Small Scale Linear Fresnel Reflector Research Articles

Experimental Investigation of the Influence of Longitudinal Tilt Angles on the Thermal Performance of a Small-Scale Linear Fresnel Reflector

This paper analyses the influence of the longitudinal tilt angle of the secondary system of a low-concentration photovoltaic system based on a small-scale linear Fresnel reflector. Several evaluation indicators, such as useful heat gain, thermal efficiency, incident solar irradiance gain on the photovoltaic cells, and total useful energy gain, were evaluated for five wind speed conditions and six locations in the Northern Hemisphere. The tests were performed with two small-scale linear Fresnel reflector configurations: the classical large-scale linear Fresnel reflector configuration (base configuration) and the optimal longitudinal tilt angle configuration (longitudinal tilt configuration). An experimental platform based on an open-loop wind tunnel was designed and built for this purpose. As far as useful heat production, the longitudinal tilt configuration performs worse as the longitudinal tilt angle and wind speed increase. A useful heat gain 33.91% lower than the base configuration is obtained with a wind speed of 10.03 (m/s) at the 36.86 (°) latitude location. Thermal efficiency decreases with increasing wind speed and longitudinal tilt angle. The thermal efficiency is between 0.3 and 0.2 with wind speeds of 4.99 (m/s) and 10.03 (m/s). The longitudinal tilt configuration shows the best increase in total useful energy gain in the absence of wind (up to 53% at a latitude of 36.86 (°)). This increase is 25% at this same location with a wind speed of 10.03 (m/s). It can be concluded that the effect of the longitudinal tilt of the secondary system has a positive effect. To highlight the importance of this work, the results obtained in the configuration comparison were used to compare a nonconcentrating photovoltaic system and a low-concentration photovoltaic system. The incident solar irradiance on the photovoltaic cells is much higher with nonconcentrating photovoltaic technology. This solar irradiance gain is over 60% for the base configuration and 45% for the longitudinal tilt configuration. The total useful energy gain is 70% in the absence of wind and at the 36.86 (°) latitude location in favour of the low-concentration photovoltaic system. The nonconcentrating photovoltaic system performs better with a wind speed of 10.03 (m/s).

Sawtooth V-Trough Cavity for Low-Concentration Photovoltaic Systems Based on Small-Scale Linear Fresnel Reflectors: Optimal Design, Verification, and Construction

Ensuring the uniformity of solar irradiance distribution on photovoltaic cells is a major challenge in low-concentrating photovoltaic systems based on a small-scale linear Fresnel reflector. A novel sawtooth V-cavity design method based on an optimization algorithm to achieve uniform irradiance distribution on photovoltaic cells is presented. The reliability of the design was verified using the Monte Carlo ray-tracing method and a laser experiment. A prototype was built using 3D printing technology with a biodegradable green polymer material known as polylactic acid. The new cavity was compared to the standard V-trough cavity, keeping the cavity aperture, reflective surface area, and photovoltaic cell width constant. In addition, the focal height, number of mirrors, mirror width, and mirror spacing were also kept constant; so, the cost of the two configurations was the same from the point of view of the primary reflector system. The new design ensured the uniform distribution of solar irradiation and significantly reduced the height of the cavity. The significant decrease in the height of the proposed cavity has the following advantages: (i) a decrease in the dimensions of the fixed structure of the small-scale linear Fresnel reflector, thus reducing its cost, (ii) a significant decrease in the surface area exposed to wind loads, thus reducing the cost of the fixed structure and secondary system structures, (iii) a reduction in the difficulty of the manufacture, maintenance, and transportation of the cavity’s reflecting walls, and (iv) an increase in the cooling surface area, which increases the electrical efficiency of the photovoltaic cells.

Numerical simulation of a solar water disinfection system based on a small-scale linear Fresnel reflector.

