Kirigami design approach to LCPV reflectors

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Background[edit | edit source]

What are Concentrator photovoltaics (CPV)??[edit | edit source]

Wikipedia : Concentrator photovoltaic systems employ curved reflectors such as lenses and mirrors to focus incoming sun rays onto the solar cells to harvest solar energy with more efficiency measured as watt-peak Wp. They are often equipped with single or dual-axis solar trackers and cooling systems that promote dual-way power generation. Based on the intensities measured in number of suns, CPV systems are classified as Low concentration PV, High concentration PV, Medium concentration PV and Luminescent solar concentrators.

This idea of concentrating sun's radiation dates back to 212 B.C.The famous Greek inventor Archimedes used mirrors, later called as burning mirrors, to set enemy ships at blaze. Concentrators/reflectors use principles of optics (focal point) to concentrate sunlight onto absorbers/Solar cells.

K. G. T. Hollands, “A concentrator for thin-film solar cells,” Solar Energy, vol. 13, no. 2, pp. 149–163, May 1971. doi: 10.1016/0038-092X(71)90001-6[edit | edit source]

  • Considerations : V-Trough reflector as side walls with solar cells at the base; Seasonal tracking alone is considered but not diurnal tracking; Axis along east-west direction; Used thin-film polycrystalline cadmium Sulphide cells.
  • Assumptions: Side walls to be perfectly specular, gray surfaces; 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.
  • Aim: To determine yearly average direct-beam concentration factor for any incidence angle, opening angle and side-wall reflectance.
  • Findings: Concludes that total yearly mean concentration factors of the order of 2 are possible with V-trough concentrators.
  • Imp concepts: Calculations on Solar geometry (N-S & E-W).
  • Limitations: Side- walls are ideal specular reflectors.

R. M. Swanson, “The promise of concentrators,” Prog. Photovolt: Res. Appl., vol. 8, no. 1, pp. 93–111, Jan. 2000. doi: 10.1002/(SICI)1099-159X(200001/02)8:1<93::AID-PIP303>3.0.CO;2-S[edit | edit source]

  • Aim: To address the issue of why concentrator systems have not gained a significant market share.
  • Information: 1. Provides overview of active concentrator developments in major universities and labs in US, UK and Japan. 2. Surmises advantages of concentrator technology, its barriers and suggestions to overcome them along with recommendations for future developments.

D. A. W. B. Dr. Simon P. Philipps and D. S. K. Kelsey Horowitz, “Current Status of Concentrator Photovoltaic (CPV) Technology,” Fraunhofer Institute for Solar Energy Systems ISE in Freiburg, Germany & National Renewable Energy Laboratory NREL in Golden, Colorado, USA, TP-6A20-63916, Sep. 2015.[edit | edit source]

  • Aim: To Summarize the status of the concentrator photovoltaic (CPV) market and industry as well as current trends in research and technology. This report is intended to guide research agendas for Fraunhofer ISE, the National Renewable Energy Laboratory (NREL), and other R&D organizations.
  • Review: 1. Clearly distinguishes between CPV strengths and weaknesses. 2. Focusses on market and industry aspects- levelized cost of electricity (LCOE) studies of current available CPV technologies. 3. Overview of research and technological developments in Fraunhofer Institute and NREL. 4. Serves as reference for stakeholders in the CPV industry and research.

A. K. Pandey, V. V. Tyagi, J. A. Selvaraj, N. A. Rahim, and S. K. Tyagi, “Recent advances in solar photovoltaic systems for emerging trends and advanced applications,” Renewable and Sustainable Energy Reviews, vol. 53, pp. 859–884, Jan. 2016.10.1016/j.rser.2015.09.043[edit | edit source]

  • Aim: To provide a comprehensive review on the solar photovoltaic (SPV) systems especially BIPV, CPV & PV/T and their recent advances along with emerging applications in the present and future scenario.
  • Review: 1. Provides estimates on energy consumption over past few decades to near future. 2. Provides abridged version of background on PV but focusses more on recent advances in the PV technology and compares numerous cell configurations in accordance to their efficiencies. 3. Gives insights of various PV materials like crystalline, thin-film, Concentrated PV, Hybrid, Organic and Polymer materials etc. 4. Discusses deeply the applications of PV technology with particular case studies which extends even for space based solar technology. 5. Provides recommendations wherein to concentrate the more R&D.

Low concentration photovoltaics (LCPV)[edit | edit source]

Low concentration PV systems can be illuminated with intensities less than 20 suns [1] which can be varied up to 100 suns. LCPV systems eliminate the need of complex cooling systems and are often facilitated with booster reflectors. LCPV systems doesn't require active tracking mechanisms due to wide acceptance angles [2]. These can sufficed with single-axis tracking system yet maintaining 35-40% increased power output. The reflected radiation incident on these modules depends on the clearness of the index of the location [3] [4] and thus they are more effective when installed where direct radiation is a significant percentage of the global radiation (South Europe, Northern Africa, Southern states of the USA, etc.).

Measuring Intensity in Suns:  Intensity of sunlight illuminating on PV cells are measured as 'Suns'. 'One Sun' is the amount of energy drawn to an object openly exposed out on a cloudless day which is approximately 100 watts per square foot.

Concept of Reflectors-Concentrators[edit | edit source]

The efficacy of incorporating reflectors or concentrators for PV cells or modules is to intensify the incident radiation i.e., to increase incident radiation per m^2. They increase the output efficiency leading to reduction of capital costs. The main features of reflectors are high reflectance, low scattering and low degradation i.e., loss of reflectance over time.

Link directly to Understanding_solar_concentrators

H. Tabor, “Stationary mirror systems for solar collectors,” Solar Energy, vol. 2, no. 3–4, pp. 27–33, Jul. 1958. doi:10.1016/0038-092X(58)90051-3[edit | edit source]

  • Aim: To provide with studies that proves tilting of solar concentrators along with usage of mirrors for concentrating radiation is more efficient.
  • Considerations:The mirror has the form of a cylindrical parabola with the cylindrical axis mounted horizontally east-west.
  • Findings: Complete stationary mirror cannot provide any useful concentration while tilting the solar collectors with varying seasons can yield more efficiencies; The maximum optical concentration of 3 is obtained at a minimum angle of acceptance of 15-17 deg for the mirrors. Employing an auxiliary side mirror for second stage concentration can increase this concentration power to about 4. One cannot apply a second stage of optical concentration to the double-sided receiver.
  • Imp concepts:An angle in solar geometry termed the EWV altitude is defined, and its variation with time and season is shown.This indicates the necessary acceptance angle of a stationary mirror system for solar collectors. Solar geometry studies. Geometrical studies of cylindrical parabola.

