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High power laser transmission is being intensively researched as a potential solution to transfer power to remote systems, being the power converter (PC) one of the main limiting factor to improve the system efficiency ( $\eta $ ). Current PCs are mostly horizontal structures in which the $\eta $ heavily decreases at large input power. In this work, we propose a novel GaAs-based vertical-tunnel-junction (VTJ) PC suitable for ultra-high (UH) input power density (P in ). This structure does not suffer from $\eta $ degradation at high P in because it is designed to have low current density, high output voltage and reduced series resistance (~ 2 orders of magnitude lower than the state-of-the-art PCs). We have demonstrated increasing $\eta $ with P in , reaching values higher than 76% at 3000 $\text{W}\cdot $ cm −2 . This vertical-based architecture enables a new set of potential applications for wireless PC to power remote systems with $\eta $ exceeding today’ s state-of-the-art PC designs.

Photovoltaic (PV) soiling profiles exhibit a sawtooth shape, where cleaning events and soiling deposition periods alternate. Generally, the rate at which soiling accumulates is assumed to be constant within each deposition period. In reality, changes in rates can occur because of sudden variations in climatic conditions, e.g., dust storms or prolonged periods of rain. The existing models used to extract the soiling profile from the PV performance data might fail to capture the change points and occasionally estimate incorrect soiling profiles. This work analyzes how the introduction of change points can be beneficial for soiling extraction. Data from nine soiling stations and a 1-MW site were analyzed by using piecewise regression and three change point detection algorithms. The results showed that accounting for change points can provide significant benefits to the modeling of soiling even if not all the change point algorithms return the same improvements. Considering change points in historical trends is found to be particularly important for studies aiming to optimize cleaning schedules.

The efficiency of solar cells can be enhanced by increasing the light intensity and/or the number of bandgaps of the structure. However, current solar cells cannot fully exploit these two factors because of various critical drawbacks. Here, we show a novel microscale, that is, side ≈ 0.5 mm, vertical solar cell structure that does not suffer the series resistance and bandgap limitations issues of current devices. The preliminary structures investigated show extreme efficiencies, >40%, at ultrahigh concentration factors of 15 000 suns. In addition, future designs with a better bandgap configuration are expected to deliver cells with efficiencies far above 50% at extreme light intensities. This early design offers a fast and reliable route to push the efficiency towards the maximum solar conversion limit and represents a promising way to develop new-generation ultraefficient and low-cost concentrator photovoltaic systems.

In this paper, the soiling impact on photovoltaic systems in Aguascalientes, in central Mexico, an area where 1.4GWp of new photovoltaic capacity is being installed, is characterised experimentally. A soiling rate of −0.16%/day in the dry season for optimally tilted crystalline silicon modules, and a stabilization of the soiling losses at 11.2% after 70 days of exposure were observed. With these data, a first of its kind novel method for determining optimum cleaning schedules is proposed based on minimising the levelised cost of energy. The method has the advantages compared to other existing methods of considering the system investment cost in the determination of the optimum cleaning schedule. Also, it does not depend on economic revenue data, which are often subject to uncertainty. The results show that residential and commercial systems should be cleaned once per year in Aguascalientes. On the other hand, cleaning intervals from 12 to 31 days in the dry season were estimated for utility-scale systems, due to the dramatic decrease of cleaning costs per unit photovoltaic capacity. We also present a comparative analysis of the existing criteria for optimising cleaning schedules applied to the same case study. The different methods give similar cleaning intervals for utility-scale systems and, thus, the choice of a suitable method depends on the availability of information.

The impact of soiling on the energy yield of PV systems has recently become a major concern for PV owners, as soiling losses have reduced significantly the revenues of several PV sites. However, a large number of PV plants still lack the equipment to monitor these losses. An appropriate knowledge of soiling losses in PV modules can significantly increase the economic profits, even if possible without any specific soiling monitoring system. In this study, a first comparison of different analytical methods to extract losses due to soiling from PV performance data, without the need for specific soiling sensors, is presented. The study is based on outdoor PV power, irradiance and module temperature measurements. The experimental campaign is conducted in a low-moderate soiling location. The first results show that two of the methods assessed in this work can estimate soiling trends with a relative high accuracy, thus allowing planning adequate cleaning schedules.

