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Optimizing reflector orientation for a solar panel at various latitudes

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Contents

Contributors[edit]

S. Novia Berriel Anup Nair

Intro[edit]

The angle of incidence of solar rays is different at different latitudes. Therefore, using the same angle of inclination for concentrators will not help in acquiring best solar energy capture. What we aim to do in this project is obtain the optimal positioning of concentrators for 6 cases of latitude ranging from 10-60 degrees with an increment of 10 degrees. For each of the latitude cases, we will consider 9 inclination angles of the PV panels ranging from 0-90 degrees with an increment of 15 degrees and test the position of concentrators aiming to obtain best energy yield. We will simulate 6 angles for the concentrators ranging from 10-60 degrees with 10 degrees increment to find the optimal solution. We ultimately want to generate a thumb of rule from this experiment.

Searches[edit]

Google Scholar:

  • low concentration solar reflectors
  • pv reflector for shaded panels
  • planar reflector for shaded solar panel
  • booster reflector

Web of Science:

  • (pv OR solar) AND planar AND reflector

IEEE Xplore:

  • (pv OR solar) AND reflector

Literature Review[edit]

The papers reviewed for the completion of this project have been listed below in chronological order of publication. Included are brief summaries of each.

Enhanced solar energy collection using reflector-solar thermal collector combinations - 1975[1][edit]

Abstract - The amount of direct light gathered by a combination of reflector plus flat-plate collector has been analyzed. The calculations were done allowing variable reflector and collector orientation angles, variables latitude, and arbitrary sun hour angle away from solar noon. The effects of reflection and transmission losses and of polarization of the incident light were included. Correction was also made for the finite size of the reflector. It was found that the optimum orientation has the collector plane almost perpendicular to the plane of the reflector. This optimum orientation is approximately independent of the sun's azimuthal dependence. The optimum reflector angle is found to be between 0° and 10° above the horizon for winter solar conditions. For typical winter operating conditions the enhancement in light gathering power for direct solar radiation is about a factor of 1·4–1·7. This results in an effective increase of 100% in the useful winter heat output from a practical reflector-collector combination with a reflector angle of 0°, over the useful heat output obtained with an optimally oriented simple flat-plate collector. An approximate calculation was also made of the overall enhancement in useful heat output for diffuse solar radiation; an increase by a factor of about 1·5 is predicted. Comparison with the preliminary analysis of the performance of the Coos Bay, Oregon solar house shows substantial agreement with the predictions of the present analysis.

  • calculations for various angles, latitudes and sun angles.
  • collector orientation perpendicular to reflector plane is optimum. Independent of time of day.

Collector performance enhancement with flat reflectors - 1975[2][edit]

Abstract - The use of diffuse and specular flat reflectors to enhance the performance of flat-plate solar collectors has been explored by means of Fortran routines which optimize the size, shape, and placement of reflector and collector. Configuration factors for systems with a diffuse reflector and a collector whose absorptance varies with incidence angle are presented. Specular reflectors are more effective than diffuse reflectors, and, if south-facing, should be used with collectors which are elongated in the east-west direction. Design curves for the specific system of horizontal collector and south-facing reflector are presented. In this system, a moderately sized reflector can increase the midwinter yield per unit collector area by several times.

  • model for horizontal collector with top-reflector(south facing)
  • diffuse and specular reflectors
  • specular more effective

The use of planar reflectors for increasing the energy yield of flat-plate collectors - 1977[3][edit]

Abstract- A mathematical model to simulate the performance of flat-plate collector-reflector systems is presented. First the collector energy balance is modified to account for the reflected energy. Then the exchange area for a diffuse reflector is obtained by integrating over both reflector and collector surfaces. For the specular reflector, the collector area exposed to reflected radiation is calculated from geometrical relations. Shading effects are also found from the system geometry. Fair agreement is obtained between the model and some experiments on a water heating collector in Brisbane, Australia. Finally, the model is used to predict the annual performance of a water heating system with several values of the reflector angle.

  • flat plate collectors tested (solar thermal collection)
  • diffuse reflectors found to have insignificant effect
  • mathematical calculation approach

Augmented solar energy collection using different types of planar reflective surfaces; theoretical calculations and experimental results - 1978[4][edit]

Abstract - The use of planar reflective surfaces can substantially improve the performance of both active and passive solar collectors. In this paper the results of theoretical calculations and experimental tests are presented on the use of different types of flat reflective surfaces to increase the collection of solar energy by flat collectors. Specular, diffuse, and combination specular/diffuse reflective surfaces are discussed. This present work differs from that of other investigators principally in that an attempt has been made to describe the reflective properties of surfaces in more generalized terms than simple specular or simple diffuse. Most real surfaces possess a combination of specular- and diffuse-like reflectivities. The reflectivity properties of a given surface can be measured in the laboratory as a function of incident and reflected angles, and these measured reflective properties can be used in the computer model to predict the increase in collector performance with such a reflector. Thus outdoor tests of a given reflector can be avoided if desired, and yet it is possible to make an estimate of the reflector's contribution to the collector's overall performance. Theoretical calculations of collector energy inputs were done for several distinct types of reflecting surfaces. These calculations based on indoor laboratory measurements of the reflective properties of the surfaces, were compared with experimental results obtained from an outdoor simulation apparatus. Predictions of system performance were made for various collector/reflector configurations, and compared with the performance of an optimally oriented collector without a reflector.

