The development of Photovoltaic (PV) systems operating under very high solar concentration has attracted considerable interest and motivated a significant amount of research and development over the past two decades, driven by the prospect of achieving exceptionally high solar-to-electricity conversion efficiency, and, ultimately, lowering the cost of solar electricity. Although this field has experienced a decline in recent years, mainly due to the rapid expansion of conventional PV, conversion under ultra-high solar flux (≥1000 suns) remains a subject of singular interest that stems from the interplay of diverse physical, optical, and thermal phenomena, the significant technical challenges inherent to its practical implementation, and its direct relevance to several high-efficiency PV cell technologies currently under development. In this article, we review the physical motivations and principles underlying the operation of PV cells under ultra-high solar concentration. We describe the limiting mechanisms that can significantly affect the performance of PV cells under such extreme conditions, before listing and analysing the strategies proposed to limit their effects. Finally, we review and discuss the emerging high-efficiency PV cell technologies and provide practical recommendations grounded in two decades of ultra-high concentration PV research.

Combined photovoltaics and concentrated solar power can concurrently provide electricity and heat. Spectral management is required in these systems to separate and store the absorbed solar energy. In this work, the performance of luminescent materials is assessed for photovoltaic concentrated solar power plants.

Photoluminescence (PL) spectroscopy is a valuable tool fordegradation studies of perovskite‐based photovoltaic materials. The wavelength‐sensitive nature of the photo‐induced processes implies a preference for sunlight as the photo‐excitation source for such PL studies. This study reports on the design and experimental validation of a new setup for the in situ study of PL degradation in metal halide perovskites using concentrated natural sunlight in a wide range of solar concentrations and sample temperatures. The system allows the sample to be excited with the entire solar spectrum while successfully filtering undesired reflected sunlight using two orthogonal polarization filters. Depending on temperature and solar concentration, we observed three types of perovskite PL behavior: stable PL response, without degradation; reversible PL degradation with stable ultraviolet–visible light absorption; and nonreversible PL degradation accompanied with the variation of light absorption.

Upconversion - the absorption of two or more photons resulting in radiative emission at a higher energy than the excitation - has the potential to enhance the efficiency of solar energy harvesting technologies, most notably photovoltaics. However, the required ultra -high light intensities and the narrow absorption bands of lanthanide ions limit efficient solar utilisation. In this paper, we report results from exciting upconverters with concentrated sunlight at flux densities up to 2300 suns, where the radiation is restricted to photon energies below the bandgap of silicon (corresponding to a wavelength lambda = 1200 nm). Upconversion to lambda = 980 nm is achieved by using hexagonal erbium-doped sodium yttrium fluoride (beta-NaYF4: Er3+) in a fluoropolymer matrix. Upconversion has a nonlinear relation with irradiance, therefore at a high irradiance a threshold occurs where the process becomes linear. For beta-NaYF4:25%Er3+, we find a two-photon threshold under concentrated sunlight at 320 suns. Notably, this threshold is lower than under corresponding laser excitation and can be related to all resonantly excited Er3+ ion levels and excited stated absorption. These results highlight a pathway that utilises a far broader portion of the solar spectrum for photovoltaics.

Combined concentrated solar power with photovoltaics can provide electricity and heat at the same system while maximizing the power output with reduced losses. Spectral splitting is required in such systems to separate the infrared part of the solar spectrum towards the thermal system, while the visible and near-infrared radiation can be converted by the photovoltaic solar cell. The performance of concentrated solar power plants comprising reflective beam splitters for combined generation of electricity and heat is presented in this work. A 50 MW power plant is considered in this work as a case of study in Southern Crete, Greece. The solar power plant consists of parabolic trough collectors and utilizes beam splitters with varying reflectivity. The dynamic performance of the power plant is modeled, and the annual energy yield can be calculated. Up to 350 MWt of thermal power can be delivered to the photovoltaic system utilizing a 50% reflecting splitter. The penalty to the high-reflectivity system is limited to 16.9% and the annual energy yield is calculated as 53.32 GWh. During summer months, a higher energy yield by up to 84.8 MWh/month is produced at 80% reflectivity compared to 90% as a result of the number of parabolic troughs. The reported energy yields with reflectivity by dynamic modeling can highlight discrete points for improvement of the performance in concentrated solar power photovoltaics.