Concentrator photovoltaic (CPV) systems replace semiconductor material by cost-efficient optical elements. This technology has doubled the efficiencies of conventional non-concentrating PV systems. However, the cost of CPV still needs to be lowered to be competitive. In these systems, approximately 60 % of the incident energy is dissipated as heat. One way to further enhance CPV systems is taking advantage of the dissipated heat energy as a source for an extra generation of electricity using a thermoelectric generator (TEG). The feasibility of hybrid CPV-TEG modules for enhancing the efficiency and lowering the cost has been discussed in recent work, with special emphasis on actively cooled designs. On the other hand, the micro-scaling of the technology could allow simple and reliable passive cooling mechanisms to be used. In this work, a numerical analysis of three-dimensional micro hybrid CPV-TEG receiver at ultra-high concentration ratios is presented. The procedure solves both the thermal and electrical effects for estimation of the power generated and the efficiency of the system. The results of performance are compared with a CPV-only receiver composed with equal solar cell properties working at similar conditions. Results show that micro CPV-TEG systems can reach an efficiency of 33.6 % versus the 31.6 % achievable with a CPV-only system, working under 4,000 suns.

Approximately 60% of the incident energy is dissipated as heat in conventional concentrator photovoltaic modules. The hybridization with thermoelectric generators (TEGs) aims to recover part of the waste heat and transform it to electricity. Recently, the feasibility of passively cooled designs has been assessed for small sized solar cells (3 mm × 3 mm). It is expected that novel prototypes will be developed according to this concept. However, the existing feasibility studies are based on reference operating conditions, while the behavior of the hybrid modules under changing atmospheric conditions remains unknown. In this article, real atmospheric data of Jaen, Southern Spain, including irradiance, temperature, and spectral data, are used to analyze the behavior of four designs of TEG-concentrator photovoltaic modules: low ZT-low temperature (A), low ZT-high temperature (B), high ZT-low temperature (C), and high ZT-high temperature (D). This behavior is compared with that of a typical concentrator photovoltaic-only module. Results show that, while the global efficiency at reference conditions can be enhanced up to 4.75%, the annual averaged global efficiency can only be increased up to 4.30%. The results of this article will help to understand the impact of the atmospheric conditions on the real behavior of these structures.

Concentrator photovoltaic technology has doubled the efficiency of conventional non-concentrating photovoltaic systems. However, still ≈60% of the incident energy is dissipated as heat, and costs of concentrator photovoltaics need to be lowered for these systems to be competitive. One promising way for taking advantage of the heat generated in the solar cells is the hybridization with thermoelectric generators. The feasibility of hybrid concentrator photovoltaic-thermoelectric modules has been shown in recently published work for enhancing the efficiency and lowering the cost, with special emphasis on actively cooled designs. However, if feasible, the use of simple and reliable passive cooling would accelerate the development of new hybrid prototypes. The performance and cost reduction limits achievable with passively cooled designs have not yet been studied in detail. In this paper, an electric/thermal/economic model of concentrator photovoltaic-thermoelectric module is developed. As the main novelty, the model allows the thermoelectric generator area to be adjusted. Some optimisation problems are formulated and solved to evaluate the efficiency improvement and cost reduction of the hybrid system in comparison to a typical 800x light concentration factor and 36.4% efficiency concentrator photovoltaic-only module. The analysis showed that optimising the thermoelectric generator area is essential for the cell operating temperature limits not to be exceeded, and that conventional passive cooling is enough for achieving efficiency gains and cost reduction considering a state-of-the-art highly efficient 3 mm × 3 mm triple junction solar cell. With advanced thermoelectric materials and cell temperature of 100 °C, a maximum efficiency of 39.2% for the hybrid system can be achieved at 800x concentration factor by using low thermal resistance heat sinks, and a maximum cost reduction of 46.0% can be achieved at the maximum analysed concentration factor (1900x) by using moderate thermal resistance heat sinks. A trade-off between enhancing the efficiency and lowering the cost was observed. The sensitivity analysis on the thermoelectric parameters showed that parameters other than thermoelectric generator area and ZT figure-of-merit barely influence the results. The existing experimental concentrator photovoltaic-thermoelectric prototypes are far from the efficiency and cost benefits predicted in this paper. Thus, the study can help in the development of future prototypes.