  • Type I Specular Alcoa Alzak aluminum sheet
  • Plywood sheet painted with good quality exterior white latex paint
  • Plywood sheet painted with inexpensive Paint Pot Chrome Aluminum 30 spray paint
  • A 1/4" plate-glass PPG back-surface silvered mirror

Effect of off-south orientation on optimum conditions for maximum solar energy absorbed by flat plate collector augmented by plane reflector - 1980[5][edit]

Abstract - A complete analysis of the off-south oriented, simple flat plate collector, augmented by flat sheet specular reflector, is developed. The enhancement of heat flux absorbed by solar collector due to the use of reflector is calculated as a function of solar altitude and azimuth angles, off-south orientation angle of collector and relative sizes and tilt angles of both collector. The shading effect due to the presence of the reflector is considered in the analysis. The collector and reflector variables are optimized for maximum solar energy flux absorbed by the collector during a pre-specified period of time. The Hooke and Jeeves optimization technique has been used in the analysis.

  • Investigation for off-south collector orientation. Analysis for 21.5°(Jedah)
  • Divide collector plane in different areas - optimized individually to get max energy yield sum.
  • Improvement in System performance if reflector-collector tilt angle changed once a year(min).
  • Divides year into two - Oct-Mar(winter) and rest(summer)

Planar concentrators for flat-plate solar collectors - 1981[6][edit]

Abstract- A systematic study has been made of the effectiveness of planar specular reflectors for solar energy collectors. Two daily averaged indices of performance were used. One, the area ratio, indicates the amount by which the reflector extends the effective receiver area. The other is the enhancement factor, which is used to compare the energy received by an augmented collector with that by a reference collector at optimum tilt.

A reflector can be mounted either above or below a flat-plate collector. Both combinations are evaluated fully, by varying separately the angular position and dimensions of the reflector and of the collector. The principal parameters are identified and the main characteristics summarised as a series of performance curves. These curves provide an easy method for determining optimum reflector geometries.

Use of the performance curves may be extended to obtain the configuration of the two reflectors in a trough concentrator. This also allows the single-reflector system to be compared directly with the trough concentrator. Evidence is presented which shows the advantages of an asymmetrical trough configuration over a symmetrical concentrator.

  • performance influenced primarily by the reflector/cover width ratio
  • reflector angular position and collector tilt also important
  • optimum angle of reflector varies a lot with seasonal movement of sun

Stationary reflector-augmented flat-plate collectors - 1981[7][edit]

Abstract-A general procedure for determining the optimum geometry of a reflector-augmented solar collector which produces a desired pattern of flux-augmentation is described. The example used for illustration is a stationary collector whose winter performance is to be improved. Consideration of both a flat-plate collector with a bottom reflector and one with a top reflector led to distinct differences in their optimum configuration and performance being identified. Since either systems can be used to augment winter flux, a criterion for selecting the appropriate system is given. This criterion is based on the displacement in collector tilt from latitude inclination.

  • performance factors - reflector width ratio, reflector angle, panel tilt angle from latitude
  • performance curves to decide b/w top- and bottom-reflectors.
  • unity reflector width ration suggested.

Effect of concentration on the performance of flat plate photovoltaic modules - 1984 [8][edit]

Abstract - The effect of low concentration ratios on the performance of passively cooled conventional photovoltaic modules has been investigated. Peak power outputs of up to 140 W per square metre of module area have been obtained with single crystal modules of high cell packing factor using a 2.2X plane mirror concentrator. Both cell temperature and series resistance losses are found to be important in limiting module efficiency. Performance simulations indicate that the use of a 4X concentrator with polar axis tracking will increase annual peak output by a factor of 3.2 over that of a fLxed fiat plate module

  • Reflectors of geometric width: 2.2, 1.6 and 1 x
  • Max Effective Concentration of 1.85
  • Temperature increase of cell: 1x - 28-32°C, 1.6x - 40-45°C, 2.2x - 50-55°C
  • Effect of concentration ratio and cell temperature on fill factor
  • Polar axis tracking with concentration modelled (Perth, Western Australia)
  • Max output at 4x concentration
  • 3.2 times greater than fixed 1x panel

Collector, collector-reflector systems—an an analytical and practical study, Energy Conversion and Management - 1986[9][edit]

This paper investigates the use of planar reflectors which substantially improve the performance of flat-plate solar collectors. The experimental setup includes a collector panel and collector-reflector system with maximum useful heat gain. A computer simulation of the analytical and experimental recordings was made to study the comparative features of the systems. The performance study is illustrated as a function of solar altitude, azimuth angles, hour angle and the relative sizes and tilt angles of both the collector and reflector. The use of a booster mirror produces an increase of 10–15°C in water temperature. The shading effect due to the presence of the reflector has also been considered in the present analysis.

