HELIOSTAT TESTING AT A NEW FACILITY IN SONORA, MEXICO

Transcription

1 HELOSTAT TESTNG AT A NEW FACLTY N SONORA MEXCO Camilo A. Aancibia-Bulnes 12 Manuel. Peña-Cuz 1 David Maoquín-Gacía 1 Rafael E. Cabanillas 2 Calos A. Péez-Rábago 13 David Riveos-Rosas 4 Jesús F. Hinojosa 2 and Claudio A. Estada 1 1 Cento de nvestigación en Enegía Univesidad Nacional Autónoma de Méico. Piv. Xochicalco s/n Col. Cento Temico Moelos Méico. Phone addess: caab@cie.unam.m 2 Depatamento de ngenieía Química Metalugia Univesidad de Sonoa. Blvd. Luis Encinas Rosales S/N Col. Cento Hemosillo Sonoa Méico 3 MDEA Eneg URJC-CAT c/ Tulipán sn Móstoles Spain 4 nstituto de Geofísica Univesidad Nacional Autónoma de Méico. Av. Univesidad 3000 Ciudad de Méico D.F Méico. Abstact A new facilit known as Heliostat Test Field has been developed in Meico. t consists of a sola towe a laboato and 16 heliostats. Thee diffeent optical tests have been implemented fo the evaluation of heliostats at this installation: sun tacking test eflected spot test and deflectomet test. These tests allow the evaluation of tacking and slope eos of the heliostats. n paticula the late povides detailed slope maps of the eflecting mios. Kewods: Heliostat; Cental eceive technolog; Deflectomet; Sola concentation. 1. ntoduction n the famewok of a National Laboato of Sola Concentating and Sola Chemist Sstems thee eseach facilities wee built in Meico: a heliostat test field HTF a high adiative flu sola funace [1] and an epeimental photocataltic wate teatment plant. n paticula it was decided to build the HTF in the state of Sonoa one of the egions with the best insolations in Meico. Developed jointl b Univesidad de Sonoa UNSON and Univesidad Nacional Autónoma de Méico UNAM with patial financing fom Consejo Nacional de Ciencia Tecnología CONACYT the HTF is located 10 Km awa fom the Cit of Hemosillo N W Fig. 1 in the campus of the Agicultue Depatment of UNSON. t is located nea the southen edge of the Sonoan deset. At the pesent stage the pupose of the HTF is to seve as a platfom fo the development and testing of heliostat technolog. t was finished and stated up in Decembe The installation consists of a 32 metes high towe with a flat Lambetian taget 8 m 6.7 m in size fo heliostat evaluation Fig. 2. A oom fo the installation of themal eceives was also built atop the towe to be used in futue stages of the poject. n fact this facilit is the fist stage of a lage poject: a laboato fo eseach in cental eceive technolog which will include the installation of 82 heliostats to each 2 MW themal powe [2]. Cuentl thee ae 16 heliostats of diffeent design installed in the HTF most of them with 6 m 6 m apetue aea and with facets canted to achieve 25 suns concentation atio. The idea is to be able to test diffeent heliostat technologies. Fo this pupose diffeent heliostat tests ae being developed at the HTF. The pupose of this pape is to descibe the new installation and to pesent pelimina esults of the evaluation methods.

2 Fig. 1. Location of the Heliostat Test Field. Fig. 2. Pictue of the HTF showing a few heliostats with the towe and the laboato at its base. 2. mplemented Tests The opeation of the HTF has been initiated with the implementation of thee kinds of tests fo heliostats: sun tacking test eflected spot test and deflectomet. All of them use an 8 bit Allied Pike camea to ecod images and MATLAB libaies fo image pocessing Sun tacking test n the sun tacking test the heliostat is opeated as a sola tacke. The cental facet is emoved fom the heliostat and a camea is installed on its place fied pependicula to the heliostat plane and pointing to the sun. n this wa the camea tacks the sun togethe with the heliostat. The camea is fied to the heliostat cental beam as close as possible to the geabo instead of fiing it to the mio suppoting stuctue in ode to educe vibation with movement. Then images fom the sun ae taken at egula intevals Fig. 3. mages ae pocessed in ode to etact the coodinates of the cente of the sola disc measued in piels

3 ove the CCD senso. B taking into account the angula diamete of the sun and the numbe of piels it coves the position can be tansfomed fom piel coodinates into angles. The wandeing of the sola disc image on the pictue allows evaluating the tacking accuac of the heliostat mechanism b means of the standad deviation of the tacking eo Reflected spot test Fig. 3. Tpical image fom a sun-tacking test. n the eflected spot test the heliostat is used to eflect the sun as to the Lambetian taget Fig. 4. The images poduced on the taget b the concentating heliostat ae ecoded at egula intevals Fig. 5. These pictues ae pocessed to obtain the coodinates of the centoid of the poduced sola image at each time step. n this wa the displacement of the sola image fom the nominal taget position can be evaluated and standad deviations computed. Sceen Heliostat Camea Fig. 4. Epeimental scheme fo the eflected spot test. Fig. 5. Tpical image obtained duing the eflected spot test left and the same pictue afte patial pocessing ight.