Utilization of solar and wind energy is increasing worldwide. Photovoltaic and wind energy systems are among the major contributing tec4hnologies to the generation capacity from renewable energy sources; however, the generation often does not temporally match the demand. Micro-compressed air energy storage (micro-CAES) is among the low-cost storage options, and its coupling with the power generated by photovoltaics and wind turbines can provide demand shifting, modeled by efficient algorithms. A model based on criteria that are preset according to the demand is presented. The model decides on the distribution of the generated energy, depending on the state of the energy storage and the preset criteria of each storage technology. The satisfaction of the demand by the energy production and micro-CAES is compared to that of storage batteries. The demand originates in a case study of a household and optimal configurations of photovoltaics and wind turbines, and the storage capacities and costs are compared. An optimal configuration of 30 photovoltaic panels and two wind turbines was found for micro-CAES. The annual stored energy of micro-CAES was 114 kWh higher than that of the system with batteries.

CombiCSP is an open source software for dynamic modeling of concentrating solar energy power plants. CombiCSP utilizes solar resource, system engineering inputs as well as financial tools to provide dynamic simulations and annual yields of concentrating solar power plants. It readily provides modeling of plants based on solar power tower and parabolic trough collectors and it can be extended to novel solar energy modeling approaches and analyses as needed.

Insular power systems are a special case of infrastructure for power production due to their particular land morphology with extensive hills and ridges. For a higher renewable energy share in the power production, a dedicated design according to local constraints is required. The high wind and solar resources of such cases can be utilized with offshore wind turbines and concentrating solar power, respectively. In addition, pumped-hydro storage is a mature and suitable technology for such terrain. A case study is presented in the island of Rhodes to obtain a renewable energy penetration higher than 70%. The technical and financial requirements for this implementation support the design of this system, while the introduction of concentrating solar power enables significant energy savings during the periods of peak demand of the island. An annual RES penetration close to 80% can be achieved with the combined operation of both plants. The economic viability of the required investment can be ensured with selling prices of the produced electricity in the range of 0.20 EUR/kWh.

Concentrating solar power is an important technological option to gradually increase the share of energy produced by renewable energy sources. Central power towers and parabolic trough collectors, are currently the most mature technologies globally installed. While the former technology requires less land area to produce the same power output, the latter operates at lower temperatures thereby requiring less demanding materials. In this paper, we investigate by dynamic modeling the potential of both technologies in the same plant configuration. We find more stable day-to-day annual power profile for a configuration of a 29 MWe tower and 25 MWe of north-south oriented parabolic trough collectors compared to single technology plants. This results in a higher maximum capacity factor of 18% at 925 W/m2 direct normal irradiance and discounted payback of 9 years at a cost of electricity of 248 Euro/MWh compared to a standalone plant based on parabolic trough technology. In this way, the advantages of both concentrating technologies can be utilized and aid towards wider utilization of solar energy.

Solar photons possessing energy less than the bandgap of a single-junction solar cell can be utilized via the upconversion (UC) of two or more photons, resulting in the emission of a single above-bandgap photon. Due to the non-linear nature of UC, highly concentrated light is required, which is typically much greater than the practical concentration limits of a solar cell. It has been proposed that concentrating upconversion solar cells (UC-SC) with optical elements integrated into the device could help realize the high solar irradiance required. To avoid scattering problems arising from common UC materials based on micro-crystalline powders, in this work, concentrators are investigated with mono-crystalline upconverters in silicon-based tandem devices. An external quantum efficiency (EQE) of 6% with 1493 nm infrared illumination at 876 W / m 2 was obtained in upconverter device with concave integrated optics. At an irradiance higher than 90 W / m 2 (equivalent to 2.95 × in the 1450–1600 nm range), the non-concentrating UC-SC exhibited 1 . 5 × higher EQE than the UC-SC with a compound parabolic concentrator (CPC), while below 90 W / m 2 the CPC UC-SC exhibited 1.95 × higher EQE than the non-concentrating reference device. Due to the negligible scattering of the UC layer, the distribution of localized irradiance is revealed along with its effect on the performance of devices. It is found that irradiance is accumulated within the first 1 mm of the UC layer with peaks at variable depths according to the concentrating scheme. These results suggest ample space for improved UC devices by using integrated optics.

