A Review of Studies on Central Receiver Solar Thermal Power Plants

AOmar Beh

a r t i c l

Article history:

Received 16 Se

Rec

31

Accepted 3 FebAvailable onlin

such key components as heliostat, receiver and hybrid solar gas turbine that are boosting in many R&D

ional collaboration during the past 30 years.

& 2013 Elsevier Ltd. All rights reserved.

solar p

. . . . . .

r (CSP):

. . . . . .

d curre

CSP tec

RS): Cu

. . . . . .

solar th

solar th

solar th

. . . 24

. . 25

3.2.1. Basic concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.2.4. Enhancement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Contents lists available at SciVerse ScienceDirect

Renewable and Sustainable Energy Reviews

Renewable and Sustainable Energy Reviews 23 (2013) 1239E-mail addresses: [email protected], [email protected] (O. Behar).4. Solar receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

1364-0321/$ - see front matter & 2013 Elsevier Ltd. All rights reserved.

http://dx.doi.org/10.1016/j.rser.2013.02.017

n Corresponding author. Tel.: 213 555 82 71 29.3.2.2. Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.2.3. Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253.1.4. Enhancement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3.2. Tracking and control system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.2.5. Central receiver solar thermal power plants in the planning [32,7880,84] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

2.3. Recent R&D activities in central receiver technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3. Heliostat eld. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.1. Heliostat and layout. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.1.1. Basic concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.1.2. Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.1.3. Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Contents

1. Inroduction: Why concentrating

2. Background . . . . . . . . . . . . . . . .

2.1. Concentrating solar powe

2.1.1. Historic . . . . . . .

2.1.2. Basic concept an

2.1.3. Factors boosting

2.2. Central receiver system (C

2.2.1. Basic concept . .

2.2.2. Central receiver

2.2.3. Central receiver

2.2.4. Central receiverower (CSP)? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Historic and current status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

nt status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

hnology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

rrent status and applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

ermal pilot plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

ermal power plants in operation [32,59,7780] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

ermal power plants under construction [32,7880] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Power conversion system

Concentrating solar power activities merging internatKeywords:

Central receiver system

Heliostat eld

Solar receivers

technology, current status and applications of the CRSs are highlighted. Next, a detailed literature

survey of existing design comprising optical, thermal and thermodynamic analysis, and techniques

used to assess components have been arranged. This is followed by experimental investigations in

which design concepts are established. The last section contains recent subsequent improvement of3

ruary 2013e 19 March 2013

the major components of central receiver solar thermal power plants including the heliostat eld, the

solar receiver and the power conversion system. After an overview of Concentrating Solar Power (CSP)eived in revised form

January 201subsystems have been booming rapidly since 1980s. This paper reviews the most important studies one i n f o

ptember 2012

a b s t r a c t

The use of central receiver system (CRS) for electricity production promises to be one of the most viable

options to replace fossil fuel power plants. Indeed, research and development activities on its basica L.E.M.I Laboratory, University of Mhamed Bougara, UMBB, Boumerdes, Algeriab Centre de Developpement des Energies Renouvelables, CDER, Bouzareah, Algeriaw of studies on central receiver solar thermal power plants

ar a,n, Abdallah Khellaf b, Kamal Mohammedi areviejournal homepage: www.elsevier.com/locate/rser

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7. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

It is obvileast 90% offorand technolAgency (IEAEuropean Usiothaundertakenatmosphereuation, the

of hunger, wenvironmen150,000 addstastaworlds popu

Meanwhimove forwaovewh99.7 mb/d insions will thover supply7 bfar

O. Behar et al. / Renewable and Sustainable Energy Reviews 23 (2013) 1239 13illion people consume far more fossil resources and produce2

to a 2.5 t savings of fossil fuels during its 25-year operation

more po grow by over 50%; from 87.4 mb/d in 2011 to2035 [1]. Cconsequently, energy-related CO2 emis-

en more than double by the year 2050 and concernssecurity will surely heighten [1,6,8]. More than

avoids the emission of 688 t of CO2 compared to a combined cyclesystem and 1360 t of CO2 compared to a coal/steam cycle powerplant. A one square mirror in the solar eld produces 400 kW hof electricity per year, avoids 12 t of CO emission and contributesr $215/barrel in 2035 [1]). This is due to increased demandich set t

[1,5,12,2732]. For instance, a one megawatt of installed CSPliving and an increased life expectancy for part of thelation [1,5,7].le, petroleum and natural gas prices are projected tord in the next 20 years (from $125/barrel in 2011 to

lantation is growing faster than any other renewable technology.This is because, as shown in Figs. 13, it offers an integratedsolution to the coming decades global problems, i.e., climatechange and associated shortage of energy, water and foodted that the fossil fuel era have resulted in an unparalleledndard of

Nowadays, concentrating solar power (CSP) technology imp-ater shortages, ooding, desertication, and severetal pollutions that are expected to cause aboutitional deaths every year [3]. It has to be though

a result, renewable energy will become the worlds second-largestsource of power generation by 2015; delivering about 30% of theelectricity needs by the year 2035 [1].extreme weather events worldwide [1,46]. As a result, manypeople around the World, mainly in Africa, face an increasing risk

particular solar energy. [1028]. According to IEA, 50% of the newpower infrastructures will base on clean-sustainable energies. Asin the climate will intensify if no decisive actions are[1,46]. The progressive build up of CO2 in theis the undisputed cause for temperature rise accent-melting of the polar ice caps and the increase in

global electricity mix is dropping down and the global energymap changing [1,2].

For these reasons, more and more countries are mandatingthat a part of the electric power be from renewable origin, inns, by 2035, will be from current industry-based economy; sot changes

Germany. As a consequence, the nuclear energy share in theogy roadmaps published by the International Energy), the German Aerospace Center (DLR) and thenion (EU) have projected that 80% of the CO2 emis-

in parts of the Middle East and North Africa (MENA) have forcedmany countries around the world to review their policiesand retreat from nuclear power. This is particularly true forpower generation and transport sector [14]. Recent studies ima Daiichi nuclear power plant, in March 2011, and the turmoilion: Why concentrating solar power (CSP)?

ous that the origin of climatic change is CO2, and atits emission amount results from fossil fuels burning

For instance, in the Mediterranean region energy consumptionis raised by a factor of three between 1980 and 2005, and afurther doubling is intended by 2020 [9].

Furthermore, catastrophic events such as those at the Fukush-1. InroductReferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354.1. Volumetric receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.1.1. Basic concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.1.2. Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.1.3. Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.1.4. Enhancement . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.2. Solar cavity receiver. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.2.1. Basic concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.2.2. Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.2.3. Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.2.4. Enhancement . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.3. Solar particle receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.3.1. Basic concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.3.2. Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.3.3. Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.3.4. Enhancement . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5. Power conversion system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.1. Solar central receiverBrayton cycle (SCR-BC) system . . . .

5.1.1. Basic concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.1.2. Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.1.3. Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.1.4. Enhancement . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.2. Solar central receiverRankine cycle (SCR-RC) system . . . .

5.2.1. Basic concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.2.2. Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.2.3. Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.2.4. Enhancement . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.3. Solar central receiverCombined cycle (SCR-CC) system . .

5.3.1. Basic concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.3.2. Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.3.3. Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.3.4. Enhancement . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6. Analysis and outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ollution than the Earth can accommodate [4,5].. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33lifetime. [33,34]

2. Background

2.1. Concentrating solar power (CSP): Historic and current status

2.1.1. Historic

Concentrating solar power (CSP) is not an innovation of thelast few years. Records of its use date as far back as 212 BC whenArchimedes used mirrors for the rst time to concentrate theSuns rays [35]. In the early seventeenth century, Salomon DeCaux developed in 1615 a small solar powered motor consistingof glass lenses and an airtight metal vessel containing water andair [35]. More than a century later, in 1774, Lavoisier and JosephPriestley developed the theory of combustion by concentratingsolar radiation on a test tube for gas collection [36]. Next,Augustin Mouchot has devised a solar steam machine to run aprinting press [37]. After that, in 1878, a small solar power plantmade up of a parabolic dish concentrator connected to an enginewas exhibited at the Worlds Fair in Paris [38]. In the early 1900s,

although interest in solar power was then lost due to advances ininternal combustion engines and increasing availability of lowcost fossil fuel, the rst CSP-plant, powered by a parabolic troughsolar eld, was installed at Al Meadi (Egypt)[39,40]. This rst CSP-plant, installed in 1913, was used for pumping water for irrigation[39,40]. In the 1960s, with the focus on photovoltaic for the spaceprogram, interest in solar energy began to arise again. During1970s the oil crisis boosted R&D activities on CSP and numerouspilot plants were built, tested and bringing CSP technology to theindustrial and commercial level [41]. As a result, the rstcommercial plants had operated in California (USA) over theperiod of 19841991, spurred, more particularly, by federal andstate tax incentives and mandatory long-term power purchasecontracts. A drop in oil and gas prices has though driven manycountries to retreat from the policy that had supported theadvancement of CSP, and thus, no new plants have been builtbetween 1990 and 2000. It was not until 2006 that interest wasonce again rekindled for the development of large scale CSP-plants. The market re-emerged more particularly in Spain and theUnited States, again in response to government measures such asthe feed-in tariffs (Spain) and the policies requiring a share of

Receiver Receiver

Ref

Fig. 1. CSP offers an integrated solution to global problems of the coming decades. Fig. 3. installed solar thermal power plants since the 1980s [32].

