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3rd International Conf. on Solar Concentrators for the Generation of Electricity or Hydrogen, Scottsdale, Arizona, 2005   ...
3rd International Conf. on Solar Concentrators for the Generation of Electricity or Hydrogen, Scottsdale, Arizona, 2005   ...
3rd International Conf. on Solar Concentrators for the Generation of Electricity or Hydrogen, Scottsdale, Arizona, 2005 ⎧ ...
3rd International Conf. on Solar Concentrators for the Generation of Electricity or Hydrogen, Scottsdale, Arizona, 20053. ...
3rd International Conf. on Solar Concentrators for the Generation of Electricity or Hydrogen, Scottsdale, Arizona, 2005ran...
3rd International Conf. on Solar Concentrators for the Generation of Electricity or Hydrogen, Scottsdale, Arizona, 2005   ...
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Cpv sun tracking at inspira


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Cpv sun tracking at inspira

  1. 1. 3rd International Conf. on Solar Concentrators for the Generation of Electricity or Hydrogen, Scottsdale, Arizona, 2005 CPV Sun Tracking at Inspira I. Luque-Heredia, J.M. Moreno, G. Quéméré, R.Cervantes, P.H. Magalhães Inspira, SL C/Chile, 10, 28290, Las Matas, Madrid, Spain, ABSTRACT skies, software failures, extreme weather conditions, or low cost & qualification installation crews. Past PV This paper presents a general overview of the projects concentration projects have shown that it is really no smallcarried out by Inspira in the field of sun tracking control feat to successfully complete this threefold development,for photovoltaic concentration, which begin with the moreover when all of these required solutions are to bedevelopment of the EPS-Tenerife® sun tracking control attained bound by strong cost constraints, and with littleunit for BP Solar’s EUCLIDES concentrator. This relied option, at least in the first stages, to learning curveon the implementation of a novel hybrid sun tracking discounts…and usually not even to The Secondstrategy devised at the Instituto de Energía Solar in the Opportunity!so called model free approach, further customized for Being this the situation, serious R&D commitment toone axis trackers such as EUCLIDES’. Later on it was to concentration tracking systems, is still required in order tobe the purpose of the Ificles project, jointly developed breed a safe mount not only for the promising very highwith the Universidad de Sevilla, to upgrade the concentration concepts now under progress in differentEUCLIDES strategy to two axis trackers, which resulted countries, but also to ease the introduction andin the adjustment of the classical PI controller to discrete implementation of those very high efficiency 3rd. generationsun tracking procedures, thus suggesting a further leapfrogging PV developments to come, which in manygeneralization of model free approaches making use of cases could profit from sunlight concentration means whenthe time series forecasting mathematical toolbox. seeking, at least in its first stages, for cost effectiveness. InSunDog constitutes Inspira’s latest sun tracking control fact it is clearly stated that the development of “…reliable,unit, powered now by a general error model for whatever low cost tracking systems …” along with that of compactone or two axis trackers, on which it can autocalibrate concentration optics are the two main areas which are now,itself. according to the European Commission PV research advisory committee PV TRAC, specially in need of1. Introduction research efforts in order for CPV technologies to significantly contribute to the fulfilment of the European Since in the late seventies, concentration systems first PV market and industry targets in the coming decades [3].captivated the interest of the solar community, whenthese went on stage as a clear track towards strong PV 2. EPS-Tenerife® Sun Tracking Control Unit forcost reduction, a reasonable amount of field experience EUCLIDESTMhas been acquired which clearly keeps on pointing outits underlying sun tracking systems as one of its most EPS-Tenerife® was the commercial name given to the Sunerror prone components [1][2], and probably one of the Tracking Control Unit designed and produced by Inspira forsignificant overloads which is delaying this the EUCLIDESTM CPV technology jointly developed by thetechnology’s definitive industrial take off. Instituto de Energía Solar (IES) of the Universidad But the low performance of tracking systems up to Politécnica