Academic literature on the topic 'Linear parabolic collector'

Estimation of an exceptionally exact model for solar parabolic collector from the experimental data is an important task for the researchers for the recreation, assessment, control and plan. Efficient optimization techniques are fundamental to accomplish this undertaking. In this paper a modified optimization technique is proposed for productive and precise estimation of the parameters of solar parabolic collector. The proposed algorithm is concentrated on the modification of Elephant Swarm Water Search Algorithm. This algorithm tested on parabolic collector parameters, namely reflectivity, Absorptivity & period of sun incidence. Response surface methodology has been used to implement the non linear model between the input & output parameters of the process. In addition, the proposed ESWSA optimization technique has been tested against the manufacture datasheet of solar parabolic reflector. Results show the effectiveness of ESWSA algorithm for modeling of the solar parabolic systems. Keyword : Solar parabolic Collector, Parameters, ESWSA, Optimization

While fossil fuel sources have declined and energy demand has increased, in addition to the climate change crisis, the world turned to using renewable energies to get its energy. Concentrated solar power (CSP) is one of the main technologies used for this purpose. This study aims to compare the different concentrated solar power technologies in terms of their efficiency, cost, concentration ratio, and receiver temperature. Results showed that technologies were arranged according to temperatures from high to low as follows; the parabolic dish reflector, central receiver collector, linear Fresnel reflector, and parabolic trough collector. According to cost, the parabolic dish reflector has the highest price, while the linear Fresnel reflector has the lowest price. Also, the parabolic dish reflector has the highest efficiency among the others, followed by the central receiver collector, then the linear Fresnel reflector, and the parabolic trough collector respectively. Additionally; the study represented that point-focus devices have a high percentage of concentration ratio than line-focus devices. Finally, in order to exploit these sources throughout the day, it is recommended to use phase change materials to store the excess thermal energy as a positive and effective approach to solving the energy problems.

In this paper, the physical parameters of the absorber pipe of a linear parabolic collector have been investigated. The types of solar collectors, specifically the linear parabolic collector, have been comprehensively studied. Then, the mathematical model of heat transfer in the absorber pipe of the collector has been presented based on valid references. Numerical solutions of the equations related to the absorber pipe were performed by MATLAB software, and the effects of the physical parameters of the absorber pipe on its efficiency were investigated. The results show that increasing the length of the absorber pipe causes a nonlinear decrease in the efficiency of the absorber pipe. One of the important results is the increase in fluid temperature due to the increase in the diameter of the adsorbent tube, which increases the diameter of the fluid temperature by 60 K, in which the parameter increases the efficiency by 0.38%.

A novel gravity-based power-free solar tracking mechanism has been developed to track a linear solar concentrating collector. Multireflector compound parabolic collectors having three parabolic segments and two flat surfaces is chosen due to its high intercept factor and suitability to the current tracking. The working of tracking mechanism is studied to find the tracking loads in the east and the west sides of collector. A generalized mathematical model is derived to simulate the tracking motion from the sunrise to sunset. The identified design variants are sprocket wheel diameter, spring stiffness, solar collector’s weight, counter balance, and tracking wheel radius. The spring length is derived from the constraints. To make a compact product, the tracking load has been minimized at large sprocket wheel, low stiff spring, lighter collector weight, and small radius of tracking. For a typical collector load of 50 kg, the designed tracking load is 50 kg with 620 mm spring length, 250 mm of sprocket wheel diameter and 60 mm tracking radius.