We present a double-layer dielectric metasurface obtained by stacking a silicon nanodisk array and a silicon photonic crystal slab with equal periodicity on top of each other. We focus on the investigation of electric near-field enhancement effects occurring at resonant excitation of the metasurface and study its optical properties numerically and experimentally. We find that the major difference in multi-layer metasurfaces when compared to conventional single-layer structures appears to be in Rayleigh–Wood anomalies: they are split into multiple different modes, which are themselves spectrally broadened. As a proof of concept, we cover a double-layer metasurface with a lanthanide-doped up-conversion particle layer and study its interaction with a 1550 nm photoexcitation. We observe a 2.7-fold enhanced up-conversion photoluminescence by using the stacked metasurface instead of a planar substrate, although only around 1% of the up-conversion material is exposed to enhanced near fields. Two mechanisms are identified explaining this behavior: First, enhanced near fields when exciting the metasurface resonantly, and second, light trapping by total internal reflection in the particle layer when the metasurface redirects light into high angle diffraction orders. These results pave the way for low-threshold and, in particular, broadband photon up-conversion in future solar energy and biosensing applications.

This article presents comparative results on the energy performance of buildings in the Mediterranean. Many buildings in the Mediterranean exhibit low energy performance ranking. Thermochromic windows are able to improve the energy consumption by controlling the gains from sunlight. In this article, reference buildings in 15 cities around the Mediterranean are investigated. In this work, a dynamic building information modeling approach is utilized, relying on three-dimensional geometry of office buildings. Calculations of the energy demand based on computational simulations of each location were performed, for the estimation of heating and cooling loads. The presented study highlighted the need for high-resolution data for detailed simulation of thermochromic windows in buildings of Mediterranean cities. Temperature is one of the main climate parameters that affect the energy demand of buildings. However, the climate of Mediterranean cities nearby the sea may affect the energy demand. This was more pronounced in cities with arid Mediterranean climate with increased demand in air-conditioning during the summer months. On the other hand, cities with semi-arid Mediterranean climate exhibited relatively increased heating demand. With this parametric approach, the article indicates the energy saving potential of the proposed measures for each Mediterranean city. Finally, these measures can be complemented by overall building passive and active systems for higher energy reductions and increased comfort.

In this paper, the technological advances in concentrating solar power are reviewed. A comprehensive system approach within this scope is attempted to include advances of highly specialized developments in all aspects of the technology. Advances in geometric optics for enhancement in solar concentration and temperature are reviewed along with receiver configurations for efficient heat transfer. Advances in sensible and latent heat storage materials, as well as development in thermochemical processes, are also reviewed in conjunction with efficient system integration as well as alternative energy generation technologies. This comprehensive approach aims in highlighting promising concentrating solar power components for further development and wider solar energy utilization.

The initial stages of photo‐degradation of CH3NH3PbI3 (MAPbI3) thin films prior to any significant change in light absorption are studied in experiments with independent control of sample temperature and intensity of concentrated sunlight from 50 to 500 suns. Photo‐stability of the MAPbI3 film is revealed to be extremely sensitive to the sample temperature. Under the combined action of light and heat (either by concentrated sunlight or by external heating), a strong reduction of the film photoluminescence (PL) without changes in the perovskite light absorption can be observed during the initial stages of degradation. In contrast, illumination of perovskite films (with intensity up to 500 suns) without heating (using chopped concentrated sunlight) induces considerable PL enhancement while the optical absorption spectrum remains unchanged. With accurate temperature control, aging under concentrated sunlight results in similar instability trends as that under 1 sun.