Concentrator photovoltaic (CPV) systems replace semiconductor material by cost-efficient optical elements. The potential cost reduction of these systems is closely related to the concentration factor because higher light concentrations imply lower amount of semiconductor material required for the solar cells. Thus, one promising way for improving this technology is moving towards ultra-high (UH) concentration levels (>2000 suns). However, the thermal management at such extreme light fluxes is difficult. Using 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 the heat and would accelerate the development of UHCPV prototypes. However, the feasibility of flat-plate heat-sinks using microscale solar cells for UHCPV applications has not been analysed in detail yet. In this work, a thermal 3D finite-element model is used to investigate the possibilities of flat-plate heat-sinks at concentration ratios not tested to date, i.e. 2000–10,000 suns. Critical parameters such as solar cell area and efficiency, substrate thickness, heat-sink area, and heat-sink material are evaluated and discussed. Results show that solar cells of 1 mm × 1 mm area or below can be thermally handled with conventional Aluminium flat heat-sinks up to 10,000 suns.

Summary Soiling is the process whereby dirt, dust, and organic/inorganic contaminants deposit on the surface of a photovoltaic (PV) module. It causes significant economic losses and can have a substantial impact on the expansion of photovoltaic technologies for energy generation. The first step to address soiling adequately is monitoring, as soiling mitigation has to be tailored to the specific conditions of each PV system and no universally valid strategy exists. The main focus of this study is to assess the current state of the art in soiling monitoring, in order to help the community better understand the needs and the challenges in this area. The potentials and the limitations of each monitoring method are discussed thoroughly in the paper, with the support of original experimental data. An estimation of the future soiling monitoring market trends is also presented, with a forecasted need for tens of thousands of new soiling monitors every year., Graphical Abstract, Applied sciences; energy engineering; engineering; industrial engineering; materials application; optical materials

The impact of non-uniform illumination on triple junction solar cells equipped with either refractive or reflective optics without secondary optical elements is characterised by varying the concentrator-to-receiver distance. Indoor experiments covering both electrical measurements and photographs with a charge-coupled device camera are performed. The non-uniformities are examined by differentiating two spectral bands, those affecting the top and middle subcells. This allows the irradiance and spectral distributions to be analysed. The analysis is complemented with ray tracing simulations. Results show a different behaviour for the refractive and reflective systems. Irradiance non-uniformities in the case of the reflective system around the on-focus position are higher than those measured in the refractive system. However, the spectral non-uniformities that characterise the refractive system constitute only a residual effect in the reflective system. The drop in the solar cell fill factor caused by non-uniformities is mainly driven by the degradation of the slope of the I–V curve near the short-circuit point in the case of the refractive system, while it is mainly driven by the degradation of the slope of the I–V curve near the open-circuit point in the case of the reflective system. Both systems are very sensitive to the concentrator-to-receiver distance, a critical parameter that must be accurately designed in any concentrator system. The findings will allow the trade-off between increasing performance and increasing cost strategies to mitigate the non-uniformities in concentrator photovoltaic systems to be better evaluated. This work has been partially funded by the project “UltraMicroCPV” (MICINN- Agencia Estatal de Investigación: PID2019-106497RB-I00/AEI/10.13039/501100011033) and by the project NACe-CPV/TE (Junta de Andalucía, PAIDI 2020: P18-RT-1595). P. M. Rodrigo thanks the Spanish Ministry of Science, Innovation and Universities because of the 2020–2024 Beatriz Galindo fellowship (BEAGAL18/00164) and, the Science and Technology National Council of Mexico (CONACYT) because of his designation as a member of the Mexican System of Researchers. E.F. Fernández thanks the Spanish Ministry of Science, Innovation and Universities for the funds received under the Ramón y Cajal programe (RYC-2017-21910). D. Chemisana thanks ICREA for the ICREA Acadèmia.

Soiling losses can be mitigated by cleaning the PV modules. However, the profitability of PV cleaning varies with time, influenced by the electricity price, the module efficiency and the cleaning costs. The present work analyzes the trends in soiling losses and soiling mitigation profitability for the continental U.S. The initial results show that, because of the lowering electricity price, the portion of PV capacity economically worth cleaning is decreasing. This means that, even if the economic impact of soiling is lowering, the fraction of energy yield lost due to soiling is actually increasing, because of the reducing mitigation activities.