This paper analyses the possible applications of medium temperature solar concentration technologies, Compound Parabolic Collector, Linear Fresnel Collector and Parabolic Trough Collector in the Spanish industrial sector. Results of this study allow evaluating whether or not solar technologies are an alternative to conventional sources. This possibility is analyzed energetically, economically and environmentally. Results show that the percentage of solar use is decisive in determining the true thermal energy generation cost. The other essential parameter is the solar field area due to produce economy of scale that reduces investment costs. Fluid temperature has significant influence mainly in Compound Parabolic Collector technology. Results obtained in this paper collect multiple alternatives and allow comparing for different scenarios the suitability to replace conventional energy sources by thermal energy obtained from medium temperature solar concentration technologies from an economic perspective. For instance, for percentage of solar use equal to 100%, the lowest thermal energy generation costs for each technology are 1.3 c€/kWh for Compound Parabolic Collector technology, fluid temperature of 100 °C and industrial process located in Seville, 2.4 c€/kWh for Linear Fresnel Collector technology, fluid temperature of 170 °C and industrial process located in Jaen, 3.3 c€/kWh for technology, fluid temperature of 350 °C and industrial process located in Jaen. These costs are lower than conventional energy sources costs.

The paper describes a methodology, very simple in its application, for measuring surface irregularities of linear parabolic collectors. This technique was principally developed to be applied in cases where it is difficult to use cumbersome instruments and to facilitate logistic management. The instruments to be employed are a digital camera and a grating. If the reflector surface is defective, the image of the grating, reflected on the solar collector, appears distorted. Analyzing the reflected image, we can obtain the local slope of the defective surface. These profilometric tests are useful to identify and monitor the mirror portions under mechanical stress and to estimate the losses caused by the light rays deflected outside the absorber.

A novel type of parabolic trough collector was characterised using a very basic theoretical model. This model looked at an ideal case and provided a basic expectation that was compared to actual measurements. The model showed that greater improvements can be achieved if heat losses to the environment are limited or omitted. This can be achieved by using a glass shield to insulate the receiver in a vacuum to limit the effect wind has and therefore limit convective losses. The experimental characterisation of the PTC consisted of taking six different temperature measurements to better understand the energy balances taking place. Four different configurations were tested, using two different types of concentrator and in each case a receiver that was either unpainted or painted with a semi matte black paint. The different types of concentrator were either stainless steel sheet metal or discretised glass mirror strips, similar to a linear Fresnel collector. Experimental runs were conducted on cloudless days for an hour and 15 minutes. This allowed for three runs to be performed on a single day. Using the theoretical model and comparing it to the experimental data, an efficiency was calculated. This efficiency averaged 14 % when the receiver was unpainted and 13 % when the receiver was painted for the metal sheets. The glass mirror strips had average efficiencies of 54 % and 45 % for an unpainted and painted receiver respectively. The model is very basic and can be improved upon if more variables are taken into consideration, such as convective heat losses. It was also recommended that wind measurements are taken in future tests. A property looked at to evaluate the effectiveness of each type of configuration was the average energy supplied to the thermal heating fluid over the course of an experimental run. For this the averaged values over all the experimental runs conducted for stainless steel sheet metal were 258 W and 332 W for an unpainted and painted pipe respectively. When using the glass mirrors an average energy value of 1049 W was supplied when the pipe was unpainted and an average of 1181 W was gained in the runs conducted after the pipe had been painted. Painting the receiver had little to no effect. The surface temperature of the receiver after painting the pipe was not higher and a slight increase in the energy gained by water was observed. This was explained by inaccuracies during testing as scattered light may have caused an interference on some of the measurements. There were also human inaccuracies in testing which should be omitted in future tests by implementing, for one, a functional tracking system. Future tests should be designed in such a way to completely omit irradiance affecting the thermocouple taking the measurement. Glass mirrors fared far better than the stainless steel sheet metal counterpart. It was recommended that they are used as the concentrator of choice. Higher efficiencies were achieved and in some cases almost four times the energy was supplied to the water in the pipe. This was attributed to a much lower concentrator temperature, on average 11 °C lower than the temperature of the metal sheets, as well as a much better ability to concentrate sunlight onto a single focal point. However, the glass mirror strips were proven to be very fragile and as such, require protection from the elements. While the strips were lighter and caused less of a load during windy conditions, they were susceptible to oscillations from gusty wind. This led to a number of strips breaking and needed to be replaced. By discretising the strips into individual pieces, they had the benefit of only needing to replace the strips that were damaged. This is also true for all future runs. It is still recommended that a tarp be used to protect the glass mirrors. Using glass mirror strips as a concentrator combined LFC technology with PTC technology and a novel PTC design was achieved. The design still required the installation area of a PTC. The novel design was compared to Industrial Solar’s industrial LFC module, LF-11, as it shares many similarities to LFC technology. The peak thermal output of the rig was significantly lower at 346 W/m2 compared to the industrial value of 562 W/m2. However, the noteworthy differences in design and optimisation between the two modules meant the results achieved were comparable. It is expected that better and more comparable results can be realised once the inherent flaws in the design, such as tracking the sun, aperture size and adding a vacuum absorber, are addressed. It is recommended that more research and emphasis is put into this field as an alternative energy power plant for South Africa.
Dissertation (MEng)--University of Pretoria, 2017.
Chemical Engineering
MEng
Unrestricted

