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Solutions that maximize the profitability and cost-competitiveness of photovoltaic projects are still necessary. Adding solar tracking mechanisms increase the energy production although it represent a cost reduction barrier. Therefore, the challenge is to balance the additional costs of trackers with yield increases. Due to the lack of studies that analyse when a tracker installation is more profitable than a fixed one, the calculation of the Levelised Cost of Electricity (LCOE), among other most common economic assessment criteria, is proposed for several locations and different configurations, i.e. fixed, horizontal one-axis and two-axis tracking, where local technical and economic parameters were used. The first result shows that fixed and one-axis systems are cost-competitive respect to electricity tariffs, whereas two-axis ones are discouraged. LCOE differences up to 213%, 240% and 262% for fixed, one and two axis systems were detected among the locations analysed, however, a better scenario in LCOE terms does not mean better profitability results. Under certain circumstances, with the same LCOE results, one-axis photovoltaic systems are preferred over fixed ones. Therefore it is essential to identify optimization strategies according to technical, economic and financial parameters, as well as to include the electricity tariffs as a strategic variable in the analysis.

In this paper, we compare the optical and electrical performance of different Fresnel-based HCPV systems equipped with different refractive secondary optical elements (SOEs) through both optical modelling and experiments. The SOEs (designed with a thorough optical modelling): i) Dielectric-cross compound-parabolic-concentrator (DCCPC), ii) (SIngle-Lens-Optical element) SILO-Pyramid, iii) Refractive truncated pyramid (RTP) and, iv) Trumpet; are fabricated (made of PMMA) and mounted on commercially available concentrator solar cell assemblies. An indoor characterisation of all these HCPV units, under controlled conditions, using a CPV Solar Simulator “Helios 3198” is performed. The angular behaviour of the HCPV units is predicted properly, in general, although the measured optical efficiencies result in lower values than in the optical simulations. The reasons for those differences are explored through some fabrication and mounting imperfections detected, among others. The impact of changed irradiance and spectrum is analysed separately. No high dependence in the efficiency or in the acceptance angle, in terms of the maximum power point, was found due to changes in the irradiance. For changed spectral conditions, the decrease in the fill factor results in up to around 4% lower than the maximum values. Moreover, the impact of the spectrum on the acceptance angle was analysed. The results showed an increment of the power-based acceptance angle for blue-rich spectra for the HCPV units with SOEs working as light pipes. From the results of efficiency and acceptance angle, none of the SOEs produces a notably performance than the others.

High Concentrator Photovoltaic (HCPV) modules (with concentrations higher than 300 times) have increased their conversion efficiency records up to more than 43% in the last years. This represents the maximum conversion efficiency by any type of photovoltaic (PV) module. Moreover, HCPV modules still have a theoretical potential for a significant efficiency growth. This work analyses the current status of efficiency records of HCPV modules and their evolution in the last 20 years, as well as the most efficient commercial HCPV modules, these last with up to around 34% efficiency nowadays. It is found that the efficiency growth of HCPV modules in the last years is considerably greater than that of other PV technologies like crystalline silicon (c-Si) or Thin Film. The values of efficiency, acceptance angle, geometrical concentration and power of current HCPV modules are gathered. Current efficiency values are typically centred in the range between 27% and 33%, whereas the current average of acceptance angle values is ± 0.9°. Regarding the geometrical concentration of the efficiency record HCPV modules, it is typically lower than 400× whereas current commercial HCPV modules work in the range of 500–1000×. Moreover, a total of 24 commercial HCPV modules were characterised indoors at the CPV solar simulator at the University of Jaen in order to compare the datasheets with the experimental data. The measurement results, including the efficiency and acceptance angle characteristics, are presented and compared with datasheet values.

The sizing of the inverter in comparison to the rated capacity of the photovoltaic generator is investigated for high-concentrator photovoltaic (HCPV) systems. An HCPV module of typical characteristics is modelled and parameterized, taking into account direct normal irradiance (DNI), ambient temperature, air mass and aerosol optical depth as atmospheric inputs, while the DC losses of the HCPV generator are allowed to vary in the ranges reported in the literature. A set of 80 commercial inverters are analysed to obtain the typical efficiency curves of state-of-the-art low-, medium-, and high-efficiency inverters. Four locations worldwide with high annual DNI levels and different average values of the weather variables influencing HCPV performance are studied. Results show that the inverter can be sized between 84% and 112% of the rated capacity of the HCPV generator at Concentrator Standard Test Conditions depending on the scenario considered for maximizing the final energy yield of the system. The proposed methodology uses analytical equations, all the model parameters are provided and justified and atmospheric inputs are obtained from meteorological databases in order to make the application easy regarding its use in other locations where the climate data is available.