A. Rabl, “Solar concentrators with maximal concentration for cylindrical absorbers,” Applied Optics, vol. 15, no. 7, p. 1871, Jul. 1976. doi: 10.1364/AO.15.001871[edit | edit source]

The differential equation is derived that describes the reflector of an ideal two-dimensional radiation concentrator with an absorber of arbitrary convex shape. For the special case of an absorber with circular cross section, the equation can be solved in closed form if suitable coordinates are used. The effect of absorption at the reflector is considered, and formulas are presented for determining the attenuation of radiation on its passage from aperture to absorber.

A. Rabl, “Comparison of solar concentrators,” Solar Energy, vol. 18, no. 2, pp. 93–111, 1976.doi: 10.1016/0038-092X(76)90043-8[1][edit | edit source]

  • Analyses the geometric concentration ratio of different types of concentrators.
  • Concludes that there is a nonuniformity of the flux density distribution on the absorber.

A. Rabl and R. Winston, “Ideal concentrators for finite sources and restricted exit angles,” Applied Optics, vol. 15, no. 11, p. 2880, Nov. 1976. doi: 10.1364/AO.15.002880[edit | edit source]

Design procedures for ideal radiation concentrators are described which are applicable to finite sources and/or restricted exit angles. Finite sources are relevant for second stage concentrators which collect and further concentrate radiation from a primary focusing element (mirror or lens) in a manner similar to the field optic element in a telescope. Restricting the exit angle is useful for improving the optical efficiency of solar collectors by eliminating grazing angles of incidence of the absorber. It also serves to extend the useful range of angular acceptance values available from solid dielectric concentrators that function by total internal reflection. Concentrators of this type can be used to construct highly efficient radiation traps (spectrally selective filters).

D. P. Grimmer, K. G. Zinn, K. C. Herr, and B. E. Wood, “Augmented Solar Energy Collection Using Various Planar Reflective Surfaces: Theoretical Calculations and Experimental Results,” Los Alamos Scientific Lab., N.Mex. (USA), LA-7041, Apr. 1978[edit | edit source]

The use of planar reflective surfaces can substantially improve the performance of both active and passive solar collectors. The results of theoretical calculations and experimental tests on the use of different types of flat reflective surfaces to increase the collection of solar energy by flat collectors are presented. Specular, diffuse, and combination specular/diffuse reflective surfaces are discussed. A computer model has been generated to describe surfaces as a combination of specular- and diffuse-like reflectivities. The reflective properties of a given surface can be measured in the laboratory as a function of incident and reflected angles. Predictions of system performance were made for various collector/reflector configurations and compared with the performance of an optimally oriented collector without a reflector.

R. W. Stacey and P. G. McCormick, “Effect of concentration on the performance of flat plate photovoltaic modules,” Solar Energy, vol. 33, no. 6, pp. 565–569, 1984. doi: 10.1016/0038-092X(84)90012-4[edit | edit source]

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 fixed flat plate module.

G. Smestad, H. Ries, R. Winston, and E. Yablonovitch, “The thermodynamic limits of light concentrators,” Solar Energy Materials, vol. 21, no. 2–3, pp. 99–111, Dec. 1990. doi: 10.1016/0165-1633(90)90047-5[edit | edit source]

To concentrate the light, photons from a larger area are collected and directed to a smaller area. Some devices use geometrical optics, or a change in index of refraction to increase the illumination on a surface above the incident solar level. Other systems use a frequency or Stokes shift to increase the illumination of light at one photon energy at the expense of another. Presented is a unification of the ideas and principles developed for the various classifications of concentrators. Equations are developed that describe the limits of concentration in geometrical and fluorescent systems. Concentration is shown to be a function of the index of refraction, angular collection range, as well as the frequency shift. Applications of the ideas involve the understanding of diffuse radiation concentrators and the solar powered laser.

R. P. Friedman, J. M. Gordon, and H. Ries, “New high-flux two-stage optical designs for parabolic solar concentrators,” Solar Energy, vol. 51, no. 5, pp. 317–325, 1993. doi:10.1016/0038-092X(93)90144-D[edit | edit source]

A new two-stage optical design for parabolic dish concentrators that can realistically attain close to 90% of the thermodynamic limit to concentration with practical, compact designs was presented. For comparison, the parabolic dish-plus-compound parabolic concentrator secondary design, at this rim angle, achieves no more than 50% of the thermodynamic limit. A new secondary concentrator is tailored to accept edge rays from the parabolic primary, and incurs less than one reflection on average. It necessitates displacing the absorber from the parabola's focal plane, along the concentrators optic axis, toward the primary reflector, and constructing the secondary between the absorber and the primary. The secondary tailored edge-ray concentrators described here create new possibilities for building compact, extremely high flux solar furnaces and/or commercial parabolic dish systems.

B. Perers and B. Karlsson, “External reflectors for large solar collector arrays, simulation model and experimental results,” Solar Energy, vol. 51, no. 5, pp. 327–337, 1993.doi: 10.1016/0038-092X(93)90145-E[edit | edit source]

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 incident radiation onto the collector, including corrections for shadowing and lost radiation above the collector, can then be calculated using 2-D geometry. The diffuse radiation is assumed to be isotropic. 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 for the incidence angles for diffuse and beam radiation are provided. 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.