We report on the first in-situ PL monitoring of methylamonium lead iodide thin films upon excitation by concentrated sunlight up to 90 suns.

Development of novel nanoscale devices requires unique functional nanomaterials. Furthermore, chemical design of different nano particles in one unit is a complex task, particularly the application of self assembly J-aggregates, which can substantially advance the nanomaterial's properties due to resonant delocalization of excitons. Here, we have demonstrated for the first time formation of resonantly coherent J-aggregates on carbon nanotubes with highly efficient energy transfer from the aggregates to the nanotubes. All the energy of photons absorbed by the aggregates is conveyed to the nanotubes, completely quenching the J-band emission and photosensitizing the nanotubes. Overall, we discovered formation of two types of J-aggregates, where one type is related to self assembly of cis-isomers on the nanotube surface and the second type is associated to self-organizing trans-isomers into free J-aggregates without the nanotubes. Importantly, the J-aggregates on carbon nanotubes with strong energy transfer peaks of photoluminescence in the near infrared range are of high interest for practical applications on biomedical imaging and nanoscale optoelectronic and nanophotonic devices.

We investigate the two-photon threshold of rare-earth up-conversion under concentrated sunlight, in a solar furnace that generates an irradiance of up to 2606 suns on the samples. One of the most efficient up-converters currently available, NaYF 4 : Er 3+ [1] was used. We established a threshold by experimentally observing the transition for up-conversion photoluminescence from a quadratic relation to linear relation as solar concentration was increased. We further investigated the role of energy transfer on the threshold, observing the same threshold for a higher Er 3+ content of 50%, but a threshold that exceeds 2300 suns at 15% Er 3+ . In this way, a tangible limit for the benefit and effect of solar concentration on up-conversion can be obtained for photovoltaic [2], [3] and solar thermal applications.

The research on halide perovskites is in its peak activity at the moment due to the materials potential application in photovoltaics. It is well known that slow processes, from seconds to minutes, are very significant in perovskite films and devices as compared to conventional photovoltaic materials. The kinetics of photoluminescence (PL) is informative data for studying such processes. In particular, tracing the change in PL intensity under continuous laser excitation provides information on charge carriers recombination and the efficiency of their extraction from the absorber layer. Although widely available, this method was applied mainly for the research on thin films. However, monitoring PL kinetics on complete solar cells as well as on incomplete device stacks at each fabrication and lifespan stage can provide an important information on the device optimization and determination of the layers and interfaces that limit device efficiency and stability. Here, we demonstrate the advantages of the method by tracing the evolution of PL kinetics at seconds-to-minutes timescale upon: (1) varying perovskite composition (MAPbI(3), Cs(0.15)FA(0.85)PbI(2.7)Br(0.3), Cs-0.05(MA(0.15)FA(0.85))(0.95)PbI2.55Br0.45); (2) layer-by-layer stack construction of Cs(0.15)FA(0.85)PbI(2.7)Br(0.3)-based solar cell and (3) the device on-shelf degradation. In this way, information on charge carrier recombination, diffusion and extraction is revealed purely by optical, contactless and non-destructive means.

Up-conversion is one of the promising approaches for energy and biomedical applications. To enable significant power conversion efficiencies, high irradiance is required. In solar energy applications, this irradiance translates to solar concentrations higher than one sun, unable to be obtained without geometrical or local-field concentration. For biomedical applications, enhanced sensitivity and imaging resolution are required, accompanied by low sample volumes. In this review, the performance of approaches with geometrical concentration on up conversion processes is reviewed based on recently reported results. Compound parabolic concentrators in c-Si and beta-NaYF4: 25%Er3+ is to-date the most promising approach, with a device external quantum efficiency of 1.8% at incident irradiance of 240 W/m(2).