O. Behar et al. / Renewable and Sustainable Energy Reviews 23 (2013) 123914Heliostat

Secondary Concentrator Fig. 2. Basic concept of the four CSP families: (A) central reReceiver

Dish

Concentrator

lector

Receiverceiver, (B) parabolic trough, (C) linear Fresnel, (D) dish.

solar power in their energy mix. As of 2011, have been worldwide1.3 GW of CSP plants in operation, 2.3 GW under construction,and 31.7 GW in the planning stage [33].

Nowadays, in 2013, 2.136 GW are operating, 2.477 GW underconstruction and 10.135 GW are announced mainly in the USAfollowed by Spain and China [32]. According to reference [34],about 17 GW of CSP projects are under development worldwide,and the United States leads with about 8 GW. Spain ranks secondwith 4.46 GW in development, followed by China with 2.5 GW.

2.1.2. Basic concept and current status

As shown is Fig. 4, a typical CSP-plant consists of three mainsubsystems: solar collector eld, solar receiver and a powerconversion system. In a hybrid plant, back-up and/or storagesystems are added to enhance performance and increase capacityfactor [13,39,42]. The solar receiver absorbs the concentratedsolar radiation by collectors and transfers it to the heat transferuid (HTF) which is used to feed high-temperature heat to apower conversion system. The subsystems are linked together byradiation transfer or uid transport. There are four CSP familiesdepending on the two major solar subsystems, i.e., the collectorand the receiver: parabolic trough, solar tower also known ascentral receiver, linear Fresnel and dish Stirling [6]. They areclassied according to the manner they focus the suns rays andthe receiver technology [17,28,33]. A brief comparison betweenthese families is illustrated in Table 1. For each technology the

overall efciency of the whole system varies with the location, thetime of day and the day of the year [4345].

In each CSP family, a variety of options is possible for solareld layout, tracking system, receiver type, heat transfer uid(HTF), storage technology and power conversion system. NorthSouth and EastWest orientations equipped with single trackingmechanism are usually applied in trough solar eld [29]. Forcentral receiver, surrounded and North eld congurations arethe most proven technologies, while MTC (Micro Tower Cong-uration) is now under development [4650]. Whereas linearreceivers are used for parabolic trough and Fresnel technologies,various congurations exist for power tower concept. Thesecongurations, for some of them under design, test or improve-ment, include the volumetric receiver, the particle receiver andthe cavity receiver [5154]. Concerning heat transfer uids (HTF),molten salt is widely used as HTF in commercial plants. Syntheticoil and saturated steam are also currently used as HTFs incommercial plants. Superheated steam has been recently intro-duced as HTF [5559]. Pressurized air and other gases, inparticular CO2 and N2, nano-uids, concrete and circulatingparticles are under development for both trough and tower, whilehelium or hydrogen is used in dish Sterling [6062].

Concerning storage, liquid molten salt is already provenstorage medium for long time whereas steam is typically reservedfor short time storage [63,64]. Phase change materials andcompact heat storage (chemical reactions) are under develop-ment [6365]. Power conversion systems (thermodynamic cycles)

PowerConversionSolarReceiver

SolarCollectorField Radiation

transfer

StorageSystem

Fluidtransfer

for

Power conversion cycle RC, CC

Concentration ratio [11] 7080

stor

O. Behar et al. / Renewable and Sustainable Energy Reviews 23 (2013) 1239 15Solar eld slope (%) [11] o12Working temperature (1C) MediumCurrent efciency (%) [35] 1516

Plant peak efciency (%) [11] 1420

Typical capacity (MW) [11,29] 10300

Annual capacity factor (%)[11] 2528 ( without storage) 2943 ( with 7 h

Development status [29,33] Commercial proven

Technology development risk [11,29] Low

Outlook for improvements [6] Limited

Efciency with improvements [33] 18

Relative rise of efciency after

improvements (%) [33]20Fig. 4. Flow diagram

Table 1Comparison of the four CSP families.

CSP technology Parabolic trough

Solar collector [6] Line focus

Solar receiver [6] MobileSystem

Back-upsystem

a typical CSP-plant.

Central receiver Linear Fresnel Dish

Point focus Line focus Point focus

Fixed Fixed Mobile

RC, BC, CC RC RC, SC

41 000 460 41 300o24 o4 10 or moreHigher Relatively lower Highest

1617 0810 2025

2335 18 30

10200 10200 0.010.025age) 55 (with 10 h storage) 2224 (without storage) 2528 (without storage)

Commercial Pilot project Demonstration stage

Medium Medium Medium

Very signicant Signicant Via mass production2528 12 30

4065 25 25

are at present Rankine cycles (RC), Brayton cycles (BC), combinedcycles (CC) for trough, tower and Fresnel types, and Stirling cycles(SC) for parabolic dish technology [42]. Advanced Brayton cycleswith pressurized air heated by volumetric solar receiver arenowadays an important issue [3]. Furthermore, supercriticalsteam and carbon dioxide cycles, air Brayton cycles are wellpositioned and promise to enhance solar power tower technology[17,50,66].

2.1.3. Factors boosting CSP technology

Besides activities in R&D and test and prototyping, numerous

2030, the market potential is estimated at least at 7 GW in theEU-MENA. This offers the opportunity to CO2 reduction prospec-tive of up to 12 million tons per year. These plants represent alsoa cost fall potential of 20% compared to the last built 80 MWeSEGS IX plant in USA. According to ECOSTAR, there are three maindrivers for cost reduction: scaling up, volume production andtechnology innovations. About 50% of the intended reductions incosts of CSP-plants will be from technology developments, andthe other half from scale up and volume production [71].

In this context solar thermal power plants will be capable ofdelivering efciently more than 3% of the EUs electricity by 2020,and at least 10% by 2030 [67]. Moreover, it offers the opportunity

and the power block within the near future. Compared with other

o

o

generating electricity with high annual capacity factors (from0.40 to 0.80 [11]) through the use of thermal storage [11,29];

lar R

O. Behar et al. / Renewable and Sustainable Energy Reviews 23 (2013) 123916Condenser

Power Conversion System Sosupports in various forms of incentives are playing a major role inthe development of power generation through CSP. Incentives inthe form of feed-in-tariff, tax relief, capital cost grants encoura-ging electricity export rates for CSP-plants during recent years, ina lot of countries (Algeria, Egypt and Morocco in North Africa;Spain, Portugal, Italy and Greece in Europe; USA in NorthAmerica; and India, China and Australia in Asia), has caused arapid growth of these future power options. Likewise, othercountries are in initiation phase or in the planning to set afavourable policy support for encouraging the development ofCSP. [1025]

Concepts such as Desertec, TRANS-SCP, MED-CSP, SolarPacesand ESTELA that aim to set up CSP technologies in EU-MENAregions are very promise to open the door for solar thermal powerplants to be more competitive [4,5,6769]. National and interna-tional organisations (Banks, Agenciesy) support also the develop-ment of CSP. For instance, in 2000, the Global Environment FacilityBank (GEF) provided 50 million US$ grant for four CSP projects inIndia, Egypt, Morocco and Mexico. This grant is to be used to coverits incremental costs, and therefore support market introduction ofhybrid congurations in developing countries [15].

The overall experience in CSP technology development has beenpositive and new opportunities are opening. At the R&D anddemonstration level, many projects have been carried out. At thecongurations and component development projects, one canname DISS, SOLAIR, EURODISH and ECOSTAR projects. SOLGATE,SOLASYS and SOLHYCO are among the projects that have beencarried out for the hybrid concepts implementation. DISTOR is aproject worth citing for storage systems development [70,71].

At the pilot and demonstration level, the projects PS10, PS20and SOLAR TRES among others have provided valuable informa-tion for the development of the CSP technology. They have offeredexcellent pattern to move CSP technology forwards [17,71].Building on this experience, new pilot projects are underway orin the planning stage (ALSOL in Algeria).