S. Hess and V. I. Hanby, “Collector Simulation Model with Dynamic Incidence Angle Modifier for Anisotropic Diffuse Irradiance,” Energy Procedia, vol. 48, pp. 87–96, 2014. doi:10.1016/j.egypro.2014.02.011[edit | edit source]

One constant collector parameter, independent from slope or weather conditions is considered. The simulation model introduced considers the varying anisotropy of sky radiance. To create realistic distributions, the approach of Brunger and Hooper is used. Three possible modes were demonstrated. The model is applied to a stationary, double-covered process heat flat-plate collector with one-sided CPC booster reflector (RefleC). The collector shows a biaxial and asymmetric IAM for direct irradiance. It is found that, compared to anisotropic modeling, the simplified isotropic model is undervaluing the annual output of this collector by 13.7% for a constant inlet temperature of 120 °C in Würzburg, Germany. An annual irradiation distribution diagram shows that this is due to an underestimation of diffuse irradiation from directions with high direct irradiation. It is concluded that isotropic modeling of diffuse irradiance can be expected to significantly undervalue the annual output of all non-focusing solar thermal collectors. Highest relevance is found for high collector slopes, complex IAMs and at low-efficiency operation. The optimal collector slope is almost not affected. Accuracy of existing models can be increased by applying Mode 2.

V. P. Anand, M. M. Khan, E. Ameen, V. Amuthan, and B. Pesala, “Performance improvement of solar module system using flat plate reflectors,” in 2014 International Conference on Advances in Electrical Engineering (ICAEE), 2014, pp. 1–4. doi: 10.1109/ICAEE.2014.6838547[edit | edit source]

The energy output of Si-cell 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. A model system to analyse the effect of reflector parameters on the overall power output is developed. 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.

S. Hess,“Stationary booster reflectors for solar thermal process heat generation,” SASEC, 2015[edit | edit source]

The performance of a flat-plate collector with glass-foil double cover is compared to that of the same collector with a one-sided external CPC booster reflector (RefleC-collector) for process heat generation up to 150 C. Efficiency curve measurements of both collector variants are compared to state-of-the-art simulations and the new model calculates significantly higher additional gains of the reflectors.Monitoring results of one reference year for the overall system performance as well as for the additional gains by the booster reflectors are provided. It is shown that the stationary booster reflectors highly increase the efficient operation temperature range and also the annual energy gain of the double covered flat-plates.

V-trough solar concentrators[edit | edit source]

J. Freilich and J. M. Gordon, “Case study of a central-station grid-intertie photovoltaic system with V-trough concentration,” Solar Energy, vol. 46, no. 5, pp. 267–273, Jan. 1991. doi:[edit | edit source]

Our presentation is a case study of an installed, central-station (no storage), utility-intertie photovoltaic (PV) system in Sede Boqer, Israel (latitude 30.9°N). The nominally 12 kW peak PV system is comprised of 189 polycrystalline silicon modules mounted on inexpensive, one-axis north-south horizontal trackers with V-trough mirrors for optical boost. The power conditioning unit operates at a fixed voltage rather than at maximum power point (MPP). The primary task in analyzing the installed system was to investigate the cause of measured power output significantly below the design predictions of the installers, and to recommend system design modifications. Subsequent tasks included the quantitative assessment of fixed-voltage operation and of the energetic value of V-trough concentration and one-axis tracking for this system. Sample results show: (i) fixed-voltage operation at the best fixed voltage (BFV) can achieve around 96% of the yearly energy of MPP operation; (ii) the sensitivity of the yearly energy delivery to the selection of fixed voltage and its marked asymmetry about the BFV; (iii) the influences of inverter current constraints on yearly energy delivery and BFV; and (iv) how the separate effects of tracking and optical concentration increase yearly energy delivery.

N. Fraidenraich, “Design procedure of V-trough cavities for photovoltaic systems,” Prog. Photovolt: Res. Appl., vol. 6, no. 1, pp. 43–54, Jan. 1998.doi: 10.1002/(SICI)1099-159X(199801/02)6:1<43::AID-PIP200>3.0.CO;2-P[edit | edit source]

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 flat-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 (ψ) 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.

J. Bione, O. C. Vilela, and N. Fraidenraich, “Comparison of the performance of PV water pumping systems driven by fixed, tracking and V-trough generators,” Solar Energy, vol. 76, no. 6, pp. 703–711, 2004. doi: 10.1016/j.solener.2004.01.003[edit | edit source]

Photovoltaic pumping systems with solar tracking, coupled to low concentration cavities, have been proposed as a viable alternative to reduce the final cost of the pumped water volume. V-trough concentrators are particularly appropriate for photovoltaic applications since, for certain combinations of the concentration ratio (C) and vertex angle (Ψ), they provide uniform illumination on the region where the modules are located. Water pumping systems are only operational when the irradiance is larger than a minimum irradiance level (IC). Solar tracking increases the average collected irradiance (Icoll) and, for a system operating with a given critical irradiance level (IC), it is verified that the smaller the relationship (IC/Icoll), the larger the useful energy. Thus, the gain, in terms of pumped water volume, provided by solar tracking systems, can be larger than the gain in collected solar radiation. The combination of both devices, tracking and concentration provides an additional increase of the benefits resulting from the use of solar trackers. By means of the “Utilizability Method”, we estimate the long-term gains of pumped water volume, for tracking systems, with and without concentration, against fixed systems. The long-term water volume has been calculated using the characteristic curve of a tested PVP system with a tracking V-trough concentrator. Results show that, for the climate of the city of Recife (PE-Brazil), the annual pumped water volume of the tracking system is 1.41 times the value obtained with the fixed system. In that case, the gains observed for the collected solar energy were around 1.23. For the PVP system with tracking V-trough concentrator the annual benefits for pumped water volume are around 2.49, while for collected solar radiation we found 1.74. The annualized cost of the cubic meter of pumped water has been estimated for the three configurations. Results show a cost reduction of the order of 19% for the tracking system and of 48% for the concentrating system, when compared to the fixed configuration.