This work investigates the possibility of using historical environmental parameter data to predict the typical soiling loss profile and the most convenient cleaning schedule for a PV site. The three-year performance of a 1 MW system in Southern Spain is evaluated using different soiling extraction methods. When the rainfall pattern is used to detect natural cleaning events, the best results are obtained if a 1.0 mm/hour threshold is considered. However, despite the optimization, setting a fixed threshold is found to lead occasionally to the over- or under-detection of cleaning events. Similar trends in the modelling results are found if the thresholds are set using the maximum hourly or the cumulative daily rainfall data, but the errors and the optimal values change depending on the rainfall dataset. The study also shows that a soiling extraction method based only on precipitation and particulate matter, calibrated against one year of PV data, is able to generate a soiling profile with a mean absolute error of 0.022 and to recommend a cleaning day within a week of the actual optimal dates. This will make it possible to estimate the soiling losses and the optimal cleaning schedule for a PV site even if no power data are available.

The present work investigates how the COVID-19 related lockdown imposed in Spain in between March and June 2020 affected the national electricity sector and the share of photovoltaics in the energy mix. The analysis is conducted by comparing actual electricity demand, generation and price data with forecasts based on their pre-lockdown trends. The results show that the lockdown decreased the electricity demand by 11%, and affected even more severely the price of electricity, causing a total loss for the electricity sector of 6.1 million € per day. These losses were unevenly distributed among the different power technologies of the energy mix. The market share of photovoltaics raised by almost 1% because of the lockdown-related demand drop, even if it performed at capacity factors lower than expected. Overall, because of the lockdown and of the recently installed capacity, photovoltaic provided, for the first time, more than 9% of the national electricity consumed in June 2020, more than twice the maximum share achieved in the previous years.

The present study analyzes the soiling losses of a 1 MW photovoltaic system installed in the South of Spain. Both the Levelized Cost of Energy and the Net Present Value are used to compare the convenience of different mitigation strategies. It is found that also photovoltaic installations located in moderate regions, where the yearly soiling losses are limited to 3%, can suffer of a severe seasonal soiling, with power drops higher than 20%. In these conditions, an optimized cleaning schedule can be considerably beneficial from an economic perspective. For the given site, an optimal cleaning schedule generates a raise in profits up to 3.6% if one yearly cleaning is performed within a ±31-day window in summer. The convenience of one and multiple cleaning strategies is investigated by considering variable electricity prices and cleaning costs. In addition, the impact of the module efficiency on the cleaning strategy is analyzed. It is found that an optimized cleaning schedule can enhance the benefits of installing high efficiency modules, as it increases the amount of energy recovered through each cleaning and, therefore, the profits.

The exponential growth of global capacity along with a reduction in manufacturing costs in the last two decades has caused photovoltaic (PV) energy technology to reach a high maturity level. As a consequence, currently, researchers from all over the world are making great efforts to analyse how different types of degradation impact this technology. This study provides a detailed review of the impact of different optical degradation mechanisms, which mainly affect the transmittance of the top-sheet encapsulant, on the spectral response of the PV modules. The impact on the spectral performance of PV modules is evaluated by considering the variations of the short-circuit current since this is the most widely used parameter to study the spectral impact in outdoors. Some of the most common types of optical degradation affecting the performance of PV modules worldwide, such as discoloration, delamination, aging and soiling have been addressed. Due to the widely documented impact of soiling on the spectral response of modules, this mechanism has been specially highlighted in this study. On the other hand, most of the publications analysed in this review report optical degradation in PV modules with polymeric encapsulant materials. Furthermore, an innovative procedure to quantify the spectral impact of degradation on PV devices is presented. This has been used to analyse the impact of two particular cases of degradation due to soiling and discoloration on the spectral response of different PV technologies.

Soiling profiles are commonly assumed to have sawtooth shapes, made of alternating cleaning events and soiling deposition periods. The rates at which soiling deposit on the PV modules are considered to be constant for each period. In reality, events such as changes in climatic conditions can lead to a sudden variation in soiling deposition rate. These changes cannot be reproduced if cleanings are the only events modelled to extract soiling profiles directly from PV performance data. For this reason, in this work, the use of change points and segmented regression is proposed to improve the extraction of soiling profiles through the model of up to two deposition rates per period in between cleanings. The results show that the quality of soiling extraction can be enhanced compared to a cleanings-only identification approach if both cleanings and change points are considered.

