Concentrator Photovoltaic Module Research Articles

A new procedure for estimating the cell temperature of a high concentrator photovoltaic grid connected system based on atmospheric parameters

The working cell temperature of high concentrator photovoltaic systems is a crucial parameter when analysing their performance and reliability. At the same time, due to the special features of this technology, the direct measurement of the cell temperature is very complex and is usually obtained by using different indirect methods. High concentrator photovoltaic modules in a system are operating at maximum power since they are connected to an inverter. So that, their cell temperature is lower than the cell temperature of a module at open-circuit voltage since an important part of the light power density is converted into electricity. In this paper, a procedure for indirectly estimating the cell temperature of a high concentrator photovoltaic system from atmospheric parameters is addressed. Therefore, this new procedure has the advantage that is valid for estimating the cell temperature of a system at any location of interest if the atmospheric parameters are available. To achieve this goal, two different methods are proposed: one based on simple mathematical relationships and another based on artificial intelligent techniques. Results show that both methods predicts the cell temperature of a module connected to an inverter with a low margin of error with a normalised root mean square error lower or equal than 3.3%, an absolute root mean square error lower or equal than 2°C, a mean absolute error lower or equal then 1.5°C, and a mean bias error and a mean relative error almost equal to 0%.

Evaluation of misalignments within a concentrator photovoltaic module by the module optical analyzer: A case of study concerning temperature effects on the module performance

Instituto de Energía Solar, Universidad Politécnica de Madrid (IES-UPM) has developed a method [referred to as the luminescence inverse (LI) method] and equipment [called module optical analyzer (MOA)] to fast measure the optical-angular properties of a CPV module without illumination system nor module movement. This paper presents how the MOA can investigate the optical performance of concentrator photovoltaic (CPV) modules optical-angular performance (in particular, misalignments between the optical components comprising the module) at different temperature conditions.

A methodology for the electrical characterization of shaded high concentrator photovoltaic modules

In this paper, a methodology for characterizing the I–V curve of partially shaded high concentrator photovoltaic modules is presented. It takes into account atmospheric parameters (direct normal irradiance, ambient temperature, wind speed and air mass) as well as the amount of shading on each receiver lens and the module electrical configuration. Two high concentrator photovoltaic modules have been characterized in order to apply the methodology. Both modules have been measured under different shading conditions and a comparison between experimental and simulated behavior has been carried out. It was found root mean squared errors for the I–V curves lower than 4% and absolute values of relative errors at the maximum power point lower than 3% in 80% of the analyzed measurements. The methodology can be regarded as a step for the development of a complete model for the electrical characterization of shaded high concentrator photovoltaic power plants.

CFK: a Fresnel–Köhler concentrator with an external confinement cavity

AbstractIn a concentrator photovoltaic (CPV) module, the solar cell surface reflects a non‐negligible portion of the incoming light, leading to a loss in module efficiency. The Fresnel–Köhler with an external confinement cavity (CFK) is a novel optical CPV concentrator designed to recover this portion of the reflected light. The design is based on an external confinement cavity, an optical element able to redirect the light reflected by the cell surface towards its surface again. Its integration into a CPV module is possible, thanks to the recent invention of advanced Köhler concentrators by LPI. This strategy, based on light recovery, leads to a significant increase in electrical efficiency. We have tested the excellent performance of these cavities by means of integrating one of them into an FK concentrator and manufacturing a proof‐of‐concept prototype. The measured results are outstanding: a relative electrical efficiency and Isc gains of up to 6% when comparing both with and without cavity designs, and a 33.2% of CFK module electrical efficiency (@Tcell = 25 °C) using a 38.5% nominal efficiency cell (without anti‐reflection coatings on the optics). Copyright © 2015 John Wiley & Sons, Ltd.

Performance optimization of dense-array concentrator photovoltaic system considering effects of circumsolar radiation and slope error.

This paper presents an approach to optimize the electrical performance of dense-array concentrator photovoltaic system comprised of non-imaging dish concentrator by considering the circumsolar radiation and slope error effects. Based on the simulated flux distribution, a systematic methodology to optimize the layout configuration of solar cells interconnection circuit in dense array concentrator photovoltaic module has been proposed by minimizing the current mismatch caused by non-uniformity of concentrated sunlight. An optimized layout of interconnection solar cells circuit with minimum electrical power loss of 6.5% can be achieved by minimizing the effects of both circumsolar radiation and slope error.

