CSP energy cost reduction projections. A range of key areas for reducing cost of manufacture and increasing annual output are identifi ed, these measures together are suggested to result in an overall reduction of cost of energy in 2025 relative to 2012 of 40–50%. Over the same time period, they suggest global installed capacity could reach between 60 and 100 GW depending on policy measures in place. Figure 1.6 illustrates the history of installed capacity to 2011 together with extrapolations based on compound growth rates of the 19% per year average since 1984 and the 40% per year average since 2005.

Figure 1.7 shows the same data on an expanded vertical axis, together with actual historical data for installed capacity of wind and PV systems. The historical high compound growth rates for these technologies can be seen together with the approximately one decade lag between PV growth

Capacity (

GW

e)

5

4

3

2

1

0

1980 1990 2000 2010 2020 2030

Year

Actual

19%/yr25%/yr40%/yr

1.6 Global installed capacity of CSP plants, both actual and possible future compound growth rates.

Capacity (

GW

e)

100

80

60

40

20

01980 1990 2000 2010 2020 2030

Year

Actual

19%/yr

25%/yr

40%/yr

WindPV

1.7 Global installed capacity of CSP plants, both actual and possible future compound growth rates together with historical data for wind and PV deployment.



and that of wind. CSP is seen to be entering a similar growth phase with a further approximately one decade lag.

Other studies support the conclusions on cost reduction potential. Kutscher et al. (2010) identifi es in detail a range of specifi c ‘bottom-up’ measures that are estimated to deliver a 40% cost of energy reduction for line focus systems by 2017. Kolb et al. (2010) identifi es measures that will deliver 50% cost reductions for tower systems by 2020.

Available evidence points to a cost reduction of 10–15% for every dou-bling in global capacity (a progress ratio of 0.9–0.85). Figure 1.8 plots the progression over time of relative costs (either cost of energy or capital costs1) under either 20% p.a. or 30% p.a. growth rates, and for cost progress ratios of 0.8, 0.85 and 0.9.

As variable renewables like wind and PV vie for a larger proportion of energy supply, the ability to provide dispatchable power will become more important. CSP has the advantages that incorporation of thermal energy storage is cost effective, improves system performance and has very little effect on the overall cost of energy. Energy storage is examined in detail in Chapter 11. Some recent studies have begun to evaluate the extra value that can be offered by the energy storage abilities of CSP systems (e.g. Sioshansi and Denholm, 2010 and Madaeni et al., 2011), and it can be 30% or more valuable than average market prices. Thus CSP can look forward to a growing recognition of the value of its energy in parallel with future cost reductions.

1.4 Organization of this book

The book is organized into three parts.

Rela

tive

LC

OE

1.0

0.8

0.6

0.4

0.2

0.02010 2015 2020 2025 2030

Year

20%/a + PR = 0.820%/a + PR = 0.85

20%/a + PR = 0.930%/a + PR = 0.830%/a + PR = 0.85

30%/a + PR = 0.9

1.8 Possible relative levelized cost of energy (LCOE) reductions over time under different growth rates and progress ratios.

1 Note that cost of energy is strongly dependent on capital cost, but also depends on operating and maintenance costs and fi nancing costs. For a fi rst approximation, cost of energy and capital cost are assumed to reduce over time according to the same progress ratio.



Part I contains fundamental introductory material of which this introduc-tory chapter forms the fi rst part. This is followed by Chapter 2 which over-views the fundamental principles behind CSP technologies. It is quite a technical chapter that can be skipped by those seeking to read directly about specifi c technology. Understanding solar resources issues, siting and feasibility studies and the techno-economic assessment of CSP systems are the subject of the other chapters in Part I.

Part II, on technology approaches and potential, contains specifi c chap-ters that review the principles, historical development and state of the art of the trough, tower, linear Fresnel and dish approaches. These are followed by further chapters on energy storage, hybridization, CPV systems and fi nally the economic outlook.

Part III, on optimization, improvements and applications, comprises chapters that provide in-depth coverage of a range of key issues around maximizing performance through technology and design optimization. Key applications to process heat and solar fuels are also presented as a comple-ment to the overall emphasis on power generation. Solar fuels derived from concentrating solar systems are presented as the last chapter of the book. This refl ects a belief on the part of the editors that whilst solar fuels is cur-rently an activity still very much in the R&D sphere, it could well become the biggest future market for solar concentrating systems, given future projections of demand outstripping supply for oil.

1.5 References

AT Kearney (2010), Solar Thermal Electricity 2025, Report for ESTELLA by A.T. Kearney GmbH, Kaistraße 16A, 40221 Duesseldorf, Germany.

IEA (2010), Technology Roadmap – Concentrating Solar Power, OECD Interna-tional Energy Agency, Publications Service, OECD 2, rue André-Pascal, 75775 Paris cedex 16, France.

EPIA (2012), Global market outlook for photovoltaics until 2016, European Photo-voltaic Industry Association, Rue d’Arlon 63-67 (1040) Brussels – Belgium, www.epia.org.

Kolb G, Ho C, Mancini T and Gary J (2011), Power Tower Technology Roadmap and Cost Reduction Plan, SANDIA REPORT SAND2011-2419, April 2011, Pre-pared by Sandia National Laboratories Albuquerque, NM 87185 and Livermore, CA 94550, http://prod.sandia.gov/techlib/access-control.cgi/2011/112419.pdf.

Kutscher C, Mehos M, Turchi C, Glatzmaier G and Moss T (2010), Line-Focus Solar Power Plant Cost Reduction Plan, NREL/TP-5500-48175, December, http://www.nrel.gov/docs/fy11osti/48175.pdf.

Madaeni S Sioshansi R and Denholm P (2011), Capacity Value of Concentrating Solar Power Plants, National Renewable Energy Laboratory Technical Report NREL/TP-6A20-51253.

Sioshansi R and Denholm P (2010), The Value of Concentrating Solar Power and Thermal Energy Storage, Technical Report NREL-TP-6A2-45833, February.



Winter C-J, Sizmann R L and Vant-Hull L L (1991), Solar Thermal Power Plants, New York, Springer Verlag.

World Bank (2006), Assessment of the World Bank/GEF Strategy for the Market Development of Concentrating Solar Thermal Power, Report Prepared for the World Bank.

WWEA (2012), Wind energy around the world, World Wind Energy Association, quarterly report, Editor-in-Chief: Stefan Gsänger, Issue 1, March.

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