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mirror structure generally consists of a steel structural support, an adhesive layer, a protective copper layer, a layer of reflective silver, and a top protective layer of thick glass. This conventional heliostat is often referred to as a glass/metal heliostat. Alternative designs incorporate recent adhesive, composite, and thin film research to bring about materials costs and weight reduction. Some examples of alternative reflector designs are silvered polymer reflectors, glass fiber reinforced polyester sandwiches (GFRPS), and aluminized reflectors. Problems with these more recent designs include delamination of the protective coatings, reduction in percent solar reflectivity over long periods of sun exposure, and high manufacturing costs.
514:
The directions of the axes need be only approximately known, since the system is intrinsically self-correcting. However, there are disadvantages, such as that the mirror has to be manually realigned every morning and after any prolonged cloudy spell, since the reflected beam, when it reappears, misses the sensors, so the system cannot correct the orientation of the mirror. There are also geometrical problems which limit the functioning of the heliostat when the directions of the Sun and the target, as seen from the mirror, are very different. Because of the disadvantages, this design has never been commonly used, but some people do experiment with it.
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85:
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281:, in France. All the heliostat mirrors send accurately parallel beams of light into a large paraboloidal reflector which brings them to a precise focus. The mirrors have to be located close enough to the axis of the paraboloid to reflect sunlight into it along lines parallel to the axis, so the field of heliostats has to be narrow. A
506:
two axes, so it points toward the sun, incorporating a solar tracker. A simple mechanical arrangement bisects the angle between the primary axis, pointing to the target, and the arm, pointing to the Sun. The mirror is mounted so its reflective surface is perpendicular to this bisector. This type of heliostat was used for
513:
There are heliostat designs which do not require the rotation axes to have any exact orientation. For example, there may be light-sensors close to the target which send signals to motors so that they correct the alignment of the mirror whenever the beam of reflected light drifts away from the target.
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arrangement in which the primary axis points toward the target at which sunlight is to be reflected. The secondary axis is perpendicular to the primary one. Heliostats controlled by light-sensors have used this orientation. A small arm carries sensors that control motors that turn the arm around the
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and heating. Instead of many large heliostats focusing on a single target to concentrate solar power (as in a solar power tower plant), a single heliostat usually about 1 or 2 square meters in size reflects non-concentrated sunlight through a window or skylight. A small heliostat, installed outside
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an
Egyptian boy holds a mirror to illuminate a wall inside a cave for a fictional archaeologist.) Elaborate clockwork heliostats were made during the 19th Century which could reflect sunlight to a target in any direction using only a single mirror, minimizing light losses, and which automatically
342:
One way that engineers and researchers are attempting to lower the costs of heliostats is by replacing the conventional heliostat design with one that uses fewer, lighter materials. A conventional design for the heliostat's reflective components utilizes a second surface mirror. The sandwich-like
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Heliostat costs represent 30-50% of the initial capital investment for solar power tower power plants depending on the energy policy and economic framework in the location country. It is of interest to design less expensive heliostats for large-scale manufacturing, so that solar power tower power
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Many other types of heliostat have also occasionally been used. In the very earliest heliostats, for example, which were used for daylighting in ancient Egypt, servants or slaves kept the mirrors aligned manually, without using any kind of mechanism. (There are places in Egypt where this is done
307:
In a 2009 article, Bruce Rohr suggested that small heliostats could be used like a solar power tower system. Instead of occupying hundreds of acres, the system would fit in a much smaller area, like the flat rooftop of a commercial building, he said. The proposed system would use the power in
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between the directions of the Sun and the target as seen from the mirror. In almost every case, the target is stationary relative to the heliostat, so the light is reflected in a fixed direction. According to contemporary sources the heliostata, as it was called at first, was invented by
312:. Rohr proposed that the system would be "more reliable and more cost-effective per square meter of reflective area" than large solar power tower plants, in part because it would not be sacrificing 80 percent of the power collected in the process of converting it to electricity.
478:. The target can be located on the same polar axis that is the mirror's primary rotation axis, or a second, stationary mirror can be used to reflect light from the polar axis toward the target, wherever that might be. This kind of mirror mount and drive is often used with
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plant in Spain, a wide field of heliostats focuses the Sun's power onto a single collector to heat a medium such as water or molten salt. The medium travels through a heat exchanger to heat water, produce steam, and then generate electricity through a steam turbine.
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theory, it calculates the direction of the Sun as seen from the mirror, e.g. its compass bearing and angle of elevation. Then, given the direction of the target, the computer calculates the direction of the required angle-bisector, and sends control signals to
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primary axis, driven by a mechanical, often clockwork, mechanism at 15 degrees per hour, compensating for the Earth's rotation relative to the Sun. The mirror is aligned to reflect sunlight along the same polar axis in the direction of one of the
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The movement of most modern heliostats employs a two-axis motorized system, controlled by computer as outlined at the start of this article. Almost always, the primary rotation axis is vertical and the secondary horizontal, so the mirror is on an
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on the ground or on a building structure like a roof, moves on two axes (up/down and left/right) in order to compensate for the constant movement of the Sun. In this way, the reflected sunlight stays fixed on the target (e.g. window).