This paper describes the details of the design of a solar water disinfection system based on a small-scale linear Fresnel reflector. The proposed system consists of a small-scale linear Fresnel reflector, a filtering system, two disinfection units, a heat exchanger, a compressed air system and the control system. A detailed mathematical model has been developed and solved through an iterative procedure. The system has been studied under different operating conditions, such as beam solar irradiance (the beam solar irradiance on a horizontal surface, corresponding to solar noon, varies from 325 to 798 W m-2, for winter solstice and summer solstice, respectively), ambient temperature (the ambient temperature varies between 19 and 29 °C at the summer solstice and from 8 to 16 °C at the winter solstice), thermal fluid flow rate (2200 L h-1, 2400 L h-1, 2600 L h-1, and 2800 L h-1) and water temperature at the outlet of the filtered water tank (8 °C, 12 °C, 16 °C, and 20 °C). The performance of the system has been studied as a function of the temperature of the thermal fluid of the small-scale linear Fresnel reflector, the water temperature of the disinfection unit, the filling and emptying of inertia tanks, clean water productivity and the daily cumulative productivity of clean water. Numerical simulations reveal that the maximum values of cumulative daily productivity of clean water were 357.14 (L m-2 day-1) at 100 (°C) and 198.41 (L m-2 day-1) at 100 (°C) for summer solstice and winter solstice, respectively, in Almeria (Spain), for a thermal fluid flow rate of 2400 L h-1. Values much higher than those obtained by other systems. The inclusion of a heat exchanger in this system significantly increases its productivity. Small-scale linear Fresnel reflector thermal fluid temperature, disinfection unit water temperature, clean water productivity and daily cumulative clean water productivity decreased with increasing thermal fluid flow rate above 2400 L h-1. On the other hand, the water temperature at the outlet of the filtered water tank between 8 and 20 °C has a negligible influence on the small-scale linear Fresnel reflector thermal fluid temperature values, disinfection unit water temperature, clean water productivity and daily cumulative clean water productivity. It is concluded that the proposed solar system offers an energy efficient and environmentally friendly water treatment method.

Preliminary estimation of the receiver tube wall temperature and the performance of CSP plants in off design-conditions by means of a simplified dynamic model

This work deals with the development of a fast and robust simulation tool to preliminary estimate the receiver tube wall temperature and the performance of small-scale Linear Fresnel Reflectors (LFRs) solar fields. Under the assumption of uniform solar flux, the proposed 1 D dynamic model includes a more detailed heat transfer analysis between the fluid and the internal wall of the receiver tube by implementing effective correlations covering all the possible flow regimes. The model is then applied to assess the performance of a LFRs solar field developed under the EU funded project “Innova Microsolar” with varying ambient and operating conditions. Results show that: (i) the buoyancy driven flow enhances the heat transfer of about one order of magnitude compared to the assumption of a constant Nusselt number in laminar flow condition; (ii) it is possible to correlate with more than 95% of confidence over the entire range the receiver tube wall temperature to a newly defined parameter called Load Temperature which is based on input data provided by sensors usually installed in these kind of plants; (iii) the proposed model improves also the estimation of the collected thermal energy by the fluid in the receiver tube during the warm-up phase of about 0.8% compared to the reference Forristall model.

Design and construction of a solar tracking system for Linear Fresnel Concentrator

An open circuit solar tracking system has been designed, manufactured, simulated and implemented for a handcrafted prototype of a small scale linear Fresnel reflector with a single axis of motion. The electronic control system is governed by an Arduino UNO R3 board and two main auxiliary systems; a Microstep Driver TB6600 and an RTC DS1302 module. Further, a mechanism was implemented that joins the reflectors to a stepper motor that executes a single movement per sequence, to move the set of reflector mirrors that make up the reflection system of the device. The positioning angles of the reflectors determined by the control algorithm models for solar tracking, allowed to feed the TONATIUH software to evaluate the path of the solar rays through the 3D modeling of the Linear Fresnel reflector on a real scale. The software was designed to follow the path of the sun by means of astronomical equations. In this way, the mirrors of the Linear Fresnel reflector can follow the solar path on a single axis from 7 am to 5 pm, making changes in the position of each element in 15-minute intervals. The percentage of position deviation of the reflectors does not exceed 1% between the location of the full-scale system mirrors and the position angles provided by the control algorithm. The efficiency of the implemented automatic solar tracking system increased by more than 50% compared to the manual tracking system.

Non-uniform illumination in low concentration photovoltaic systems based on small-scale linear Fresnel reflectors

Low concentration photovoltaic systems improve performance by absorbing and concentrating more sunlight than non-concentration ones. However, they require uniform illumination of the PV cells, as their electrical performance can decrease dramatically otherwise. A thorough analysis of the design causes of non-uniform illumination in small-scale linear Fresnel reflectors (SSLFR) is carried out, yielding the main parameters to be optimized. Then, such an optimized SSLFR guaranteeing uniform illumination is designed, and an optimum operation interval is estimated during which, furthermore, neither shading nor blocking on the mirrors happens. The study requires computing the maximum optimal transverse incidence angle, θt0, whose influence on the time-span of optimum operation, width of the SSLFR, annual solar irradiation, width of the mirrors, and position of the mirrors is also studied. We include a detailed example showing the accuracy of our calculations, using Monte Carlo Ray Tracing.