Soiling impacts the photovoltaic (PV) module performance by reducing the amount of light reaching the photovoltaic cells and by changing their external spectral response. Currently, the soiling monitoring market is moving toward optical sensors that measure transmittance or reflectance, rather than directly measuring the impact of soiling on the performance of photovoltaic modules. These sensors, which use a single optical measurement, are not able to correct the soiling losses that depend on the solar irradiance spectra and on the spectral response of the monitored PV material. This work investigates methods that can improve the optical detection of soiling by extracting the full soiling spectrum profiles using only two or three monochromatic measurements. Spectral transmittance data, measured with a spectrophotometer and collected during a 46-week experimental soiling study carried out in Ja\'en, Spain, was analysed in this work. The use of a spectral profile for the hemispherical transmittance of soiled PV glass is found to significantly improve the soiling detection, returning the lowest errors independently of the PV materials and irradiance conditions. In addition, this work shows that it is also possible to select the measurement wavelengths to minimize the soiling loss detection error depending on the monitored PV semiconductor material (silicon, CdTe, a-Si, CIGS and a representative perovskite). The approaches discussed in this work are also found to be more robust to potential measurement errors compared to single wavelength measurement techniques., Comment: Accepted Manuscript (Postprint)

Nowadays, photovoltaic (PV) technology has reached a high level of maturity in terms of module efficiency and cost competitiveness in comparison with other energy technologies. As PV has achieved high levels of deployment, the development of devices that can help to reduce PV operation and maintenance costs has become a priority. Soiling can be cause of significant losses in certain PV plants and its detection has become essential to ensure a correct mitigation. For this reason, accurate and low-cost monitoring devices are needed. While soiling stations have been traditionally employed to measure the impact of soiling, their high cost and maintenance have led to the development of innovative low-cost optical sensors, such as the device presented in this work and named “DUSST” (Detector Unit for Soiling Spectral Transmittance). The thermal characterization of DUSST’s components and the methodology used to predict soiling transmittance losses are presented in this study. The results show that the losses can be predicted with an error lower than 1.4%. The method has been verified with an experimental campaign with naturally soiled coupons exposed outdoors in Jaen, Spain.

The accumulation of soiling on photovoltaic (PV) modules affects PV systems worldwide. Soiling consists of mineral dust, soot particles, aerosols, pollen, fungi and/or other contaminants that deposit on the surface of PV modules. Soiling absorbs, scatters, and reflects a fraction of the incoming sunlight, reducing the intensity that reaches the active part of the solar cell. Here, we report on the comparison of naturally accumulated soiling on coupons of PV glass soiled at seven locations worldwide. The spectral hemispherical transmittance was measured. It was found that natural soiling disproportionately impacts the blue and ultraviolet (UV) portions of the spectrum compared to the visible and infrared (IR). Also, the general shape of the transmittance spectra was similar at all the studied sites and could adequately be described by a modified form of the Ångström turbidity equation. In addition, the distribution of particles sizes was found to follow the IEST-STD-CC 1246E cleanliness standard. The fractional coverage of the glass surface by particles could be determined directly or indirectly and, as expected, has a linear correlation with the transmittance. It thus becomes feasible to estimate the optical consequences of the soiling of PV modules from the particle size distribution and the cleanliness value.

Dust accumulation significantly affects the performance of photovoltaic modules and its impact can be mitigated by various cleaning methods. Optimizing the cleaning frequency is essential to minimize the soiling losses and, at the same time, the costs. However, the effectiveness of cleaning lowers with time because of the reduced energy yield due to degradation. Additionally, economic factors such as the escalation in electricity price and inflation can compound or counterbalance the effect of degradation on the soiling mitigation profits. The present study analyzes the impact of degradation, escalation in electricity price and inflation on the revenues and costs of cleanings and proposes a methodology to maximize the profits of soiling mitigation of any system. The energy performance and soiling losses of a 1 MW system installed in southern Spain were analyzed and integrated with theoretical linear and nonlinear degradation rate patterns. The Levelized Cost of Energy and Net Present Value were used as criteria to identify the optimum cleaning strategies. The results showed that the two metrics convey distinct cleaning recommendations, as they are influenced by different factors. For the given site, despite the degradation effects, the optimum cleaning frequency is found to increase with time of operation.

