This literature review supported the following publications:

## Low Concentration

##### K.G.T. Hollands, "A concentrator for thin-film solar cells," Solar Energy, vol. 13, 1971, pp. 149–163.
• Discusses use of V-trough concentrators for PV
• Tracks seasonal but notdiurnal motion of sun – several times per year
• Direct-beam concentration factor determined as function of incidence angle of solar beam, side-wall reflectance and opening angle of trough.
• Firstly, it assumes the side walls to be perfectly specular, gray surfaces. Secondly, it restricts the trough geometries studied to those where, with the solar beam normal to the base, two conditions are met: (a) the base is uniformly irradiated; (b) no ray suffers more than one reflection.
##### R.M. Swanson, "The promise of concentrators," Progress in Photovoltaics: Research and Applications, vol. 8, 2000, pp. 93–111.

Abstract: This paper addresses the issue of why concentrator systems have not gained a significant market share. The history of concentrator development is reviewed, and the status of existing concentrator efforts outlined. A critical look at the requirements to propel concentrators to a prominent market role in large-scale power production is presented. Various concentrator and ¯at-plate PV system approaches are compared by computing the expected cost of energy, and conclusions are drawn as to what the best course of action will be. Concentrator systems are projected to be the lowest-cost, lowest-risk PV option for medium and large PV power plants.

• Discusses policies and history behind concentration in solar
• Growth of concentration and it's relation to the oil crisis of the 80s
• Discusses the future
##### J. Nilsson, "Optical Design and Characterization of Solar Concentrators for Photovoltaics," Lund Univeristy, 2005.
• A thorough thesis
• Covers different reflectors for concentration
• Mathematical models to represent them

## CPC

##### R. Winston, "Principles of solar concentrators of a novel design," Solar Energy, vol. 16, 1974, pp. 89–95.

Abstract--A new principle for collecting and concentrating solar energy, the ideal cylindrical light collector, has been invented. This development has its origins in detecting Cherenkov radiation in high energy physics experiments. In its present form, the collector is a trough-like reflecting wall light channel of a specific shape which concentrates radiant energy by the maximum amount allowed by phase space conservation. The ideal cylindrical light collector is capable of accepting solar radiation over an average ~8-hr day and concentrating it by a factor of -10 without diurnal tracking of the sun. This is not possible by conventional imaging techniques. The ideal collector is non-imaging and possesses an effective relative aperture (f-number)= 0.5. This collector has a larger acceptance for diffuse light than concentrating collectors using imaging optics. In fact, the etficiency for collecting and concentrating isotropic radiation, in comparison with a fiat plate collector, is just the reciprocal of the concentration factor.

## V-Trough

##### N. Fraidenraich, "Design procedure of V-trough cavities for photovoltaic systems," Progress in photovoltaics: Research and applications, vol. 6, 1998, pp. 43–54.

Abstract: The combination of photovoltaic (PV) systems with V-trough cavities has been identified as an attractive option to reduce, in the short time scale, the prices of the PV electrical energy. In places of good radiation level, the output energy of these devices can be almost doubled, compared to PV ¯at-plate fixed systems. Additionally, V-trough cavities are simple to manufacture and can be used with conventional (1-sun) solar cells. In this work we present a design procedure for V-trough cavities used in combination with PV generators. The main design requirements are: uniform illumination on the plane of the PV module, within a finite interval of incidence angles; minimum cost of energy; and heat dissipation by natural, passive means. The V-trough cavities depend on two parameters. We obtain a first analytical relation between the concentration ratio (C) and the V-trough angle (c) for concentrators with uniform illumination at the absorber. The region of minimum cost of the V-trough PV ensemble yields a second relation. Then, a unique pair of cavity parameters, satisfying the above criteria, is found. A design example of a V-trough cavity for the city of Recife, PE, Brazil, is presented.