Ultra-high concentrator photovoltaic systems aim to enhance the conversion efficiency of sunlight and to reduce the cost of electricity. However, it is still necessary to develop optical systems with higher efficiencies and angular tolerances for them to become a reality. This Letter proposes a novel design that is able to achieve a geometric concentration of 4096 × . The system consists of four concentrator units based on parabolic mirrors and optical guides that concentrate the sunlight onto a single cell. Additionally, a preliminary proof-of-concept module has been assembled for validation purposes. The novel design exceeds the optical efficiency of the existing systems, ≈ 84 % , and offers almost double acceptance angles, ≈ 0.6 ∘ .

High Concentrator Photovoltaic (HCPV) units are typically based on the use of Fresnel lenses, refractive secondary optical elements (SOE), and triple-junction (TJ) solar cells. In this work, a detailed optical modeling is applied to analyze the performance of four Fresnel-based HCPV units equipped with different refractive SOEs while considering the subcells current density generation. Wavelength-dependent material properties are utilized while simulating the optical performance. The spectral response of a typical TJ solar cell is also included. This modeling allows to establish the subcell current limitation and the spectral matching ratio, SMR , values in each case. The following SOEs have been used for simulating the HCPV units: (i) Dielectric-cross compound-parabolic-concentrator (DCCPC), (ii) (SIngle-Lens-Optical element) SILO-Pyramid, (iii) Refractive truncated pyramid (RTP) and, (iv) Trumpet. Results show that the HCPV units with SOEs RTP and Trumpet, exhibit bottom subcell current limitation and lowest optical polychromatic efficiency, this is partly due to the irradiance absorption in the bottom cell spectral region and longer optical path length of the concentrated rays within the SOE material. In the case of the HCPV unit with the DCCPC SOE, top and bottom subcells limit the current generation alternatively depending on the misalignment angle of the HCPV unit respect to the simulated sunrays. None of the SMR parameters are equal to 1 under normal alignment of the HCPV units. The short-circuit current density distributions for each subcell in each case are studied under normal alignment and under 1° of misalignment angle.

The current-voltage output of concentrator photovoltaic (CPV) modules shows a complex behaviour under irradiance variations due to the use of multi-junction solar cells and optical elements. The single exponential model (SEM) relates the I-V curve of a PV device and its five characteristic parameters. Hence, it is fundamental to understand the dependence of the SEM model and I-V parameters of CPV modules with irradiance. In this paper, two samples of concentrator modules were characterized under fully controlled conditions by using a CPV solar simulator for light intensities within 700–1000 W/m 2 . Results show that the photo-generated current increases linearly with irradiance, the diode ideality factor and saturation current present a stable behaviour under irradiance variations while the parasitic resistances, i.e. series and shunt, trend to decrease as the intensity increases. In addition, different approximations are carried out in the SEM model equation to explain the dependence of the performance of the concentrators with light intensity. Finally, the prediction of the I-V curves and key electrical parameters from reference values is discussed. Results show a good fitting of the I-V curves until 750 W/m 2 and a high accuracy in the estimations of the electrical parameters with a MAPE lower than 1.2%, a MRE within 1% and a R 2 equal of higher than 0.9.

Photovoltaic system performance is affected by changes in the input sunlight spectrum. Moreover, the different photovoltaic materials employed show different spectral responses, having different spectral behaviour as a result. Many authors have developed methods and proposed indexes for quantifying the spectral influences in photovoltaic systems under the time-varying weather variables. These methods use different equipment, different procedures and assumptions, present different levels of complexity and accuracy, and have advantages and disadvantages in each specific context and application. In this paper, for the first time, a systematic review of the available methods and photovoltaic spectral indexes is presented. Each alternative is analysed in detail and a comparative study is done. In addition, as several authors have measured and/or calculated the spectral impact on the energy yield of the different photovoltaic technologies at particular locations and climates, the existing results are summarized and discussed in order to elucidate the spectral behaviour of each technology as a function of the relevant atmospheric parameters, i.e. air mass, aerosol optical depth and precipitable water. The presented study covers non-concentrating and high-concentrating photovoltaic technologies and is intended for clarifying the methods available for the spectral analysis and the spectral impact on energy harvesting of the photovoltaic technologies.

Numerous exhaustive analyses of the economic assessment of conventional PV systems are available in the literature. However, there is a lack of these studies concerning High Concentrator Photovoltaic (HCPV) technology. Besides, future owners and potential investors on HCPV plant demand information relating to the economic feasibility of their investment. In this work the profitability and competitiveness of HCPV plants in several countries are analysed. To analyse the profitability the internal rate of return (IRR) criterion has been used, while the competitiveness has been analysed based on estimating the so-called HCPV generation parity. As a result of the economic profitability analysis conducted the group of countries where the investment in HCPV could be interesting has been identified. The results obtained could be also useful for researchers to identify the weaknesses of the HCPV technology and take actions at making it more competitive. From the competitiveness analysis carried out in several Eurozone countries and USA for two possible scenarios 2015 and 2020, the results show that HCPV could be competitive in some locations in 2020. Therefore, government organizations of the studied countries, which participate in the design or the selection of support mechanisms for HCPV, can be guided by the results obtained.