High-efficiency thin and compact concentrator photovoltaics with micro-solar cells directly attached to a lens array

We propose a thin and compact concentrator photovoltaic (CPV) module, about 20 mm thick, one tenth thinner than those of conventional CPVs that are widely deployed for mega-solar systems, to broaden CPV application scenarios. We achieved an energy conversion efficiency of 37.1% at a module temperature of 25 °C under sunlight irradiation optimized for our module. Our CPV module has a lens array consisting of 10 mm-square unit lenses and micro solar cells that are directly attached to the lens array, to reduce the focal length of the concentrator and to reduce optical losses due to reflection. The optical loss of the lens in our module is about 9.0%, which is lower than that of conventional CPV modules with secondary optics. This low optical loss enables our CPV module to achieve a high energy conversion efficiency.

High concentrator photovoltaic module simulation by neuronal networks using spectrally corrected direct normal irradiance and cell temperature

The electrical modelling of HCPV (high concentrator photovoltaic) modules is a key issue for systems design and energy prediction. However, the electrical modelling of HCPV modules shows a significantly level of complexity than conventional photovoltaic technology because of the use of multi-junction solar cells and optical devices. In this paper, a method for the simulation of the I–V curves of a HCPV module at any operating condition is introduced. The method is based on three different ANN (artificial neural networks)-based models: one to spectrally correct the direct normal irradiance, one to predict the cell temperature and one to generate the I–V curve of the HCPV module. The method has the advantage that is fully based on atmospheric parameter and outdoor measurements. The analysis of results shows that the method accurately predicts the I–V curve of a HCPV module for a wide range of atmospheric operating conditions with a RMSE (root mean square error) ranging from 0.19% to 1.66% and a MBE (mean bias error) ranging from −0.38% to 0.40%.

Shutter Technique for Noninvasive Individual Cell Characterization in Sealed CPV Modules

An optical shutter technique for quality control and degradation analysis of concentrating photovoltaic (CPV) modules is presented. Shuttering configurations are described and used to determine individual component degradation or failure in field-exposed commercial modules. Cells are shuttered in specific patterns, intentionally engaging internal bypass diodes, and current–voltage ( I – V ) curves are measured at the housing terminals of the sealed module. Individual cell characteristics may be qualitatively determined by contrasting module I – V responses to different shutter configurations and quantitatively determined by fitting an extended equivalent circuit model to the shutter data.

Development of a mirror‐based LCPV module and test results

AbstractThe design of a specific low concentration photovoltaic module is described here, with a report of the results of the first experimental tests of its industrial version. The product is a 20× reflective concentrating photovoltaic module based on silicon solar cells. The optics were designed to mount these modules on 2‐axis trackers with angular pointing accuracy of up to about ±4° without significant power loss. The high angular acceptance of the non‐imaging optics permits the collection of a high fraction of the circumsolar light impinging on the module's frontal aperture, providing high direct normal irradiance efficiency in real operative conditions. Many technical features of the product are described here, in which features are the result of 5 years of product development in order to improve performance, reliability and cost issues. Copyright © 2015 John Wiley & Sons, Ltd.

CPV module electric characterisation by artificial neural networks

Concentrating photovoltaic (CPV) is a relatively new technology with promising future expectations. However, it is at an early stage of development and it has much room for improvement. In order to gain knowledge about CPV technology, outdoor measurements are necessary to adjust models and to study the influence of the atmospheric conditions on the modules performance. In this work, multilayer perceptron models are applied to generate I–V characteristic curves of one of the most extended commercial module of concentrating photovoltaic technology, using the influential atmospheric variables as inputs to the networks. To train these networks an experiment with real measurements was carried out in Jaén, Spain, from July 2011 to June 2012. In addition to a model based on I–V curves expressed as a list of points in Cartesian coordinates, we present an alternative model trained with curves represented in polar coordinates. A previous selection of the most representative samples from the initial dataset was performed using a Kohonen self-organising map. This procedure allows the simulation of the curves even under non-frequent atmospheric conditions. Using the proposed models, it is possible to obtain the characteristic curve of other CPV modules under different meteorological conditions, with high accuracy and fidelity.

Temperature-dependent model of concentrator photovoltaic modules combining optical elements and III–V multi-junction solar cells

A temperature-dependent model, combining optical elements and III–V multi-junction solar cells, is proposed for the performance analysis of concentrator photovoltaic (CPV) modules. Compared with the previous theoretical characterizing methods for solar cells, our model takes into account the impact of the primary and secondary optical elements in a realistic concentrator photovoltaic module by ZEMAX modeling approach, making it possible to simulate the flux intensity and spectral distribution on the active area of the solar cell according to the practical direct normal irradiation. Then a two-diode equivalent circuit semi-empirical model is presented to characterize the temperature-dependence of the GaInP/GaInAs/Ge triple-junction cells used in the CPV module. The circuit parameters are extracted by a synthetical approach, which combines the global numerical optimization technique with the analytical extraction method using the measured illuminated I–V characterization curve of the CPV module at the determined condition and the temperature coefficients for short circuit current and open circuit voltage of the triple-junction cell assembly given in the product datasheet from the cell manufacturer. The temperature-dependent performance of the CPV module analyzed by this model agrees well with the measured results.