At the industrial and commercial plants of 50 MW to 400 MWpower are underway or in operation in Spain, USA, Algeria, Egypt,Morocco, Mexico, Greece, Iran, India and China. The exploitationsof these plants have been conclusive that there is a move to thedeployment of large scale CSP plants [1028]. Up to the year

HRSGTurbineGeneratorFig. 5. The three main subsystems of centro Greater potential for costs reduction and efciency improve-ments (4065%) [11,29,71].

2.2.1. Basic concept

As shown in Figs. 57, a typical central receiver system,also known as a solar tower power, consists of three majorsubsystems, namely the heliostat eld, the receiver and the powerconversion system. The solar eld consists of numerouscomputer-controlled mirrors that track the sun individually intwo axes and reect the solar radiation onto the receiver locatedon the top of the tower. The receiver absorbs the heliostatreected solar radiation and converts it into heat at high tem-perature levels. Depending on the receiver design and the heattransfer uid nature, the upper working temperatures can range

eceiver Heliostat Fieldal rEasily integrated in fossil plants for hybrid operation in a widevariety of options (see Section 5.3) and has the potential forHigher temperatures (up to 1000 1C) and thus higher efciencyof the power conversion system [11,71];perCSP options, the central receiver system could not only providecheaper electricity than trough and dish systems but also better

formance [3,11]. As shown in Table 1, CRS offers:to generate about 50% of the electricity needs of the EU-MENAregion [4,5] and supply over 10% of the worlds electricity by2050 [6]. Advanced scenario by IEA, EU and DLR has anticipatedthat global CSP capacity will reach 1.5 TW at this year [4,6,11,33].

2.2. Central receiver system (CRS): Current status and applications

Of all CSP technologies available today the CRS is moving tothe forefront and it might become the technology of choice[11,72]. This is mainly due to the expected performance improve-ments and cost reductions associated with technology innova-tions of the three main subsystems, i.e., the heliostat, the receivereceiver solar thermal power plant.

lucar Platform in Seville, Spain [32]. (B) Variable Geometry Central Receiver Solar Test

Table 2Central receiver solar thermal pilot plants in the 20th century [29,32,7880].

Project acronym Capacity MW Country Starting year

SSPS 0.5 Spain 1981

TSA 1 Spain 1993

CESA-1 1 Spain 1983

Solar one 10 USA 1982

MSEE/Cat B 1 USA 1984

Solar Two 10 USA 1996

m L

Mesa

O. Behar et al. / Renewable and Sustainable Energy Reviews 23 (2013) 1239 17from 250 1C to 1000 1C [11,71]. A power conversion system isused to shift thermal energy into electricity in the same way asconventional power plants [11,29].

The heliostat eld is the main subsystem and its opticalefciency has a signicant impact on the performance of thepower plant; it represents about 50% of the total cost [73] and itsannual energy losses are around 47% [74].The receivers are madeup of material which withstands high temperature changes andhigh energy density such as ceramic and metal alloys. There are

Fig. 7. Advanced research projects; from left to right. (A) SOLUGAS project at the SoFacility at CTAER [32].Fig. 6. Examples of CRS power plants in operation, underway or in the planning; froplant under construction, 75% completion, CA, USA [32]. (C) Artists design of Riodifferent types of receivers that can be classied into three groupsdepending on their functionality and geometric congurations.The three groups are the volumetric receivers, the cavity receiversand the particle receivers. In a power conversion system thermalenergy can be converted into electricity with higher efciency inRankine cycle, Brayton cycle or combined cycle.

2.2.2. Central receiver solar thermal pilot plants

The tower technology has since the early 1980s attractedworldwide a lot of interest. It has then been thoroughly studiedand successfully tested in numerous pilot projects such as theAmerican Solar Two (upgrade Solar One) [3], the Spanish CESA1 and TSA, and the French THEMIS [41,75,76]. The most relevantCRS tested in the 20th century are reported in Table 2. Thesedemonstration power plants have proved the feasibility and theeconomical potential of the tower technology. They have alsopermitted the improvement in the design and performance of thetower power, mainly its components, its hybrid concepts, its heattransfer uids and storage system.

2.2.3. Central receiver solar thermal power plants in operation

[32,59,7780]

Concerning the heat transfer uids (HTF), water/steam hasinitially been adopted in some solar towers such as PS10, PS20,Beijing Balading, Sierra and Yanqing. Molten salt is also a verycommonly used HTF. It has been used for example in Gemasolarthermo-solar plant. Lately, there has been a big interest ineft to right. (A) PS10 PS20 (front) in operation nearby Seville, Spain [79]. (B) Ivanph

solar project (planned) [84].developing air as a HTF. Julich solar tower is an example ofthis case.

Depending on the receiver design and the heat transfer uid,the working temperatures of the power conversion system rangefrom 250 1C, for water/steam cycles, to around 600 1C withcurrent molten salt design. The development of Direct SteamGeneration (DSG), which is currently in its early stage, as HTF isvery promising for reducing costs and enhancing thermal ef-ciency by eliminating the heat exchangers network [59,77].

In 2006, the 11 MWe CRS power plant PS10 was built byAbengoa Solar in Sevilla Spain. It has been followed by the20 MWe power tower plants PS20 in the same location, the5 MW Sierra Sun Tower (in Lancaster, USA) and the 1.5 MW inJulich Germany in 2009. Since 2011, the Gemasolar power plant,built in Spain as large as the PS 20 power plant, but withsurrounded heliostat eld and15 h storage, has been operatingand delivering power around the clock [77]. After the threepioneer CSP countries, i.e., the USA, Germany and Spain, Chinahave entered the CSP market by implementing, in 2010, theBeijing Yanqing solar power plant. It has been then followed byBeijing Badaling Solar Tower in 2012.The most important centralreceiver power plants in operation throughout the world arereported in Table 3.

THEMIS 2.5 France 1984

EURELIOS 1 Italy 1981

SUNSHINE 1 Japan 1981

SPP-5 5 Russia 1986

around 75% completion. This power tower is the result of a close

same technology that has been adopted for the Crescent Duneswhich is underway by the same company in Tonopah, Nevada.Intended to be operational two years after breaking ground, thepower facilities are expected to supply more than 500 GW h peryear of green electricity to Arizona or California.

2.3. Recent R&D activities in central receiver technology

dunes

Khi solar

one

100 South, Africa Upington 2014

Delingha 50 China, Delingha 2013

e-Cube 1 1 China, Hainan 2013

THEMIS 1.4 France, Pyrenees-

Orientales

() not available.

Stye

Au

20

Ap

De

20

Ju

20

Ap

20

Ju

Ju

O. Behar et al. / Renewable and Sustainable Energy Reviews 23 (2013) 123918collaboration between BrightSource and the pioneer corporationGoogle. Africa is a very promising market for CSP. For example,near the Kaxu Solar One parabolic trough power station, thelargest 50 MW Khi Solar One plant is under construction in SouthAfrica. Details about underway solar towers are presented inTable 4.

2.2.5. Central receiver solar thermal power plants in the planning

[32,7880,84]

More than 10.135 GW CSP power installations are announcedmainly by the USA and Spain but also by China [79]. Projects inthe eld are also under consideration in the Sun Belt countriessuch as Algeria, Morocco, Saudi Arabia and India [80]. SaudiArabia has recently announced an enormous deployment of CSPtechnology in over the next 20 years, with a target of 25 GW by2.2.4. Central receiver solar thermal power plants under

construction [32,7880]

Nowadays many power tower projects are underway world-wide and most of them will be operational in 2013. In Spain,about 700 MW of CSP-plants are being commissioned this year.For the USA, a total of 1.2 GW CSP power installations areunderway and should be in operation in 2013. Near San Bernar-dino County, California, the largest plant Ivanpah has reached

Table 3Central receiver solar thermal power plants in operation [32,7883].

Name Country, location Owners Capacity(MW)

Breakground date

Beijing

Badaling

China Beijing Academy of

sciences

1.5 July 2009

Gemasolar Spain, Andaluca

(Sevilla)

Torresol

energy

19.9 February

2009

Julich Germany, Julich DLR 1.5 July 31, 2007

Planta

solar 10

Spain, Sanlucar la

mayor (Sevilla)

Abengoa solar 11.0 2005

Planta

solar 20

Spain, sanlucar la mayor

(Sevilla)

Abengoa solar 20.0 2006

Sierra United States lancaster

California

eSolar 5.0 July 2008

Yanqing China, yanqing county Academy of

sciences

1 2006

() not available.2032 [32]. Table 5 illustrate the announced CRS to be operationalbefore 2020 [32,79]. The main planned CRS power plants to beoperational by 2020 are listed in Table 5. In the USA, a large partof the projects are for the 200500 MW CRS power plants. Forinstance, BrightSource Energy has taken over the Palen SolarPower project after Solar Millennium bankruptcy in 2012. How-ever, the concept is expected to switch from the parabolic troughtechnology to the CRS one.