  • specular reflectivity 0.8
  • reflector-on-collector shading effect neglected but not vice-versa
  • 9.07% incr. in solar irradiation - one adjustment a year

Enhancement of solar energy on flat-plate collector by plane booster mirrors - 1988[10][edit]

Abstract - A comprehensive analysis of a system consisting of a flat-plate collector augmented with two reflectors is presented. The model facilitates the prediction of the total energy absorbed by the collector at any hour of the day for any latitude for random tilt angles and azimuth angles of the collector and reflectors. The effect of overlapping of the shadows of the two reflectors has been taken care of. The model was numerically simulated for conditions prevailing in three different Indian stations. For each station, the variation of the total input energy, with tilt angles of the reflectors was studied for three different months for the case of collector tilt angle (1) equal to zero and (2) equal to latitude

  • Enhancement of solar energy on flat-plate collector by plane booster mirrors
  • system simulation for three different locations in india
  • Reflector - 30°-110°(for top) 0°-90°(for bottom)
  • Max enhancement in dec - more with incr. in latitude

Modeling daylight availability and irradiance components from direct and global irradiance - 1990[11][edit]

Abstract - This paper presents the latest versions of several models developed by the authors to predict short time-step solar energy and daylight availability quantities needed by energy system modelers or building designers. The modeled quantities are global, direct and diffuse daylight illuminance, diffuse irradiance and illuminance impinging on tilted surfaces of arbitrary orientation, sky zenith luminance and sky luminance angular distribution. All models are original except for the last one which is extrapolated from current standards. All models share a common operating structure and a common set of input data: Hourly (or higher frequency) direct (or diffuse) and global irradiance plus surface dew point temperature. Key experimental observations leading to model development are briefly reviewed. Comprehensive validation results are presented. Model accuracy, assessed in terms of root-mean-square and mean bias errors, is analyzed both as a function of insolation conditions and site climatic environment.

  • Models for predicting relevant quantities like solar energy in short intervals and availability of light - can be used for specific user needs.
  • First model relates irradiance value to the light from sun/sky as comprehended by the human eye.
  • Second approximates illuminance and irradiance for horizontally surface tilted.
  • Third - angular distribution of light instead of the diffuse values.

A Comprehensive Physical Model for Light Reflection - 1991 [12][edit]

Abstract - A new general reflectance model for computer graphics is presented. The model is based on physical optics and describes specular, directional diffuse, and uniform diffuse reflection by a surface. The reflected light pattern depends on wavelength, incidence angle, two surface roughness parameters, and surface refractive index. The formulation is self consistent in terms of polarization, surface roughness, masking/shadowing, and energy. The model applies to a wide range of materials and surface finishes and provides a smooth transition from diffuse-like to specular reflection as the wavelength and incidence angle are increased or the surface roughness is decreased. The model is analytic and suitable for Computer Graphics applications. Predicted reflectance distributions compare favorably with experiment. The model is applied to metallic, nonmetallic, and plastic materials, with smooth and rough surfaces.

  • Light reflection explained
  • Components of light reflection

Energy contribution by booster mirrors[13][edit]

Abstract - The standard textbooks and research publications hint at possible methods for computing the energy contribution by plane booster mirrors but do not elaborate the specific stages of a computational procedure. We hope the algorithm presented in this paper fills this gap. An algorithm to assess the contribution of solar energy on a horizontal receiver by plane booster mirrors is discussed in this paper. The choice of horizontal receiver reduces the number of variables and, therefore, simplifies the analysis and enhances understanding of the phenomenon of energy contribution by booster mirrors. The original impetus for this work was to study the input variables in a solar cooker, widely distributed in India. In these cookers, the aperture is invariably horizontal and a single plane booster mirror is the standard complement

  • theoretical model created for using (top, bottom, or wing mirrors)
  • 3d model determines area illuminated and shadowed by reflector
  • computer code used beam radiation values calculated by Hottel's (model of clear sky atmospheric transmittance)
  • algorithms can be applied to 3d model for PV reflector

External reflectors for large solar collector arrays, simulation model and experimental results - 1993[14][edit]

Abstract - A model for the calculation of incident solar radiation from flat- and CPC-shaped external reflectors onto flat plate solar collector arrays has been developed. Assuming an infinite length of the collector/reflector rows, the basic calculations of incident radiation in the collector plane from the reflector become very simple. The direct radiation from the sun is projected into a vertical plane perpendicular to the collector and reflector plane. The incident radiation onto the collector, including corrections for shadowing and lost radiation above the collector, can then be calculated using 2-D geometry. For very short collector/reflector rows a 3-D model is given for correction for the loss of specular radiation in the east west direction. The diffuse radiation is assumed to be isotropic. The diffuse radiation in the collector plane is calculated using view factors. CPC-shaped reflectors can be treated with the same models by introducing an equivalent flat reflector. The incidence angle for the solar radiation from the reflector onto the collector is in most cases higher than the incidence angle for the radiation directly from the sun. Therefore the incidence angle characteristics of the collector glazing and absorber become more important in this application. Equations are given for the incidence angles for diffuse and beam radiation. An annual performance increase of over 30%, 100–120 kW h/m2, has been measured for aged (four operating seasons) flat reflectors in the Swedish climate. With a CPC-shaped reflector and new reflector materials, a performance increase of up to 170 kW h/m2 is not unrealistic. This means that the collector and ground area requirement can be reduced by more than 30% for a given load.

  • 2-D and 3-D models of panel/ reflector pairs
  • gives limiting angles for solar altitude for a particular reflector
  • four solar altitude cases for planar reflector, three for CPC

Performance of east/west plane booster mirror - 1994[15][edit]

Abstract - A detailed analysis of the energy contribution by the east/west booster mirror on a horizontal receiver is presented in this paper. The east/west mirror is known to make the energy flux distribution flatter in a day. A quantitative analysis of the degree of flatness of the energy flux distribution due to the east/west mirror, on the basis of flux ratio, is made. It is observed that the energy enhancement factor or boost factor due to the east/west mirror is significant all through the year. These factors make the east/west mirror more attractive in photo-voltaic power generation applications. An algorithm based on a vectorial approach and the laws of reflection developed by the authors is used in the present analysis.