4 2.3. Deflectomet test n the deflectomet test also known as finge pojection method [34] finge pattens ae pojected at night on the Lambetian sceen. Then the heliostat is oiented in such a wa as to eflect the image of the taget and the finges towads a camea located atop the towe Fig. 6. Due to the mio slope impefections the eflected finges ae distoted Fig. 7. Theefoe fom this distoted images it is possible to etact the slope eos to evaluate the eflecting facets of the heliostat. Camea Sceen Heliostat Pojecto Fig. 6. Epeimental aangement fo the deflectomet test. Fig. 7. Pictues fom the deflectomet test: finges pojected on the Lambetian sceen left and afte eflection b a heliostat ight. n paticula the fou step phase shifting method is used to etact the infomation. n this method fou sinusoidal pattens with finges of equal fequenc ae pojected on the sceen successivel. Each patten diffes fom the peceding one b a / 2 shift in the phase. Mathematicall this is epessed b fo the case of hoizontal finges n n A B cos[2 f ] whee the n is the intensit of the n-th patten as a function of the coodinates ove the Lambetian taget f is the spatial fequenc of the finges m -1 and the phase shift takes the values / / 2 fo the fou diffeent pattens. The fou pattens as seen b the camea afte eflection b the heliostat can be epessed as

5 2] / 3 cos[ ] cos[ 2] / cos[ ] cos[ b a b a b a b a The phase contains all the infomation of the geomet of the eflecting facets. This phase does not depend lineal with the coodinate as the oiginal pojected pattens did but the functional elationship is abita instead. To etact this function fom the eflected pattens the following fomula can be deduced fom the peceding equations ] tan[ The phase is said to be wapped in this epession; it cannot be etacted simpl b the actangent function because the tangent function is not biunivocal. Atificial phase jumps ae intoduced due to this fact when the actangent function is used. These can be easil mistaken with phase jumps due to noise and othe souces. To etact the phase coectl unwapping algoithms ae needed that would be long to descibe hee [5]. n the pesent case a vaiation of toh s algoithm has been emploed. Once the phase is obtained the local phase diffeence with espect to a efeence plane ideal flat mio is calculated. The local angula defomation of the facets with espect to the flat suface is given b the following equation tan2 f p f p f p Z Z Y Y Z Z f The quantities appeaing in this equation ae as depicted in Fig. 8. This paticula fomula is fo the analsis of the vetical defomation in a heliostat located along the cental ais of the field b means of hoizontal finges but it is easil etended to othe cases. Fig. 8. Quantities involved in the mathematical analsis of deflectomet tests.

6 3. Results n this section some eamples of esults obtained fom the thee implemented tests ae discussed. n Fig. 8 a gaph is pesented fo the sun tacking test. The data epesent the angula deviation of the tacking duing the test. As can be obseved the elevation tacking woked ve well in this paticula un; i.e. the sun s image emained neal static on the same vetical position on the CCD. On the othe hand the azimuth pesented a ve ponounced dift. Fig. 8. Angula dift in the azimuth and elevation aes as a function of time fo a sun tacking test. Fom the above one can note that it is impotant to decouple the tacking eos caused b the accuac of the mechanism fom those due to calibation eos in the tacking algoithm; i.e. andom vibations due to the mechanism need to be sepaated fom the sstematic eo intoduced b tacking calculation an calibation eos. This pat of the pocess ma be a subtle one. n the paticula case pesented the dift in the azimuth diection is quite obvious with almost linea behavio. Supeposed on this we can see seveal spikes due to wind loading which ae moe chaacteistic of the backlash effect of the mechanism. Note that spikes in both tacking diections ae cleal simultaneous but those found in elevation ae of much smalle amplitude. The amplitude of the spikes can be used to evaluate the tacking eo due to the mechanism. Fo the paticula case pesented a staight line is fitted to the azimuth data to epesent the oveall dift. Then the standad deviation of the data with espect to this aveage behavio is calculated to obtain the tacking eo due to the mechanism. t is found that the standad deviation in the azimuth diection amounts to mad. t Anothe featue that can be obseved in Fig. 8 is the pesence of high fequenc oscillations. Howeve the ae not a eflection of the behavio of the mechanism. The ae an atifact due to the piel size of the camea which limits the accuac of the measuement. n Fig. 9 esults fom a eflected spot test ae pesented. As well as in the pevious test dift spikes and high fequenc oscillations can be obseved. Simila infomation to the pevious test could be etacted but with the sstem acting as a heliostat instead of being used atificiall as a sola tacke. Again to analze this infomation it would be necessa to sepaate the dift fom the oscillato behavio. t is inteesting to note again the highe accuac of the elevation as compaed to the azimuth mechanism. This occus because the fist is a linea actuato while the second is a wom gea and shaft mechanism.