##### R.W. Stacey and P.G. McCormick, "Effect of concentration on the performance of flat plate photovoltaic modules* 1," Solar energy, vol. 33, 1984, pp. 565–569.
• 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
##### C. Sangani and C. Solanki, "Experimental evaluation of V-trough (2 suns) PV concentrator system using commercial PV modules," Nov. 2006, p. 7.
• Determine max gain in output power from 2 suns (V-trough)
• Three V-trough designs
• seasonal tracking, one axis north-south tracking, diurnal tracking
• reflector material - anodized aluminum sheet and mirror
• 10% gain (output power) with aluminum over mirror
• Max module temp under concentration was 82 - 90 C
• higher than non-concentration by 20 - 30 C
• Large temp diff (between 2 suns and 1 sun concen) only occured at noon - other times temp observed to be within non - concentrating max temp
• Gain in power of 40% - reduction in cost of 24%
##### B.J. Huang and F.S. Sun, "Feasibility study of one axis three positions tracking solar PV with low concentration ratio reflector," Energy conversion and management, vol. 48, 2007, pp. 1273–1280.
• Experiment with one axis tracking – three positions – morning, noon, afternoon
• Simple control circuit –two sensors with slit between – shading determines when tracking changes
• Liu and Jordan's model
• Tracking power increase 24.5% vs. fixed PV module
• effect of misalignment calculated for system
• negligible (<2%) for alignment error <15
• for mid-low latitude region ( < 40)
• 5% for alignment error of 35
##### F.H. Klotz, H.D. Mohring, C. Gruel, F.B. ZSW, J. Sherborne, T. Bruton, B.P. Solar, M.A. Abella, and P. Tzanetakis, "Field test results of the Archimedes photovoltaic V-trough concentrator system," Proceedings of the 17th European Photovoltaic Solar Energy Conference and Exhibition, Munich, Germany, 2001, pp. 492–495.

ABSTRACT: A new photovoltaic concentrator system with passive tracking has been developed and tested (EU Joule III Project ARCHIMEDES). It is based upon irradiation enhancement in the module plane by flat plate mirrors in Vtrough configuration and elimination of losses from off axis incidence using a maintenance free solar tracking unit, the thermohydraulic actuator (THA). The new ARCHIMEDES system is designed for highly efficient and long term reliable water pumping and can offer up to more than 40% cost advantages compared to conventional fixed flat plate systems. Prototypes are installed since summer 2000 in Germany, Spain and on Crete. The field test results confirm the concept. Effective concentration factors of more than 1.8X are reached under clear sky conditions. The operation temperature is comparable to conventional non concentrating systems. An annual energy harvest of 3000 – 3500 kWhdc per installed kWp can be reached for Southern Europe

##### F. Reis, M. Brito, V. Corregidor, J. Wemans, and G. Sorasio, "Modeling the performance of low concentration photovoltaic systems," Solar Energy Materials and Solar Cells, vol. 94, Jul. 2010, pp. 1222-1226.
• 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)
##### S. Nann, "Potentials for tracking photovoltaic systems and V-troughs in moderate climates," Solar Energy, vol. 45, 1990, pp. 385-393.
• Using anisotropic model for diffuse radiation
• More diffuse radiation when tracking
• "The Perez model comes closest in predicting the actual h-radiance on a tilted surface, given hourly global horizontal and direct normal it-radiance."
• Perez model used for tracking, Hays model used for V-troughs
• Increase in solar insolation by double-axis tracking:
• 33%-37 % at Delhi, Bombay, and Trivandrum.
• Annual system efficiency of 0.85 is used (sourced to another paper, is shown to be reasonable)
• Results show econ benefit vs. area related costs & BOS costs
##### F. Reis, V. Corregidor, M.C. Brito, R. Rodrigues, J. Wemans, and G. Sorasio, "POWER GENERATION AND ENERGY YIELD USING DOUBLESUN® PHOTOVOLTAIC SOLAR CONCENTRATION," 24th European Photovoltaic Solar Energy Conference, pp. 803–806.

