This page was developed by the Queen's University Applied Sustainability Research Group.

Low Concentration

Effect of Concentration on the Performance of Flat Plate Photovoltaic Modules

• 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

The enhancement of energy gain of solar collectors and photovoltaic panels by the reflection of solar beams

• 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)

The Promise of Concentrators

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.

V-trough:

Experimental evaluation of V-trough (2 suns) PV concentrator system using commercial PV modules

• 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%

Potentials for Tracking Photovoltaic Systems and V-Troughs in Moderate Climates

• 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.
  • 37%.at northern Colorado
• 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

Feasibility study of one axis three positions tracking solar PV with low concentration ratio reflector

• 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

A Concentrator for Thin-Film Solar Cells

• 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.

Design Procedure of V-trough Cavities for Photovoltaic Systems

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.

Modeling the performance of low concentration photovoltaic systems

• 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)

Power Generation and Energy Yield Using Doublesun® Photovoltaic Solar Concentration

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

Field Test Results of the Archimedes Photovoltaic V-Trough Concentrator System

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

Heat transfer

Convective Heat Transfer in Vee-Trough Linear Concentrators

• 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

Cooling of photovoltaic cells under concentrated illumination: a critical review

• 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.

V-Trough Concentrator on A Photovoltaic Full Tracking System in a Hot Desert Climate

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.

Reflectors

Prisms with Total Internal Reflection as Solar Reflectors

• Patent for solar reflectors
• Use of TIR as reflectors for solar thermal application
• Describes TIR for – line focus parabola, trough-shaped, cone shaped, point-focused parabola system

Principles of Solar Concentrators of a Novel Design

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.

Comparison of Solar Concentrators

Abstract--Even though most variations of solar concentrators have been studied or built at some time or other, an important class of concentrators has been overlooked until very recently. These novel concentrators have been called ideal because of their optical properties, and an example, the compound parabolic concentrator, is being tested at Argonne National Laboratory. Ideal concentrators differ radically from conventional instruments such as focussing parabolas. They act as radiation funnel and do not have a focus. For a given acceptance angle their concentration surpasses that of other solar concentrators by a factor of two to four, but a rather large reflector area is required. The number of reflections varies with angle of incidence, with an average value around one in most cases of interest. In order to help provide a rational basis for deciding which concentrator type is best suited for a particular application, we have compared a variety of solar concentrators in terms of their most important general characteristics, namely concentration, acceptance angle, sensitivity to mirror errors, size of reflector area and average number of reflections.

The connection between concentration, acceptance angle and operating temperature of a solar collector is analyzed in simple intuitive terms, leading to a straightforward recipe for designing collectors with maximal concentration (no radiation emitted by the absorber must be allowed to leave the concentrator outside its acceptance angle). We propose some new concentrators, including the use of compound parabolic concentrators as second stage concentrators for conventional parabolic or Fresnel mirrors. Such a combination approaches the performance of an ideal concentrator without demanding a large reflector: it may offer significant advantages for high temperature solar systems.

Mismatch and shading effects

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.

Additional

---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 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

---M.D.J. Pucar, A.R. Despic, The enhancement of energy gain of solar collectors and photovoltaic panels by the reflection of solar beams, Energy. 27 (2002) 205-223.

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

--H.M.S. Hussein, G.E. Ahmad, M.A. Mohamad, Optimization of operational and design parameters of plane reflector-tilted flat plate solar collector systems, Energy. 25 (2000) 529-542.

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

--B. Huang, F. Sun, Feasibility study of one axis three positions tracking solar PV with low concentration ratio reflector, Energy Conversion and Management. 48 (2007) 1273-1280.

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

--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 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

--S. Subramanyam, A.V. Narasimha Rao, T.L. Sitharama Rao, Strip element mirror boosters for solar devices, Energy Conversion and Management. 30 (1990) 107-113.

--A.V.N. Rao, S. Subramanyam, T.L.S. Rao, Performance of east/west plane booster mirror, Energy Conversion and Management. 35 (1994) 543-554.

--A. Narasimha Rao, R. Chalam, S. Subramanyam, T. Sitharama Rao, Energy contribution by booster mirrors, Energy Conversion and Management. 34 (1993) 309-326.

--H.P. Garg, D.S. Hrishikesan, Enhancement of solar energy on flat-plate collector by plane booster mirrors, Solar Energy. 40 (1988) 295-307.

--D.G. Burkhard, D.L. Shealy, Design of reflectors which will distribute sunlight in a specified manner, Solar Energy. 17 (1975) 221-227.

--G.E. Ahmad, H.M.S. Hussein, Comparative study of PV modules with and without a tilted plane reflector, Energy Conversion and Management. 42 (2001) 1327-1333.