The Palen project includes two 250 MW adjacent power plantssimilar to Ivanpah technology. Each plant is designed with about85,000 heliostats for sunlight reection to the receiver located onthe top of a 228 m tower. Expected to be operational by June2016, this project realisation is projected to start by the end of2013. Likewise, BrightSource is developing another two 500 MWprojects named Rio Mesa and Hidden Hills. These two projects arestill in the certication process.

On the other hand, in Arizona, Crossroads Solar Energy Projectthat includes a 150 MW tower technology and a 65 MW solarphotovoltaic (PV) technology is being developed by SolarRe-serves. The Crossroads central receiver technology is a moltensalt heat transfer uid and storage medium technology. It is theTable 4Central receiver solar thermal power plants underway [32,7880].

Name Capacity (MW) Country location Expectedcompletion

Ivanpah

facility

(3 units)

377 USA, San Bernardino

county, CA

2013

Crescent 110 USA, Nye county, NV 2013/14

artingar

Heliostat eldarea (m2)

Receivertype

Powercycle

Storage Type

gust

12

10,000 Cavity Rankine 1 h Fossil

solar

ril 2011 304,750 Cavity Rankine 15 h Fossil

solar

cember

08

17,650 Volumetric Rankine 1.5 h Fossil

solar

ne 25,

07


solar

ril 22,

09


solar

ly 2009 27,670 Cavity Rankine Solar

only

ly 2011 10,000 Cavity Rankine Two-stage heat

storage

Recent R&D activities in particular, ECOSTAR, have focused onthe most important factors and actions that contribute signi-cantly to achieve a cost reduction in tower concept. Scaling upand mass production can contribute to about 50% in LEC reduc-tion, while the other half in LEC reduction is the result of R&Defforts, according to these studies [11,29,71].

The ECOSTAR study pointed out that the lowest LEC for largescale CSP-plants would be for solar tower concept with pressur-ized air and molten salt technology [71]. These results areconrmed by latest studies [40].

Over the last decade, R&D efforts have been growing sharply inthe USA (SNL, NREL) and the Europe (DLR and CIEMAT); China,India and Australia are starting momentous R&D activities, whileother developing countries have expressed interest, in particularAlgeria, Morocco and UEA [1028,32,80,85]. Progress in R&D, andso, performance improvements of the three major componentscan achieve very signicant costs reduction [3,7,8,11,71].

After a stagnation period that extended from 1996 to 2000, severalR&D projects have been launched mainly in Europe and the USA toinvestigate the solar tower technology under real solar conditions. Asa result, many pilot plants have been erected and their O&Mmethods

O. Behar et al. / Renewable and Sustainable Energy Reviews 23 (2013) 1239 19Table 5Planned Central receiver solar thermal power plants [32,7880].

Name Country

Rio mesa solar project USA

BrightSource PPA5 USA



Rice solar energy project USA

Crossroads solar energy project USA

Suntower USA

eSolar 1 USA

eSolar 2 USA

AZ 20 Spain

Alcazar Solar Thermal Power Project Spain

Almaden Plant Spain

Unknown Chinaand components optimized. With special focus on the hybrid cong-urations and with the aim of developing the three main subsystemsof the central receiver concept, ConSolar, Solair and Solgate haveconrmed the viability of the full-scale application of central receivertechnology [70].

More recently, the US department of Energy has announcedthe SunShot program. In order to achieve signicant costs reduc-tion and to develop some innovative concepts such as the use ofsupercritical CO2 as heat transfer uid for Brayton cycle plants orfalling particle receiver [32]. More than 21 R&D projects (totaling$56 million over three years) have been launched. In order toenhance the falling particle receiver technology performance andreduce costs, four important R&D projects in the eld have beenawarded to NREL, SNL, Brayton Energy LLC and the University ofColorado. These R&D projects are outlined in Tables 610.

Likewise, Sandia National Laboratories (SNL) has announcedthe commissioning of its Molten Salt Test Loop (MSTL) at National

Table 6Recent and announced R&D projects of CRS.

Research project Country Location Mai

ConSolar [29,86,70] Israel Israel WIS

SOLAIR [70] Spain Almeria DLR

SOLHYCO [70] EUAlgeria

Spain DLR

SOLASYS [70] EU Israel DLR

SOLGATE [29,70,87] EU Spain ORM

SOLUGAS [29,32] Spain Seville Abe

EU-SOLARIS [32] EU EU CTA

Variable geometry test facility [32] Spain Tabernas,

Almeria

CTA

Particle receiver integrated with a uidized [32] USA USA NRE

Temperature falling-particle receiver [32] USA USA SNL

Small-particle solar receiver for high-temperature

Brayton power cycles [32]

USA USA San

Uni

10 MW s-CO2 turbine[32] USA USA NRE

s-CO2 turbo-expander and heat exchangers [32] USA USA Sou

inst

New solar receiver that uses s-CO2 as transfer uid

[32]

USA USA Bray

Molten salts loop test facility [32,85] USA Albuquerque,

New Mexico

SNL

() not available.Capacity (MW) Location

500 Riverside county, California

200 Mojave, California



150 Riverside County, California

150 Maricopa County, Arizona

92 Dona Ana County, New Mexico

84 Los Angeles County, California

66 Los Angeles County, California

50 Sevilla

50 Alcazar de San Juan

20 Albacete

2000 Mongolian desert, ChinaSolar Test Facility (NSTF) in Albuquerque, New Mexico. The MSTLconsists of 3 parallel test platforms with 38 t of melting salts.The tests have been successively meeting, or even exceeding all ofthe design requirements in plant-like conditions by achievingtemperature range of 300585 1C. [32,85]

In Europe, besides the pioneering Solar Platform of Almeria, aninnovative research project named the Variable Geometry CentralReceiver Solar Test Facility has been launched by the Spanishresearch center CTAER (Advanced Technology Center for Renew-able Energy). In this demonstration plant, the heliostats arereplaced by the so-called helio-mobiles. These helio-mobiles areplaced over a mobile platform which moves over rails around thetower. The receiver, located at the top of a xed tower, is housedin a rotating platform [32,88].

In order to demonstrate the feasibility and examine the thermalperformance of a CRS- hybrid Brayton cycle plants, Abengoa havebeen built a SOLUGAS facility at the Solucar Platform in Seville,

n Developer HTF Budget Main subsystem focus

Pressurized air Volumetric receiver hybrid

Brayton cycle

, SIEMAT Air h3.3

million

Volumetric receiver

Pressurized air h3,088,218 Hybrid Brayton cycle

cogeneration

Pressurized air h2,536,077 Syngas hybrid Brayton

cycle

AT Pressurized air h3.2

million

Volumetric receiver hybrid

Brayton cycle

ngoa Pressurized air h6 million Receiver Heliostat eld

ER Various h4,45 M The three main

subsystems

ER Various h5 million Advanced concepts

L Gas/solid, two-

phase ow

$3.8

million

Particle receiver

and DLR Recirculation

Particles

$4.4

Million

Particle receiver

Diego State

versity (SDSU)

Air a and carbon

particles

$3.8

millions

Particle receiver Brayton

cycle

L CO2 $8 million Brayton cycle

thwest research

itute (SWRI)

CO2 $6.8

million

Power conversion cycle

ton energy LLC CO2 Particle receiver Brayton

cycle

Molten salt HTF

Table 8Heliostat eld design data of operational solar power towers [32,7886].

Name/Type

Latitude,longitude

Solar radiation(kW h/m2/yr)

Landarea

Field area(m2)/ Type

Area-N ofHelios

Heliostatmanufacturer

Heliostat Design

Beijing Badaling solar tower/

demonstration

401400 North,1151900 East

1290 13

acres

100,000 North

eld

100 m2

N100Himin solar 64 facets, each facet

1.251.25 m2Gemasolar thermosolar plant/

commercial

371330 North,51190 West

2172 195 ha 304,750

surrounded

120.0 m2

N2,650Sener Sheet metal stamped facet

Julich solar tower/

demonstration

Rhineland 902 17 ha 17,650 North

eld

8.2 m2

N2,153

Planta solar 10/commercial 371260 North,61140 West

2012 55 ha 75,000 North

eld

120.0 m2

N624Abengoa Solucar 120: Glass-metal

Planta solar 20/ commercial 371260 North,61140 West

2012 80 ha 150,000 North

eld

120.0 m2

N1,255Abengoa Solucar 120: Glass-metal

Sierra suntower/

demonstration

341460 North,118180 West

2629 27,670 1.136 m2

N24,360eSolar

Yanqing solar power/

demonstration

401400 North1151400 West

208

acres

10,000 100 m2

N100Himin solar

() not available.