7 The eflected spot test is potentiall ve inteesting as infomation of the shape of the sola image could be used fo caing out compaisons with a tacing which would help to futhe evaluate optical eos. This kind of compaisons will be implemented in the nea futue. Fig. 9. Reflected spot dift in the and aes as a function of time fo a sun-tacking test. Finall in Fig. 10 an eample of the esults fom the deflectomet test is shown. As can be obseved the test allowed detemining the local deviation of the facet suface fom the ideal plana geomet. A diagonal bending line can be obseved at the cente of the mio as well as stess points at the left side. Fom this data the standad deviation of the contou eo was detemined as σ c = 1.90 mad fo this paticula facet. Tpical values found fo othe facets wee close to 1 mad. Fig. 10. mage of finges eflected b a mio facet left and map of local angula deviations of the facet with espect to an ideal plane ight. 4. Conclusions A new towe facilit fo the development and testing of heliostat technolog has been established in Meico.

8 This is the fist installation of its kind in the count and in Latin Ameica. Diffeent kinds of heliostat tests which complement each othe have been implemented o ae being developed. This allows obtaining a vaiet of useful infomation of the heliostats unde evaluation. Pesentl tests to evaluate the tacking and slope eos of the heliostats ae implemented. The latte based on deflectomet techniques povides detailed slope maps ove the whole suface of the mios. The fist esults of the tests allow us to evaluate the cuent heliostats in the field. We obseve a bette accuac in the elevation tacking with espect to the azimuth tacking. Also we obseve both stochastic and dift eos in the tacking the stochastic eo occus with a standad deviation of mad. With egads to the deflectomet test the implemented technique allows to get a map of the local deviation of the facet suface fom the ideal plana geomet. The facets evaluated have a standad deviation between 1 and 2 mad. Acknowledgements This wok has been funded jointl b CONACYT Gants and Univesidad de Sonoa UNSON and Univesidad Nacional Autónoma de Méico UNAM. D. Maoquín-Gacía and M.. Peña Cuz acknowledge CONACYT fo gaduate scholaships. C. A. Aancibia-Bulnes acknowledges UNSON fo financial suppot duing a sabbatical leave. R. Peón Anaa and P. Sosa Floes fom UNSON ae gatefull acknowledged fo thei technical suppot in heliostat installation and in the implementation of the diffeent tests. J.J. Quiñones Aguila fom UNAM is also acknowledged fo technical suppot in equipment selection. Refeences [1] D. Riveos-Rosas J. Heea-Vázquez C. A. Péez-Rábago C. A. Aancibia-Bulnes S. Vázquez- Montiel M. Sánchez-González F. Ganados-Agustín O. A. Jaamillo C. A. Estada Sola Eneg [2] David Riveos Calos A. Peez-Rábago Camilo A. Aancibia-Bulnes Manuel Romeo Efaín Regalado Rafael Cabanillas Claudio A. Estada. Sizing and pefomance analsis of a 2 MWth epeimental sola heliostat field in Sonoa. Poceedings of the 2009 Sola PACES smposium Belin Geman. [3] C. E. Andaka S. Sadlon B. Me K. Tapeznikov C. Liebne SOFAST: Sandia optical finge analsis slope tool fo mio chaacteization. Poceedings of the 2009 Sola PACES smposium Belin Geman. Aticle [4] S. Ulme T. Mäz C. Pahl W. Reinalte B. Belhomme Sola Eneg [5] D. C. Ghiglia M. D. Pitt Two-Dimensional Phase Unwapping: Theo Algoithms and Softwae. Wile New Yok.