Nowadays, the integration of photovoltaic (PV) systems into the grid involves new and competitive ways to realize this. Thus, it is necessary to define procedures that not only include energy calculations but also incorporate economic and funding feasibility features. According to the literature review, there are numerous tools that are available to carry out a profitability analysis of a photovoltaic system. However, certain shortcomings have been identified, either in the definition of the economic and financial scenarios or in the results obtained, as they do not provide all the necessary information, do not use all the most common economic criteria, or in some cases the complexity and training requirements for their correct implementation may discourage their use. Therefore, in this paper a complete procedure that can be used as a preliminary decision tool prior to the design of an in-depth PV self-consumption system is proposed. Realistic input data makes it possible to not only obtain results for common economic and financial feasibility criteria (Net Present Value, Internal Rate of Return, Discounted Pay-Back Time and Net Cash Balance), but it also allow for a cost-competitiveness evaluation based on the Levelised Cost of Electricity (LCOE). The novel concept of the direct cost of PV self-consumed electricity is also introduced.

The potential cost reduction of Concentrator photovoltaic (CPV) systems is closely related to the concentration factor because higher light concentrations imply lower amount of semiconductor material required for the solar cells. However, the thermal management at such ultra-high light fluxes is difficult. The use of small-sized solar cells is beneficial for improving the thermal management. Among the possible cooling strategies, the use of flat-plate heat-sinks for passive cooling, if feasible, would be the simplest way to dissipate heat and would accelerate the development of ultra-high CPV prototypes. In this work, a thermal 3D finite-element model is used to investigate the possibilities of flat-plate heat-sinks for passive cooling at concentration ratios within 2,000-10,000 suns. Results show that a micro solar cells of 1mm x 1mm area can be thermally handled with conventional Aluminium flat plate heat-sinks up to 10,000 suns.

In the frame of the Concentrator Photovoltaic (CVP) technology, to achieve ultra-high (UH) concentration levels is a promising strategy to reduce the cost of the PV electricity, since it takes advantage of the reduction of the solar cell area and also of the physical behavior of the solar cells. This work analyzes a previous optical concentrator design for a module with a geometrical concentration of 2000×, i.e. in the range of the UHCPV (ultra-high CPV), in terms of its geometrical design. This optical design can be called Cassegrain-Koehler, since it uses different optical units based on the basic Cassegrain design for telescopes (with a paraboloid primary mirror and with a hyperboloid secondary mirror) as well as takes advantage of the Koehler illumination technique on the solar cell. In order to optimize this design, the f- number of the primary mirrors is varied while the f-number of the secondary mirrors is maintained constant ‒3.5. This allow the impact of the compactness of this UHCPV design to be determined. The results show an optimum trade-off of optical efficiency and acceptance angle when the f-number of the primary mirrors is around 0.63, which is not the most compact design obtained. However, the irradiance uniformity over the solar cell, evaluated through the peak-to-average ratio (PAR) results lowest in the most compact designs.In the frame of the Concentrator Photovoltaic (CVP) technology, to achieve ultra-high (UH) concentration levels is a promising strategy to reduce the cost of the PV electricity, since it takes advantage of the reduction of the solar cell area and also of the physical behavior of the solar cells. This work analyzes a previous optical concentrator design for a module with a geometrical concentration of 2000×, i.e. in the range of the UHCPV (ultra-high CPV), in terms of its geometrical design. This optical design can be called Cassegrain-Koehler, since it uses different optical units based on the basic Cassegrain design for telescopes (with a paraboloid primary mirror and with a hyperboloid secondary mirror) as well as takes advantage of the Koehler illumination technique on the solar cell. In order to optimize this design, the f- number of the primary mirrors is varied while the f-number of the secondary mirrors is maintained constant ‒3.5. This allow the impact of the compactness of this UHCPV design to be...

Numerous works of exhaustive analysis of the economic assessment of PV systems are available in the literature. However, there is a lack of this kind of studies concerning High Concentrator Photovoltaic (HCPV) technology. In this work, a worldwide economic feasibility analysis of HCPV systems is performed through the LCOE estimation, since it is a commonly method to assess and compare energy generation systems of different technologies. The LCOE of HCPV grid-connected systems is estimated and analysed for 133 countries. The analysis and detection of the optimal zones for HCPV technology is conducted in terms of the LCOE, and in addition, an innovative global map of the LCOE of HCPV is presented. Moreover, the grid parity in the domestic market segment for the year 2014 is analysed and found to be a reality for several developed countries. Finally, a prospective scenario comparing the LCOE of HCPV and conventional PV systems for the year 2020 is analysed and plotted in a global map, in which many countries have found to be preferable for the HCPV technology in terms of the LCOE. As an important result, although the Annual Final Yield, Yf, and LCOE are apparently inversely proportional, when comparing both parameters, Yf and LCOE, on one hand, it is obtained that some countries with relative high Yf values are also of relative high LCOE values (e.g. Iran and Sudan), and, on the other hand, some other countries with relative low Yf values are also of relative low LCOE values (e.g. Canada and France).