Il mercato del solare termodinamico offre varie soluzioni tecnologiche e impiantistiche in funzione dei livelli di temperatura che si vogliono ottenere. Le esigenze energetiche nei vari settori industriale, residenziale e commerciale, però, spingono il mercato verso i collettori solari capaci di operare con rendimenti maggiori del 50% a temperature superiori a 100 °C, fino anche a 250 °C (nel range cosiddetto “a media temperatura”'). In questo ambito, la tecnologia che dimostra di essere più matura per la penetrazione del mercato risulta essere quella dei collettori parabolici lineari (PTC), e in particolar modo quelli di piccola taglia. L'assorbitore solare riveste un ruolo di estrema importanza per il buon funzionamento dell'intero PTC. In particolare la scelta del coating superficiale per il tubo rappresenta un punto focale per lo sviluppo e l'ottimizzazione del sistema in termini tecnici ed economici. Per il raggiungimento degli obiettivi è necessario orientarsi verso soluzioni tecnologiche che abbiano proprietà chimiche, fisiche e ottiche tali da garantire elevate prestazioni in termini di efficienza energetica e stabilità nel tempo alle temperature di esercizio desiderate. I coatings a base di cromo nero presentano ottime caratteristiche ottiche (α≈0.90-0.92; εT≈0.10-0.15) e risultano essere stabili anche fino a 300 °C. Il più grande problema legato alla realizzazione di rivestimenti cromati è legato all'inquinamento conseguente all'utilizzo nel bagno elettrolitico di ossidi di cromo esavalente. Agli inizi del nuovo secolo, con l'avvento di nuove soluzioni chimiche meno inquinanti per la produzione di oggetti cromati e con il crescente interesse verso i collettori solari piani, le tecniche galvaniche hanno trovato largo uso nella produzione di impianti solari termodinamici. L'assorbitore che è stato studiato è un assorbitore a base di cromo nero, e questo rientra nella categoria dei “tandem-absorber”: lo studio è cominciato quindi dal substrato. Lo studio del substrato ha portato alla comprensione delle caratteristiche che questo deve possedere e quali sono le condizioni operative per ottenerle. Il substrato per il cromo nero deve possedere appropriate caratteristiche ottiche, ovvero bassa emittanza, ma deve anche favorire la deposizione e l'adesione dell'assorbitore. I materiali candidati a questo scopo sono stati il nichel, ottenuto con due diversi processi di deposizione e il rame. Poiché questi tre materiali favoriscono egualmente deposizione ed adesione del cromo nero, è da preferire il materiale che garantisce la minore emittanza, ovvero il nichel ottenuto con il processo di deposizione di Watts (ε300 °C≈ 0.4). Si è mostrato inoltre, facendo chiarezza rispetto a quanto riportato in letteratura, come gli spessori dei substrati non influenzino le caratteristiche ottiche. Quindi al fine di contenere i costi di produzione è da preferire il minore spessore che garantisca una buona adesione del substrato e questo è stato individuato in uno spessore di 2 µm. Si sono poi trattate le caratteristiche ottiche dell'assorbitore, ponendo particolare attenzione al contesto in cui questo verrà utilizzato: infatti il parametro di selettività, comunemente utilizzato in letteratura per il confronto degli assorbitori solari selettivi, non fornisce indicazioni valide sul comportamento dell'assorbitore nell'impianto solare. Si è quindi introdotto il parametro di efficienza η che tiene conto delle condizioni in cui verrà impiegato l'assorbitore. Ipotizzando un plausibile caso di lavoro con temperatura di esercizio 300 °C e rapporto di concentrazione di 40, si è mostrato come sia necessario cercare di massimizzare l'assorbanza del materiale assorbitore al fine di ottimizzare l'efficienza, piuttosto che limitarne l'emittanza. L'analisi dei parametri di deposizione che ha portato a determinare l'insieme di condizioni da cui deriva la migliore efficienza ha mostrato la fondamentale importanza della composizione chimica del bagno galvanico: infatti, oltre alla presenza del costituente principale, ovvero il Cr+3, si è verificato il contributo determinante apportato dai ``catalizzatori''. Questi facilitano il trasporto dello ione principale in soluzione e la sua deposizione al catodo, limitando al contempo le reazioni collaterali. In questo modo si riesce ad ottenere il cromo nero con un miglioramento di η del 5-8 % ed a densità di corrente molto inferiori rispetto al caso in cui i catalizzatori non sono presenti. Densità di corrente e temperatura del bagno galvanico sono i parametri principali su cui operare. I migliori risultati sono stati ottenuti a 20 °C con una densità di corrente di 60 A dm-2. Il tempo della deposizione è molto importante: infatti, dagli studi condotti, il tempo ottimale di deposizione è 1 minuto, poiché sia per tempi minori che maggiori si ha un peggioramento dell'efficienza. Dall'analisi della superficie si è visto che il cromo nero è uno strato di materia soffice, non compatta, con aspetto estremamente frastagliato e composta da globuli di piccole dimensioni costituiti da un nucleo di cromo metallico circondato da uno strato di ossidi e idrossidi di cromo. L'aspetto della superficie influenza le caratteristiche ottiche del materiale: infatti esiste una correlazione tra la rugosità superficiale e α/εT secondo cui all'aumentare di Rz si ha una perdita di selettività. Numerose e importanti informazioni si sono ottenute dalla valutazione degli effetti provocati dai trattamenti termici: infatti per un assorbitore solare è di fondamentale importanza conoscere le caratteristiche ottiche alla temperatura di funzionamento. Il cromo nero analizzato è caratterizzato da un miglioramento della selettività dopo essere stato esposto alle alte temperature (300 °C e 400 °C) soprattutto nei casi in cui il substrato sia Ni Watts. Si è potuto valutare anche che il rame non è un buon substrato per applicazioni che possano trovarsi a temperature superiori ai 300 °C a causa della sua facile interdiffusione con altri metalli. L'esposizione dell'assorbitore alla temperatura