Table 9Solar receiver data of operational solar power towers [32,7886].

Name Tower height Receiver manufacturer Receiver type HTF Inlet temp. (1C) Outlet Temp. (1C)

Beijing Badaling 118 m Dongfang Boiler Group Co.,Ltd Cavity Water/Steam 104 400

Gemasolar 140 m Sener Cavity Molten salts 290 565

Julich 60 m Kraftanlagen Munchen Volumetric Air 80100 680

Planta solar 10 115 m Tecnicas reunidas Cavity Water/ steam 250300

Planta solar 20 165 m Tecnicas reunidas Cavity Water/ steam 250300

Sierra 55 m Babcock & Wilcox victory energy Dual-cavity receiver &

tubular external

Water 218 440

Yanqing 100 m Cavity Superheating steam 390

() not available.

Table 7Expected improvements for the three main subsystems of CRS [33,71,93].

Heliostats eld Solar receiver Power conversion system

Enhancements Benets (%) Enhancements Benets (%) Enhancements Benets (%)

Heliostat and layout Efciency: 3 [93] Multi-tower conguration Efciency: 5 [93] Central receiver- Brayton cyclesystem (up to 50 MW)

LEC reduction: 39 [71]

Cost reduction: 1726 [93] Cost reduction: 25 [93] Cost reduction: 1729 [33]

LEC reduction: 917 [71] LEC reduction: 17 [71] Central receiver-rankine cycle

system (current Efciency)

Supercritical: 2226 [33]

Superheated: 1617 [33]

Tracking system Cost reduction: 40 [93] Higher operating

temperature

Efciency: 4060 [93] Central receiver -combined

cycle system

Cost reduction: 1728 [71]

LEC reduction: 17 [71] LEC reduction: 314 [71]

Table 10Power conversion cycle design of operational solar power towers [32,7886].

Name Turbine capacitygross/net

Turbinemanufacturer

Power cycle Cooling system Fossilback-up

Thermal storage

Beijing Badaling 1.5 MW/1.5 MW Hangzhou steam

turbine

Steam rankine 400 1C,4 MPa Wet cooling Oil-redboiler

Two stages; saturated

steam/oil

Gemasolar 19.9 MW/19.9 MW Siemens SST-600 2-cylinder Reheat

steam turbine

Wet cooling Natural gas Tow tank; Molten salt

Julich 1.5 MW/1.5 MW Siemens Steam Rankine 480 1C, 26bar Dry cooling Ceramic heat sinkPlanta solar 10 11.02 MW/11.0 MW GE Steam Rankine 40 bar 250 1C,

2 Pressures

Wet cooling, refrigeration

towers

Natural gas

Planta solar 20 20.0 MW/20.0 MW GE Steam Rankine 45.0 bar Wet cooling, Refrigeration

towers

Natural gas

Sierra 5.0 MW/5.0 MW Steam Rankine Wet cooling, Cooling

towers

None

Yanqing 1 MW/1 MW Steam Rankine 2.35 MPa two-stage heat storage

system

() not available.

O. Behar et al. / Renewable and Sustainable Energy Reviews 23 (2013) 123920

Spain. The R&D plant consists of a modied gas turbine locatedclose to a 351 inclined receiver collecting solar radiation reectedby a 69 heliostat eld. It has been a truly close collaborationbetween all of the participants with DLR, Turbomach, GEA Tech-nika Cielpina, New Energy Algeria being the developers andAbengoa the constructor [32,8991].

Another important European project is EU-SOLARIS, the Eur-opean CSP research Mega-facility. The project is very promising. Inaddition to ESTELA, Germany, Spain, Greece, Italy, France, Cyprus,Portugal, Turkey and Israel are collaborating in this project [32,92].

The following sections review the most important R&D activitiesand published papers on the major components of the centralreceiver solar thermal power plants. The R&D studies and theirresults are reported and classied into three groups according tothe subject treated, namely heliostat eld, solar receiver and powerconversion system. In each group the analysis of existing design,experiments and suggested development and expected improve-ments are presented in order to make the article more helpful forfuture research.

3. Heliostat eld

The performance of CRS depends strongly on the solar eldefciency which in its turn is related to the heliostat design, theeld layout, the tracking system and control system. In thissection, the published studies focused on the heliostat eld arereviewed and their results are briey reported. Also, methods andtechniques used or proposed for enhancing the heliostat and theheliostats eld performance are sketched out.

a tracking system, a frame, a structure foundation and controlsystem. The basic design of single heliostat is illustrated in Figs.817. Heliostat eld performance is a function of the opticalefciency. Cosine effect, shadowing effect, blocking effect, mirrorreectivity, atmospheric attenuation, and receiver spillage are themain factors affecting a heliostat optical efciency [29]. It is wellknown that the half of the total investment cost and 40% of totalenergy losses are attributed to the heliostat eld. It is thenessential to optimize its design to reduce the capital cost and toimprove the overall efciency of the power plant [36,29].

3.1.2. Design

Siala and Elayeb [94] have presented the mathematical mod-eling of a graphical method for no-blocking radial stagger helio-stats layout. In the proposed method, the eld is divided intocertain groups of heliostats to increase its density and the Authorsreported that the method is simple compared to cell-wiseprocedure.

For positioning the heliostats, Sanchez and Romero [95] haveproposed a new procedure, named Yearly Normalized EnergySurface (YNES). In this method, the heliostats positioning isdetermined using the yearly direct solar radiation available atany location. The inferred results agree closely with that that ofWinDelsol and SOLVER codes; nevertheless, the annual opticalefciency needs to be calculated by ray tracing method, and thus,the procedure is time consuming.

Wei et al. [96] have coupled the ray tracing technique with the

stag

yllot

O. Behar et al. / Renewable and Sustainable Energy Reviews 23 (2013) 1239 213.1. Heliostat and layout


The solar eld consists of a large number of tracking mirrors,called heliostats. A single heliostat includes a set of mirrors,

Mirrors

Frame

Tracking

Control

Foundation

Fig. 8. Basic concept of heliostat (left); radial

Fig. 9. Field density and optical efciency of radially staggered layout (left) and ph

reduces land area by 0.36% and 15.8%, compared with radial layout [112].axis spiral layout (right). Spiral layout respectively enhances optical efciency andparametric search algorithm to estimate the optical efciency andto optimise the heliostat eld layout. Using this method they haveinvestigated four different layout types, i.e., NorthSouth corn-eld, NorthSouth stagger, Radial corneld and Radial staggered,and found that NorthSouth corneld layout is the most suitablefor 1 MWe solar tower power plant in China.

gered layout for positioning heliostats (right).

arge

O. Behar et al. / Renewable and Sustainable Energy Reviews 23 (2013) 123922Azimuth Axis

Spinning

TWei et al. [97] have developed a new method and a faster codecalled HFLD (Heliostat Field Layout Design) for heliostats layout.In this method the heliostat eld optimization is based on thereceiver geometrical aperture and an efciency factor. Applyingtheir technique to the PS10 power plant, they proposed a newlayout for PS10 eld as good as that is already implanted.Furthermore; the Authors introduced a new methodology basedon sunshine duration to investigate the possibility of framingunder heliostats.

Wei et al. [98] have detailed the mathematical formulations oftracking and ray tracing techniques for the target-aligned helio-stat. To this end they have created and incorporated in the HFLD

Axis

Fig. 10. Spinningelevation (left) and Azimu

Tem

Hot Air

Porous Structure

Concentrated Direct Radiation

e

Fig. 11. Volumetric effect o

Fig. 12. Volumetric receiver used in HiTRec and Solair projectAzimuth Axis Target

Elevation Axiscode a new module to analysis such heliostat with asymmetricsurface and compared the simulated results with the well knownsoftware Zemax with good agreement.

Wei et al. [99] have implemented in the HFLD code a modulefor design and analyze of aspherical toroidal heliostat eld. Theyfound that the toroidal heliostat eld has higher performancethan that of spherical heliostat if the design and tracking systemare ideal. They have also recommended the selection of cropaccording to the distribution map of the sunshine duration whenframing under heliostats.

Wei et al. have developed and incorporated into the HFLD codea new module for the beam-down central receiver system based

thelevation (right) tracking methods.

Inlet Outlet

Structure

Air

e

perature

Absorber thickness

f volumetric receiver.

ts (left), solar receiver at PSA (right) [53] (experiments).

on the ray tracing method. The selected power plant for the studyhas consisted of 3 heliostats and a hyperboloid reector. Theyhave found good agreement between their results and thatobtained by the well-known software Zemax. [100]

Zhang et al. [101] have dened a new factor named availableland efciency. This factor is function of the cosine effect, atmo-spheric attenuation and the intercept efciency. It has been usedto position in an optimumway the heliostats of 1 MW solar towerpower plant and found that their technique grants an annualefciency of 71.36% when incorporated in the HFLD code.