Design, fabrication and outdoor performance analysis of a low concentrating photovoltaic system

A prototype concentrating photovoltaic (CPV) module was designed and constructed with a low concentrating dielectric compound parabolic concentrator (DiACPC) for outdoor characterisation. The designed concentrator has acceptance half angles of 0° & 55° with a concentration ratio of 2.8. This concentrator design is suitable for building facade integration in higher latitude (>55°) locations. A small prototype CPV module of 300mm×300mm was constructed with 2 strings of 14 solar cells in series. The prototype CPV module was characterised in Edinburgh for different weather conditions and the performance is compared with a similar non-concentrating counterpart (i.e. a flat-plate module with the same PV cell area and technology) in real time. The electrical output results for a cloudy day, rainy day and a day with sunny intervals have been reported to evaluate the performance of the concentrating system with direct and diffuse irradiance. The maximum power output of the CPV module on the day with sunny intervals was found to be 5.88W for a solar radiation input of 943W/m2, which is 2.27times higher than that for the flat-plate module. The average short circuit current of the CPV module was found to be 2.22times higher than that of the flat-plate module. The average open circuit voltage and fill factor of the CPV module were also found to be 2.5% and 1.6% higher than that for the flat-plate module. The CPV module is found to be very effective on the rainy day with an average power output of 0.13W, which is 2.17times higher than the average output power for the flat-plate module.

Methodology for the characterization of the humidity behavior inside CPV modules

In this study the characterization of the humidity behavior inside concentrating photovoltaic (CPV) modules is addressed. To this purpose, several experimental tests have been carried out by using two different CPV modules and three different breathers, collecting in each analyzed case the evolution of temperature, relative and specific humidity of the air volume contained inside the module for many days. Results indicates that, for each of the CPV modules analyzed, it is possible to construct a characteristic curve in the temperature-specific humidity psychrometric chart, that can be used for estimating the specific humidity of the air inside the CPV module as a function of the internal air temperature. The characteristic curve can be also used to estimate the saturation temperature of the air inside the CPV module, and consequently to detect the eventuality of moisture condensation during cloudy days or night-time, namely when the temperature of the air inside the module is low and reaches the external ambient one. This methodology can be used in CPV modules design for the choice of the breather and of the construction materials, in order to obtain a saturation temperature as low as possible.

Optimizing Defocus to Increase Efficiency in Concentrator Photovoltaic Modules

We describe a process for increasing power efficiency of concentrator photovoltaic (PV) systems by optimizing the lens-to-cell spacing. We find that there is an optimum defocus position with improved power output and reduced sensitivity to pointing errors, which, in combination, can result in a more than 10% enhancement. The improvement can be realized by minor changes to module cases which should not require changes to other manufacturing, installation, or component costs. In fact, optimizing the defocus position allows for lower costs per unit power due to increased power and relaxed system tolerances. This paper focuses on detailed data illuminating the behavior of ultrahigh concentration PV modules, while one can look forward to optimizing defocus through sufficiently detailed simulation; at present, we find that an empirical determination of optimum defocus is necessary. The data reveal that even without design parameters changing, supply chain changes can have a significant impact on the optimum defocus; data from five different module configurations with components from different manufacturing lots are presented. These different configurations serve to illustrate the consequences of component changes and the importance of verifying the optimum defocus. A detailed discussion of the effects that are important to determine the optimum defocus and which underlie these differences is included.

Analytical Modelling of High Concentrator Photovoltaic Modules Based on Atmospheric Parameters

The goal of this paper is to introduce a model to predict the maximum power of a high concentrator photovoltaic module. The model is based on simple mathematical expressions and atmospheric parameters. The maximum power of a HCPV module is estimated as a function of direct normal irradiance, cell temperature, and two spectral corrections based on air mass and aerosol optical depth. In order to check the quality of the model, a HCPV module was measured during one year at a wide range of operating conditions. The new proposed model shows an adequate match between actual and estimated data with a root mean square error (RMSE) of 2.67%, a mean absolute error (MAE) of 4.23 W, a mean bias error (MBE) of around 0%, and a determination coefficient (R2) of 0.99.