di esercizio si comporta inoltre come una sorta di livellante nei confronti di η il cui valore medio si attesta a circa 0.8. Infatti il trattamento termico a 300 °C provoca un miglioramento delle efficienze degli assorbitori che inizialmente possedevano delle η abbastanza basse e un cambiamento esattamente opposto per gli assorbitori che appena deposti presentavano le migliori efficienze. La presenza dello ione fluoruro nella composizione del bagno galvanico comporta invece una minore resistenza dello strato assorbitore nei confronti della temperatura. Alla luce di queste considerazioni la composizione ottimale del bagno galvanico individuata è costituita da CrCl3·6H2O 266 g l-1, H2SiF6 10 g l-1, NaH2PO4 4 g l-1 e CoCl2 ·6H2O 15 g l-1 . Infine, nonostante in precedenza si sia individuato il miglior substrato in base alle sue caratteristiche ottiche, si è visto sperimentalmente come questo parametro non si rifletta in maniera determinante sull'efficienza finale. Infatti, come già detto, è importante massimizzare l'assorbimento piuttosto che limitare l'emissione dell'assorbitore. Per questo motivo e considerate le prove effettuate, si può affermare che i substrati considerati sono tra loro equivalenti. Alla luce di ciò il substrato più adatto è il nichel ottenuto con il metodo di Wood, poiché è quello che necessita di minor lavorazione e non presenta le limitazioni riguardo alle temperature di utilizzo viste per il rame. Il miglior campione ottenuto, che rispetta le condizioni appena elencate, presenta una efficienza di conversione energetica η=0.88: questo valore non è molto lontano, e talvolta migliore, delle efficienze dei ben più costosi CERMET (η=0.85-0.93), oltre ad essere migliore delle efficienze dei campioni ottenuti da cromo esavalente. ***************** The use of a low-intensity source like sunlight, for energy generation requires an efficient system to concentrate and capture radiation and to transfer the energy to the exchange fluid. Sunlight is abundant, renewable and free of charge. Therefore the development and diffusion of solar energy exploitation is a key issue for the future. However, at present solar energy technologies are generally affected by a not high enough efficiency and a high cost, making them not fully competitive yet over conventional fossil fuels. Thus, it is clear that both increasing the efficiency and reducing the cost is mandatory to promote solar energy exploitation. Systems operating at mid-temperatures (i.e. using fluids at about 200-300 °C) and in particular parabolic trough collectors (PTCs) offer several advantages in comparison with conventional flat plates thanks to their higher efficiency and reduced receiver surface. In these systems the incident solar radiation is converted into heat either by sunlight absorption by blackened or specially developed absorbing surfaces that collect the solar energy and transfer it to the fluid. Required characteristics for the absorber surface are chemical and physical stability at the operating temperatures, as well as good performances in terms of energy efficiency. Moreover a production process characterized by a low cost and a high repeatability should promote a large scale diffusion. Several direct industrial applications, like Direct Steam Generation (DSC) and Solar Heating and Cooling (SHC), could exploit mid-temperature solar energy as energy source. This interest drives the research of novel technologies focused on this market sector where the technologies developed for systems operating at higher temperatures (e.g. CSP plants) cannot be used. Electrodeposition techniques are a promising route to obtain surfaces with tailored optical characteristics. Black chrome coatings have excellent optical properties, as they are strongly absorbing in the sunlight spectral region, with a high absorbance α ≈ 0.90-0.92 and a low thermal emittance ε ≈ 0.10-0.15. Moreover they remain stable up to 300 °C. However, a relevant drawback correlated to chrome electrodeposition is represented by pollution derived from Cr6+ ions. Because of that, the technological development of these processes underwent a sharp slowdown since '90. Only with the advent of new studies about Cr3+ baths, since the beginning of 2000's, the electrodeposition processes have found new interest in mass production of components for thermal solar plants. To obtain a good coating by black chrome, a preliminary deposition of a nickel layer on the substrate is needed to ensure a better chrome adherence to the surface and an improved wear and corrosion resistance. Moreover this creates an ``absorber/reflector tandem'' having both the high solar absorbance of the black exterior deposit and the low thermal emittance of the metallic inner coating. The first step of this study was the investigation of structural features and optical properties of the nickel and copper surfaces, correlating them to coating thickness and deposition process, in the perspective to assess optimal conditions for solar absorber applications. The second step of this study was the investigation of structural features and optical properties of the black chrome absorber taking into account several bath's operational parameters. This black chrome was obtained by a solution of Cr+3. In order to compare the performance obtained by the materials in a working configuration has been paid attention to a parameter that can provide some information: this parameter is the efficiency η that take into account the working temperature and the concentration ratio. Moreover has been done several thermal aging cycle on the materials in order to predict the effect of the aging on the optical properties. The optimal set-up that has been found is: for a galvanic bath composition CrCl3·6H2O 266 g l-1, H2SiF6 10 g l-1, NaH2PO4 4 g l-1 and CoCl2 ·6H2O 15 g l-1; for the operational parameters 20 °C and current density of 60 A~dm-2. With this set-up the best result is a sample with η=0.88: this value is rather similar to the efficiency of the more expensive CERMET (η=0.85-0.93).