C. S. Sangani and C. S. Solanki, “Experimental evaluation of V-trough (2 suns) PV concentrator system using commercial PV modules,” Solar Energy Materials and Solar Cells, vol. 91, no. 6, pp. 453–459, Mar. 2007.doi: 10.1016/j.solmat.2006.10.012[edit | edit source]

V-trough photovoltaic (PV) concentrator systems along with conventional 1-sun PV module is designed and fabricated to assess PV electricity cost ($/W) reduction. V-trough concentrator (2-sun) system is developed for different types of tracking modes: seasonal, one axis north–south and two axes tracking. Three design models based on these tracking modes are used to develop the V-trough for a 2-sun concentration. Commercially available PV modules of different make and types were evaluated for their usability under 2-sun concentration. The V-trough concentrator system with geometric concentration ratio of 2 (2-sun) increases the output power by 44% as compared to PV flat-plate system for passively cooled modules. Design models with lower trough angles gave higher output power because of higher glass transmissivity. PV modules with lower series resistance gave higher gain in output power. The unit cost ($/W) for a V-trough concentrator, based on different design models, is compared with that of a PV flat plate system inclined at latitude angle (Mumbai, φ=19.12°).

N. Martín and J. M. Ruiz, “Optical performance analysis of V-trough PV concentrators,” Prog. Photovolt: Res. Appl., vol. 16, no. 4, pp. 339–348, Jun. 2008. doi: 10.1002/pip.817[edit | edit source]

This paper proposes a method for the analysis of the optical losses that take place inside PV concentrators, which is useful in the design of such systems. The study is focused in V-trough concentrators with two-axis tracking. Those are low concentration systems that use nearly conventional flat PV modules. Optical losses are shown to depend on the cavity angle, the mirrors spectral and angular reflectance and the surfaces dirtiness. Final effective concentration ratio and relative cost should consider all these analysed factors. This will help in the search of the most efficient solution in each case.

C. S. Solanki, C. S. Sangani, D. Gunashekar, and G. Antony, “Enhanced heat dissipation of V-trough PV modules for better performance,” Solar Energy Materials and Solar Cells, vol. 92, no. 12, pp. 1634–1638, Dec. 2008. doi: 10.1016/j.solmat.2008.07.022[edit | edit source]

A concentrator photovoltaic (PV) module, in which solar cells are integrated in V-troughs, is designed for better heat dissipation. All channels in the V-trough channels are made using thin single Al metal sheet to achieve better heat dissipation from the cells under concentration. Six PV module strips each containing single row of 6 mono-crystalline Si cells are fabricated and mounted in 6 V-trough channels to get concentrator V-trough PV module of 36 cells with maximum power point under standard test condition (STC) of 44.5 W. The V-trough walls are used for light concentration as well as heat dissipation from the cells which provides 4 times higher heat dissipation area than the case when V-trough walls are not used for cooling. The cell temperature in the V-trough module remains nearly same as that in a flat plate PV module, despite light concentration. The controlled temperature and increased current density in concentrator V-trough cells results in higher Voc of the module.

F. Reis, M. C. Brito, V. Corregidor, J. Wemans, and G. Sorasio, “Modeling the performance of low concentration photovoltaic systems,” Solar Energy Materials and Solar Cells, vol. 94, no. 7, pp. 1222–1226, Jul. 2010. doi: 10.1016/j.solmat.2010.03.010[edit | edit source]

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.

G. M. Tina and P. F. Scandura, “Case study of a grid connected with a battery photovoltaic system: V-trough concentration vs. single-axis tracking,” Energy Conversion and Management, vol. 64, pp. 569–578, Dec. 2012. doi: 10.1016/j.enconman.2012.05.029[edit | edit source]

Photovoltaic systems (PVSs) combined with either some form of storage, such as a battery energy storage system (BESS), or direct load control, can play a crucial role in achieving a more economical operation of the electric utility system while enhancing its reliability with additional energy sources. At the same time, it is also important to use cost-effective PV solutions. In this context, a low-concentration PVS (CPVS) is analysed as a feasible alternative. This paper, present a case study of a complex PVS, composed of two PVSs, a storage system (BEES) and an inverter that allows the system to operate in both the island and grid-connected modes. The first PVS, is a 2.76-kWp single-axis tracking system (azimuth) with modules facing south and tilted 30°, while the second PVS is a dual-axis tracking system, rated 860 Wp, consisting of a concentrator at the flat mirrors. The system is installed on the roof of the main building of the “ITIS Marconi” school (Italy). A detailed description of the system is provided, and preliminary operating data are presented and discussed. The efficiencies of the PV systems are calculated and measured to evaluate the cost effectiveness of a low-concentration system.

Compound Parabolic Concentrators (CPC)[edit | edit source]

The Compound Parabolic Concentrator (CPC) is a nonimaging optical-design concept that allows maximum concentration of incident energy onto a receiver. This design incorporates a trough-like reflecting wall by which radiation is concentrated to the maximum allowed by physical principles of optics.

A. Rabl, N. B. Goodman, and R. Winston, “Practical design considerations for CPC solar collectors,” Solar Energy, vol. 22, no. 4, pp. 373–381, Jan. 1979. doi: 10.1016/0038-092X(79)90192-0[edit | edit source]

Several practical problems are addressed which arise in the design of solar collectors with compound parabolic concentrators (CPC's). They deal with the selection of a receiver type, the optimum method for introducing a gap between receiver and reflector to minimize optical and thermal losses, and the effect of a glass envelope around the receiver. This paper also deals with the effect of mirror errors and receiver misalignment, and the effect of the temperature difference between fluid and absorber plate. The merits of a CPC as a second stage concentrator are analyzed.

T. Tao, Z. Hongfei, H. Kaiyan, and A. Mayere, “A new trough solar concentrator and its performance analysis,” Solar Energy, vol. 85, no. 1, pp. 198–207, 2011. doi: 10.1016/j.solener.2010.08.017[edit | edit source]

  • A solar concentrator system consisting of a CPC, a secondary reflection plane mirror, and a parabolic trough concentrator.

The operation principle and design method of a new trough solar concentrator is presented in this paper. Some important design parameters about the concentrator are analyzed and optimized. Their magnitude ranges are given. Some characteristic parameters about the concentrator are compared with that of the conventional parabolic trough solar concentrator. The factors having influence on the performance of the unit are discussed. It is indicated through the analysis that the new trough solar concentrator can actualize reflection focusing for the sun light using multiple curved surface compound method. It also has the advantages of improving the work performance and environment of high-temperature solar absorber and enhancing the configuration intensity of the reflection surface.