de Madrid and BP is not at all unjustified; in the one hand, the trackerusually demanded by CPV technologies, requires astructure able to maintain an overall stiffness within thesubdegree range, not to induce acceptance angle losseson the supported concentrating system, and thisconsidering, apart from the payload, maximum servicewind loads in the 10 to 20 m/s range. In the other handthe tracking drive, by means of jointly conferring highpositioning resolution and low backlash, is to achieve ahighly precise aiming of its heavy load - which undersome design options further imposes the extra burden ofvery high torques - and this even more with the recentrising trends in the concentration factors which onaccount of etendue conservation furthermore decreaseacceptance angle. And also of the utmost importance, is Figure 1. Afternoon view of the southern flank of thethe development of a fully reliable sun tracking control EUCLIDESTM plant showing the EPS-Tenerife® units atsystem, immune to factors such as overcast and hazy this end of each of the 14 troughs. I.Luque-Heredia, J.M.Moreno, G.Quéméré, R.Cervantes, P.H.Magalhães
  2. 2. 3rd International Conf. on Solar Concentrators for the Generation of Electricity or Hydrogen, Scottsdale, Arizona, 2005 EUCLIDES has been one of the biggest attempts done implementation is a must for error model based calibration.up to date towards the industrialisation of a PV Model-free error correcting routines make no initialconcentration technology. The resultant concentrator was assumptions on the tracking errors that will be encountered,formed by an 84m long and 3,8m wide parabolic trough being of a general purpose conception able to cope with anycollector with one axis tracking, oriented North/South sort of tracking error sources at whichever tracker design.and parallel to ground, casting sunlight on its 138 series However routines offering this versatility require permanentconnected PV receiving modules with a geometrical error surveillance of greater or lesser degree, at timesconcentration of 40X. 14 units of this concentrator where implying scanning movements which to some extent willdeployed in the facilities of ITER (Instituto Tecnologico increase motor consumption and fatigue and might bringy de Energias Renovables) at Tenerife (Canary Islands, down average tracking accuracy.Spain) which with its 480kWp still remains the world’s The IES strategy pertains to the model-free class,biggest PV concentration plant ever built. basically being a set of routines for the maintenance and This was Inspira’s first contact with precision sun updating of a look-up table which stores an array oftracking control and more generally with the CPV field, corrections to the coordinates supplied by the open loopwhere working under contract with BP Solar, it was our stage. Whenever this strategy was devised thinking on thecommitment to implement in an embedded system a EUCLIDES one axis tracker the table of corrections is a setnovel sun tracking strategy devised by the IES [4]. This of values, one for every one degree subinterval in which thestrategy was developed following the so called hybrid tracking range in this axis is divided, which represents anapproach, which built around a calculated sun ephemeris estimate of the error found when sun pointing the trackercore, adds different types of error correcting routines to within each of this sectors. The EUCLIDES concentratorcompensate on the one hand for drifts in the ephemeris default tracking range is ±70º, therefore the table consistedtime base, and on the other for self-characterization ⎧( −69 ) ( −68) ( 0 ) ( 69 ) ( 70 )⎫errors due to a faulty installation, assembly, or of 140 values [ε i ] = ⎨ ε i , ε i ,..., ε i ,..., ε i , ε i ⎬ , wheremanufacturing, or in the time evolving side those caused ⎩ ⎭by stress or resonance bending, or landslides, which (k )ultimately blur the “picture” the tracking control has of every error estimate ε i , refers to the tracking angularits tracker. subinterval ranging from k − 1 degrees to k degrees, and Hybrid sun tracking strategies intend to combine the the sub index is due to the dynamic character of the tablebest of both open-loop ephemeris computing, and which is iteratively updated. In every single positioningclosed-loop sun pointing sensor based controllers, while made by the tracker a tracking error measurement attempt isavoiding their respective problems. By using an open- made, taking as the best sun aiming position that one givingloop