  • East/west mirrors are used (FP reflector on top of collector)
  • thermal system and looks into the performance increase)
  • optimal mirror angle calculated (latitudes of 0 to 40 N)

Modeling the solar irradiation on flat plate collectors augmented with planar reflectors - 1995[16][edit]

Abstract - An analytical model has been developed and used to determine solar irradiation on flat collectors augmented with planar reflectors. The model uses measured insolation data from the NREL National Solar Radiation Data Base. In addition the model accounts for direct and reflected components of beam, diffuse and ground reflected insolation, considers finite length systems, accounts for shading of the collector by the reflector, and considers different configurations of the reflector relative to the collector. Thus the model represents an extension and refinement of many previous models. Computer simulations have been carried out over different time spans to assess the effects of including these features. In general, the addition of reflectors enhances the radiation received by the collector. Reflected beam radiation is the major contributor to the enhancement, although reflected sky diffuse and ground reflected radiation can be significant in many instances. To optimize effectively the design of the system with respect to selecting tilt angles and specifying a reflector-above or below-collector configuration requires proper modeling of the energy received by the collector system. Finite length analysis used in the model enables the optimization of reflector size relative to that of the collector. The model presented can be the basis of an analytical design tool for optimizing the design of a variety of reflector-enhanced solar energy collection systems.

  • Increase in irradiation with planar reflector - finite size system
  • Includes model for sky diffuse and ground reflected component, shading effects
  • top-reflector blocks sky diffuse and bottom-reflector blocks ground reflected

Effect of flat reflectors on the performance of photovoltaic modules - 2000[17][edit]

Abstract- To convert solar energy directly into electrical energy, photovoltaic modules are widely being used. Different techniques such as retrofitting of reflectors and concentrators are adopted to increase the amount of radiation flux falling on the module and the output of the module thereby increases. The present work investigates the effect of flat reflecting materials such as flat mirrors, shinny aluminum and white tiles on the performance of a PV module. The performance was compared with an identical module without such a reflector; both were studied under the same environmental conditions. It was found that the performance depends on the sky condition and has no advantage on a rainy or cloudy day. The reflector fitted module output based on maximum power point showed a significant increase, and there was also an increase in temperature of the module.

  • reflectors on top, bottom, and sides of panel
  • mirrored reflectors give most improvement, but most temp increase

Optimization of operational and design parameters of plane reflector-tilted flat plate solar collector systems - 2000 [18][edit]

Abstract- Due to the increased interest in the utilization of solar energy, it is essential to enhance the energy collection of solar energy devices. In this paper, a theoretical analysis of the instantaneous, daily, and yearly enhancement in solar energy collection of a tilted flat-plate solar collector augmented by a plane reflector is developed. The shadow effect due to the reflector on the collector is considered in the analysis. A FORTRAN computer program has been constructed based on the analysis in order to study the effect of different operational and design parameters of plane reflector-tilted flat-plate solar collector system on the collector solar energy collection. These parameters include collector-reflector system orientation and tilt angles, collector elongation ratio, and reflector overhang ratio.

  • top-reflector - angled towards the sky
  • specular reflectivity of 0.88
  • Considers only a single panel, therefore edge losses
  • Geometric interpretation including plane transformations are discussed
  • Summer boost of 5%-10% winter of 30%-35%
  • System not optimized for yearly boost

The enhancement of energy gain of solar collectors and photovoltaic panels by the reflection of solar beams - 2002[19][edit]

Abstract - The use of reflecting panels for increasing energy gain, as demonstrated by use in greenhouses, was applied to conventional solar (thermal) collectors and photovoltaic panels. Several types of reflectors were considered in order of increasing sophistication, cost and enhancement coefficients. Calculations showed that the increase in energy gain ranged from 20 to 250%, depending on the type of equipment and season.

  • 5 types of flat-reflectors for increased reflected radiance. Heat and electricity not estimated.
  • Type1 - same dimension as receiving surface.
  • Type2 - incli. adjusted in type 1 so (x/a)=1.
  • Type3 - rotating axis for reflector; angle should be = (90+θ/2); θ=azimuth angle of sun; entire receiving surface not covered.
  • Type4 - Correction for type3; flaps for reflector; reflected beam width increased accordingly.
  • Type5 - receiver angle 90° wrt vertical inclination & sun's azimuth angle.
  • Rotating reflector better than changing inclination.

Concentrating solar module with horizontal reflectors - 2003[20][edit]

Abstract - A non-sun-tracking concentrating solar module is described that is designed to achieve photovoltaic (PV) systems with higher generation power density. The proposed concentrating module consists of a solar panel having a higher tilt angle than that of a conventional one and with a solar reflector placed in front of the solar panel on a downward inclination angle towards the panel. As a result of this configuration, the solar panel receives reflected as well as direct sunlight so that maximum irradiance and short-circuit current were increased. This configuration is expected to reduce the area required for solar panels, resulting in lower cost PV system.