N. Sarmah, B. S. Richards, and T. K. Mallick, “Evaluation and optimization of the optical performance of low-concentrating dielectric compound parabolic concentrator using ray-tracing methods,” Applied Optics, vol. 50, no. 19, p. 3303, Jul. 2011.doi: 10.1364/AO.50.003303[edit | edit source]

Presented a detailed design concept and optical performance evaluation of stationary dielectric asym-metric compound parabolic concentrators (DiACPCs) using ray-tracing methods. Three DiACPC designs,DiACPC-55, DiACPC-66, and DiACPC-77, of acceptance half-angles (0° and 55°), (0° and 66°), and (0° and77°), respectively, are designed in order to optimize the concentrator for building façade photovoltaicapplications in northern latitudes (>55°N). The dielectric concentrator profiles have been realizedvia truncation of the complete compound parabolic concentrator profiles to achieve a geometric concen-tration ratio of 2.82. Ray-tracing simulation results show that all rays entering the designed concentra-tors within the acceptance half-angle range can be collected without escaping from the parabolic sidesand aperture. The maximum optical efficiency of the designed concentrators is found to be 83%, whichtends to decrease with the increase in incidence angle. The intensity is found to be distributed at thereceiver (solar cell) area in an inhomogeneous pattern for a wide range of incident angles of direct solarirradiance with high-intensity peaks at certain points of the receiver. However, peaks become moreintense for the irradiation incident close to the extreme acceptance angles, shifting the peaks to the edgeof the receiver. Energy flux distribution at the receiver for diffuse radiation is found to be homogeneouswithin �12% with an average intensity of 520 W/m2.

M. A. Schuetz, K. A. Shell, S. A. Brown, G. S. Reinbolt, R. H. French, and R. J. Davis, “Design and Construction of a ~7x Low-Concentration Photovoltaic System Based on Compound Parabolic Concentrators,” IEEE Journal of Photovoltaics, vol. 2, no. 3, pp. 382–386, Jul. 2012. doi: 10.1109/JPHOTOV.2012.2186283[edit | edit source]

Reports on the design, construction, and initial performance measurements of a low-concentration photovoltaic system based on compound parabolic concentrators (CPCs). The system is approximately a 7× concentration system and uses commercially available laser groove buried contact monocrystalline silicon photovoltaic cells. The CPCs are fabricated using a second-surface aluminized acrylic mirror with proven weather durability. The asymmetric CPC optical design was driven by a balance between concentration factor, thermal issues, and optical angle of acceptance and was thoroughly evaluated by optical ray tracing. The design was targeted for a single-axis tracking system, with extruded aluminum heat sinks doubling as structural components. We fabricated a 120-cell (10 × 12) prototype array, and over three months of operation, we estimated an approximate peak total system power efficiency of 7.9%, limited mostly by the CPC optical efficiency (∼55%) and the cell conversion efficiency. We discuss several issues regarding system performance, reliability, and cost.

N. Sellami and T. K. Mallick, “Optical efficiency study of PV Crossed Compound Parabolic Concentrator,” Applied Energy, vol. 102, pp. 868–876, Feb. 2013. doi: 10.1016/j.apenergy.2012.08.052[edit | edit source]

  • Uses a ray-tracing method to design and optimize three stationary dielectric asymmetric compound parabolic concentrators (DiACPCs) with acceptance half-angles of (0°/55°), (0°/66°) and (0°/77°), respectively to optimize in order to optimize the designs of concentrator applications in northern latitudes (>55 °N)
  • Concludes that Energy flux distribution at the receiver for diffuse radiation is found to be homogeneous

H. Ali and P. Gandhidasan, “Performance Evaluation of Photovoltaic String with Compound Parabolic Concentrator,” Journal of Clean Energy Technologies, vol. 3, no. 3, pp. 170–175, 2015. doi: 10.7763/JOCET.2015.V3.190[][edit | edit source]

Photovoltaic (PV) system is used to directly converting the solar energy into the electrical energy. Compound Parabolic Concentrator (CPC) is a non-imaging concentrator which is considered in this study for reducing the cost of electrical energy. Two configurations are numerically studied namely one with simple typical flat PV string and the other PV string with CPC. The truncated CPC with concentration ratio of 2.3 and an acceptance angle of 41.75° is considered in the analysis of PV string with CPC (PV-CPC). Transient System Simulation Software (TRNSYS) is used for the evaluation of PV cell performance with and without CPC. The mathematical model for PV and PV-CPC is developed for the performance estimation of thermal and electrical characteristic of the system. Engineering Equation Solver (EES) code is written to solve the mathematical model and is linked with TRNSYS for simulation. The simulation is carried out for the average day of the months of June and December for Riyadh city. Results indicated that the use of the CPC increases the absorbed energy and electrical power output of PV system. The electrical power of PV string increases almost 35% when CPC is used with PV compared to simple typical flat PV string.

Booster reflectors[edit | edit source]

H. Tabor, “Mirror boosters for solar collectors,” Solar Energy, vol. 10, no. 3, pp. 111–118, Jul. 1966. doi: 10.1016/0038-092X(66)90025-9[edit | edit source]

Fixed flat-plate collectors produce outputs on clear days that are low and peaky: the addition of side mirrors to increase the amount of radiation reaching the collector increases the yield and permits higher temperatures of operation. By considering direct and diffuse components of sunlight separately and the geometry of the system, the instantaneous increase due to the mirrors can be determined and integrated graphically over the whole day. As indicated in an earlier paper, the retention efficiency N is a more basic characteristic of collectors than the collection efficiency η even though they are related by η = (αβ) N. Because (αβ) varies during the day the concept of “filtered” sunshine is introduced. This permits treating the collector or, if (αβ) were constant but using a modified or filtered sunshine input curve, large changes in (αβ) can be accommodated without having to use a different filter characteristic. The Shuman case of side mirrors on the north and south edges of a collector is discussed in detail: the yield is increased but is very peaky. An alternative system uses an east-facing mirror placed on the west edge of the collector in the forenoon, which is transferred (manually) at noon to be west facing on the east edge. This system produces about the same amount of boost as the Shuman case but the output is approximately rectangular. Several configurations and transposition systems are given: one has been used in a turbine power installation.