ABSTRACT: DoubleSun® technology is a V-trough concentration system that makes use of commercial photovoltaic monocrystalline silicon modules. The system integrates a 2-axes tracking system and increases the amount of radiation falling upon the modules by using two flat mirrors. The purpose of the present work is to demonstrate the power and energy increase of commercial modules when integrated in a V-trough system as to a fixed flat-plate system. A theoretical model was developed to estimate such improvement. This model was validated by on-field data, which was acquired during an experimental campaign performed from June to August and also during November of 2008 in WS Energia laboratory, Portugal. DoubleSun® technology, with 1.9x concentration, showed an increase of 50% on the DC power of commercial modules at solar noon.

• Briefly shows effects of cloud cover on concentration
##### M.A.M. Shaltout, A. Ghettas, and M. Sabry, "V-trough concentrator on a photovoltaic full tracking system in a hot desert climate," Renewable Energy, vol. 6, Jul. , pp. 527-532.

Abstract- A V-trough concentrator with a two-axis tracker system to increase the performance of photovoltaics was designed by the authors and installed on the roof-top of the building of the National Research Institute of Astronomy and Geophysics at Helwan in South Cairo. The V-trough concentrator system comprises two flat mirrors with dimensions 50 cm x 18 cm. They are fixed with the reflecting surfaces facing each other with a separation of about 11 cm, on a wooden table of 50 cm axis length. A sample of polycrystalline and amorphous silicon solar cells were fixed into the system, and similar solar cells of each type were fixed separate to the system, to estimate the electrical gain. The measurements were performed daily at different air masses for one complete year. The temperature of the solar cells in and out of the system were measured for comparison. Also, measurements for beam and global solar radiation and other meteorological conditions were recorded. The optical losses of the system were analyzed and details of collectable energy calculations are presented. The energy gain from the isolated contribution of the Vtrough concentrators is also evaluated.

## PV

##### J. Wennerberg, J. Kessler, J. Hedström, L. Stolt, B. Karlsson, and M. Rönnelid, "Thin film PV modules for low-concentrating systems," Solar Energy, vol. 69, Jul. , pp. 243-255.
* applying low concentration to CIGS technology
* discusses using CPC or planar reflectors
* references previous work by in sweden of use of planer reflectors
* discusses non-uniform illumination with respect to CIGS
* effects of temp and light intensity on CIGS
* experimental work is done with CPCs at 4x concentration

##### S.C. Seitel, "Collector performance enhancement with flat reflectors," Solar Energy, vol. 17, Nov. 1975, pp. 291-295.
* Specular and diffused flat reflectors to enhance collector performance.
* Moving reflector and Steady collector.
* Discusses direct power equations for direct radiation and reflected radiation ( Specular and Diffused).
* discusses factors such as Solar Intensity, Absorptivity, Reflectivity, Exchange Factor, Angle Factor.
* Defines: Solar Intensity, Absorptivity, Reflectivity, Exchange Factor, Angle Factor.
* FORTRAN routine is used to develop results .
* Analysis of energy absorbed with respect to the included angle.
* Observed the behavior of Angle factor with respect to included angle.
* references work from The Franklin Institute and books on Thermal Radiation and heat transfer.

##### A.A. Al-Baali, "Improving the power of a solar panel by cooling and light concentrating," Solar & Wind Technology, vol. 3, 1986, pp. 241–245.
* Cooling system and concentration on normal PV panels
* three PV panels (33 cells in series)
o 1 solar panel, no accessories ;
o 1 solar panel + reflecting plane mirror ;
o 1 solar panel + reflecting plane mirror + water
* temperature measured - thermocouple connected to YSI-47 Tc thermometer
* ambient temp as high as 50C
* cooling system fix panel temp at 35 to 45 C