Sewage collectors for domestic waste water and rainwater have flow sections that are standardized in shape and size. The collector with vertical dimension H > 1.50 m is admitted to be visitable and for H ≤ 0.80 m it is not visitable. Sewage collectors can be made in demanding situations with non standardized flow sections. A series of natural and anthropogenic action can change the geometric and hydraulic parameters of the flow section over time. Thus, the flow section no longer respects the initial geometric and hydraulic parameters and becomes a non-standardized section. Knowing the hydraulic parameters at such a flow section becomes difficult for monitoring the mining process. The circular, ovoid, circular bell, parabolic bell type flow section transforms into sections consisting of straight lines and circular arcs or only circular arcs. The factors that produce are erosion, siltation and cementation of transported material, repair and rehabilitation works and others. The erosion phenomenon also causes a change in the roughness on the watered perimeter of the section. In order to obtain the hydraulic operating parameters of the visitable sever collectors with non-standard flow section, several calculation programs have been elaborated on the forms of permanent water movement.

A performance model has been programmed for a solar thermal collector based on a linear parabolic trough reflector focused on a coated absorber tube enclosed in an evacuated transparent tube: a Parabolic Trough Solar Collector (PTSC). This steady state, single dimensional model is based on fundamental material and energy balances together with heat transfer correlations programmed in the Engineering Equation Solver (EES). The model considers the effects of solar intensity, incident angle, collector dimensions, material properties, fluid properties, ambient conditions, and operating conditions on the performance of the PTSC. The model has been used to size system devices, to choose proper operating conditions, and to detect possible operating problems for the solar cooling and heating system for the Intelligent Workplace (IW) at Carnegie Mellon University (CMU) in Pittsburgh. The IW installed 52 - square meter PTSCs coupled with a 16 kW absorption chiller for space cooling and heating in August of 2006. The tests on PTSC performance are now being carried out. After the model is validated by experimental data of the tests, it will be further used to improve PTSC design and to optimize system operation and control for the IW.