M. Rönnelid, B. Karlsson, P. Krohn, and J. Wennerberg, “Booster reflectors for PV modules in Sweden,” Prog. Photovolt: Res. Appl., vol. 8, no. 3, pp. 279–291, May 2000. doi: 10.1002/1099-159X(200005/06)8:3<279::AID-PIP316>3.0.CO;2-#[edit | edit source]

The performance of photovoltaic modules with planar booster reflectors with variable length and tilts for Swedish conditions is analysed. It is shown that a stationary flat booster reflector can increase the annual output of the module in the order of 20–25%, provided that the influence of short lateral length of the reflector and temperature rise can be limited. The principal difference between using modules with crystalline silicon cells or thin film modules is discussed and numerical examples together with experimental results are given. The electrical coupling of rows in a PV module and/or the electrical coupling of modules in a PV installation are important when booster reflectors are used. If horizontal rows of cells in a module are parallel coupled, the module better utilises radiation reflected from a booster reflector in front than if the rows are coupled in series. Low serial resistance, low module temperature and small edge effects, i.e. not too short lateral length of the booster reflector, are important to achieve good performance of modules with booster reflectors.

H. Tanaka, “Solar thermal collector augmented by flat plate booster reflector: Optimum inclination of collector and reflector,” Applied Energy, vol. 88, no. 4, pp. 1395–1404, Apr. 2011. doi: 10.1016/j.apenergy.2010.10.032[edit | edit source]

Reports 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. Its 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. It is 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.

Advantage of corrugated reflectors[edit | edit source]

M. RÖNNELID and B. KARLSSON, “THE USE OF CORRUGATED BOOSTER REFLECTORS FOR SOLAR COLLECTOR FIELDS,” Solar Energy, vol. 65, no. 6, pp. 343–351, Apr. 1999. doi:10.1016/S0038-092X(99)00009-2[edit | edit source]

The use of booster reflectors in front of solar collectors is an established technique for increasing the irradiation onto solar collectors. By using corrugated instead of flat booster reflectors it is possible to increase the annual irradiation onto the collector plane, thereby maximising the annual output from the collector–reflector arrangement. The paper includes a description of a ray tracing program which calculates the annual optical performance of a collector–booster reflector system with different V-corrugated reflectors. Calculations based on Swedish solar radiation data show that the use of a booster reflector with varying V-corrugations along the reflector, instead of a flat booster reflector, can increase the annual reflected direct radiation on to the collector by 10%. This is estimated to result in a 3% increase in the annual collector output. The ray-tracing calculations are compared with measurements of the reflection characteristics of single V-shaped reflector arrangements.

B. Perers, B. Karlsson, and M. Bergkvist, “Intensity distribution in the collector plane from structured booster reflectors with rolling grooves and corrugations,” Solar Energy, vol. 53, no. 2, pp. 215–226, Aug. 1994.doi: 10.1016/0038-092X(94)90485-5[edit | edit source]

While testing different reflector materials for external reflectors for solar collector arrays, it was found that standard rolled aluminium and corrugated aluminium materials could perform almost as well as mirror-like materials. A ray tracing model was developed to calculate the intensity in the collector plane for solar radiation from reflector materials with grooves or corrugations. Laboratory measurements, for reflector samples, with a specially designed spectral scatterometer were used to determine the angular intensity distribution of the reflected radiation. Calculations with the model using measured intensity distributions show that the scatter from aluminium materials with rolling grooves will be directed close to the specular direction and along an almost circular arc in the collector plane. The intensity in the collector plane will be redistributed slightly upward or downward depending on the season and time of day; therefore, both an increase and decrease in average intensity can occur during the year relative to a mirror-like material with the same total reflectance. For rolled aluminium, a small performance improvement can be achieved compared to a mirror reflector with equal total reflectance. Corrugated surfaces will yield a significant increase in average intensity onto the collector aperture at times when the radiation from a mirror-like reflector would otherwise be lost above the collector.

Tracking Systems[edit | edit source]

Solar tracking systems are actuator devices employed to concentrate reflectors towards the Sun's direction. Concentrators should be able to direct the sunlight precisely onto solar cells with the aid of these devices. Single axis systems can turn the panels around the centre axis while Dual axis tracking is used to position a mirror and concentrate incoming radiation along a fixed axis towards a stationary receiver.

A. K. Agarwal, “Two axis tracking system for solar concentrators,” Renewable Energy, vol. 2, no. 2, pp. 181–182, Apr. 1992. doi: 10.1016/0960-1481(92)90104-B[edit | edit source]

A two axis tracking system is described for the focussing of sunlight in paraboloid-type solar reflectors used in solar thermal devices like solar cookers. This system consists of wormgear drives and four bar type kinematic linkages for effortless and accurate focussing of reflectors at low cost.

J. C. Arboiro and G. Sala, “‘Self-learning Tracking’: a New Control Strategy for PV Concentrators,” Prog. Photovolt: Res. Appl., vol. 5, no. 3, pp. 213–226, May 1997. doi: 10.1002/(SICI)1099-159X(199705/06)5:3<213::AID-PIP171>3.0.CO;2-7[edit | edit source]

Usually the tracking system is not given much importance when designing a photovoltaic (PV) concentrator, partly because the intensive work carried out on this subject has provided it with a false sense of maturity. However, only a few tracking systems have ever been successfully implemented in practical concentrators and many systems never worked in spite of the perfect theoretical design. In this paper we present a review of the experience in tracking systems from the Institute of Solar Energy. This experience runs in parallel with the evolution and development of such systems. It starts with the SANDIA experience in 1977 and moves on to discussing the problems and lessons learned with both open and closed loop systems in the Ramón Areces project (1978). After a brief description of self-aligning systems, we finish by discussing a new approach to tracking: the self-learning concept. In this case the tracking system monitors continuously the operation current, refines constantly its knowledge of the errors and misalignments affecting tracking accuracy and performs the corrections required. The algorithm for this scheme, which has already proved reliable for operation in the EUCLIDES concentrator prototype (1995 to date), is described in some depth.