sun primary acquisition phase, hybrid controllers maximum short-circuit current. This error observation iswake and stow at specified positions and times and their (k )effectiveness is immune to sunshine conditions or drifts taken as valid, and denoted as ~ i , whenever the in plane εin sensor calibration, thus avoiding the problems in irradiance – supplied by an external PV cell fixed toacquiring and locking onto the sun that occur with aperture plane of the collector – is over a certain threshold.closed-loop systems. By using a closed-loop error (k ) ~ i , is then fed into an IIR low band pass filter producing εcorrection phase, hybrid controllers avoid the open-loop (k )controller problems of needing accurate alignment, an updated error estimate εi +1 for the tracking subintervalassembly, and time information. These error correctionroutines usually take as feedback signal the array’s in which it has been made:power output, or some approximately equivalent (k ) (k ) (k ) (k ) (k )variable, thus relying on the most obvious equivalence εi +1 = µi εi + (1 − µi ) ~ i ε (1)between precise sun pointing and maximum generation. (k ) The main difference between the error correcting Where µi ∈ [0,1] is known as the certainty of a certainroutines integrated into hybrid strategies to date, remainson whether they are based or not on a tracking error tracking subinterval and operates as the time constant of themodel. Model-based error correction routines resort to a filter, determining the relative weight of the last errorphysical model, which accounts for the set of the measurement and the past error estimate in its updated (k )systematic errors which may affect a sun ephemeris value. µi , is formally identical to the error estimate, i.e.based tracking routine in a certain tracker design.Characterized by a set of parameters, this model will be there is one value for each tracking subinterval which is alsofitted with an array of tracking error measurements or updated after each ⎧( −69 ) ( −68 ) ( 0) ( 69 ) ( 70 )⎫ positioning [µi ] = ⎨ µi , µi ,..., µi ,..., µi , µi ⎬ . Its dynamicobservations acquired at onset, after which and if timevarying error sources can be disregarded, it should not be ⎩ ⎭necessary to undertake further calibration. However behaviour reflects the confidence – the certainty – there iserror sources overlooked by the model, even if of a static on its associated error estimate. This time two are the IIRnature, will degrade the model’s best fit, and filters used which determine its evolution:consequently its correcting power. Therefore a goodmodel adequately tailored to the tracker of its I.Luque-Heredia, J.M.Moreno, G.Quéméré, R.Cervantes, P.H.Magalhães
  3. 3. 3rd International Conf. on Solar Concentrators for the Generation of Electricity or Hydrogen, Scottsdale, Arizona, 2005 ⎧ the present error estimate and not expecting to find severe ⎪ (k ) (k ) (k ) ~ departures from it in the coming error measurement. Finally ⎪ µi +1 = K H µi + (1 − K H ) µH if ε i exists the computed scanning movements drop below the ⎨ (2) ⎪ (k ) (k ) (k ) threshold of the shortest admitted tracking displacement, ⎪ µ = K µ + (1 − K ) µ if ~ i does not exist ε necessarily imposed in order to prevent the tracker’s ⎩ i +1 L i L L hunting, due to backlash, motor inertia, or other dead zone When in the present positioning movement non-linearities, and reduce power consumption.irradiance was high enough and an error measurement The usual way in which all this so called by their authorshas been successfully made, the certainty is updated “self-learning” strategy operates, clearly manifests in theusing the first filter expression which is always fed by a first sunny day after the set up on which, considering theconstant µH ∈ [0,1] , and which if repeatedly computed default tuning of the strategy’s parameters, the controlconverges to this value – the highest allowed value of makes several back and forth explorations per trackingcertainty on error estimates – and more rapidly the subinterval whenever the computed sun ephemeris enter intosmallest the learning constant K H . But if in the present it, scanning movements which progressively damp out withmovement no valid error measurement is made due to the increase in the error estimate certainty. In this way afterfor example overcast skies, the second expression is used a full day of sun the controller ends up by completing itsto update certainty which makes this tend to the lowest look-up table of tracking error estimates and