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An evaluation of the impact of using supercritical carbon dioxide mixtures (s-CO2/C2H6, s-CO2/CH4, s-CO2/Kr, and s-CO2/SF6) as a working fluid is made here for Brayton s-CO2 power cycles. The considered complex configurations include recompression with two reheating (RCC-2RH), recompression with three reheating (RCC-3RH), recompression with main compressor intercooling and two reheating (RCMCI-2RH), and recompression with main compressor intercooling and three reheating (RCMCI-3RH), which were coupled to a linear-focus solar system with Solar Salt (60% NaNO3/40% KNO3) as the heat transfer fluid (HTF). The design parameters evaluated the solar plant performance at the design point, the aperture area of the solar field, and variations in costs regarding the plant's total conductance (UAtotal). The methodology used to calculate the performance established the total conductance values of the heat recuperator (UAtotal) to between 5 and 25 MW/K. The main conclusion is that the cycle efficiency has a considerable improvement compared with that obtained using pure s-CO2. The s-CO2/Kr mixture with a molar fraction ratio of 30/70 increases the cycle efficiency between 7-11% relative to pure s-CO2 and as a function of the UAtotal. The s-CO2/CH4 mixture with a molar fraction of 45/55 increases between 3-7%, and the s-CO2/C2H6 and s-CO2/SF6 mixtures only increase between 1- 2%. For the solar field unitary costs, the s-CO2/Kr mixture has the lowest cost at $29-34 million USD, which depends on the solar field aperture area and the UAtotal for the RCC-2RH and RCMCI-2RH configurations. Finally, the results demonstrate that variations in the working fluid properties play a significant role due to the positive impact on the increased thermal efficiency of the s-CO2 Brayton cycle when using the RCC and RCMCI configurations.

The standardization of VIPV (Vehicle-integrated photovoltaic) has been driven by the international discussion among scientists and engineers, from photovoltaic research, photovoltaic industries, automobile and other industries, and testing laboratories. Since the VIPV is not flat and fixed installation, as well as a wide variety of designs, the knowledge of CPV (Concentrator Photovoltaic) technology, has been useful for developing testing technologies. This paper took two examples in the performance testing and the test for the tolerance for the partial/dynamic shading, utilizing various techniques exclusively used in CPV technologies.

Glass molded optics have a wide range of applications in commercial industry such as for secondary optical elements in concentrator photovoltaics (CPV), optics for light emitting diodes (LEDs), etc… In micro-CPV the reduction in size of all the components demands a very good optical quality of the primary lenses to achieve high concentrations and high efficiencies without the need of secondary optics. Glass for molding is a good candidate due to benefits such as a high abbe number, great mechanical properties, low coefficient of thermal expansion (CTE), low thermal coefficient of the refractive index (dn/dT), proven reliability, and manufacturing by a straight forward compression molding process. In collaboration with the company Holophane S.A.S. in France, several arrays of plano-convex concentrator lenses were manufactured using a manual compression mold. These first prototypes have shown absolute optical efficiency over 80% at 178X using a 1mm2 multi-junction (MJ) solar cell. Further results and potential improvements are discussed.

The suitability of metal-wrap-through solar cells has been explored through a set of solar cells developed and optimized by Fraunhofer ISE for LCPV operation. Flexural strength testing and finite element modeling give evidence of the feasibility of MWT cells as a receiver for low concentration PV systems. MWT cells encapsulated as receivers withstand mechanical stresses equivalent to very large thermal loads (higher than those defined in the qualification standard) and show no fatigue effects after a number of bending loading cycles equivalent to their expected lifespan. Dark I-V curve screening and the comparison of electroluminescence images monitor cell damage. Large losses are found under non-uniform concentrated light, which implies that a strong tradeoff still lies between acceptance angle and efficiency. A redesign of the MWT cell metal grid or via spacing might be required to reduce series resistance losses under realistic concentrated spot illumination profiles.The suitability of metal-wrap-through solar cells has been explored through a set of solar cells developed and optimized by Fraunhofer ISE for LCPV operation. Flexural strength testing and finite element modeling give evidence of the feasibility of MWT cells as a receiver for low concentration PV systems. MWT cells encapsulated as receivers withstand mechanical stresses equivalent to very large thermal loads (higher than those defined in the qualification standard) and show no fatigue effects after a number of bending loading cycles equivalent to their expected lifespan. Dark I-V curve screening and the comparison of electroluminescence images monitor cell damage. Large losses are found under non-uniform concentrated light, which implies that a strong tradeoff still lies between acceptance angle and efficiency. A redesign of the MWT cell metal grid or via spacing might be required to reduce series resistance losses under realistic concentrated spot illumination profiles.

Adding a dielectric Secondary Optical Element (SOE) to a Concentrating Photovoltaic (CPV) system provides several advantages. Besides increasing the concentration-acceptance angle product attainable by the system, a more uniform irradiance on the solar cell can also be achieved. The most common solution to glue the SOE and the solar cell consists in using an elastomer such as silicone. In this case, the silicone is acting both as an optical coupler to reduce Fresnel losses and as a mechanical bond. In this paper, we present a new approach to fix the thickness of the silicone in order to ensure a good adherence.