  • proposed module and reflector setup
  • bottom reflector - width is 2x, length is 2.7x that of panel
  • test conducted in solar simulator
  • tests conducted outdoors - short circuit measured throughout day (compared to conventional module)
  • power output determination did not seem to take into acount efficiency drops - estimated power generation increase of 1.5 times

Optical Design and Characterization of Solar Concentrators for Photovoltaics - 2005 [21][edit]

AbstractStationary solar energy concentrators are a promising option for decreasing the price of photovoltaic electricity. This thesis studies stationary concentrators in PV/Thermal applications. The studied systems are parabolic troughs intended for building integration

  • A thorough thesis
  • Covers different reflectors for concentration
  • Mathematical models to represent them

Feasibility study of one axis three positions tracking solar PV with low concentration ratio reflector - 2007[22][edit]

Abstract - A new PV design, called “one axis three position sun tracking PV module”, with low concentration ratio reflector was proposed in the present study. Every PV module is designed with a low concentration ratio reflector and is mounted on an individual sun tracking frame. The one axis tracking mechanism adjusts the PV position only at three fixed angles (three position tracking): morning, noon and afternoon. This “one axis three position sun tracking PV module” can be designed in a simple structure with low cost. A design analysis was performed in the present study. The analytical results show that the optimal stopping angle β in the morning or afternoon is about 50° from the solar noon position and the optimal switching angle that controls the best time for changing the attitude of the PV module is half of the stopping angle, i.e. θH = β/2, and both are independent of the latitude. The power generation increases by approximately 24.5% as compared to a fixed PV module for latitude ϕ < 50°. The analysis also shows that the effect of installation misalignment away from the true south direction is negligible (<2%) if the alignment error is less than 15°. An experiment performed in the present study indicates that the PV power generation can increase by about 23% using low concentration (2X) reflectors. Hence, combining with the power output increase of 24.5%, by using one axis three position tracking, the total increase in power generation is about 56%. The economic analysis shows that the price reduction is between 20% and 30% for the various market prices of flat plate PV modules.

  • switching angle and stopping angle independent of latitude
  • reflectors at 60 degrees to panel
  • power increase with reflectors

Performance Enhancement of PV Solar System by Diffused Reflection - 2009[23][edit]

Abstract - Various methods are being adopted to enhance the performance of a solar panel. The most common method is to track the sun for performance enhancement. Such method needs complicated control and drive circuits for implementation. Also, the power required for the tracking motor has to be provided by the solar panel and the battery system. Although better performance is achievable by the sun tracker, higher cost and frequent maintenance are required. In this paper, performance enhancement of solar panels has been experimented utilizing diffused reflectors. Application of diffused reflectors is cheap, simple and does not require any additional equipments or devices. Simple white reflectors can be used to optimize the performance of the solar panel. Experimental results indicate appreciable enhancement in the overall output of the solar panel. For comparative study, experimental readings were simultaneously taken with i) sun tracking, ii) the panel aligned at 23.5° with the horizontal using diffused reflectors and iii) the panel aligned at 23.5° with the horizontal without diffused reflectors. Comparative results depicted for different conditions show encouraging enhancement of the performance of the solar panel.

  • reflectors placed on north-south sides of panel at 25° with vertical
  • diffuse reflectors = maybe better than sun tracking
  • in cloudy weather short circuit output current shows higher values w/ diffuse than with no reflector

Optimizing Reflection and Orientation for Bifacial Photovoltaic Modules - 2009[24][edit]

Abstract - Currently, the world market for photovoltaic (PV) solar panel technology is expanding rapidly. The increasing market for PV panels reflects the increasing demand for a clean, reliable energy solution and indicates that PV panels may be the method of choice for supplementing today’s global energy needs. Although PV solar panel production is rising, PV panels are still a relatively new and high-priced technology. There remains a need for a commercially-viable method of implementing residential-scale photovoltaic systems for consumer homes. The purpose of this study is to ultimately maximize the irradiance (solar radiation energy) incident on a geometrically constrained 6.84-kilowatt photovoltaic array system, and thereby maximize the energy production. In this study, the optimum height and angle of bifacial (two-sided) PV modules are investigated both analytically and experimentally. Analytical methods utilize the sun’s position and average irradiance throughout the course of a day. Data is collected under actual, outdoor sunlight conditions. Furthermore, stationary flat reflectors with specular (mirror-like) and diffuse (light-scattering) reflection are used to experimentally characterize the amount of sunlight directed on the back face of the PV modules. By validating the theoretical results with experimental evidence, the analytical model can be used to accurately predict the optimum orientation and reflective material for any location and time of year. The findings suggest that a diffusely scattering reflector is a cost-efficient solution for the proposed PV array design.

  • discusses flat reflectors and partial shading
  • reduction in power output proportional to area in shade
  • adjusts reflector for time of year
  • need for uniform irradiance

Modeling the performance of low concentration photovoltaic systems - 2010[25][edit]

Abstract - A theoretical model has been developed to describe the response of V-trough systems in terms of module temperature, power output and energy yield using as inputs the atmospheric conditions. The model was adjusted to DoubleSun® concentration technology, which integrates dual-axis tracker and conventional mono-crystalline Si modules. The good agreement between model predictions and the results obtained at WS Energia laboratory, Portugal, validated the model. It is shown that DoubleSun® technology increases up to 86% the yearly energy yield of conventional modules relative to a fixed flat-plate system. The model was also used to perform a sensitivity analysis, in order to highlight the relevance of the leading working parameters (such as irradiance) in system performance (energy yield and module temperature). Model results show that the operation module temperature is always below the maximum working temperature defined by the module manufacturers.