Within the last years, Linear Fresnel (LF) collector systems have been developed as a technical alternative to parabolic trough collector (PT) systems. In the past, LF systems focused on low- and medium temperature applications. Nowadays, LF systems equipped with vacuum receivers can be operated at the same temperatures as PT systems. Papers about the technical and economical comparison of specific PT and LF systems have already been published, [1–3]. However, the present paper focuses on the systematic differences in optical and thermodynamic performance and the impact on the economic figures. In a first step the optical performance of typical PT and LF solar fields has been examined, showing the differences during the course of the day and annually. Furthermore, the thermodynamic performance, depending on the operating temperature, has been compared. In a second step, the annual electricity yield of typical PT and LF plants are examined. Solar Salt has been chosen as heat transfer fluid. Both systems utilize the same power block and storage type. Solar field size, storage capacity, and power block electrical power are variable, while all examined configurations achieve the same annual electricity yield. As expected for molten salt systems, both systems are the most cost-effective with large storage capacities. The lower thermodynamic performance of the LF system requires a larger solar field and lower specific costs in order to be competitive. Assuming specific PT field costs of 300 €/m2 aperture, the break-even costs of the LF system with Solar Salt range between 202 and 235 €/m2, depending on the site and storage capacity.

The SkyTrough™ is a new high-efficiency parabolic trough solar collector that has been designed with features to reduce capital cost, shorten installation time, and reduce O&M cost. This collector builds on the excellent success of prior generation utility-scale parabolic trough designs, but incorporates several engineering and material innovations, listed below. 1. Lightweight, low cost, unbreakable non-glass reflectors using ReflecTech® Mirror Film with reflectance equal to silvered glass mirrors — and easy to install and replace, 2. Large aperture area parabolic trough module with more than double the aperture area of the Nevada Solar One (NSO) module, 3. Longer linear receiver (SCHOTT PTR™80) utilized to match the larger aperture width SkyTrough, 4. Aluminum space frame structure that is considerably lighter per unit of aperture area compared to NSO, 5. Total component “part count” that is considerably reduced per unit of aperture area, yielding a shorter assembly time per unit of aperture than the NSO modules, 6. Hydraulic-based rotary actuation system that provides built-in “stow” locking capability and higher torque capability compared to NSO, 7. SkyTrakker™ control system reduces inrush currents and reduces parasitic power consumption associated with collector sun tracking.