##### H.P. Garg and D.S. Hrishikesan, "Enhancement of solar energy on flat-plate collector by plane booster mirrors," Solar Energy, vol. 40, 1988, pp. 295–307.
* flat collector tilted and two reflectors.
* 2 reflectors ( north and south) and a collector in the middle.
* Specular reflections, multiple reflections not considered
* Calculations using vectors and coordinate system ( pretty complex)
* No change in absorbed energy tilting the collector.
* references are very good and useful

##### A.V. Narasimha Rao, R.V. Chalam, S. Subramanyam, and T.L. Sitharama Rao, "Energy contribution by booster mirrors," Energy Conversion and Management, vol. 34, 1993, pp. 309–326.
* 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

##### B. Perers and B. Karlsson, "External reflectors for large solar collector arrays, simulation model and experimental results," Solar Energy, vol. 51, 1993, pp. 327-337.
* high lattitudes -> large row spacing
* 2D model to be used for FP or CPC reflectors
* Diffuse treated isotropic -> using view factors -> described in Duffie
* theoretical
o infinite collector rows / reflectors
o 4 cases of reflection for specular
o explained for CPCs as wel
o for finite lengths a correction factor is used
o CPCs are 15% better for same reflector / collector width ratio
* experimental
o Four identical 11m^2 flat plate collector modules
o one was used as reference
o three equipped with external reflectors of w = 3m and L= 7m
o collector w = 2.4m and L= 5m
* An annual performance increase of over 30% - four operating seasons in the Scandinavian climate (latitude 60 ° )

##### A.V. Rao, S. Subramanyam, and T.L. Rao, "Performance of east/west plane booster mirror," Energy Conversion and Management, vol. 35, 1994, pp. 543–554.
* East/west mirrors are used (FP reflector on top of collector)
* thermal system and looks into the performance increase
* increases the fill factor (thermally)
* optimal mirror angle calculated (latitudes of 0 to 40 N)

##### M. Rönnelid, B. Karlsson, P. Krohn, and J. Wennerberg, "Booster reflectors for PV modules in Sweden," Progress in Photovoltaics: Research and Applications, vol. 8, 2000, pp. 279–291.
* benefits of having planer reflectors in row spacing
* discusses temp increase problem and potential solutions
* no cooling is done in study
* looks at reflector geometry and annual changes
* 20% increase in output in one test -> drop to 0 when panel half covered
* A-Si is better an dealing with uneven illumination

##### Y. Tripanagnostopoulos, M. Souliotis, and T. Nousia, "Solar collectors with colored absorbers," Solar Energy, vol. 68, 2000, pp. 343-356.
* Solar Thermal Collectors used for water heating applications
* Performance results of three FP solar collectors: black, blue and red brown absorbers (with or without glazing)
* Used polished stainless steel thin sheet reflectors (0.68 reflectivity)

##### V. Poulek and M. Libra, "A new low-cost tracking ridge concentrator," Solar Energy Materials and Solar Cells, vol. 61, Mar. 2000, pp. 199-202.
* Panel on either side of two flat booster mirrors back to back
* one axis tracking throughout day
* seasonal tracking by adjusting slope of axle
* recommend use of rolled aluminum alloy sheet (protected by weather resistant polymer)
* concentration ratio of 1.6 to 1.7
* Clear day -> energy surplus of 107%

##### M.D.J. Pucar and A.R. Despic, "The enhancement of energy gain of solar collectors and photovoltaic panels by the reflection of solar beams," Energy, vol. 27, Mar. 2002, pp. 205-223.
• reflectors on upper edge of the receivers considered
• Continuously adjustable reflecting panels - higher costs - higher efficiencies - are analyzed
• Only theoretical - no testing of devices
• Computed for PV panel at 44° NL (Belgrade, Yugoslavia) - inclined at 35° wrt horizontal
• Modeled for 4 days: 21 December, 21 March/September ,21 June
• 5 different types of reflectors (tracking - both horizontally and vertically)
##### T. Matsushima, T. Setaka, and S. Muroyama, "Concentrating solar module with horizontal reflectors," Solar Energy Materials and Solar Cells, vol. 75, Feb. 2003, pp. 603-612.
* proposed module and reflector setup
* reflector: width of reflector is 2x, length is 2.7x that of panel
* test conducted in solar simulator
* tests conducted outdoors
o short circuit measured throughout day
o compared to conventional module
* power output determination did not seem to take into acount efficiency drops
* estimated power generation increase of 1.5 times (seems very high - no losses)