Theoretical Deduction of the Optimum Tilt Angles for Small-Scale Linear Fresnel Reflectors

A theoretical justification and computation of the optimum values of the two longitudinal tilt angles of a small-scale linear Fresnel reflector is provided. The optimum angle of the mobile structure is proved to be half the latitude of the geographic location, while the optimum angle of the secondary reflector system is proved to be equal to that latitude. Brute-force verification is carried out for five EU cities, each in one of the five European climate zones.

Design and construction of a solar tracking system for small-scale linear Fresnel reflector with three movements

A new open-loop solar tracking system for a small-scale linear Fresnel reflector with three movements has been designed, fabricated, and simulated. The control system of the solar tracker is governed by a Raspberry Pi together with other auxiliary devices which include a Global Positioning System. The electronic control system consists of a master controller (Raspberry pi 3), 4 slave microcontrollers (Arduino), Global Positioning System module, thermocouples, laser sensors, transversal positioning sensors, and longitudinal positioning sensors. It also allows the communication between these microcontrollers based on long range wireless solutions (XBee). All the electronic circuits have been designed and constructed. The solar tracking system uses offline data. The software has been designed and developed to track the sun path using astronomical equations. In this way, the solar tracking system is able to position itself automatically using the solar position algorithm and the Global Positioning System with an accuracy of ±0.006°. The solar tracking system can be deployed automatically at any location on the Earth. The total cost of the implemented solar tracking system has been calculated. The system performance, in terms of the tracking error, annual energy, energy-to-area ratio and levelized cost of energy has been evaluated. Tracking errors smaller than 0.06 (°) are acceptable (they cause power losses smaller than 1%), whereas errors larger than 0.36 (°) start being noticeable (power losses greater than 3%). The proposed new tracking system gives 16.64% more energy, a 78.46% higher energy-to-area ratio, and a 4.62% less levelized cost of energy that the classic tracking system with one movement used in large-scale linear Fresnel reflectors.

Wind effects on heat loss from a receiver with longitudinal tilt angle of small-scale linear Fresnel reflectors for urban applications

Abstract This paper presents an analysis of the wind effects, wind velocity and wind direction, on heat losses from a receiver with the longitudinal tilt angle of small-scale linear Fresnel reflectors for urban applications. In urban applications, the area required to install a solar collector is a critical parameter, therefore the parameter given by the energy-to-area ratio must reach its maximum value. Different combinations of longitudinal tilt angles are analyzed and compared with the typical configuration of a large scale linear Fresnel reflector (C1 configuration). The analysis is performed by SolidWorks Flow Simulation for different wind velocities and wind directions. Heat losses from the receiver have been estimated using a 3-D computational fluid dynamics model. Based on the numerical simulation of the receiver, the heat loss analysis has been calculated for several wind velocities, wind directions, and maximum energy-to-area ratio configurations. The effect of wind direction on heat losses is almost negligible. Although, heat losses are slightly higher in the North wind direction in most simulations. It will be demonstrated that the heat losses dramatically increase with a maximum energy-to-area ratio configuration, with the increase in longitudinal angle and, obviously, with the wind velocity. On the other hand, heat losses are higher at those locations with greater maximum energy-to-area ratio configuration. The heat losses, for wind velocity of 10 ( m / s ) and North direction, are, approximately, 120 % of C 1 , 131 % of C 1 , 143 % of C 1 , 165 % of C 1 and 174 % of C 1 , in Almeria, Rome, Budapest, Berlin and Helsinki, respectively. The longitudinal inclination of the receiver has positive effects on the performance of small scale linear Fresnel reflectors for urban applications.

Proportional–integral‐like fuzzy controller of a small‐scale linear fresnel reflector solar plant

This study reports on the development and implementation of the fuzzy incremental controller on a small-scale linear fresnel reflector solar plant. The control problem is concerned with forcing the output temperature to follow the reference, despite the existence of disturbances. Owing to the non-linear effects of solar plants, the capability of fixed parameters of the proportional–integral controller to cope with the control problem is limited and leads to unsatisfactory control performance. The proposed controller is a modification to a conventional proportional–integral algorithm with better tuning flexibility. Firstly, the ant colony optimisation algorithm is used to define the optimal parameter of proportional–integral plus series feed-forward controller while guaranteeing a satisfactory performance of the plant. Secondly, the resulting controller is replaced with an equivalent fuzzy knowledge-based controller with the error and change of error of the plant as the input variables and flow rate as an output variable. The proposed controller is tested on a quasi-dynamic model of linear fresnel reflector plant using conventional and renewable energy optimisation toolbox in the environment of MATLAB/Simulink. The controller's performance is compared to the proportional–integral controller, where its effectiveness is evaluated under nominal conditions, measurement delay, noise, and presence of disturbance.