  • Modeling performance of DoubleSun V-trough concentrator (2 axis tracking)
  • Using MatLab to model
  • Model compared to data collected at WS Energia laboratory, in Portugal
  • 86% increase in power output, (25% from tracking, 50% from concentrator)
  • Temperatures lower in collected data compared to model (due to neglecting of radiative heat transfer from panels)

Influence of reflectance from flat aluminum concentrators on energy efficiency of PV/Thermal collector - 2010[26][edit]

Abstract - In this paper the results of the influence of reflectance from flat plate solar radiation concentrators made of Al sheet and Al foil on energy efficiency of PV/Thermal collector are presented. The total reflectance from concentrators made of Al sheet and Al foil is almost the same, but specular reflectance which is bigger in concentrators made of Al foil results in increase of solar radiation intensity concentration factor. With the increase of solar radiation intensity concentration factor, total daily thermal and electrical energy generated by PV/Thermal collector with concentrators increase. In this work also optimal position of solar radiation concentrators made of Al sheet and Al foil and appropriate thermal and electrical efficiency of PV/Thermal collector have been determined. Total energy generated by PV/Thermal collector with concentrators made of Al foil in optimal position is higher than total energy generated by PV/Thermal collector with concentrators made of Al sheet.

  • Measurements during July-Aug
  • upper concentrator at 10° and lower at 34° - increase in solar radiation intensity 43.6%(Al sheet) & 65.6%(Al foil).
  • total reflectane same for sheet and foil, but specular reflectance bigger for Al foil. Therefore, more electricity generated.

Optimal design of orientation of PV/T collector with reflectors - 2010[27][edit]

Abstract - Hybrid conversion of solar radiation implies simultaneous solar radiation conversion into thermal and electrical energy in the PV/Thermal collector. In order to get more thermal and electrical energy, flat solar radiation reflectors have been mounted on PV/T collector. To obtain higher solar radiation intensity on PV/T collector, position of reflectors has been changed and optimal position of reflectors has been determined by both experimental measurements and numerical calculation so as to obtain maximal concentration of solar radiation intensity. The calculated values have been found to be in good agreement with the measured ones, both yielding the optimal position of the flat reflector to be the lowest (5°) in December and the highest (38°) in June. In this paper, the thermal and electrical efficiency of PV/T collector without reflectors and with reflectors in optimal position have been calculated. Using these results, the total efficiency and energy-saving efficiency of PV/T collector have been determined. Energy-saving efficiency for PV/T collector without reflectors is 60.1%, which is above the conventional solar thermal collector, whereas the energy-saving efficiency for PV/T collector with reflectors in optimal position is 46.7%, which is almost equal to the values for conventional solar thermal collector. Though the energy-saving efficiency of PV/T collector decreases slightly with the solar radiation intensity concentration factor, i.e. the thermal and electrical efficiency of PV/T collector with reflectors are lower than those of PV/T collector without reflectors, the total thermal and electrical energy generated by PV/T collector with reflectors in optimal position are significantly higher than total thermal and electrical energy generated by PV/T collector without reflectors.

  • Experimental and analytical
  • South oriented (movable tilt) collector at 45° - 43°19'N, Serbia
  • Top- and bottom- Al reflector
  • total, diffuse and specular reflectance - 0.65–0.82, 0.52–0.61 and 0.13–0.21, respectively.
  • upper and bottom reflector angles 0° and 36°, respectively - sun peak feb-oct
  • Additional cost 10% - energy gain 20.5-35.7%

Theoretical analysis of solar thermal collector with a flat plate bottom booster reflector - 2011[28][edit]

Abstract - A theoretical analysis of a solar thermal collector with a flat plate bottom reflector is presented. The bottom reflector extends from the lower edge of the collector. The variations of daily solar radiation absorbed on the collector with inclinations from horizontal for both the collector and reflector throughout the year were predicted, and the optimum inclinations of the collector and reflector which maximize the daily solar radiation absorbed on the collector were determined for each month at 30°N latitude. The effects of the size of the collector and reflector on the daily solar radiation absorbed on the collector were also investigated. The optimum collector inclination is lower in summer and higher in winter, while the optimum reflector inclination is higher in summer and lower in winter. The average daily solar radiation absorbed on the collector throughout the year can be increased about 20%, 27% and 33% by using a bottom reflector if the ratio of reflector length to collector length is 0.5, 1.0 and 2.0, respectively, when the collector’s length is equal to its width.

  • theoretical analysis - bottom reflector @ 30°N
  • optimum collector incln. higher-winter and lower-summer. opp. for reflector
  • opt incln. for both incr. with collector L/W ratio.
  • solar radiation decr. with L/W but incr. with Lr/Lc.

Solar thermal collector augmented by flat plate booster reflector: Optimum inclination of collector and reflector - 2011[29][edit]

Abstract - In this report we present a theoretical analysis of a solar thermal collector with a flat plate top reflector. The top reflector extends from the upper edge of the collector, and can be inclined forwards or backwards from vertical according to the seasons. We theoretically predicted the daily solar radiation absorbed on an absorbing plate of the collector throughout the year, which varies considerably with the inclination of both the collector and reflector, and is slightly affected by the ratio of the reflector and collector length. We found the optimum inclination of the collector and reflector for each month at 30°N latitude. An increase in the daily solar radiation absorbed on the absorbing plate over a conventional solar thermal collector would average about 19%, 26% and 33% throughout the year by using the flat plate reflector when the ratio of reflector and collector length is 0.5, 1.0 and 2.0 and both the collector and reflector are adjusted to the proper inclination.