Augsburger and Favrat [102] have studied the thermoeco-nomic of heliostat eld to nd design parameters of solar towerpower plant that offers better performance, in particular, ef-ciency, investment costs and environmental benets.

Collado [103] has developed a simplied model to be used for

conditions of vertical and horizontal wind direction. They have

HotAir

Cold Air

ConcentratedDirectRadiation

VolumetricReceiver

TubularReceiver

Water/Steam

PorousMaterial

Fig. 13. Top view of dual volumetric-tubular receiver (suggested enhancement).

Air jet

Heliostat Field

AperturePanel

Fig. 14. Basic design of a cavity receiver made of ve panels, an aperture and anaerowindow for the protection.

Concentratedsolar radiation

Heliostat

Fig. 15. Basic concept of solid particle receiver; a cylindrical receiver where particles

O. Behar et al. / Renewable and Sustainable Energy Reviews 23 (2013) 1239 23found that the maximum wind pressure at each test point andblockage is obtained in the wind speed of 14 m/s. This latter havebeen used to estimate the maximum displacement and strain ofthe heliostat structure.

Chen et al. [108] have designed, constructed and tested therst prototype of a 4 m2 non-imaging focusing heliostat. Theyhave reported that a solar furnace system using this prototype hassuccessfully reached in access of 3400 1C.

Schell [109] has reported the design, the realisation, thetesting-calibration, and performances measurement of esolarheliostat elds which focuses on low-cost design, high-volumemanufacturing and ease of installation.

Fernandez-Reche [110] has carried out a statistical analysis ofthe reectance in the heliostat eld at the Plataforma Solar de

Inlet, Cold particles

Outlet,Hot particlespreliminary studies of surrounding heliostat eld and successfullycompared its performance to Solar Tres demonstration plant data.

Utamura et al. [104] have proposed a methodology to get anoptimal layout of group of heliostats in beam-down centralreceiver. They found that, due to spillage effect, the optical lossesbecome signicant at heliostats located at a distance from thetower farther than four times the tower height.

Wang and Wei have proposed a layout of 100 heliostats for1 MW solar tower power plant in China. [105]

Lopez-Martinez et al. [106] have predicted the cloud passageby computing heliostat eld cover factor. They have suggestedturning off some heliostats to bring down the receiver tempera-ture before the cloud covers, and therefore, prevent the receiverfrom thermal stress.

3.1.3. Experiment

Wang et al. [107] have experimentally measured the effects ofwind on a 100 m2 area Dahan heliostat under various operatingare injected from the top-center to be heated up and returned from the bottom.

ssu

Bra

tem

am

O. Behar et al. / Renewable and Sustainable Energy Reviews 23 (2013) 123924Storage Sys

StePre

Air Intake

Compressor

Turbine

Combustor

To stack

Fig. 16. Solar central receiver

SteamTurbineAlmeria (PSA) in order to determine nd the minimum number ofmeasurements necessary to provide a total reectance andpointed out that the methodology is useful in other solar thermalsystems such as parabolic trough and dish collectors.

Collado [111] has examined the accuracy of UNIZAR andHFCAL analytic ux density models by comparing their perfor-mance to measured ux densities sent by 10 off-axis alignedheliostats onto a vertical receiver plane at PSA. They concludedthat both HFCAL and UNIZAR are efcient tools to simulate theenergetic images from heliostats, although the UNIZAR is lesssimple and slightly less accurate than the former HFCAL.

3.1.4. Enhancement

Noone et al. [112] have proposed a new pollytaxis spiral eldlayout based on heliostats discretization approach. They havecompared the results of the proposed layout approach withcurrent PS10 eld arranged in a radially staggered conguration,as well as, with the simulated results of Wei et al. [97]. Theyconcluded that the spiral layout allow placing heliostats in highefciency eld positions, and thus, offers higher optical efciencyand signicantly reduce land area and Levelized Energy Cost LEC.

Leonardi and Aguanno [113] have developed a code namedCRS4-2 to evaluate the optical performance of solar eld made upof both square and circular heliostats of diverse geometricalparameters. They have then introduced a new factor called thecharacteristic function that depends on the zenith and theazimuth angles. This factor has been applied to estimate the totalenergy collected by the eld; while the shading-blocking effectshave been determined by a tessellation of the heliostats.In addition to the comparisons of concentrating solar thermal

Wet Cooling

Fig. 17. Solar power tower with saturated steam cavirized Receiver Heliostat Field

yton cycle (SCR-BC) system.

Heliostat Field

Drumsystems, the code going to be extended to the analysis of Multi-Tower conguration, Beam-Down and Multi-Apertures concepts.

Danielli et al. [114] have introduced a new concept namedConcatenated Micro-Tower CMT. They have compared its perfor-mance with that of larger conguration and have revealed thatCMT with a dynamic receiver allocation can improve the annualoptical efciency by 1219%.

Pitz-Paal et al. [115] have coupled genetic algorithm withNelderMead algorithm to design heliostat eld for high tem-perature thermo-chemical processes for fuels production. Theyhave found that the selected chemical process has a strong impacton the eld design and performance.

Collado [116] has developed a simplied radial staggeredmethod for surrounded heliostat eld that uses only two para-meters for the optimisation, i.e., a blocking factor and an additionalsecurity distance, required for installation and maintenance. Hehas conrmed that the Houston cell-wise method (UHC-RCELL)needs some improvements to nd optimum mean radial andazimuth spacing of the heliostat eld.

Collado and Guallar have partially described a new code, calledcampo. This code is meant to be used to solve the complexproblem of the optimized design of heliostat eld layouts, byperforming accurate evaluation of the shadowing and blockingfactor for heliostats placed in radial staggered conguration. Theyhave compared the resulting optimized layout to that of theGemasolar plant with good agreement. [117]

Chen et al. [118] have developed and constructed a secondgeneration of non-imaging heliostat, which is three times largerthan the rst generation. They have then applied the newheliostat prototype for potato peeling and results have been verypromising.

Tower-Receiver

ty receiver and storage system (PS 10-like plant).

heliostat.Moeller et al. have presented a control strategy for the

handling and provides better predictions of the heliostat eldperformance with high resolution of about 1 million points per

O. Behar et al. / Renewable and Sustainable Energy Reviews 23 (2013) 1239 253.2.1. Basic concept

In the solar eld, each heliostat tracks the sun to minimize thecosine effect, and therefore maximize the solar energy collectionthrough positioning its surface normal to the bisection of theangle subtended by sun and the solar receiver. Heliostat suntracking can be classied either as Open loop system or as closedloop system [14]. The open loop system is based on astronomicformulae relating the suns position to the system geometry. Thissystem is reliable-low cost and it is recommended for larger solareld because the heliostat is under computer control. On theother hand, the closed loop system uses sensor to track the sun.This system is then more accurate and very useful for smallheliostat elds. However, this system suffers from lower perfor-mance during cloudy period. Two sun-tracking methods areusually applied in CRS, i.e., the AzimuthElevation (AE) andSpinningElevation (SE) [28]. Compared with AE the SEtracking method allows more solar energy collection at thereceiver and reduces spillage losses by 1030% [28].

3.2.2. Design

Chen et al. [123] have analyzed the optical performance of twodifferent sun tracking methods at the level of a single heliostatand at that of a heliostat eld. They have been considered the caseof a xed geometry non-imaging focusing heliostat usingSpinningElevation (SE) axis and the case of a spherical geome-try heliostat using AzimuthElevation (AE) axis are considered.They have found that the SE tracking system can reduce thereceiver spillage losses by 1030%; moreover, the SE trackingprovides much more uniform concentrated sunlight at the recei-ver without huge variations with the time of day compared to theAE system.

Chong and Tan [124] have detailed in a comparative study onthe range of motion of an AE and an SE tracking systems forboth single heliostat and heliostat eld. They have concluded thatthe annual power consumption of SE tracking method is lowerthan AE method.

Chen et al. [125] have derived a new sun tracking formulas fora non-imaging focusing heliostat that has no xed optical geo-metry based on the non-imaging optical concept to focus thedirect solar irradiation on the receiver.

Liang et al. [126] have proposed an open loop control systemVazquez [119] has analyzed the mechanical structure andtracking of SENER heliostat. He has been developed the SENSOLcode that could be used for design of heliostat structure takinginto account the wind loads, and proposed a new lighter designfor SENER heliostat equipped with cheaper tracking system.

Augsburger and Favrat [120] have focused on the effects ofcloud passage, over of the heliostat eld, on the receiver uxdistribution. They have then proposed a strategy for the progres-sive start-up/shut-down of the heliostats to ensure regulartransients. The study is applied to the case of a Gemasolar-likecircular heliostat eld with a cylindrical receiver.