Electrical mismatches have a larger impact in high-concentrator photovoltaic power plants than in conventional photovoltaic systems because of the narrow acceptance angles and the unavoidable self-shading between sun trackers. In this paper, a commercial point-focus Fresnel lens-based high-concentrator photovoltaic module is characterized outdoors and results of this characterization are used to develop a power plant model which allows electrical mismatch energy losses to be investigated. Different inverter configurations (micro, string and tracker-oriented inverters) are analyzed with it. This research offers an approach based on energy loss calculation rather than instantaneous power loss calculation as was done in the reviewed literature. Moreover, realistic 28.5 kWp trackers are analyzed rather than small trackers and a novel procedure for obtaining direct normal irradiance daily profiles is presented. From the simulations, it is concluded that micro and string inverters are very useful to minimize mismatch energy losses, reinforcing the conclusions previously published by Kim and Winston (2014). The coefficients obtained in this paper are expected to help in energy yield calculations without the need of using advanced electrical modeling, although it was found that the bigger the capacity of the inverters, the higher the uncertainty to establish electrical mismatch loss coefficients due to shading.

The interest in Ultra-High Concentrator Photovoltaic (UHCPV) devices has motivated the use of solar cells under ultra-high irradiance levels (+1000 suns). Temperature effects and variations in the spectrum of the incoming light on the solar cells need to be analysed to understand their performance under real operating conditions. In this work an experimental setup, based on an indoor multi-flash solar simulator, is presented. This arrangement allows high efficiency multi-junction solar cells to be characterized up to 1500 suns of irradiance under controlled conditions of temperature and spectrum. Also, different I-V curves obtained by varying each of these parameters separately are attached.

To reduce the cost of generated electrical energy, high-concentration photovoltaic systems have been proposed to reduce the amount of semiconductor material needed by concentrating sunlight using lenses and mirrors. Due to the concentration of energy, the use of tracker or pointing systems is necessary in order to obtain the desired amount of electrical energy. However, a high degree of inaccuracy and imprecision is observed in the real installation of concentration photovoltaic systems. The main objective of this work is to design a knowledge-based controller for a high-concentration photovoltaic system (HCPV) tracker. The methodology proposed consists of using fuzzy rule-based systems (FRBS) and to implement the controller in a real system by means of Internet of Things (IoT) technologies. FRBS have demonstrated correct adaptation to problems having a high degree of inaccuracy and uncertainty, and IoT technology allows use of constrained resource devices, cloud computer architecture, and a platform to store and monitor the data obtained. As a result, two knowledge-based controllers are presented in this paper: the first based on a pointing device and the second based on the measure of the electrical current generated, which showed the best performance in the experiments carried out. New factors that increase imprecision and uncertainty in HCPV solar tracker installations are presented in the experiments carried out in the real installation.

Ultra-High Concentrator Photovoltaic (UHCPV) designs with up to more than 6000× geometrical concentration and optical efficiency of 80% are demonstrated in this paper by means of ray tracing simulations. These are developed based on Cassegrain-Koehler concentrators [Opt. Lett. 41(9), 1985 (2016)], with four pairs of paraboloid-hyperboloid mirrors and a central receiver composed of four Cartesian ovals of revolution. Designs at different geometrical concentrations are analyzed based on their aspect ratios (F-number). The most compact designs exhibit highest optical efficiencies. Moreover, a 3015× geometrical concentration one-cell prototype, made of aluminum and PMMA (poly(methyl methacrylate)), is fabricated and characterized indoors, achieving an effective concentration of 938 suns. This represents the CPV module with the highest geometrical concentration that has been experimentally investigated that could be found in the scientific literature.

High Concentrator Photovoltaics (HCPV) modules are typically equipped with multi-junction solar cells (MJSC) based on III-V compound semiconductors, which are typically either triple-junction (TJSC) or four-junction solar cells (FJSC). This work analyzes the impact of changing the number of subcells and their bandgaps in the optical efficiency. An exhaustive optical modelling is applied for estimating subcell short-circuit current density values under the concentrated illumination. The same typical concentrator of Fresnel lens plus a refractive homogenizer concentrator is applied to two different MJSCs. The optical efficiency when using the FJSC is 86.0%-almost 2% higher than with the TJSC. The acceptance angle results are similar for both cases, around 1.22°. Concerning the spectral matching ratio, SMR, the FJSC unit shows more distant values respect to the equivalent conditions to the standard illumination than the TJSC, due to the lower bandgaps of the FJSC.