with a rathercertainty allowed µ L , where µL ∈ [0,1]; µH > µL . high confidence (Fig. 2) on them, which will be used from then on and only be revised, this meaning the reactivation of Certainty Error estimates (deg.) scanning movements, whenever the certainty on the error 0,6 0,08 estimates of a certain tracking subinterval or set of 0,5 0,06 subintervals goes down due to repeated tracking movements within them without producing error measurements due to 0,4 0,04 low irradiance. This means it is the entrance of bad weather periods working as “purging periods” those which enable 0,3 0,02 the discovery of variations in the compiled errors. The present strategy was implemented in an 16 bit 0,2 0,00 microcontroller, integrated with its required sensing resources regarding tracking axis position, and measurement 0,1 -0,02 of array’s current output and in plane irradiance, provided also with motor switching and speed control capabilities, 0,0 -0,04 -90 -70 -50 -30 -10 10 30 50 70 90 and with an atomic time source, by means of a GPS Tracking angle - origin @ zenith (deg) receiver, which is to periodically adjust the drifts in theFigure 2. Correction and certainty table of the most controller’s internal RTC for the precise computation of theeastern EUCLIDES concentrator in the Tenerife plant on sun ephemeris. In its front panel an LCD display &13/01/99 after its learning session. Note how certainty is keyboard along with a serial connection, enable in-field edition of operation parameters, downloading of thealready very close to µH = 0.6 in most of the tracking internally compiled historic logs to a laptop PC, uploadingrange, excepting the least mature dawn sector where of SW updates, manual positioning, and reporting ofmaybe due to morning clouds certainty is still in its mid system failures along with guiding self diagnosis. Alsorange and error estimates are not yet well determined supporting RS-485 networking it can be remotely controlledcausing discontinuity in the error estimate function. from a local computer or even using the Internet and through a local web server. Everything was integrated in a Besides this updating mechanism of the look-up table, rugged enclosure, and tested in certified labs on temperaturethere is a scanning procedure devised to acquire tracking cycles and humid and saline ambient, CE marked anderror measurements. In it, every tracking movement is verified IP-65. Also having in mind its SW reliabilityalways done in such a way that it overtakes the several redundancy cells were distributed in the most criticalsupposedly correct pointing orientation, calculated by sections of its almost 10.000 lines code.adding to the computed sun position supplied by the sun Since their installation in 1998 in the EUCLIDES plantephemeris, the associated error estimate. The amplitude the 14 EPS-Tenerife units have performed almost flawlesslygiven to this advancement is directly related to the withstanding high temperatures, direct insolation, and thecertainty we have on the error estimate at the involved corrosive and dusty seaside and windy environment, andsubinterval, the higher the certainty the smaller this quite a faulty power supply with plenty of microcuts,overtaking and the closer we end to the correct pointing. summing up by now more than 800.000 operating hours,This means that when error measurements accumulate and being an example of how the tracking system is notwithout interruption for a certain subinterval, the necessarily the weakest point of the concentrator system ascertainty we have on the computed error estimate usually assumed [5].steadily increases while the tracking explorations aroundthe assumed correct aiming progressively diminish,because on every new iteration we are a bit more sure of I.Luque-Heredia, J.M.Moreno, G.Quéméré, R.Cervantes, P.H.Magalhães
  4. 4. 