Ballestrin and Marzo [122] have been interested in the solarradiation attenuation loss between the heliostats and the recei-ver. They have compared the results of three simulation software,i.e., MODTRAN, DELSOL and MIRVAL, to that obtained by thePitman and VantHull model [121]. They have considered twoatmosphere types, i.e., the rural atmosphere (visibility 23 km) andpoor atmosphere (visibility 5 km), and concluded that the MOD-TRAN software is more accurate and more versatile than theDELSOL and the MIRVAL under various climate types.

3.2. Tracking and control systemfor heliostat tracking based on astronomic formulae to calculateheliostat and measurement time of 1 min/heliostat. Furthermore,it can be used to measure other solar concentrators such as dishand parabolic trough.

3.2.4. Enhancement

Arqueros et al. [134] have suggested the use of star reectionon the mirror at night to move the heliostat in order to getenough information for determining the local surface normal atvarious points on the reector.

Berenguel et al. [135] have used articial vision technique anda B/W CCD camera to correct and control heliostat positioningoffset in an automatic way. The proposed control system allowsthe elimination of the manual regulation.

Mehrabian and Aseman [136] have developed a computerprogramming algorithm for evaluating the typical angles ofindividual heliostats. The algorithm can be used for open loopcontrol and to predict blocking and shading effect of theheliostat eld.

Bonilla et al. [137] have coupled the hybrid heliostat eldmodel and a wrapped model to handles the real-time simulationdetection of cloud passage. The control system turns the helio-stats to standby position, and then returns them automatically totheir original orientation after could passage [130].

3.2.3. Experiment

Aiuchi et al. [131] have designed, constructed and tested theaccuracy of a photo-sensor sun tracking system for controllingheliostat using an equatorial mount in addition to two Aided-sensors to maintain stable tracking in a cloudy sky. They haveachieved sun-tracking with an error of 0.6 mrad in clear weather.Nevertheless, the error is larger during cloudy periods and hencethe larger are the energy losses.

Kribus et al. [132] have tested, at the Weizmann Instituteheliostat eld, a closed loop control system. This control systemautomatically corrects the tracking error though a dynamicmeasurement of spillage, detection of aiming errors, and feedbackof a correction signal to the tracking algorithm that can reach theprecision of 0.1 mrad.

Ulmer et al. [133] have designed, implemented and tested, atCESA-1 heliostat eld, an automatic measurements system ofheliostat slope deviation which based on the reection of regularpatterns in the mirror surface and their distortions due to mirrorsurface errors. The method offers signicant gain in speed andthe solar zenith and azimuth angles with a 0.052 mrad precision,taking into consideration the errors occurring during the helio-stats installation.

Badescu [127] has investigated the heliostat tracking errordistribution of concentrated solar radiation on the receiver. Hehas compared the obtained results with the measurements dataof Kosuke Aiuchi et al. [131]. He has deduced that some empiricalprobability distributions models such as Gaussian and the Uni-form Distribution Approaches have many advantages in practice.

Jones et al. [128] have developed the so-called V-shot mea-surement system for measuring the local slopes of a heliostatmirror by scanning it with a laser beam, detecting the point ofincidence of the reected beam and calculating the resultingsurface normal.

Chen et al. [129] have reported the algorithm and the meth-odology of residual aberration analysis of non-imaging focusingand communication between the heliostat eld simulator and

to inertial permeability coefcient lead to stable ow.

Sciti et al. [152] have conducted experiments to examine the

O. Behar et al. / Renewable and Sustainable Energy Reviews 23 (2013) 123926Marcos et al. [142] have studied the effect of geometricalparameters on the Air Return Ratio ARR in volumetric receiverand obtained a higher average value of 70%. They have concludedthat further improvements in design should take into accountreceiver edge, lateral wind and air injection angle.

Villafan-Vidales [143] has numerically analysed the heattransfer into volumetric receiver made of porous ceramic foamand applied in a thermo-chemical solar reactor for hydrogenproduction. He has validated the simulated results with experi-mental data of a reactor tested at a solar furnace. The Author hasHeliostat Field Control software HelFiCo. The Authors has alsoreported some techniques to improve simulation performance.

Roca et al. [138] have designed, simulated and tested anautomatic controller that employs the mean hydrogen reactortemperature as feedback and selects the heliostats to be focusedor taken out of focus, to make the CRS-hydrogen reactor withinthe margins of safety and for eliminating the manual control ofheliostats. The ensuing experimental results of Hydrosol facility atCIEMATPSA have been very promising.

4. Solar receiver

In a CRS, the solar receiver is the heat exchanger where thesolar radiation is absorbed and transformed into thermal energyuseful in power conversion systems. There are different classica-tion criteria for solar receivers, depending on the geometricalconguration and the absorber materials used to transfer theenergy to the working uid. In this survey, receivers are classiedinto three groups widely employed in central receiver system, i.e.,volumetric receivers, cavity receivers and particle receivers. Theresults of numerous articles concerned with receivers design,experiments and improvements are presented in this part.

4.1. Volumetric receiver


Volumetric receivers consist of porous wires or either metal orceramic. A good volumetric receiver produces the so-calledvolumetric effect, which means that the irradiated side of theabsorber is at a lower temperature than the medium leaving theabsorber [29]. The porous structure acts as convective heatexchanger where the HTF (in particular air) is forced to absorbthe direct solar irradiation by convection heat transfer mode [29].

4.1.2. Design

Avila-Marn [53] has presented a detailed review of more thantwenty volumetric receivers including their design, material andperformance and then classied them into four groups based onair pressure and type of material: two open-loop receiver groups(Phoebus-TSA and SOLAIR), and two closed-loop receiver groups(DIAPR and REFOS).

Sani et al. [139] have investigated the use of ceramic zirco-nium carbide samples as absorbers in solar power plants. Theyhave concluded that ZrC-based ultrahigh temperature ceramicshas lower emissivity than SiC already used in volumetric solarreceiver.

Kribus et al. [140] have dealt with unstable gas ow involumetric receiver to nd out overheating regions that causelocal failures such as melting or cracking.

Becker et al. [141] have studied theoretically and numericallythe ow behaviour in porous material and indicated that volu-metric receivers with a high heat conductivity, a quadraticpressure drop and high ratio of viscous permeability coefcientalso reported that the receiver length has a weak inuence on thepotential of Ceramics, hafnium and zirconium diborides whenused in high-temperature solar receivers. They have measured theroom-temperature hemi- spherical reectance spectra from theultraviolet (UV) to the mid- infrared (MIR) wavelength regions.They have concluded that diboride family has a very high solarabsorber performance because of higher absorbance over emit-tance ratio compared with SiC.

Fend et al. [144] have made comparative studies between thethermo-physical and heat transfer properties of six porous mate-rials used in volumetric solar receivers. They have concluded thatcombining materials of high specic surface and porosity withgood thermal conductivity (eg. SiC catalyst carrier) improvesreceiver performance although ceramic-based materials are arestill offers better solution.

Fend et al. [153] have analyzed two high porosity materialsthat are suitable for volumetric receivers. The metal foam ofdifferent cell density has been investigated. The obtained resultshave shown that double layer silicon carbide metal foam hasbetter performance than single layer.

Albanakis et al. [154] have experimentally compared the heattransfer and pressure drop of nickel and inconel metal foamswhen used as volumetric solar receiver and revealed that thepressure drop and the heat transfer of nickel foam are higher thanthose of inconel metal.

Wu et al. [155] have experimentally and numerically investi-gated the pressure drop in ceramic foam employed in volumetricreceiver considering ten sorts of ceramic foam structures. Theyhave derived a new pressure drop correlation that is moreaccurate than the existing ones.

Garcia-Martin et al. [156] have developed and implanted, atthe Plataforma Solar de Almeria (PSA), an automatic controltemperature distribution of the uid and solid phases. Moreover,he has found that the foam cell size does not affect considerablyfoam and uid temperature distributions.

Wu [145] has developed a steady state macroscopic model fortemperature distribution in a ceramic foam volumetric receiver.He has examined the effect of numerous design parameters andmaterial proprieties on the temperature distribution of the uidand solid phases by comparison to experimental data of [144]. Hehas concluded that the heat ux is strongly related to uid mediaand appropriate distribution is obtained for thin ceramic foamsizes of 13 mm.

He et al. [148] have introduced a new method and uniedMonte Carlo Ray-Trace (MCRT) code for calculating the solarenergy ux density distribution in volumetric solar receiver withsecondary concentrator. They have applied the proposed methodto predict photo-thermal conversion process of solar energy. Theyhave then found an error of 10% when comparing the numericalresults with the measured data and the simulation results of Bucket al. [146,147].