  • opt. inclination yearlong (collector+flat top reflector) for 30°N - theoretically.
  • new graphical method for irradiation through reflection.
  • Angle of reflector inclination - forward in winter/backward in summer (less than 30°). Directly affected by ratio of collector & reflector length.
  • Collector Incli. - lower in summer/higher in winter. Not affected much by length ratio.

Model of loss mechanisms for low optical concentration on solar photovoltaic arrays with planar reflectors - 2011[30][edit]

Abstract - The use of low optical concentration with planar reflectors represents a relatively simple method for improving solar photovoltaic (PV) specific efficiency. A coupled optical and thermal model was developed to determine the effects on yearly performance of a planar concentrator on array-scale solar PV installations. This model accounts for i) thermal, ii) angle of incidence, iii) reflectivity, and iv) string mismatch loss mechanisms in order to enable informed design of low optical concentration systems. A case study in Canada is presented using the model and the simulation results show that a planar reflector system installed on a traditional crystalline silicon-based PV farm can produce increases in electrical yield from 23-34% compared to a traditional optimized system and thus represents a potential method of achieving practical gains in PV system yield.

  • Framework for planar concentrator model - Independent of PV module.
  • Accounts for loss - includes thermal, incident angle, reflectivity and string mismatch
  • Case Study (with c-Si PV) - yield by 23-34%. Say better gains than tracking or parabolic concentrators.

Optimal position of flat plate reflectors of solar thermal collector-2011[31][edit]

Abstract - In this paper the results of the influence of position of the flat plate reflectors made of Al sheet on thermal efficiency of solar thermal collector with spectrally selective absorber are presented. Analytical and experimental results on determination of the optimal position of flat plate solar reflectors during the day time over the whole year period are shown. Both numerical calculation and experimental measurements indicate that optimal angle position of the bottom reflector is the lowest (5°) in December and the highest (38°) in June for collector fixed at β = 45° position. The thermal efficiency of thermal collector without reflectors and with reflectors in optimal position has been determined. Though the thermal efficiency of thermal collector decreases slightly with the solar radiation intensity, the total thermal energy generated by thermal collector with reflectors in optimal position is significantly higher than total thermal energy generated by thermal collector without reflectors. These results show the positive effect of reflectors made of Al sheet and there is an energy gain in the range 35–44% in the summer period for thermal collector with reflectors, which is expected to reduce the cost pay back time.

  • Experiment Setup: top- and bottom- Al sheet reflectors; collector 45 degrees inclination. Coordinates (43°19′N, 21°54′E)
  • Analytical model for day time - whole year | Compared with and w/o reflectors
  • Total solar irradiation = direct radiation (collector) + reflected radiation (top & bottom) + diffuse radiation (mathematical equations given)
  • Increased energy yield; decreased thermal efficiency.

Analytical model for solar irradiance near a planar vertical diffuse reflector – Formulation, validation, and simulations - 2013[32][edit]

Abstract- An analytical model is formulated for the irradiance on a surface (collector) with a rear (opposite the sun) planar vertical diffuse reflector, as is common for a lower roof on a multi-story building. The vast majority of research on solar reflectors has been for specular, or mirror, reflectors, with any diffuse reflections modeled about the specular reflection angle. This model is capable of calculating incident and reflected direct, diffuse, and ground-reflected radiation using components borrowed from the Hay, Davies, Klucher, Reindl (HDKR) irradiance model, and is easily implemented in any computation programming software capable of numeric integration. The model accounts for reflector edge effects and shading of diffuse and ground-reflected radiation by the reflector, but it does not account for shading of beam radiation by the reflector.

The model shows good overall agreement with experimental tests, and is three percentage points more accurate than a standard radiation model for tilted surfaces. The model indicates that a planar vertical diffuse reflector increases the irradiance at high clearness indices and low reflector incidence angles, and decreases the irradiance otherwise. Increasing the reflector height and decreasing the collector pitch and distance between the collector and reflector increases the irradiance during clear periods, but decreases the irradiance, to a lesser absolute extent, during cloudy periods. Annual simulations show a gain in winter insolation and a loss in summer insolation for an average collector/reflector, with an increase in annual insolation for collectors near high albedo reflectors.

  • very related to our project
  • discusses diffuse reflection from adjacent buildings
  • HDKR irradiance model used, most accurate

Performance improvement of solar module system using flat plate reflectors - 2014[33][edit]

Abstract- Photovoltaic (PV) modules based on silicon solar cells are widely used to convert solar energy into electrical energy. The energy output of these modules is very low due to their low power conversion efficiencies of approximately 15%. Reflectors are used to improve the power output of PV modules, by increasing the effective capture area. The performance of the solar panel with reflector depends mainly on three parameters namely length, tilt angle and reflectivity of reflector. Hence it is necessary to choose the optimum values of these parameters to attain maximum power output from the system. We have developed a model system to analyse the effect of reflector parameters on the overall power output. This has an arrangement for varying the tilt angle of the reflector. Also a simplified mathematical model was developed which is capable of estimating the optimum tilt angle for a particular reflector length, and the optimality of the tilt angles predicted by this model was verified using the above mentioned experimental setup. Finally, the suitability of various materials for use as reflectors was studied using the setup. Interestingly, paper based reflectors like bond paper and thermocole showed excellent results with increase in power output of more than 60%. Also, the cost per watt of the system is minimal when we use aluminium foil as the reflector at optimum tilt angle.