The recent development of wafer bonded four-junction concentrator solar cells (FJSCs) with record efficiency among all the existent photovoltaic (PV) cells offers new possibilities for improving the High Concentrator PV (HCPV) technology. However, the concentrator optical systems utilized in HCPV modules may have to be adapted to the new requirements of FJSC in order to properly take advantage of the increased number of p-n junctions. This research theoretically compares two identical optical concentrator systems, a Frensel lens plus a kind of refractive SILO (SIngle-Lens-Optical element) secondary (both made of PMMA, poly(methyl methacrylate)), which are equipped with a typical triple-junction concentrator solar cell (TJSC) in the one case, and with an FJSC in the other case. Both HCPV units are analyzed through ray tracing optical simulations applying an exhaustive optical modelling that takes into account the spectral responses of the different subcells within the multi-junction cells. The HCPV unit with the FJSC and PMMA SOE (secondary optical element) shows much less efficiency than that with the TJSC due to the light absorption through the PMMA SOE in the wavelength range of the bottom subcell. Therefore, PMMA SOEs may be not appropriate for FJSC in general.

In this paper, it is shown that the inverter size that maximizes the energy yield in CPV plants is influenced by self-shading between sun trackers. For this purpose, a detailed CPV power plant model was developed from experimental data obtained in the outdoor characterization of a typical 700x concentration factor Fresnel lens-based CPV module. The simulated results indicate that neglecting the impact of shading can lead to inaccurate values of the optimum inverter capacity from an energetic point of view. However, applying an economic optimization criterion, the inverter sizing ratio seems to be independent on ground cover ratio. In the study, the influence of the inverter efficiency characteristics is also discussed.

Numerous works analyze the refractive secondary optical elements (SOEs) in their application to HCPV modules, since the improvement in their optical tolerances, specifically, in the acceptance angle. Comparative theoretical and some experimental works are already published about this matter. However, this work also provide the validation of an optical modelling previously published, in which key features of the HCPV units were taken into account. Specially, that modelling considered wavelength-dependent properties in the light-matter interaction, like in the optical polychromatic efficiency of the solar cell (through its spectral response), or in the light absorption coefficient of the PMMA material. Then, four SOEs are manufactured and utilized to assemble different HCPV units to be characterized under controlled conditions in a CPV Solar Simulator. The four SOEs are: (i) SILO-Pyramid (SIngle-Lens-Opical elment), (ii) DCCPC (dielectric-cross compound-parabolic-concentrator), (iii) RTP (refractive truncated pyramid) and (iv) Trumpet. The correspondent HCPV units are characterized at 1000 W/m2 and at spectral conditions SMR = 1 under normal alignment respect to the simulated light and also at different tilted orientations. This last allows to measure the acceptance angle of each HCPV unit. These values are compared to those simulated by ray tracing. The results show measured acceptance angle values are in general similar to the simulated ones, with a deviation lower than 8%, except for the case of the SILO-Pyramid unit.

Concentrator photovoltaic (CPV) systems provide higher efficiencies than conventional photovoltaic technologies. These systems increase the concentration ratio by using cheap optical assemblies in order to reduce the size of high efficiency solar cells. This chapter outlines designs in low-, medium-, and high-concentrator photovoltaic systems, with a focus on high-concentrator photovoltaic systems. Topics such as multijunction solar cells, concentrator optics, thermal management, module performance, influences of irradiance, temperature, spectrum, and other variables are covered in the text. Several methods for directly or indirectly estimating the output energy of a CPV system are discussed. Electrical mismatches causing energy losses are detailed through illustrations and equations that calculate the energy yield of a concentrator photovoltaic system.

A worldwide comparison of the annual yield between conventional c-Si photovoltaic (PV) technology and high concentrated photovoltaic (HCPV) technology is presented. The idea of this paper is to find the most appropriate locations for HCPV systems in terms of the annual energy produced when comparing to fixed tilt PV systems and two-axis oriented PY systems. For estimating the annual energy generation, the method of the Performance Ratio is used. For some locations with high annual direct normal irradiation values, which are distributed around the world, HCPV systems are found to be more advantageous than fixed tilt PV systems. World maps showing this comparison are presented.

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.

Costs for High Concentrator Photovoltaic (HCPV) power plants dropped dramatically during 2013 and are expected to continue to fall in the next few years. Moreover, when viewed from the perspective of life cycle cost, HCPV becomes even more competitive than other renewable technologies in some geographical areas. Consequently, an analysis of the economic feasibility of the HCPV systems in future scenarios is necessary for comparison with other electricity generation technologies. One of the methods commonly used for the economic feasibility analysis in electricity generation projects is the levelised cost of electricity (LCOE). In this paper a cost analysis of electricity generation of HCPV technology in Spain by using the LCOE has been carried out. The results obtained in this LCOE analysis show that in 2020 the LCOE will be able to reach values for HCPV systems from 0.035 to 0.080 €/kW h, lower than LCOE for conventional PV systems, in some geographical areas of Spain. The results obtained in this analysis have been shown in innovative maps.