Ultra-high concentrator photovoltaic systems (UHCPV), usually referred to CPV systems exceeding 1000 suns, are signalled as one of the most promising research avenues to produce a new generation of high-efficiency and low-cost CPV systems. However, the structure of current concentrator solar cells prevents their development due to the unavoidable series resistance losses at such elevated concentration ratios. In this work, we investigate the performance of the so-called vertical-tunnel-junction (VTJ), recently introduced by the authors, by using advance TCAD. In particular, we carry out an optimisation procedure of the key parameters that affect its performance and conduct a deep investigation of the impact of the main recombination mechanisms and of sun concentration up to 10,000 suns. The results indicate that the performance of the novel structure is not significantly affected by these two factors. A record efficiency of 32.2% at 10,000 suns has been found. This represents a promising way to obtain state-of-the-art efficiencies above 30% for single-band-gap cells, and offers a new route towards the development of competitive CPV systems operating at ultra-high concentration fluxes E. F. Fernández and F. Almonacid thank the Spanish Economy Ministry and FEDER funds received under the project ENE2016-78251-R. N. Seoane and A. J. García Loureiro thank Spanish Ministry of Economy and Competitiveness and FEDER funds (TIN2016-76373-P) and the Xunta de Galicia and FEDER funds (GRC 2014/008). N. Seoane and E.F. Fernández also thank the Spanish Ministry of Science, Innovation and Universities (RYC-2017-23312, RYC-2017-21910). C. Outes also thanks the Ayudas predoctorales para la Formación de Personal Investigador con cargo a la Acción 9.a) del Plan de Apoyo a la Investigación de la Universidad de Jaén (ERC_2019_1) 2022-04-20 SI

The identification and prediction of the daily soiling profiles of a photovoltaic site is essential to plan the optimal cleaning schedule. In this article, we analyze and propose various methods to extract and generate photovoltaic soiling profiles, in order to improve the analysis and the forecast of the losses. New soiling rate extraction methods are proposed to reflect the seasonal variability of the soiling rates and, for this reason, are found to identify the most convenient cleaning day with the highest accuracy for the investigated sites. Also, we present an approach that could be used to predict future soiling losses through the implementation of stochastic weather generation algorithms whose ability to identify in advance the best cleaning schedule is also successfully tested. The methods presented in this article can optimize the operation and maintenance schedule and could make it possible, in the future, to predict soiling losses through analysis based only on environmental parameters, such as rainfall and particulate matter, without the need of long-term soiling data.

High-power laser transmission (HPLT) is attracting a huge interest from both the scientific and industrial community due to its large number of potential applications and future perspectives. This technology consists of the use of a monochromatic light source to power supply a remote system by using a photovoltaic converter. HPLT offers a technological paradigm shift with the possibility of transmitting kilowatts to several kilometres without the use of wires. However, HPLT is still under development and the current efficiency, ≈20%, needs to be improved to achieve the actual potential of the technology. This work is focused on the investigation of the most suitable materials to improve the performance of HPLT systems under a wide range of scenarios. For the first time, the monochromatic efficiency of PV converters, considering the attenuation of the atmosphere with the distance, and for various input light intensities and series resistance scenarios, is deeply investigated. The results indicate that high energy gap materials such as ZnS (3.54 eV) or 6H–SiC (3 eV) could lead to record efficiencies and improve current values in more than 30%.

Non-uniformity is a relevant concern of concentrator photovoltaic systems (CPV) due to its impact on the performance of multi-junction (MJ) solar cells. This work is focused on a state-of-the-art investigation related to the effects of shading on the irradiance profiles and electrical performance of MJ cells. For doing this, three different CPV single-units with a concentration of ≈559x have been experimentally investigated indoors at the CPV laboratory of the University of Jaen. The units are made up of poly(methyl methacrylate) (PMMA) Fresnel lens and standard GaInP/GaInAs/Ge MJ cells. Also, single-lens-optical element (SILO-Pyramid) and refractive truncated pyramid (RTP) homogenizers have been considered. The results indicate that shading produces additional spatial and spectral non-uniformities, and that these are reduced by the use of homogenizers. In addition, the non-uniform spectral illumination has been identified as the main cause of the additional reduction of the performance of MJ solar cells. In this sense, the SILO-Pyramid provides the best results and shows a significantly stable spectral performance under shading conditions. For a no-homogenizer case, the maximum power shows a reduction of 86.3% for a shading factor of 80%, while it is only reduced by 83.2% and by 81.6%, respectively, for the RTP and SILO-Pyramid.

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.