##### H. Tanaka, "Solar thermal collector augmented by flat plate booster reflector: Optimum inclination of collector and reflector," Applied Energy, vol. 88, Apr. 2011, pp. 1395-1404.
* Solar thermal collector with FP top reflector
* adjustable inclination of reflector for seasons
* looked at shading effects of top reflector
* determined optimal angles and adjustments for angle throughout year


#### S.L. Grassie, N.R. Sheridan, The use of planar reflectors for increasing the energy yield of flat-plate collectors, Solar Energy. 19 (1977) 663-668.

* presents a derivation of view factor for use with diffuse reflectors, this could possibly be used to estimate the diffuse
* diffuse reflector estimated by use of a white painted sheet.Had a negligable effect
* also presents optical derivation for light
* 14% increase due to reflector
* reflector above the panel is good for winter time, below is good for summer


#### D. McDaniels, D. Lowndes, H. Mathew, J. Reynolds, R. Gray, Enhanced solar energy collection using reflector-solar thermal collector combinations, Solar Energy. 17 (1975) 277-283.

* H.Thomanson, energy increase of 30%
* non-specular mirrors used by sherman, babor and others [11-15]
* Solar collector mounted vertically
* Includes correlation for reflectance at large angles of incidence
* Takes into account beam and diffuse radiation
* preliminary impovment of 1.6+/-0.6 over straight collector
* uses spectrally averaged data for reflectivity, 0.9 new 0.7 weathered, coated with SiO
* optimum performance when angle between panel and reflector is 90 degrees
* focus on winter improvement
* recommends reflector length of twice the height of the panel in winter, 1.6 in summer
* good graph showing enhancement factor of the array


## Heat Transfer of concentration

##### [1] B.A. Meyer, J.W. Mitchell, and M.M. El-Wakil, "Convective heat transfer in Vee-trough linear concentrators," Solar Energy, vol. 28, 1982, pp. 33–40.
• Physical model and theoretical model
• Physical – two aluminum plates (isothermal) – sidewall (reflectors) polystyrene foam with aluminum sheets ontop
• Numerical shown to be close to physical model
• Heat transfer modeled for – concentration 2 to 5x – angles 30 to 90
##### [2] A. Royne, C.J. Dey, and D.R. Mills, "Cooling of photovoltaic cells under concentrated illumination: a critical review," Solar Energy Materials and Solar Cells, vol. 86, 2005, pp. 451–483.
• Decreased efficiency and long term degradation with increase cell temperature
• Concentration method, level or geometry effect cooling
• Single-cell geometries, passive cooling - feasible  -most cost-efficient solution for concentration >=1000 suns

(**cells and lenses kept small)

• Linear concentrators  -
• cooled passively, (heat sinks get

intricate -> expensive - for concentration > 20 suns)

• active cooling (water or other coolants) - considered for concentration> 20 suns
• Densely packed cells - only active cooling.
• thermal resistance must be < 10^-4Km2/W for concentration > 150 suns.