Parabolic trough can be considered the state of the art for solar thermal power plants thanks to the almost 30 years experience gained in SEGS and, recently, Nevada Solar One plants in US and Andasol plants in Spain. One of the major issues that limits the wide diffusion of this technology is the high investment cost of the solar field and, particularly, of the solar collector. For this reason, since several years research activity has been trying to develop new solutions with the aim of cost reduction. This work compares commercial Fresnel technology with conventional parabolic trough plant based on synthetic oil as heat transfer fluid at nominal conditions and evaluates yearly average performances. In both technologies, no thermal storage system is considered. In addition, for Fresnel, a Direct Steam Generation (DSG) case is investigated. Performances are calculated by a commercial code, Thermoflex®, with dedicated component to evaluate solar plant. Results will show that, at nominal conditions, Fresnel technology have an optical efficiency of 67% which is lower than 75% of parabolic trough. Calculated net electric efficiency is about 19.25%, while parabolic trough technology achieves 23.6%. In off-design conditions, the gap between Fresnel and parabolic trough increases because the former is significantly affected by high radiation incident angles. The calculated sun-to-electric annual average efficiency for Fresnel plant is 10.2%, consequence of the average optical efficiency of 38.8%, while parabolic trough achieve an overall efficiency of 16%, with an optical one of 52.7%. An additional case with Fresnel collector and synthetic oil outlines differences among investigated cases. Finally, because part of performance difference between PT and Fresnel is simple due to different definitions, additional indexes are introduced in order to make a consistent comparison.

This paper presents an optimization methodology for designing linear concentrating solar collectors. The proposed algorithm makes intelligent design updates to the collector surface geometry according to specialized numerical algorithms. The process is much more efficient than traditional “trial-and-error” methods, producing a final solution that is near-optimal. A Monte Carlo technique is used to quantify the performance of the collector design in terms of an objective function, which is then minimized using a modified Kiefer-Wolfowitz algorithm that uses sample size and step size controls. The methodology is applied to the design of a linear parabolic concentrating collector, successfully arriving at the known optimal solution.

Solar brightness profiles were used to model the optical performance of a parabolic linear solar concentrator. A sensitivity analysis of the sun size on collector performance was completed using analytical methods. Ray traces were created for solar brightness profiles having circumsolar ratios from 0–40%, slope errors of the optical surface from 2–5 mrads, and angles of incidence varying from 0–60 degrees. Using typical meteorological data for two locations, the optical performance was calculated and averaged over a year. Intercept factors of these simulations were compared to simpler analytical models that cast the sun shape as a Gaussian function. Results showed that collector performance is relatively insensitive to solar profile, and that using a representative Gaussian solar profile will tend to underestimate collector performance compared to using exact weighted solar profiles by about 1%. This difference is within the uncertainty propagation of the intercept factor calculated with analytical methods.

The parabolic trough linear receiver is one of the primary reasons for the high efficiency of the Luz parabolic trough collector design used at the Solar Energy Generating Systems (SEGS) plants. Experience from the SEGS plants has shown that the reliability and lifetime of the parabolic trough receiver tube is the most significant issue for existing and future parabolic trough plants. Although highly efficient, the original Luz receiver tubes experienced high failure rates (approximately 4% to 5% per year). Failures included vacuum loss, glass envelope breakage, and degradation of the selective coating. This paper reviews receiver failure rates, the primary failure causes at two of the SEGS plants, and discusses receiver technology developments during the last several years that focus on improving the reliability of parabolic trough receivers. Data are provided on the performance and reliability of a new commercially available trough receiver.