The prediction of the energy yield of HCPV (high concentrator photovoltaic) systems is crucial to evaluate the potential and promote the market expansion of HCPV technology. Currently, there is a lack of experience in the modelling of these kinds of systems due to the special features of such technology. In this work, a practical model based on simple mathematical expressions and atmospheric parameters is introduced. The proposed model takes into account the main important parameters which influence the output of a HCPV system such as cell temperature, spectrum and efficiency of the inverter and other losses of the BOS (balance of system). The results obtained are validated using the data of a HCPV installation located at the University of Jaen in southern Spain and monitored daily every minute since 2011. The model accurately predicts the monthly energy yield with a deviation ranging from 4.07% to −0.47% and the annual final energy yield with a deviation of 0.9%.

Due to its special features, one of the problems of high concentrator photovoltaic (HCPV) technology is the estimation of the electrical output of an HCPV module. Although there are several methods for doing this, only some of them can be applied using easily obtainable atmospheric parameters. In this paper, four models to estimate the maximum power of an HCPV module are studied and compared. The models that have been taken into account are the standard ASTM E2527, the linear coefficient model, the Sandia National Laboratories model, and an artificial neural network-based model. Results demonstrate that the four methods show adequate behavior in the estimation of the maximum power of several HCPV modules from different manufacturers.

Point-focus Fresnel lens-based High Concentrator Photovoltaic (HCPV) systems are usually equipped with refractive secondary optical elements (SOE) in order to improve their performance. Two basic SOE designs are optically modeled and simulated in this work: Domed-Kaleidoscope (D-K) with breaking-symmetry top and SILO (SIngle-Lens-Optical element). Wavelength-dependent optical material properties like refractive index and absorption coefficient, as well as the spectral response of a typical triple-junction (TJ) solar cell, are included in the ray tracing simulations. Moreover, using a CPV Solar Simulator “Helios 3198”, both HCPV units are experimentally characterized. The acceptance angle characteristics of both HCPV units, obtained through optical simulations and through indoor characterization, are compared. The acceptance angle characteristic is better for the HCPV unit with the D-K SOE both in simulations and in experimental measurements, showing concordance between simulation and experiment. However, ...

The solar cell operation temperature is an important input in models for the electrical characterization of high concentration photovoltaic cells and modules. However, the direct measurement of this temperature is difficult in these kinds of devices. Because of this, in recent years, the scientific community has proposed different methods for indirectly calculating the cell temperature in high concentration photovoltaic modules from atmospheric parameters and/or easily measurable parameters on the module. In this paper, a comprehensive review of existing methods for cell temperature calculation in high concentration photovoltaic modules for electrical characterization is presented. The different methods are summarized and a comparative analysis is done. Required inputs, advantages and technical difficulties of each method are highlighted. Also, an experimental campaign has been carried out at Jaen, south of Spain, in order to quantify the accuracy of the methods. Results show that methods based on direct measurements on the module are somewhat more accurate than methods only based on atmospheric parameters. The choice of the most suitable method for a specific application will depend on the availability of module information, on the required accuracy and on technical issues.

One of the problems of some renewables energies is that the output of these kinds of systems is non-dispatchable depending on variability of weather conditions that cannot be predicted and controlled. From this point of view, the short-term forecast is going to be essential for effectively integrating solar energy sources, being a very useful tool for the reliability and stability of the grid ensuring that an adequate supply is present. In this paper a new methodology for forecasting the output of a PV generator one hour ahead based on dynamic artificial neural network is presented. The results of this study show that the proposed methodology could be used to forecast the power output of PV systems one hour ahead with an acceptable degree of accuracy.

The operating cell temperature of a HCPV module or system is a key factor, because it directly affects efficiency and reliability. Hence, the accurate estimation of cell temperature in a HCPV module is crucial. Under real operating conditions, HCPV modules work at the maximum power point, because they are connected to an inverter. At the maximum power point, the cell temperature is lower than the cell temperature of open circuit, because solar cells are generating power which is not transformed into heat. At present, none of the existing methods are valid to estimate the operating cell temperature of a HCPV module connected to an inverter. In this paper, a procedure for estimating this temperature is introduced. The results show that the proposed method performs effectively in the estimation of the cell temperature in a HCPV module connected to an inverter. In addition, an analysis of the difference between the cell temperature of open circuit and the cell temperature at the maximum power point in a HCPV is conducted and a difference of up to 21 °C has been found.