V. Poulek and M. Libra, “New solar tracker,” Solar Energy Materials and Solar Cells, vol. 51, no. 2, pp. 113–120, Feb. 1998.doi : 10.1016/S0927-0248(97)00276-6[edit | edit source]

A new very simple solar tracker is described in detail in the paper as well as a tracking strategy which enables high-collectible energy surplus at medium tracking accuracy

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, no. 4, pp. 1273–1280, Apr. 2007. doi: 10.1016/j.enconman.2006.09.020[edit | edit source]

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.

H. Mousazadeh, A. Keyhani, A. Javadi, H. Mobli, K. Abrinia, and A. Sharifi, “A review of principle and sun-tracking methods for maximizing solar systems output,” Renewable and Sustainable Energy Reviews, vol. 13, no. 8, pp. 1800–1818, Oct. 2009. doi: 10.1016/j.rser.2009.01.022[edit | edit source]

Finding energy sources to satisfy the world’s growing demand is one of society’s foremost challenges for the next half-century. The challenge in converting sunlight to electricity via photovoltaic solar cells is dramatically reducing $/watt of delivered solar electricity. In this context the sun trackers are such devices for efficiency improvement.The diurnal and seasonal movement of earth affects the radiation intensity on the solar systems. Sun-trackers move the solar systems to compensate for these motions, keeping the best orientation relative to the sun. Although using sun-tracker is not essential, its use can boost the collected energy 10–100% indifferent periods of time and geographical conditions. However, it is not recommended to use tracking system for small solar panels because of high energy losses in the driving systems. It is found that thepower consumption by tracking device is 2–3% of the increased energy.In this paper different types of sun-tracking systems are reviewed and their cons and pros arediscussed. The most efficient and popular sun-tracking device was found to be in the form of polar-axis and azimuth/elevation types.

C.-Y. Lee, P.-C. Chou, C.-M. Chiang, and C.-F. Lin, “Sun Tracking Systems: A Review,” Sensors, vol. 9, no. 5, pp. 3875–3890, May 2009. doi: 10.3390/s90503875[edit | edit source]

The output power produced by high-concentration solar thermal and photovoltaic systems is directly related to the amount of solar energy acquired by the system, and it is therefore necessary to track the sun’s position with a high degree of accuracy. Many systems have been proposed to facilitate this task over the past 20 years. Accordingly, this paper commences by providing a high level overview of the sun tracking system field and then describes some of the more significant proposals for closed-loop and open-loop types of sun tracking systems.

S. Ozcelik, H. Prakash, and R. Challoo, “Two-Axis Solar Tracker Analysis and Control for Maximum Power Generation,” Procedia Computer Science, vol. 6, pp. 457–462, 2011. doi: 10.1016/j.procs.2011.08.085[edit | edit source]

Many of the solar panels throughout the world are positioned with the fixed angles. To maximize the use of the solar panel we use a solar tracker which orients itself along the direction of the sunlight. The solar tracker positions the panel in a hemispheroidal rotation to track the movement of the sun and thus increase the total electricity generation. This paper focuses on the development of new approach to control the movement of the solar panel. The purpose of this paper is to simulate and implement the most suitable and efficient control algorithm on the dual-axis solar tracker which can rotate in azimuth and elevation direction. The simulation gives the tracker angles that position the solar panel along the sun's rays such that maximum solar irradiation is absorbed by the panel.

S. I. Klychev, A. K. Fazylov, S. A. Orlov, and A. V. Burbo, “Design factors of sensors for the optical tracking systems of solar concentrators,” Appl. Sol. Energy, vol. 47, no. 4, pp. 321–322, Mar. 2012. doi: 10.3103/S0003701X11040086[edit | edit source]

Basic diagrams for the sensors of the optical tracking systems of solar concentrators are considered, the design factors that determine their accuracy are analyzed, a new sensor design is suggested, and its optimal parameters are determined.

P. K. Sen, K. Ashutosh, K. Bhuwanesh, Z. Engineer, S. Hegde, P. V. Sen, and P. Davies, “Linear Fresnel Mirror Solar Concentrator with Tracking,” Procedia Engineering, vol. 56, pp. 613–618, 2013. doi: 10.1016/j.proeng.2013.03.167[edit | edit source]

Solar energy is the most abundant, widely distributed and clean renewable energy resource. Since the insolation intensity is only in the range of 0.5 - 1.0 kW/m2, solar concentrators are required for attaining temperatures appropriate for medium and high temperature applications. The concentrated energy is transferred through an absorber to a thermal fluid such as air, water or other fluids for various uses. This paper describes design and development of a ‘Linear Fresnel Mirror Solar Concentrator’ (LFMSC) using long thin strips of mirrors to focus sunlight onto a fixed receiver located at a common focal line. Our LFMSC system comprises a reflector (concentrator), receiver (target) and an innovative solar tracking mechanism. Reflectors are mirror strips, mounted on tubes which are fixed to a base frame. The tubes can be rotated to align the strips to focus solar radiation on the receiver (target). The latter comprises a coated tube carrying water and covered by a glass plate. This is mounted at an elevation of few meters above the horizontal, parallel to the plane of the mirrors. The reflector is oriented along north-south axis. The most difficult task is tracking. This is achieved by single axis tracking using a four bar link mechanism. Thus tracking has been made simple and easy to operate. The LFMSC setup is used for generating steam for a variety of applications.

S. Yilmaz, H. Riza Ozcalik, O. Dogmus, F. Dincer, O. Akgol, and M. Karaaslan, “Design of two axes sun tracking controller with analytically solar radiation calculations,” Renewable and Sustainable Energy Reviews, vol. 43, pp. 997–1005, Mar. 2015. doi: 10.1016/j.rser.2014.11.090[edit | edit source]

In order to design new PV systems that will be installed to operate in more efficient and more feasible way, it is necessary to analyze parameters like solar radiation values, the angle of incidence of the genus, temperature etc. Therefore, in this study, theoretical works have been performed for solar radiation and angle of incidence values of any location, plus an experimental study was carried out on a system tracking the sun in two axes and in a fixed system. The performed prototype is also adapted into a PV system with 4.6 kW power. Theoretical data are consistent with the data obtained from the PV system with 4.6 kW power. This study will be an important guide for the future PV power stations.