Wu [150] has numerically investigated the convective heattransfer coefcient between the air ow and porous ceramic foamin volumetric receiver. He has proposed a new correlation as afunction of cell size valid for porosity in the range of0.66oeo0.93 and Reynolds number in the range 70oReo800.His results were in good agreement with the experimental data ofYounis et al. [149].

Fricker [151] has proposed a thermal storage system to protectsolar receiver during transient conditions by feeding hot heattransfer uid into the receiver when quick change in radiationintensity occurs.

4.1.3. Experimentsystem that allows appropriate distribution of temperature in a

[163], they have shown that modular absorber design with smallsizes is not necessary because the duct receiver appears to be

Temperature gradients, i.e., between 200 K and 400 K, the radia-tive heat transfer is more important that convective heat transfer.

O. Behar et al. / Renewable and Sustainable Energy Reviews 23 (2013) 1239 27inherently stable.Pritzkow [165] has simulated the dynamic behavior of volu-

metric receiver during cloudy periods. He has then proposed anattenuator to protect the receiver from transient conditions andvolumetric receiver, based on a heuristic knowledge-based helio-stat control strategy. They have also reported the tests details andthe results.

4.1.4. Enhancement

Lenert and Wang [157] have presented a combined modelingand experimental study to optimize the performance of a cylind-rical nano-uid volumetric receiver. Their results suggest thatoptimized nano-uids have signicant potential as receivers forCSP systems because their efciencies are expected to exceed 35%when coupled to a power conversion cycle.

Cheng et al. [158] have developed a general numerical model-ling method and homemade unied code with the MCRT tosimulate the thermal conversion process of REFOS-SOLGATEpressurized volumetric receiver. They have pointed out to thefact that the non-uniformity of the radiation ux density dis-tribution is very signicant; it could reach the maximum at thecenter-left area near the symmetry axis, and the minimum nearthe pressure vessel wall, with the order of magnitude of 8 and 3,respectively. The proposed design-simulation tool is very power-ful for simulating other CSP systems and it is capable of providingbehaviour information on many parameters and phenomenadifcult to study experimentally.

Cheng et al. [159] have combined the Finite Volume Method(FVM) and the Monte Carlo Ray Tracing (MCRT) method toexamine the effects of geometric parameters of the compoundparabolic concentrator (CPC) and the properties of the porousabsorber on the performance of solar conversion process inpressurized volumetric receiver (PVR). He has concluded thatCPC exit aperture has much larger effects on the characteristicsand the performance of the PVR than that of the CPC entryaperture with a constant acceptance angle.

Veeraragavan [160] has developed an analytic model through thecombination of radiative and convective losses coefcients to evalu-ate the effect of design features and solar radiation on the perfor-mance of volumetric receiver with nano-particle-HTF. He has selectedthe heat transfer uid VP-1 suspended graphite nano-particle as acase study. The obtained results have been very interested. He hasthen pointed out that the proposed model is a good tool to optimisethe efciency of various receiver congurations.

Arai et al. [161] have considered transient radiative heating ofa semi-transparent liquid suspension in taller solar receivers.They have found that volumetric receiver with such uid mediawould have higher performance.

Buck et al. [162] have developed a hybrid receiver made up of atube absorber and an open volumetric receiver. They have comparedits performance with that of PS10 saturated steam receiver. TheAuthors have indicated that the new concept offers many advantages;in particular, the reduction of thermo-mechanical stress induced byvariations in the extent of the evaporation section during transientsas occurred it has occurred in Solar One plant. They have indicatedthat the proposed receiver could improve the net annual energy by27% compared with the solar air heating system.

Garcia-Casals et al. [164] have studied the possibility ofenhancing duct volumetric receiver performance by analyzingthe effect of numerous design parameters, in particular selectivitymechanisms. Unlike A. Kribus et al. [140] and Pitz-Paal et al.clouds.Yang and Yang [176] have considered the relation between theheat transfer performance and the efciency of a molten salt tubereceiver. They have found that the Nusselt number of the spiraltube is on average about three times larger than that of thesmooth tube.

Paitoonsurikarn and Lovegrove [177] have numerically exam-ined three different cavity geometries. They have then established4.2. Solar cavity receiver


In a cavity receiver, the radiation reected from the heliostatspasses through an aperture into a box-like structure beforeimpinging on the heat transfer surface.

4.2.2. Design

James and Terry [166] have investigated the thermal perfor-mance of ve cavity receivers of different geometries comprisingspherical, hetero-conical, conical, cylindrical and elliptical. Theyhave found that the rim angle and cavity geometry have a strongeffects on the energy absorption efciency.

Zhilin et al. [167] have provided a quick overview of the basicdesign of cavity air receiver. They have also reported the designdata of the rst demonstrative hybrid solar gas turbine of 70 kWin Nanjing, China.

Yu et al. [168] have evaluated and simulated the dynamicsperformance of solar cavity receiver for full range operationconditions using combined model which mainly couples theradiationheat conversion process and three heat transfer para-meters. They have also tested the effect of wind and DNI on theperformance of DAHAN receiver. Their results show that windangle or velocity can obviously inuence the thermal losses.

Fang et al. [169] have described a methodology for evaluatingthermal performance of saturated steam solar cavity receiverunder windy environment. To this end, the MonteCarlo method,the correlations of the ow boiling heat transfer and the calcula-tion of air ow eld were coupled to assess absorbed solar energy.They have concluded that the air velocity attained the maximumvalue when the wind came from the side of the receiver and thethermal loss of receiver also reached the highest value due to theside-on wind.

Yang et al. [170] have used Computational Fluid Dynamics(CFD) to look into the distributions of temperature, heat ux andthe heat transfer characteristics of a molten salt tube receiver of acentral receiver system. They have concluded that temperaturedistribution of the tube wall and HTF is irregular and the heat uxof the exposed surface rise with the rise of molten salt velocity.

Sobin et al. [171] have considered the design of the receiverthermal cyclic life. They have found that asymmetrical shapes ofthe receiver caused by expected ux by suitable sensing andcontrolling the energy intensity.

Li et al. [172] have performed a steady-state thermal model for100 kW t molten salt cavity receiver. They have analyzed theeffect of optical parameters on the design of such a receiver.

Hinojosa et al. [173] have presented the numerical results ofnatural convection and surface thermal radiation for open cavitybased on Boussinesq approximation.

Gonzalez et al. [175] have numerically analyzed the heattransfer by natural convection and surface thermal radiation ina two-dimensional square cavity receiver with large temperaturegradients. Comparing their results to those of Hinojosa et al. [173]and Chakroun et al. [174], they have concluded for largera correlation of the Nusselt number for natural convection.

balance between the hot receiver and the energy transfer acrossthe aperture. He has divided the internal area of cavity receivers

power but is not by changes in the ow rate; however, the closer

O. Behar et al. / Renewable and Sustainable Energy Reviews 23 (2013) 123928into a convective zone and a stagnant zone, to compute theconvection heat losses, examined the effect of the geometricdesign of the aperture on the heat transfer coefcient.

Clausing [183] has compared the results between analyticalpredictions [182] and experimental results of cubical cavityreceiver with good agreement.

Taumoefolau et al. [184] have carried out a theatrical study ofnatural convective loss of an electrically heated cavity receiverwith different inclination angles varying from 901 to 901 andtemperature ranging from 450 1C to 650 1C and ratios of apertureto cavity diameter between 0.5 and 1. Their results were in goodagreements with the experimental results.

Li [185] has developed a steady model that easily estimatesthe heat losses from cavity receivers.

Ferriere and Bonduelle [186] have proposed a lumped para-meter model for the solar receiver of France Themis plant. Theyhave simulated the time-dependent parameters involved in theenergy balances.

Fang [187] has proposed an iterative method, based onMonteCarlo Ray Tracing technique, to determine surface tem-perature and to investigate the performance of cavity receiverunder windy conditions.

4.2.3. Experiment

Kribus. et al. [188] have experimentally developed and tested amultistage solar cavity receiver to reduce the heat losses bydividing the aperture into separate stages according to theirradiance distribution levels. They have been able to get an airexit temperatures of up to 1000 1C.

Melchior et al. [189] have designed, fabricated, and tested a5 kW cylindrical cavity receiver comprising a tubular absorber, forperforming thermo-chemical reaction. The reactor has beenmodeled using a 2D steady-state model coupling the three heattransfer modes to the chemical kinetics, and solved using MonteCarlo and nite difference techniques. The prototype has achievedsolar-to-chemical energy conversion efciency of 28.5% at areactor temperature of 2300 K for an input solar power per

A Review of Studies on Central Receiver Solar Thermal Power Plants

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