66:
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Typically, the heliostat mirror moves at a rate that is 1/2 the angular motion of the Sun. There is another arrangement that satisfies the definition of a heliostat yet has a mirror motion that is 2/3rd of the motion of the Sun.
653:
969:
Hartmann, W.; Schorr, R. R. E. (1928). "Beitrag zur
Geschichte und Theorie der astronomischen Instrumente mit rotierendem Planspiegel und fester Reflexrichtung : (Heliostat, Siderostat, Zölostat, Uranostat)".
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or sun-trackers that point directly at the sun in the sky. However, some older types of heliostat incorporate solar trackers, together with additional components to bisect the sun-mirror-target angle.
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compensated for the Sun's seasonal movements. Some of these devices are still to be seen in museums, but they are not used for practical purposes today. Amateurs sometimes come up with
725:
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Graf, D.; Monnerie, N.; Roeb, M.; Schmitz, M.; Sattler, C. (2008). "Economic comparison of solar hydrogen generation by means of thermochemical cycles and electrolysis".
470:. There is a perpendicular secondary axis allowing occasional manual adjustment of the mirror (daily or less often as necessary) to compensate for the shift in the Sun's
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designs which work approximately, in some particular location, without any theoretical justification. An essentially limitless number of such designs are possible.
304:
Genzyme Center, corporate headquarters of
Genzyme Corp. in Cambridge, Massachusetts, uses heliostats on the roof to direct sunlight into its12-story atrium.
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sunlight to heat and cool a building or to provide input for thermal industrial processes like processing food. The cooling would be performed with an
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The target may be a physical object, distant from the heliostat, or a direction in space. To do this, the reflective surface of the mirror is kept
818:
Ortega, J. I.; Burgaleta, J. I.; Téllez, F. L. M. (2008). "Central
Receiver System Solar Power Plant Using Molten Salt as Heat Transfer Fluid".
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alignments are two of the three orientations for two-axis mounts that are, or have been, commonly used for heliostat mirrors. The third is the
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221:, so they turn the mirror to the correct alignment. This sequence of operations is repeated frequently to keep the mirror properly oriented.
707:
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and other electric lights, heliostats were widely used to produce intense, stationary beams of light for scientific and other purposes.
138:, which turns so as to keep reflecting sunlight toward a predetermined target, compensating for the Sun's apparent motions in the sky.
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285:
control system is used. Sensors determine if any of the heliostats is slightly misaligned. If so, they send signals to correct it.
991:
Mills, A. A. (1985). "Heliostats, Siderostats, and
Coelostats: A Review of Practical Instruments for Astronomical Applications".
756:
231:
There are older types of heliostat which do not use computers, including ones that are partly or wholly operated by hand or by
70:
378:
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It has been proposed that the high temperatures generated could be used to split water producing hydrogen sustainably.
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A somewhat different arrangement of heliostats in a field is used at experimental solar furnaces, such as the one at
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with the seasons. The setting of the drive clock can also be occasionally adjusted to compensate for changes in the
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prior to the availability of cheap computers, but after the initial availability of sensor control hardware.
940:
Cornu, M. A. (1900). "On the law of diurnal rotation of the optical field of the siderostat and heliostat".
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586:, a town in Norway that uses a heliostat to illuminate a portion of the town square during winter months
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80:. Every mirror in the field of heliostats reflects sunlight continuously onto the receiver on the tower.
42:
332:) and environmental durability are factors that should be considered when comparing heliostat designs.
228:
comprising many mirrors. Usually, all the mirrors in such a field are controlled by a single computer.
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335:
92:
near
Seville in Spain. When this picture was taken, dust in the air made the converging light visible.
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Kennedy, C. E.; Terwilliger, K. (2005). "Optical
Durability of Candidate Solar Reflectors".
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This article is about solar tracking devices. For optical communication equipment, see
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Mar, R.; Swearengen, J. (1981). "Materials issues in solar thermal energy systems".
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of the heliostat's position on the Earth and the time and date. From these, using
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plants may produce electricity at costs more competitive to conventional coal or
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96:
37:
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654:"Heliostat, contrived by the late G. Johnstone Stoney, D.Sc., F.R.S., c. 1875"
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Most modern heliostats are controlled by computers. The computer is given the
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189:. A few are used experimentally to reflect motionless beams of sunlight into
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1049:"On mechanically compensating the rotation of the field of a siderostat"
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in France can reach temperatures up to 3,500 °C (6,330 °F)
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185:, usually to generate electricity. They are also sometimes used in
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194:
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134:, as in stationary) is a device that includes a mirror, usually a
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Large installations such as solar-thermal power stations include
723:
Interview with Lou
Capozzi, Facilities Manager of Genzyme Center
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254:
89:
350:
641:
Daniel
Gabriel Fahrenheit's Letters to Leibniz and Boerhaave
461:
One simple alternative is for the mirror to rotate around a
253:
is a similar device which is designed to follow a fainter
490:, so as to concentrate sunlight onto the cooking vessel.