Influence of solar tracking error on the performance of a small-scale linear Fresnel reflector

Abstract Solar tracking systems are an indispensable requirement for optimal efficiency in small-scale linear Fresnel reflector systems. A thorough study of the influence of solar tracking errors on energy production is, therefore, required. The power produced by each mirror at any moment is also explicitly computed, as well as its variation under error. We study the large effect that the distance between the mirror and the absorber tube, solar time, and the day of the year have on the variation of power. Our results provide the foundations for the analysis of small-scale solar tracking systems. Solar tracking errors of less than 0.09 ∘ are acceptable (they cause power losses less than 1 % ), whereas errors larger than 0.36 ∘ start being noticeable (power losses greater than 3 % ).

A cost-energy based methodology for small-scale linear Fresnel reflectors on flat roofs of urban buildings

This paper proposes a new methodology for determining the geometrical parameters and the optimal distribution of small-scale linear Fresnel reflectors on flat roofs of urban buildings. This engineering problem is highly complex as it involves 21 variables; in contrast to present-day studies available in the literature, our method provides a global solution. The algorithm involves several stages, in which it uses multiple objective functionals: maximization of the used area of the roof, minimization of the cost, minimization of losses. The solution found by this method combines all the relevant aspects from the technical and/or economic point of views and obtains, as the final objective, the maximization of the absorbed annual energy for the stated problem.

Investigating the influence of longitudinal tilt angles on the performance of small scale linear Fresnel reflectors for urban applications

The potential use of the small scale linear Fresnel reflectors in building applications can help European Union countries meet their sustainable development goals. The sizing of a small scale linear Fresnel reflector directly influences its primary cost as well as the annual energy output and, hence, its financial attractiveness. In addition, the area required for its installation is a critical parameter in most of the urban applications. This paper presents the analysis of the effects of the longitudinal inclination of the rows of mirrors and/or the absorber tube on the performance of small scale linear Fresnel reflectors. The effect of three parameters (i.e. energy absorbed by the absorber tube, energy area ratio, and primary cost) is evaluated for five cities in European Union. Different combinations of longitudinal tilt angles are analyzed and compared with the typical configuration of a large scale linear Fresnel reflector. Numerical simulations were carried out using a MATLAB code to calculate the energy absorbed by the absorber tube, the energy area ratio, and the primary cost. The comparison of the configurations provided insight into how latitude impacts on the results. It will be demonstrated that the energy absorbed by the absorber tube increase strongly with longitudinal tilt angles, and the primary cost increases weakly with longitudinal tilt angles, while the energy-to-area ratio decreases.

A study of the effect of the longitudinal movement on the performance of small scale linear Fresnel reflectors

The sizing of a small-scale linear Fresnel reflector directly influences its primary cost as well as the annual energy output and, hence, its financial attractiveness. In addition, the area required for its installation is a critical parameter in most of the applications. This paper presents the analysis of the effects of the longitudinal movement on the performance of small-scale linear Fresnel reflectors. Our design, patented in year 2017, shows to be really innovative when compared to the existing designs shown in the literature. The three-movement option marks the novelty of the design. The effect of three parameters (i.e. energy absorbed by the absorber tube, primary cost, and reflector area ratio) is evaluated for two locations in Europe. Different configurations are analyzed and compared with the typical configuration of a large-scale linear Fresnel reflector. Numerical simulations were carried out using a MATLAB code to calculate the energy absorbed by the absorber tube, the primary cost, and the reflector area ratio. The comparison of the configurations provided insight into how latitude impacts on the results. It will be demonstrated that both the energy absorbed by the absorber tube and the primary cost increase with longitudinal movement, while the reflector area ratio decreases.

Cost estimation relationships of a small scale linear Fresnel reflector

This paper presents a cost estimating relationship (CER) of a novel small scale linear Fresnel reflector (SSLFR). The CER has been developed analyzing in detail the manufacturing processes of the SSLFR, its parameters, and the possible sub-components. As a result of this analysis, the SSLFR has been divided into 8 sub-components: fixed and mobile structures, movement units, mirror units, secondary reflector system, tracking system, assembly, and foundation. These sub-components are described in detail and designed using Autodesk Inventor, specifying manufacturing materials and processes. The study includes a full stress analysis of the sub-components, considering self weight, snow loads, and wind loads. For each sub-component an estimate of the primary costs is presented and also a relationship between the cost and the geometric parameters of the SSLFR. The primary costs considered include material, labor, and tooling costs. A numerical example shows the suitability of the proposed approach.