Plasma etching antireflection nanostructures on optical elements in concentrator photovoltaic systems

Transmission-type concentrator photovoltaic (CPV) systems are a potential candidate to achieve high efficiency and low cost solar energy. The use of optical elements in these systems creates reflection losses of incoming solar energy that account for about 8% to 12% depending on the optical design. In order to reduce these losses, we have nanostructured the air/optical-elements’ interfaces by using plasma etching methods on the Fresnel lens made of poly(methyl methacrylate) (PMMA) and the homogenizer made of glass. On flat PMMA and glass substrates, transmittance enhancement measurements are in agreement with relative Jsc gains. The field test results using a CPV module with all textured optical-elements’ interfaces achieved 8.0% and 4.3% relative Jsc and efficiency gains, respectively, demonstrating the potential of this approach to tackle the reflection losses.

Estimation of operating temperature and energy output of concentrator photovoltaic module under concentration conditions

The operating temperature of a concentrator photovoltaic (CPV) module is a dominant factor in its conversion efficiency. It is necessary to reduce the operating temperature to generate a high output of a CPV module under field operation. Therefore, we estimated the operating temperature and conversion efficiency of a cell or module under real concentrating operations. First, we developed a heat transfer model for the CPV module. The operating temperature in the CPV module was calculated as functions of the thermal resistance and the heat transfer coefficient. A low thermal resistance between the solar cell and the back-surface and a high heat transfer coefficient of the back-surface were effective for reducing operating temperature. Next, the conversion efficiency of a triple-junction solar cell was calculated using an equivalent circuit simulation. We can evaluate the cell performance under actual operating conditions using the calculated operating temperatures of the cell.

Reliability potential of silicone molding compounds for LED application

As the development of light emitting devices (LEDs), integrate circuits (ICs) and concentration photovoltaic (CPV) modules towards higher density, packaging materials are facing the challenges of withstand with heat generation and high energy. Epoxy molding compound (EMC) is the latest technology for LED and solar cell package to replace PPA and PCT. However, it is well known that the thermal and radiation resistance of epoxy is limited. Recently, silicone based composites are attracting attention as ideal materials because they are insensible to high energy density and good resistance to UV light and heat. Epoxy and silicone both have reliability issues during long-term service at high temperature and high energy. Thermal and radiation degradation of reflector materials will largely affect their reflectance and their contribution to a higher light output and energy efficiency. Therefore, it is very essential to evaluate reliability performance of SMC and EMC based reflecting materials. Aging under multiple environmental conditions has generated considerable interest for evaluating the life and behavior of materials in a real environment. Radiation and thermal aging are two quite different types of aging. The combination of these two situations will cause the aging process to accelerate further. The objective of this study is to investigate the synergetic influence of thermal and radiation aging on optical performance of SMC and EMC based packaging materials. It is concluded that SMC is the preferred choice for packaging LEDs, ICs and solar cells for its superior thermal and radiation resistance.

Key parameters in determining energy generated by CPV modules

AbstractWe identify the key inputs and measurement data needed for accurate energy rating of concentrator photovoltaic (CPV) modules based on field observations of multiple CPV modules. Acceptance angle is shown to correlate with the observed module‐level performance ratio (PR) for the modules studied. Using power ratings based on concentrator standard test conditions, PRs between 90% and 95% were observed during the summers with up to ~10% lower PRs during the winters. A module fabricated by Semprius showed 94% ±0.7% PR over almost 2 years with seasonal variation in PR of less than 1% showing how a module with relatively large acceptance angle may show very consistent average efficiency (calculated from the energy generated relative to the energy available), potentially simplifying energy ratings. The application of the results for translation of energy rating from one location to another is discussed, concluding that most of the translation differences may be correlated with temperature differences between sites with the largest variation happening when optical efficiency depends on temperature. Copyright © 2014 John Wiley & Sons, Ltd.

Development of a high/low concentration photovoltaic module with dichroic spectrum splitting

AbstractA concentrating photovoltaic module design incorporating a spatial spectral splitting approach with dichroic mirrors is presented. The advantages of this technology are reported, as well as a short description of the design evolution process. The experimental results are summarised, highlighting possible improvements through the use of different production processes and components. Materials, design and assembly procedures are taken into account, keeping in mind the fundamental constrains of cost and reliability of the final product. Finally, the possibilities for market exploitation of this technology in the current photovoltaic landscape are analysed. Copyright © 2014 John Wiley & Sons, Ltd.