3rd International Conf. on Solar Concentrators for the Generation of Electricity or Hydrogen, Scottsdale, Arizona, 20053. Hybrid Sun Tracking through Time Series Aside from the routines for the automatic acquisition ofForecasting : The PI algorithm tracking errors in two axes the PI strategy was essentially another hybrid, model-free strategy, which resulted from the The PI strategy results from the cooperation between adjustment of the classical PI (Proportional Integral)Inspira and the Department of Systems Engineering and controller to sun tracking, considered as a discrete timeAutomatics of the Universidad de Sevilla [6], and seeks process in which sun ephemeris computation remains theto further develop the IES hybrid approach into a more core routine – the feedforward path of the control loop – butgeneral strategy able to cope also with two axis trackers. tracking error measurements are permanently sought The main blank to fill here had to do with the scanning through the referred maximization, and also when necessaryroutine used by the IES strategy for the acquisition of preliminary scanning, and fed back to a controller whichtracking error measurements, whose back and forth tries to forecast the present error and adjust the ephemerismovement is only valid for the exploration of a one axis output (Fig. 3). This controller can be taken in a generaltracking range. Its straightforward extension to the sense as a time series forecasting method which generatesbidimensional tracking range of a two axis system is the error estimates out of past estimates and observations.rectangular spiral, i.e. essentially the interleaving of the In the particular case of the PI controller the estimate ofback and forth movements in the two axes, in which the error is produced as a weighted sum of the last errorevery successive movements in the same axis exceeds measurement (the proportional part) and the integration ofthe previous in such a way that the least angular distance the discrete time series of tracking error measurements sincefrom any point in the spiral described to its adjacent their commencement (the integral part):paths, is always smaller than twice the acceptance angle ⎧ ⎛ 1 ⎞of the scanning sensor employed, this being that of the ⎪εi = K P ⎜ ~i + ⎜ ε K Si ⎟ ⇒ ⎟concentrator itself when working on the feedback of ⎨ ⎝ I ⎠some variable of its power output. In this way there is no ⎪S = S + T ~ εi ⎩ i i −1 mi (3)chance to miss the sun in the scanning. Polar spirals ⎛ T ⎞outperform rectangular spirals regarding mean scanning εi +1 = εi + K P ⎜1 + mi +1 ⎟~i +1 − K P ~i ⎜ ε εtime to a target, but require joint control of both axis and ⎝ KI ⎟ ⎠the tuning of their speeds therefore adding complexity Where K P and K I are the respective weights of theand imposing some preliminary calibration. proportional and the integral parts in the error estimate, and Once the scanning maneuvers place the sun within theacceptance angle distance, the maximization of some Si computes the integral of the discrete series of trackingpower output variable follows and requires the error measurements, with Tmi being the time interval inintroduction of some two dimensional algorithm for this between measurements. As seen in (3) this PI expressionpurpose. In the simplest case if the profile of this can be developed into the recognizable form of an ARMAfeedback variable as a function of the two axes angular process, a well known member of the time series forecastingcoordinates is rotationally symmetric, then the maximum toolbox, while the error estimator in the IES strategy (1)-(2)can be sought first in one axis and then in the other thus can be presented as an adaptive version of the exponentialarriving to the global maximum, if not some set of smoothing filter, an efficient and simple forecaster on timeconjugate directions will have to be generated by means series with no clear trends or seasonality. Other moreof e.g. Powell’s algorithms and linear maximization complex nonlinear models, such as neural networks, couldsuccessively performed along them, this again adding the play the estimator role, and in order to profit from dailycomplexity of speed control & calibartion. correlations error estimate averages can be stored in time or space segmented look-up tables ( ε i,t j or ε i ,θ j respectively) so they can be used whenever observations can be made such as occurs in the IES strategy. 4. SunDogTM: A Universal Sun Tracking Control Unit As said the model free approaches justify themselves in the argument that if using instead a tracking error model to correct, after fitting its parameters at onset, the sun ephemeris output, and this model happens to neglect whichever error sources, these might cause a defective parameter fit and therefore even possibly a worsening of the sun ephemeris output. However reluctance on error models and opting for model free strategies imposes permanent surveillance of the tracking error evolution, with theFigure 3. Block diagram of an hybrid, model free sun associated mechanical and motor stress surplus, excess oftracking strategy. motor self consumption, and presumably a decrease in the mean overall tracking accuracy. Moreover the major causes for the time variation of tracking errors do not have a I.Luque-Heredia, J.M.Moreno, G.Quéméré, R.Cervantes, P.H.Magalhães