## Concentration losses

##### Experimental study of mismatch and shading effects in the I–V characteristic of a photovoltaic module
• Looks at effect of mismatch and shading
• Using Fluke Data Logger – measure I-V characteristics of each cell + module at same time
• significant variance in reverse bias IV characteristics of identical cells
• Power loss between 19% (one cell half shaded) to 79% (1 cell completely shade)(33 cells in module)
##### Partial shadowing of photovoltaic arrays with different system configurations: literature review and field test results

Abstract: Partial shadowing has been identified as a main cause for reducing energy yield of grid-connected photovoltaic systems. The impact of the applied system configuration on the energy yield of partially shadowed arrays has been widely discussed. Nevertheless, there is still much confusion especially regarding the optimal grade of modularity for such systems. A 5-kWp photovoltaic system was installed at K.U. Leuven. The system consists of three independent subsystems: central inverter, string inverter, and a number of AC modules. Throughout the year, parts of the photovoltaic array are shadowed by vegetation and other surrounding obstacles. The dimensions of shadowing obstacles were recorded and the expectable shadowing losses were estimated by applying different approaches. Based on the results of almost 2 years of analytical monitoring, the photovoltaic system is assessed with regard to shadowing losses and their dependence on the chosen system configuration. The results indicate that with obstacles of irregular shape being close to the photovoltaic array, simulation estimates the shadowing losses rather imprecise. At array positions mainly suffering from a reduction of the visible horizon by obstacles far away from the photovoltaic array, a simulation returns good results. Significant differences regarding shadow tolerance of different inverter types or overproportional losses with long module strings could not be confirmed for the system under examination. The negative impact of partial shadowing on the array performance should not be underestimated, but it affects modular systems as well as central inverter systems.

H.Thomanson, energy increase of 30%

non-specular mirrors used by sherman, babor and others [11-15]

Solar collector mounted vertically

Includes correlation for reflectance at large angles of incidence

Takes into account beam and diffuse radiation

preliminary impovment of 1.6+/-0.6 over straight collector

uses spectrally averaged data for reflectivity, 0.9 new 0.7 weathered, coated with SiO

optimum performance when angle between panel and reflector is 90 degrees

focus on winter improvment

reccomends reflector length of twice the height of the panel in winter, 1.6 in summer

good graph showing enhansement factor of the array

First reflection work by Shuman [1]

McDaniels et al. [3], Seitel [4], Grassie and Sheridan [5], Baker et al. [6] and Larson [7] investigated the energy enhancements received by thermal collector–reflector systems under different conditions

Reflector attached to the top edge of the system

optimization for a single panel

does not take into account the electrical properties of the PV cell

does not take into account diffuse radiaiton

does not look at thermal effects on panel performance

assumes p=1

good derivation of radiation reflection onto a panel

gains of 71,24, 19% for December March/September and June resp.

Discussion of tracking concepts

McDaniels et al. [1], Baker et al. [2], and Larson [3]. Optimal winter tilts of reflector and collector for winter space heating

Narasimha Rao et al. [8] optimized the reflectors' tilt angles of a two plane reflectors-collector system with the reflectors located facing East/West

South or North [4–7].

reflector located above the panel

specular reflectivity of 0.88

Considers only a single panel, therefore edge losses

Geometric interpretation including plane transformations are discussed

Summertime boost of 5%-10% wintertime of 30%-35%

once a day, once a month, once a season, twice a year, and once a year16.9%, 16.3%, 14.4%,13.3%, and 6.6%, respectively

reflector is angled towards the sky

System not optimized for yearly boost

Integrates the concentrator into the module

uses a three position tracking system, that tracks one module by itself.

Increase due to concentration: 23%, increase due to tracking , 56%

Performs economic analysis assuming the cost of modules is 3-5\$/Wp, this is too high now

presents a derivation of view factor for use with diffuse reflectors, this could possibly be used to estimate the diffuse radiation boost.

diffuse reflector estimated by use of a white painted sheet.Had a negligable effect

also presents optical derivation for light

14% increase due to reflector

reflector above the panel is good for winter time, below is good for summer

Page data
Authors Nabeil Alazzam, Rob Andrews, Dolphin Patel 2010 CC-BY-SA-4.0 3,299 No main image, Sections nested too deep, Lists nested too deep Nabeil Alazzam, Rob Andrews, Dolphin Patel (2010). "Low level concentration for PV applications literature review". Appropedia. Retrieved August 19, 2022.
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