Micro concentrator photovoltaics (micro-CPV) is an unconventional approach for developing high-efficiency low-cost PV systems. The micrifying of cells and optics brings about an increase of efficiency with respect to classical CPV, at the expense of some fundamental challenges at mass production. The large costs linked to miniaturization under conventional serial-assembly processes raise the need for the development of parallel manufacturing technologies. In return, the tiny sizes involved allows exploring unconventional optical architectures or revisiting conventional concepts that were typically discarded because of large material consumption or high bulk absorption at classical CPV sizes.

Linear Fresnel collectors are becoming an attractive option to generate electricity from solar radiation. This paper is focused in the thermal performance of Fresnel collectors working with different heat transfer fluids: synthetic oil, water-steam, molten salt and air, also comparing the results of the Fresnel technology with those obtained in reference parabolic trough loops. Although there are two basic designs of the Fresnel receiver: multi-tube and single-tube with secondary concentrator, this work only studies in depth the single-tube option, as this design is more suitable for a proper comparison with parabolic troughs. The receiver in parabolic troughs has been modeled as an evacuated tube with a selective coating and a glass cover. For Fresnel receivers it has been simulated two different configurations: non-evacuated receiver, with a glass window at the cavity aperture and evacuated receiver, characterized by a tube with a glass cover and a selective coating.

Implementation of a high-efficiency quantum dot intermediate-band solar cell (QD-IBSC) must accompany a sufficient photocurrent generation via IB states. The demonstration of a QD-IBSC is presently undergoing two stages. The first is to develop a technology to fabricate high-density QD stacks or a superlattice of low defect density placed within the active region of a p-i-n SC, and the second is to realize half-filled IB states to maximize the photocurrent generation by two-step absorption of sub-bandgap photons. For this, we have investigated the effect of light concentration on the characteristics of QDSCs comprised of multi-layer stacks of self-organized InAs/GaNAs QDs grown with and without impurity doping in molecular beam epitaxy.

There is a need for a short-term characterization after the installation of a CPV plant to determine the real power installed according to contractual conditions. Outdoor power rating of large High-CPV systems and plants has to face the challenge of the strong spectral dependence of the performance of multijunction cells. We present a method for the spectrally correction of the DNI based on component cells. Besides, the reference and operating conditions suitable for power rating of CPV arrays and plants are discussed. The method demonstrated high precission, with deviations in the rated power within ± 3% applicated to the same system over a year under very different spectral conditions.

Synthetic and empirical data have been used to explore the influence of spectral mismatch between MJ cell technologies on outdoor CPV module rating uncertainty. Calibration biases are attenuated by tightly filtering spectral conditions to a spectral matching ratio (SMR) of 1 ± 2.5%. The sensitivity of calibrated current to spectral deviations greatly depends on the direction and distribution of the deviations on the SMR space.

This paper presents the experimental characterization of the efficiency thermal sensitivity of a system whose optics is composed of a silicone on glass Fresnel lens and a secondary element also made of silicone. In addition, some indications are provided on the adequate chemical formulation of the silicone that withstands longtime outdoor exposure under concentrated light without showing appreciable degradation.

In the frame of the European project SOPHIA a concentrator photovoltaic (CPV) module measurement round robin has been initiated. The round robin includes measurements of four CPV modules at seven different test laboratories located in Europe. IV curves of the modules are measured with different measurement equipment under various climatic conditions. The aim of this activity is to perform at each site a rating of the modules at concentrator standard operating conditions CSOC according to IEC 62670-1. The outcome of the round robin is intended for direct feedback to the current draft standard IEC 62670-3 “Concentrator Photovoltaic (CPV) Performance Testing - Performance Measurements and Power Rating”. The paper discusses initial results from the first three partners that have already finished the measurements up to now.

Ozone and ultraviolet (UV) radiation are two important issues in the study of Earth’s atmosphere. The anthropogenic perturbation of the ozone layer has induced change in the amount of UV radiation that reaches the Earth’s surface, mainly through the Antarctic ozone hole. Also clouds have been identified as the main modulator of UV amount over short time scales. While clouds can decrease direct radiation, they can produce an increase in the diffuse component, and as a consequence the surface UV radiation may be higher than during an equivalent clear sky scenario. In particular this situation can be important when a low ozone column and partially cloud coverered skies occur simultaneously. These situations happen frequently in southern Patagonia, where the CEILAP Lidar Division has established the Atmospheric Observatory of Southern Patagonia, an atmospheric remote sensing site near the city of Rio Gallegos (51°55’S, 69°14’W). In this paper, the impact of clouds on UV radiation is investigated by the use of ground based measurements from the passive remote sensing instruments operating at this site, mainly broad and moderate narrow band filter radiometers. Cloud modification factors (CMF, ratio between the measured UV radiation in a cloudy sky and the simulated radiation under cloud-free conditions) are evaluated for the study site. CMFs higher than 1 are found during spring and summer time, when lower total ozone columns, higher solar elevations and high cloud cover occur simultaneously, producing extreme erythemal irradiance at the ground surface. Enhancements as high as 25% were registered. The maximum duration of the enhancement was around 30 minutes. This produces dangerous sunbathing conditions for the Rio Gallegos citizen.