  5. 5. 3rd International Conf. on Solar Concentrators for the Generation of Electricity or Hydrogen, Scottsdale, Arizona, 2005random or physically complex origin, such as let’s say When working on trackers that, seeking a low windstructural deformation due to aging or resonance profile, employ a multi-secondary axis configuration, all ofepisodes, or landslides affecting the tracker’s foundation them mechanically linked and driven by a single motor,etc. neither will they evolve as subtly as these would. In such as happens in the some times proposed tilt-roll rows,the contrary the most important sources, which give way the model grows up to a 7n parameter model, n being theto time evolving tracking errors can be set down number of secondary axes. Here every secondary axis hasmathematically in a reasonably compact form by its own set of six parameters plus a weight parameter whichdescribing the preliminary errors made in the characterizes its overall contribution to the tracker’sinstallation, assembly and manufacturing processes, pointing vector, due to the electrical and acceptance anglewhich will modify the assumptions expected by the sun mismatches in between the CPV systems separately held byephemeris, i.e. the idea the tracking control has of its different axes, jointly considered with the series-paralleltracker. Once these sources are properly modeled, the connection among them. θ = 30 º λ = 20 º ; δ = − 20 ºprecise parameters quantifying the extent to which theyact on a particular tracker can be fitted at onset, and will p ÅÅÅÅ ÅÅÅeventually permit the tracking control, to work on its sun 4ephemeris core, corrected by the model tuned to thefitted parameters, without needing any further feedback. p - ÅÅÅÅÅÅÅ p - ÅÅÅÅÅÅÅ p ÅÅÅÅÅÅÅ p ÅÅÅÅ ÅÅÅ 3p ÅÅÅÅÅÅÅÅÅÅÅÅ Returning to the EUCLIDES case, the importance of 2 4 4 2 4installation errors and its significant time evolvingnature, can be seen in Figure 4 where the tracking error Figure 5. Error model correction applied to a rectangularas a function of the hour angle, due to a 5º tilt in the NS grid in the azimuth-elevation plane of sun ephemerisaxis of the concentrator, due to e.g. terrain slope, is coordinates when the model is working with parametersimulated and presented for both the winter and summer values θ = 30º , λ = 20º , δ = −20º .solstices. Not only there is there a significant differencebetween these two curves, but curiously enough the Some fine tuning customization of this generic model isprofile closely resembles that of the error estimate look- allowed whenever required by the tracker under control, e.g.up table in Figure 2, thus suggesting that that specific in order to consider the errors introduced by displacing theEUCLIDES row is to some extent affected also by axis coupling of encoders from the main axis to some hub alongtilt, which if characterized at onset could avoid its specific drive transmission chain, which might permitsubsequent surveillance. backlash errors to creep into the readings, or in the case of error − ζ H deg L structures were bending or torsion of the aperture structure, 6 and therefore of the pointing vector, due to gravitational 4 moments or dynamic stress varies with the axes position. 2 To maintain the model as generic as possible, no hour angle − ω H rad L simplifying linearizations have been done, and parameter-0.6 -0.4 -0.2 0.2 0.4 0.6 -2 least mean squares fitting is obtained by means of multistart -4 global optimization techniques, based ultimately in -6 Levenberg-Marquardt local searches. The tracking error data set is acquired using the scanning and maximizationFigure 4. Simulated tracking error vs. hour angle in the techniques developed for the PI strategy, error observationswinter (blue) and summer (red) solstices, due to a 5º tilt which are screened by an outlier filter prior to their ultimatein the horizontal NS tracking axis of an EUCLIDES admission.tracker. To explore the capabilities of model based hybridroutines a tracking error model was developed, forwhichever configuration of one or two axis, and amongthe latter those in the multisecondary axis approach. Built out of the composition of different transformsoperating over Az./El. coordinates, it is characterized bysix parameters each one representing an error source: • Primary axis tilt azimuth ( φ) and zenith angle (θ ) • Primary axis offset (ψ ) • Pointing vector axial tilt ( δ ) • Non-orthogonality of axes ( λ ) Figure 6. A Levenberg-Marquardt local search (red path) • Secondary axis offset ( η) progressing in a two dimensional subspace of the error model parameter search space. As can be seen model’s dependence in the parameters is periodic. I.Luque-Heredia, J.M.Moreno, G.Quéméré, R.Cervantes, P.H.Magalhães
