Solar Energy Perspectives - IEA

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Solar Energy Perspectives: Solar heat Photo 7.7 Scheffler dishes associated in pairs in a cooking system at Hyderabad (India) Source: Deepak Gadhia. Key point Pairing Scheffler dishes helps obtain even sunlight throughout the year. Figure 7.9 Towers (central receiver systems) Solar tower Heliostats Key point Towers offer higher large-scale concentration levels. Field size seems to be limited to a thermal power of about 600 MW th , for which heliostats are located about 1.5 km from a tower of about 160 m height. Longer distances would further complicate the exact directing of the reflected sun on the tower, while atmospheric attenuation near ground level would reduce the energy flux. 136 © OECD/IEA, 2011
Chapter 7: Solar heat Figure 7.10 Blocking, shading and cosine losses in heliostat fields Incident solar flux Blocking loss Heliostat Cosine loss Shadowing loss Source: Stine and Geyer, 2011. Key point Heliostats must be distanced from each other to minimise blocking and shading. Field design optimisation also depends on the desired power. Typical heliostat fields in low latitudes tend to be circular and surround the central receiver, while in higher latitudes they tend to be semi-circular, to reduce cosine losses. Small fields will be more concentrated to the polar side of the tower, larger ones more circular, as atmospheric attenuation reduces the efficiency of far-field heliostats. While linear systems require flat land areas, central receiver systems may accommodate some slope, or even benefit from it as it could reduce blocking and shadowing, and allow increasing heliostat density. There are two basic receiver designs: external and cavity. External receivers offer vertical pipes to the concentrated solar flux from the heliostats, in which a heat transfer or working fluid circulates. In case of direct steam generation, different heliostats might be pointed to two or three different stages where the water is pre-heated, then vaporised, and if required the steam superheated. In the cavity design, the solar flux enters the cavity, possibly closed by a window. “Beam-down” designs use a secondary reflector on top of the tower, of hyperboloid shape, which redirects the concentrated solar flux to ground level, where it might be refocused by a secondary compound parabolic concentrator before it falls on the receiver (Photo 7.8). This design, conceived and first assembled at the Weizmann Institute in Israel, reduces optical efficiency but conveniently allows keeping the receiver at ground level. Heat transfer or working fluids, or reactants, are specific to the applications and are described in Chapters 5, 8 and 9. Recently, scientists at the Massachusetts Institute of Technology have suggested a simpler concept called CSPond – provided hilly landscape. Light from a hillside of mirrors goes through a small open window in a small insulated building and is volumetrically absorbed 137 © OECD/IEA, 2011
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Renewable Energy Renewable TECHNOLO
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Renewable Energy Technologies Solar
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INTERNATIONAL ENERGY AGENCY The Int
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Foreword Foreword Solar energy tech
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Acknowledgements Acknowledgements T
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Table of contents Table of Contents
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Table of contents Chapter 7 Solar h
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Table of contents Chapter 3 Chapter
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Table of contents Chapter 4 Figure
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Table of contents Figure 10.4 • N
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Executive Summary Executive Summary
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Executive Summary A possible vision
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Chapter 1: Rationale for harnessing
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PART A MARKETS AND OUTLOOK Chapter
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Chapter 2: The solar resource and i
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Chapter 3: Solar electricity Chapte
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Chapter 3: Solar electricity Versat
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Chapter 3: Solar electricity Figure
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Chapter 3: Solar electricity Figure
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Chapter 3: Solar electricity to a t
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Chapter 3: Solar electricity New in
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Chapter 3: Solar electricity Variou
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Chapter 3: Solar electricity as fro
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Chapter 3: Solar electricity peak t
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Chapter 3: Solar electricity Kenya
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Chapter 3: Solar electricity • Ad
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Chapter 4: Buildings Chapter 4 Buil
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Chapter 4: Buildings South Africa,
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Chapter 4: Buildings Figure 4.3 Bui
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Chapter 4: Buildings Défense near
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Chapter 4: Buildings larger the col
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Chapter 4: Buildings Pumps variant,
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Chapter 4: Buildings radiators or h
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Chapter 4: Buildings Most widesprea
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Page 111 and 112: PART B TECHNOLOGIES Chapter 6 Solar
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Page 173 and 174: PART C THE WAY FORWARD Chapter 10 P
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Chapter 10: Policies and can hardly
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Chapter 10: Policies fossil-fuel pl
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Chapter 10: Policies It would make
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Chapter 10: Policies In the retail
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Chapter 11: Testing the limits Chap
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Chapter 11: Testing the limits grow
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Chapter 11: Testing the limits betw
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Chapter 11: Testing the limits Phot
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Water availability is unlikely to b
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Chapter 11: Testing the limits tran
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Chapter 12: Conclusions and recomme
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Chapter 12: Conclusions and recomme
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Annex A Annex A Definitions, abbrev
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Annex A REC RPS SACP sc-Si SEI SEII
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Annex B Annex B References A.T. Kea
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Annex B Greenpeace International, S
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Annex B Malbranche, Ph. et C. Phili
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