  • 400mW panel, 16cm reflector
  • mathematically estimates optimal angle for two reflectors attached

Variation of reflected radiation from all reflectors of a flat plate solar collector during a year - 2015[34][edit]

Abstract - In this paper the impact of flat plate reflectors (bottom, top, left and right reflectors) made of Al, on total solar radiation on a solar collector during a day time over a whole year is analyzed. An analytical model for determining optimum tilt angles of a collector and reflectors for any point on the Earth is proposed. Variations of reflectors' optimal inclination angles with changes of the collector's optimal tilt angle during the year are also calculated. Optimal inclination angles of the reflectors for the South directed solar collector are calculated and compared to experimental data. It is shown that optimal inclination of the bottom reflector is the lowest in December and the highest in June, while for the top reflector the lowest value is in June and the highest value is in December. On the other hand, optimal inclination of the left and right side reflectors for optimum tilt angle of the collector does not change during the year and it is 66°. It is found that intensity of the solar radiation on the collector increases for about 80% in the summer period (June–September) by using optimally inclined reflectors, in comparison to the collector without reflectors

  • The impacts of flat plate reflectors on solar radiation on the collector are given.
  • The results of the optimal inclinations of reflectors during the year are shown.
  • The solar radiation on the collector with reflectors is 80% higher in the summer.
  • This model may be applied on thermal, PV, PV/T and energy harvesting systems.

Photovoltaic System Performance Enhancement With Nontracking Planar Concentrators: Experimental Results and Bidirectional Reflectance Function (BDRF)-Based Modeling - 2013/2015 [35] [36][edit]

Abstract - Nontracking planar concentrators are a low-cost method of increasing the performance of traditional solar photovoltaic (PV) systems. This paper presents new methodologies for properly modeling this type of system using a bidirectional reflectance function for nonideal surfaces rather than traditional geometric optics. This methodology allows for the evaluation and optimization of specular and nonspecular reflectors in planar concentration systems. In addition, an outdoor system has been shown to improve energy yield by 45% for a traditional flat glass module and by 40% for a prismatic glass crystalline silicon module when compared with a control module at the same orientation. When compared with a control module set at the optimal tilt angle for this region, the energy improvement is 18% for both systems. Simulations show that a maximum increase of 30% is achievable for an optimized system located in Kingston, ON, Canada, using a reflector with specular reflection and an integrated hemispherical reflectance of 80%. This validated model can be used to optimize reflector topology to identify the potential for increased energy harvest from both existing PV and new-build PV assets.

  • Two papers Same name - 2nd derived from 1st
  • new irradiance model - BRDF based
  • calculate irradiance-then module output (Isc) | obtain cell temperature-estimate power
  • 2nd paper - optimal module arrangement for Kingston (44.2312° N, 76.4860° W) - energy yield 18% up

Experimental and numerical study of the influence of string mismatch on the yield of PV modules augmented by static planar reflectors - 2015[37][edit]

Abstract - Photovoltaic (PV) modules are generally installed by the application of empirical rules aimed at reducing shadows during the periods of high solar irradiation. A traditional installation on a horizontal surface results in largely spaced rows of modules with a relatively low tilt angle. The addition of inter-row reflectors results in more direct and diffuse flux transmitted to the cells. The “Aleph” (Amélioration de l'Efficacité Photovoltaïque) project aims to define clear rules for optimal settings of systems of PV module rows with fixed inter-row planar reflectors in a given location and under a given climate. Two PV technologies are tested for performance with this type of system: amorphous silicon (a-Si) and polycrystalline silicon (p-Si). This work combines experiments on panel behavior in an outdoor environment on the SIRTA (Site Instrumental de Recherche par Télédétection Atmosphérique) meteorology platform and a multiphysics numerical model used to couple all the important physical phenomena and accurately describe the system behavior. The model includes a ray tracing radiation/optics module based on the Monte-Carlo method, as well as an electrical module simulated in SPICE. This work presents the influence of the string mismatch losses, present at periods of heterogeneous illumination, on the yield of PV modules augmented by static planar reflectors.

  • Most relevant: part IV, Numerical Modeling
  • ray tracing: many models and formulas referenced, Hoang, Bourdin

New integrated simulation tool for the optimum design of bifacial solar panel with reflectors on a specific site - 2015[38][edit]

Abstract - The use of a commonly available planar reflector such as a plane mirror can boost the energy output of a bifacial solar panel effectively without increasing much in the overall cost. However, the actual energy yield from the solar panel in this case is dependent on the light reflected from the reflector and surrounding objects to the rear surfaces of the solar cells. The design of the bifacial solar panel with the reflector has to be optimized in order to achieve the maximum yield on a specific site setup. Therefore, a new simulation tool consisting of several open-source software packages with the bifacial solar cell model is developed to predict the yearly yield of the bifacial solar panel with the reflector accurately. The simulation tool includes the effects of the temperature changes in solar cells and the variation in solar irradiance incident on both front and rear sides at different time in a day, the manufacturing mismatch of the solar cells, and also the reflected light from the nearby objects. The simulation tool is verified experimentally and used to determine the optimum design of a site-specified bifacial solar panel that can achieve the maximum increase of 26% in yearly yield.

  • borrow simulation principles for our sim
  • simulates solar irradiance at a specific location
  • only bifacial solar panels

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