Large Scale PV systems[edit | edit source]

C. Deline, A. Dobos, S. Janzou, J. Meydbray, and M. Donovan, “A simplified model of uniform shading in large photovoltaic arrays,” Solar Energy, vol. 96, pp. 274–282, Oct. 2013. doi:10.1016/j.solener.2013.07.008[edit | edit source]

Kirigami approach[edit | edit source]

Kirigami and Technology[edit | edit source]

Graham P. Collins, “Kirigami and technology cut a fine figure, together,” Proceedings of the National Academy of Sciences, vol. 113, no. 2, pp. 240–241. doi:10.1073/pnas.1523311113[edit | edit source]

  • Notion : Kirigami is a variant of origami, the art of paper folding. The words derive from the Japanese for cutting (kiru), folding (oru), and paper (kami).
  • Aim: To discuss how this art form has emerged into science to help develop new technologies.Author aims to provide insights into collaborations leading to authentic design forms in different fields.
  • Summary: 1. Kirigami pathway provides an excellent design opportunity to convert 2D forms to 3D forms just by simple folding and cutting transforms which can be applied from various scales nano to meso. 2. Kirigami way can alleviate stresses in structures leading to fracture and thus can be widely applied in 3D structures of optoelectronics and nanostructured biomedical devices. 3. This design pathway inspired people from ASU to manufacture flexible chain of Li-Ion batteries and also provided flexible design methodologies of single atom thick, out structured graphene sheets. This paper surmises current and future creative collaborations with a broader view of invocating new design principles.

T. C. Shyu, P. F. Damasceno, P. M. Dodd, A. Lamoureux, L. Xu, M. Shlian, M. Shtein, S. C. Glotzer, and N. A. Kotov, “A kirigami approach to engineering elasticity in nanocomposites through patterned defects,” Nat Mater, vol. 14, no. 8, pp. 785–789, Aug. 2015. doi: 10.1038/nmat4327[edit | edit source]

Efforts to impart elasticity and multifunctionality in nanocomposites focus mainly on integrating polymeric and nanoscale components. Yet owing to the stochastic emergence and distribution of strain-concentrating defects and to the stiffening of nanoscale components at high strains, such composites often possess unpredictable strain–property relationships. Here, by taking inspiration from kirigami—the Japanese art of paper cutting— a network of notches were made in rigid nanocomposite and other composite sheets by top-down patterning techniques prevents unpredictable local failure and increases the ultimate strain of the sheets from 4 to 370%. The sheets’ tensile behaviour can be accurately predicted through finite-element modelling. Moreover, in marked contrast to other stretchable conductors the electrical conductance of the stretchable kirigami sheets is maintained over the entire strain regime. The unique properties of kirigami nanocomposites as plasma electrodes open up a wide range of novel technological solutions for stretchable electronics and optoelectronic devices, among other application possibilities.

How does a Kirigami approach helps solar photovolatics?[edit | edit source]

A. Lamoureux, K. Lee, M. Shlian, S. R. Forrest, and M. Shtein, “Dynamic kirigami structures for integrated solar tracking,” Nat Commun, vol. 6, p. 8092, Sep. 2015. doi:10.1038/ncomms9092[edit | edit source]

Optical tracking is often combined with conventional flat panel solar cells to maximize electrical power generation over the course of a day. However, conventional trackers are complex and often require costly and cumbersome structural components to support system weight. kirigami designing is used to as integral to the structure at the substrate level for GaAs. Specifically, an elegant cut pattern is made, which are then stretched to produce an array of tilted surface elements which can be controlled to within ±1°.Source angle and extent of tracking are varied and tested. The combined optical and mechanical properties of the tracking system demonstrates a mechanically robust system with optical tracking efficiencies matching conventional trackers. This design suggests a pathway towards enabling new applications for solar tracking, as well as inspiring a broader range of optoelectronic and mechanical devices.

Modelling[edit | edit source]

Link directly to Low level concentration for PV applications literature review

BDRV Based Modelling[edit | edit source]

R. W. Andrews, A. Pollard, and J. M. Pearce, “Photovoltaic system performance enhancement with non-tracking planar concentrators: Experimental results and BDRF based modelling,” in Photovoltaic Specialists Conference (PVSC), 2013 IEEE 39th, 2013, pp. 0229–0234. doi: 10.1109/PVSC.2013.6744136[edit | edit source]

Non-tracking planar concentrators are a low-cost method of increasing the performance of traditional solar photovoltaic (PV) systems. In this study such an outdoor system has been shown to improve energy yield by 45% for a traditional flat glass module and by 35% for a prismatic glass crystalline silicon module. In addition, this paper presents new methodologies for properly modelling this type of system design and experimental results using a bi-directional reflectance function (BDRF) of non-ideal surfaces rather than traditional geometric optics. This methodology allows for the evaluation and eventual optimization of specular and non-specular reflectors in planar concentration systems.

Citations[edit | edit source]

  1. S. Kurtz, “Opportunities and challenges for development of a mature concentrating photovoltaic power industry,” Technical Report, NREL/TP-520- 43208, 2009
  2. Andrews, Rob W.; Pollard, Andrew; Pearce, Joshua M., "Photovoltaic system performance enhancement with non-tracking planar concentrators: Experimental results and BDRF based modelling," Photovoltaic Specialists Conference (PVSC), 2013 IEEE 39th, pp.0229,0234, 16–21 June 2013. doi: 10.1109/PVSC.2013.6744136
  3. A. L. Luque and A. Viacheslav, Eds., "Concentrator Photovoltaics," vol. 130. Berlin, Heidelberg: Springer Berlin Heidelberg, 2007.(Chapter: 1 and 6). ISBN: 978-3-540-68796-2
  4. M. Šúri, T. A. Huld, E. D. Dunlop, and H. A. Ossenbrink,“Potential of solar electricity generation in the European Union member states and candidate countries,” Solar Energy, vol. 81, no. 10, pp. 1295–1305, Oct. 2007. doi: 10.1016/j.solener.2006.12.007