  6. 6. 3rd International Conf. on Solar Concentrators for the Generation of Electricity or Hydrogen, Scottsdale, Arizona, 2005 Aside from these six parameters a time drift parameter 4. Conclusionhas been introduced, which enables also the adjustmentof the controllers internal clock. This may prove useful The approaches taken by Inspira in the development ofwhenever its synchronization by means of an external different precision sun tracking controllers for CPVprecise time source is not feasible. technologies have been here described. Error tabulation and In this way the complete strategy proceeds in such a forecasting, in which model free strategies rely, becomeway that, after a one sunny day session of tracking error inefficient after cloudy periods, during which estimates canacquisition, and the following night of parameter fitting, not be updated and error trends evolve unobserved. SunDog– the autocalibration phase – it switches to a fully open instead implements a strategy based on a sun tracking errorloop mode where sun ephemeris are corrected by the model, compliant with any one or two axes configuration,precisely tuned error model. Periodically new which once autocalibration is performed at onset, permitsautocalibration processes may be triggered, checking for open loop tracking with no need for error scanning. Thesome long term variation in the parameters due to e.g. autocalibration stage requires on the one hand errorstructural permanent bending, or simply working on the acquisition routines devised in the PI strategy, and on thetime drift parameter which will presumably vary other nonlinear LMS fitting.basically due to temperature effects in the controller’sinternal quartz oscillator.Figure 7. Inspira’s new SunDogTM STCU (left) along Figure 8. Two of Inspira’s Trell Trackers which integratewith its SunDog Monitor virtual interface software the SunDog STCU.(above right), and WWW remote control panel hosted byits web server (below right). REFERENCES SunDogTM, (sun’s best friend, always walking by his [1] Schmela, M. “Concentration Please!”, Photonside) is the commercial name given to the Sun Tracking International, Dec.1999-Jan.2000.Control Unit (STCU), which is quite similar EPS-Tenerife, regarding its hardware resources leaving aside [2] Lepley, B, Hammond and A. Harris “Evaluation ofthe necessary updating of many of its components Tracking Flat Plate and Concentrator PV Systems”(Fig.7). The LCD & keyboard MMI has now been Proceedings. of the 26th IEEE PV Specialistreplaced by a simpler frontpanel, and a Windows Conference, (Anaheim, 1997)application – SunDog Monitor – which permits a very [3] Photovoltaic Technology Research Advisory Councilversatile management and control (manual mode, Committee A Vision for Photovoltaic Technologymanagement of calibration operations, historic log (Directorate General for Research, 2005), 42, decoding and organization, operationmonitoring, edition of internal parameters, etc.) of the [4] Arboiro, J.C., Sala, G. “Self-learning tracking: a newSTCU from a PC connected to its serial port. In order to control strategy for PV concentrators”, Progress infurther enhance its remote monitoring capabilities, an Photovoltaics, 1997, 5, pp.213-226.internal mail and web server has been integrated alongwith an interchangeable modem for PSTN, RF, Ethernet [5] McConnell, R. “Solar Electric Concentrator Myths:or GSM/GPRS Internet connectivity. Seven Deadly Sins” Proceedings of the International SunDog, has also been integrated into 4m2 aperture Solar Concentrator Conference for the Generation ofsun tracker devised by Inspira for laboratory testing of Electricity or Hydrogen, (Alice Springs, 2003)CPV technologies (see Fig. 8). Named Trell Tracker,and already having been supplied to several research [6] Luque-Heredia, I. Gordillo, F. Rodríguez, F. “ A PIcentres, it admits payloads up to 100 kg, and provides Based Hybrid Sun Tracking Algorithm for Photovoltaicaccuracies in the 0.1º range. Concentration”, Proceedings of the 19th European Photovoltaic Solar Energy Conference, (Paris, 2004) I.Luque-Heredia, J.M.Moreno, G.Quéméré, R.Cervantes, P.H.Magalhães