57:
experimental station in France. The mirror rotates on an
575:, a similar non-tracking device, used for communication
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Sunalign free heliostat software and related material
900:
David
Delaney, rev 22-Feb-2009, retrieved 5-June-2011
522:
today, for the benefit of tourists. In the 1997 film
628:
A New and Complete Dictionary of Arts and Sciences,
381:. Unsourced material may be challenged and removed.
1018:Monthly Notices of the Royal Astronomical Society
328:Besides cost, percent solar reflectivity (i.e.
705:U.S. Green Building Council: LEED Case Studies
265:In a solar-thermal power plant, like those of
8:
778:
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41:Heliostat by the Viennese instrument maker
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737:
486:. For this application, the mirror can be
1110:Overview of heliostat reflector materials
1072:
1037:
441:Learn how and when to remove this message
680:International Journal of Hydrogen Energy
242:Heliostats should be distinguished from
177:Currently, most heliostats are used for
1014:"Notes on the Coelostat and Siderostat"
620:
891:Notes on Scheffler Community Kitchens
166:(1686–1736). A heliostat designed by
7:
379:adding citations to reliable sources
847:Journal of Solar Energy Engineering
820:Journal of Solar Energy Engineering
158:(1688–1742). Other contenders are
25:
746:"The Promise of Small Heliostats"
557:
543:
355:
296:Smaller heliostats are used for
366:needs additional citations for
972:Astron. Verh. Hamburger Sternw
692:10.1016/j.ijhydene.2008.05.086
1:
235:, or are controlled by light-
193:. Before the availability of
924:"Red Rock Energy Heliostats"
805:10.1016/0165-1633(81)90057-5
630:vol 2, London, 1763, p. 1600
239:. These are now quite rare.
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29:
181:or for the production of
164:Daniel Gabriel Fahrenheit
1053:Mon. Not. R. Astron. Soc
913:, downloaded 5-June-2011
744:Rohr, B. (Spring 2009).
728:January 8, 2010, at the
183:concentrated solar power
160:Giovanni Alfonso Borelli
1012:Plummer, H. C. (1905).
881:, retrieved 5-June-2011
872:The Scheffler-Reflector
551:Renewable energy portal
257:, rather than the Sun.
168:George Johnstone Storey
1089:Field of 63 heliostats
1074:10.1093/mnras/61.3.122
1047:Turner, H. H. (1901).
1039:10.1093/mnras/65.5.487
785:Solar Energy Materials
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643:, Leiden, 1983, p. 7.
639:Pieter van der Star,
347:Tracking alternatives
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126:, the Greek word for
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27:Solar tracking device
993:J. Br. Astron. Assoc
826:(2): 024501–024506.
658:Science Museum Group
605:Solar thermal energy
484:Scheffler reflectors
375:improve this article
292:Small-scale projects
261:Large-scale projects
226:fields of heliostats
172:Science Museum Group
156:Willem 's Gravesande
1065:1901MNRAS..61..122T
1030:1905nocs.book.....P
1005:1985JBAA...95...89M
984:1928AAHam...4....1H
954:1900ApJ....11..148C
797:1981SoEnM...5...37M
110:Pyrenees-Orientales
78:Daggett, California
76:power project near
53:A heliostat at the
896:2011-08-14 at the
877:2008-04-22 at the
710:2009-12-01 at the
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310:absorption chiller
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1059:(23): 122.
508:daylighting
503:target-axis
495:alt-azimuth
472:declination
390:"Heliostat"
298:daylighting
283:closed loop
179:daylighting
766:2010-01-25
616:References
590:Solar cell
573:Heliograph
499:polar-axis
482:, such as
401:newspapers
251:siderostat
170:is in the
32:Heliograph
18:Siderostat
999:(3): 89.
791:: 37–41.
233:clockwork
206:longitude
118:heliostat
88:The 11MW
71:Solar Two
45:(c. 1850)
1124:Category
978:: 1–36.
894:Archived
875:Archived
726:Archived
708:Archived
537:See also
217:, often
202:latitude
147:bisector
1105:Odeillo
1093:Odeillo
1091:at the
1061:Bibcode
1026:Bibcode
1001:Bibcode
980:Bibcode
950:Bibcode
948:: 148.
793:Bibcode
663:20 June
488:concave
415:scholar
279:Odeillo
269:or the
237:sensors
149:of the
145:to the
108:in the
106:Odeillo
584:Rjukan
531:ad hoc
417:
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396:
388:
330:albedo
316:Design
215:motors
195:lasers
130:, and
123:helios
120:(from
55:THÉMIS
43:Ekling
760:(PDF)
749:(PDF)
422:JSTOR
408:books
151:angle
665:2022
497:and
493:The
394:news
271:PS10
255:star
204:and
132:stat
100:The
90:PS10
69:The
1103:at
1069:doi
1034:doi
958:doi
855:doi
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