Low concentration photovoltaic (LCPV) modules for building integration are considered to have great potential because it offers several advantages over conventional photovoltaic technology. However, one of the problems of this technology is that as yet there are no models in the literature to directly calculate the maximum power of these kinds of systems. The development of models is an important task to promote the application of this technology because it allows the prediction of the energy yield. In this paper a model based on artificial neural networks has been developed to address this important issue. The model takes into account all the main important parameters that influence the electrical output of these kinds of systems: direct irradiance, diffuse irradiance, module temperature and the transverse and longitudinal incidence angles. The results show that the proposed model can be used for estimating the maximum power of a LCPV module for building integration with an adequate margin of error.

Ascertaining the operating cell temperature of a high concentrator photovoltaic (HCPV) module is critical because its electrical parameters are influenced by this factor. However, measuring the cell temperature of an HCPV module is a complex task due to the unique features of such a module. This paper calculates the cell temperature in an HCPV module by using different methods to address this important issue. We conducted a comparative study of four methods used to estimate the cell temperature of an HCPV module, including the IEC 60904-5 method, a method based on thermal resistance proposed by the Instituto de Sistemas Fotovoltaicos de Concentracion, the Lineal method and an artificial neural network-based method introduced in this paper. The complete procedures, parameters and coefficients required to estimate the cell temperature with each method are provided. The results show that methods based on direct measurements of the HCPV module perform better than methods based on atmospheric parameters. However, all of the studied methods can be used to estimate cell temperatures with an acceptable margin of error.

Estimating the energy provided by the generators of grid-connected photovoltaic systems is important in order to analyze their economic viability and supervise their operation. The energy harvesting calculation of a photovoltaic generator is not trivial; there are a lot of methods for this calculation. The aim of this paper is to develop a novel classification of methods for annual energy harvesting calculation of a generator of a grid-connected photovoltaic system. The methods are classified in two groups: (1) those that indirectly calculate the energy, i.e. they first calculate the power and from this, they calculate the energy, and (2) those that directly calculate the energy. Furthermore, the indirect methods are grouped in two categories: those that first calculate the I–V curve of the generator and from this, they calculate the power, and those that directly calculate the power. The study has shown that the existing methods differ in simplicity and accuracy, so that the proposed classification is useful in order to choose the most suitable method for each specific application.

Nowadays, there is wide experience on selecting an adequate ratio between the photovoltaic array peak power and the inverter capacity for conventional photovoltaic systems. However, when dealing with concentrator photovoltaic plants, the problem is more complex and the results obtained with conventional methods are not directly applicable. There are few studies regarding concentrator photovoltaic technology and all of them neglect the impact of shading. In this paper, based on the experimental characterisation of a typical concentrator photovoltaic module, a power plant model is developed, which takes into consideration shading, module misalignment, and different inverter configuration schemes for optimising the inverter capacity. The inverter size is analysed for different ground cover ratios (from 12% to 52%), inverter schemes (micro-, string-, and tracker-inverters), inverter efficiencies (low-, medium-, and high-efficiency), climatic conditions (Granada, Marrakech, and Frenchman Flat), and economic conditions (system cost excluding inverters from 850 to 1400 €/kWp). Results show values for the DC-to-AC sizing ratio ranging from 1.01 to 1.67 (maximum performance ratio), and from 1.53 to 1.79 (minimum levelised cost of energy). String-inverters exhibit the best behaviour in terms of levelised cost of energy, except in shadow-free systems, in which tracker-inverters behave better.

This paper presents the outdoor measurements that have been carried out on two high concentration photovoltaic receivers integrated with Fresnel lens-based primary optics by reproducing partial shading conditions on the primary optics. Each solar receiver is composed of a multi-junction solar cell, a bypass diode, a heat sink and a secondary optical element. From the measurements, the electrical behavior of the concentration receivers under partial shading on the primary lens is analyzed. A method is then proposed for the calculation of the maximum power output of concentration receivers under partial shading on the primary lens based on the determination of the equivalent irradiance. The accuracy of the method is evaluated taking into account the experimental data.

The aim of this paper is to find a simple model to predict the maximum power of a high concentrator photovoltaic (HCPV) module under real conditions from easily obtainable atmospheric parameters. The model is based on a simple easy to use equation. This equation is the function of direct normal irradiance and air temperature and has an additional correction based on air mass. In order to define this equation, two HCPV modules from different manufacturers were measured over a period of two years to provide a complete set of measurements, representing the behaviour of HCPV modules in different outdoor conditions. The proposed model shows an adequate match between actual and estimated data for the particular HCPV modules located in Southern Spain.