Optimization of the distribution of small scale linear Fresnel reflectors on roofs of urban buildings

• We present a new optimization method, related to the packing mathematical problem. • The objective is to maximize the collection area considering gaps and shadows. • The influence of the form and orientation of the available roof area is analysed. • The algorithms present good convergence and time efficiency figures. This paper analyses the optimization of the distribution of small-scale linear Fresnel reflectors on roofs of urban buildings. The effects of the two major design parameters (i.e., the form and orientation of the available roof area) on the performance of the reflectors are assessed. We present three new algorithms, related to the classical packing mathematical problem, to develop the optimization method. As decision variables, we use the mirror length and the mirror field width (bounded between upper and lower bounds), jointly with the spacing arrangement of the reflectors. The specific objective is to maximize the collection area considering gaps and shadows. To this end, we will optimize the arrangement, number and dimensions of the reflectors. Finally, we present examples based on real cases and analyse the convergence and accuracy of the algorithms, as well as the required computational effort.

Development of a fiber daylighting system based on a small scale linear Fresnel reflector: Theoretical elements

This paper describes the details of the design of a small scale linear Fresnel reflector (SSLFR) applied to a daylighting system based on optical fiber bundles (OFBs). This study shows the influence of the SSLFR design parameters (mirror width, mirror length, reflector cavity height, and number of mirrors) and the parameters of the optical fiber. A new reflector cavity is designed, consisting of two right trapeziums. Each trapezium collects the incident solar irradiance of the mirrors located at each side of the central mirror. The reflector cavity has two focal points, located in the middle of the aperture of each trapezium. A MATLAB code was developed in order to obtain the optical efficiency of the new reflector cavity and numerical simulations are presented. Two SSLFR configurations, C1 and C2, are studied. C1 is the configuration used in large-scale LFRs and does not consider lateral movement of the OFBs, as is the case in configuration C2. Each of these configurations is analyzed considering the optimal length and longitudinal position of the OFB. Numerical simulations are presented for both configurations using the MATLAB environment. Power consumption based calculations are carried out using the lumen method and the potential electric energy saving is evaluated. The illumination levels obtained are then compared using the lighting design software DIAlux, a free software widely used as a planning tool by lighting designers. The results show a considerable electric energy saving with configuration C2, although configuration C1 also presents good energy savings.

Parametric study of the small scale linear Fresnel reflector

Abstract This paper addresses the influence of the transversal and longitudinal parameters in the performance of a small scale linear Fresnel reflector (SSLFR) without longitudinal movement. The main purpose of this study is to show the influence of the design parameters (receiver height, mirror length, and mirror width) on the energy absorbed by the absorber tube. In addition, the influence of these parameters on the shading of the absorber tube is also analysed. Different configurations are analysed regarding the longitudinal angle that the mirrors and the absorber tube form with the horizontal plane. Each of these configurations is analysed considering the optimal length and longitudinal position of the absorber tube. Numerical simulations show the influence of mirror width, mirror length, and receiver height on the energy absorbed. The simulations allow us to analyze the monthly variation of this influence throughout the year, considering also the effect of the latitude. A sensitivity analysis is also carried out in order to evaluate the importance of the parameters.

Theoretical elements for the design of a small scale Linear Fresnel Reflector: Frontal and lateral views

This paper addresses the problem of the mathematical design of a Linear Fresnel Reflector, specifically the design of a reflector concentrator with flat mirrors and a single absorber tube. The mathematical aspects of the design, i.e., the number, width and position of the primary mirrors and the height, length and relative position of the single absorber tube, are analysed. The optimization of the relative position with respect to the primary reflectors and the size of the single absorber tube are both addressed, further analysing up to 12 different configurations. To do so, both the frontal and lateral view of the structure are taken into account. The lateral optical performance factor analysed here, has been overlooked until now, as it may be insignificant in large-scale concentrators. It is shown in this paper that it is a key aspect in medium- and small-scale concentrators, the most common in applications in the Household Sector like, for example, micro-cogeneration. Finally, a number of numerical simulations performed in a custom-designed program compiled using Mathematica® is presented. At the time of this writing, a prototype is being built at CIFP in La Felguera, Asturias, Spain.