High concentration photovoltaic technology promises the large-scale generation of clean-renewable energy with competitive costs. Like any other systems for electricity generation, it is important to know the electrical characteristics of the system. However, while there is a wide experience in modeling the behavior of traditional photovoltaic systems, not every model for flat-plate solar cells or modules is directly applicable to high concentration photovoltaic cells or modules because of the special features of these devices (use of multijunction cells, use of optics for high concentration, etc.). So, in recent years, the scientific community has devoted considerable efforts in developing models that reproduce the electrical behavior of high concentration cells and modules. These models allow calculating the main electrical parameters of the device from its operating conditions (irradiance, cell temperature, spectral distribution of the radiation, etc.). In this paper, a comprehensive review of existing models for the electrical characterization of high concentration photovoltaic cells and modules is presented with the aim of helping the photovoltaic professionals and researchers in the design, monitoring and energy prediction tasks.

This paper presents a simple accurate model that allows calculating the shading power losses in photovoltaic generators in a fast, easy to implement way. Calculated losses for different generators and shading scenarios are compared to those obtained with a detailed model based on solving the whole current–voltage curve of the generators. Results show a good agreement between the proposed model and the detailed model. The proposed model is useful for the calculation of the instantaneous power losses and also gives good results in the calculation of the energy yield, requiring less information as input than other detailed models and requiring low computational effort.

While single junction solar cells are mainly influenced by changes in irradiance and temperature, multi junction concentrator solar cells show complex behaviour as their performance is also strongly influenced by changes in spectrum. Despite this, when studying the system, it is possible to reduce the problem to a set of parameters that could easily be measured and fitted. A simple model to obtain the maximum power point of multi junction solar cells under temperature and spectral changes is proposed. This model is based on a single diode model and is described by a simple set of equations that are easy to fit within a computational program. The model could be useful to understand the behaviour of multi junction solar cells and also CPV technology under real conditions. The main purpose of this paper is to define a simple way to estimate the maximum power point of a multi junction solar cell under spectral and temperature changes at one sun conditions.

The peculiarities of High Concentrator Photovoltaic (HCPV) modules make it very difficult to estimate their output. There are some methods to estimate the maximum power of an HCPV module which provide good results, but they are not easy to apply for the following reasons: a) they do not offer a comprehensive explanation of the entire procedure, b) they need some intrinsic parameters of MJ (multi-junction) solar cells which are difficult to obtain, c) it is necessary to have either complex and expensive devices for indoor measurements, and/or an accurate and complete set of outdoor measurements. This paper is intended to propose a model based on Artificial Neural Networks (ANNs) to predict the maximum power of an HCPV module using easily measurable atmospheric parameters. To this end, a group of atmospheric parameters together with the maximum power of an HCPV module have been measured throughout a whole year at a research centre located in the south of Spain. The results showed that using atmospheric parameters, the proposed ANN is capable of estimating the maximum power of an HCPV module with a mean square root error of 3.29%. This model could be extended to other modules and other places.

In this paper, an artificial neural network (ANN) is used for the generation of ambient temperature hourly time series for some Spanish locations. The model was trained and tested with ten locations and different years of data. Results show that the proposed artificial neural network provides a better approach than other methods. The aim of this paper is to provide a complete description of this ANN so that, it can be used by anyone avoiding all the design, training and testing process again.

Ultra-high concentrator photovoltaics (UHCPV), with concentrations higher than 1000 suns, have been pointed out by different authors as having great potential for being a cost-effective PV technology. This Letter presents a UHCPV Cassegrain-based optical design in which the sunrays are concentrated and sent from four different and independent paraboloid-hyperboloid pairs optical units onto a single central receiver. The optical design proposed has the main advantage of the achievement of ultra-high concentration ratios using relative small mirrors with similar performance values of efficiency, acceptance angle, and irradiance uniformity to other designs.

A Cassegrainian optical design reaching ultra-high concentration fluxes (more than 1000 suns) is presented. The system is based on the use of four independent off-axis pairs of parabolic-hyperbolic reflectors that concentrate sunrays onto a central receiver (TOE, tertiary optical element) which works as a Kohler integrator. This design reaches an effective concentration ratio simulated of 1682 suns while using relative small mirrors. The acceptance angle characteristic is analyzed in terms of both the detailed ray tracing on the TOE and the irradiance pattern on the solar cell for a misalignment situation near to the acceptance angle of the design, which is 0.61°.

The design and analysis of CPV systems require knowledge of direct normal solar irradiation but ground-based measurements of these data are only available for very few locations. Nowadays, meteorological databases that estimate direct normal irradiation from satellite images and other data sources are used. However, values provided by the different existing databases show large dispersion due to different estimation methods, input data and base years. In this paper, a simplified method for calculating direct normal irradiation is presented. It has been obtained from previous models proposed by several authors. One of its advantages is that it only requires latitude and global horizontal irradiation as input data. As global irradiation is easy to find or measure, the procedure becomes a useful tool in renewable energy applications. The accuracy of this method is similar to that of the existing databases and it is able to easily generate a mass of direct normal irradiation data for different areas worldwide.