Estimation of solar resource for vehicle-integrated photovoltaics in urban environments using image-based shade detection.

Vehicle-Integrated Photovoltaics (VIPV) in urban environments face challenges in accurately estimating solar resource due to dynamic shading effects. This research presents a methodology for evaluating VIPV solar resource by analyzing imagery and detecting shade conditions along driving routes. Street image mapping services and obstacle detection algorithms are utilized to determine the shaded or sunny condition of the vehicle at each point. The approach enables the calculation of solar irradiance, considering direct and diffuse components, and identifies energetically optimal driving routes. The methodology provides valuable insights for optimizing MPPT algorithms and assessing VIPV performance in urban settings. It offers a practical tool for sustainable mobility and renewable energy integration.

Characterization method and analysis of misalignments in micro-concentrator photovoltaic modules.

Micro-scale concentrator photovoltaics (micro-CPV) is an emerging trend for the development of high-efficiency, low-cost photovoltaic systems. The miniaturization of optics and cells offers advantages in terms of performance and enables differentiation in the PV market. However, the sub-millimeter size of the solar cells used, the intrinsic narrow angular tolerance of CPV optical systems (typically around 0.5° and 2°), and the massive number of cells per module lead to very tight mechanical tolerances. Therefore, determining the misalignments between cells and optics is important for quality control inspection of modules. In this paper, we describe a method for characterizing these misalignments based on image acquisition and its subsequent processing and apply it to a micro-CPV module composed of 572 lens-cell units. This method is validated, using a unique experimental technique that takes advantage of the tracking system embedded in the module. The statistical distributions of misalignments are compared for two tracking positions, residuals are determined and shows the consistency of the method. Finally, the impact of misalignment distributions on the IV curve of the module is discussed.

Comparison of achromatic doublet on glass Fresnel lenses for concentrator photovoltaics.

Silicone on glass (SoG) Fresnel lenses are the reference technology in concentrator photovoltaics (CPV) because of their simplicity and low cost. Nevertheless, their performance is strongly limited by chromatic aberration. As an alternative, in order to overcome such limitation, achromatic doublet on glass (ADG) Fresnel lenses were proposed. Such lenses are achromatic cemented doublet specifically designed for CPV applications. In this paper, a novel ADG architecture is presented and its performance analyzed and compared to previous proposals. The results show that most of the intrinsic optical losses are minimized and a superior optical efficiency can be achieved. The novel ADG design provides an achromatic lens for CPV whose efficiency is almost equal to the reference SoG technology and, at the same time, maintains all the advantages provided by the achromatic design such as the higher maximum attainable concentration and the strongly reduced temperature dependency.

Roll-to-roll nanoimprint lithography of high efficiency Fresnel lenses for micro-concentrator photovoltaics.

Roll-to-roll nanoimprint lithography (R2R-NIL) is an enabling technology for the low-cost mass production of high-quality micro- and nano-sized optical elements. Particularly, the fabrication of Fresnel lenses using R2R-NIL is a promising approach to produce optical arrays for micro-concentrator photovoltaic modules. This work investigates the application of a continuous R2R imprinting process based on ultraviolet curing of transparent photopolymer resins (UV-NIL) to fabricate high-efficiency and low-cost Fresnel lenses. The morphological attributes and the related optical performance of the lenses fabricated using roll-to-roll UV-NIL on flexible PET sheets yielded optical efficiency values up to ∼ 69% at a concentration ratio of 178X, whereas a value of ∼ 77% was obtained for the UV-NIL batch processed on a flat rigid substrate. Further improvement of the optical efficiency has been achieved by adding moth-eye inspired antireflective (AR) features on the side opposite to the Fresnel motifs via a double-sided R2R UV-NIL process. The process developed paves the way for cost-effective mass production of high-efficiency Fresnel lenses for micro-concentrator photovoltaics.

Design and modeling of a cost-effective achromatic Fresnel lens for concentrating photovoltaics.

This paper presents a novel Fresnel lens capable of significantly reducing chromatic aberration in solar applications. The optical performance of this achromatic lens has been analyzed through ray-tracing simulations, showing a concentration factor three times higher than that attained by a classic silicone on glass (SOG) Fresnel lens while maintaining the same acceptance angle. This should avoid the need for a secondary optical element, reducing the cost associated with its manufacturing and assembly and increasing the module reliability. The achromatic lens is made of inexpensive plastic and elastomer which allows a highly scalable and cost-competitive manufacturing process similar to the one currently used for the fabrication of SOG Fresnel lenses.

On the optimization of the interconnection of photovoltaic modules integrated in vehicles.

The design of photovoltaic modules for vehicle-integrated photovoltaics (VIPVs) must consider specific operating conditions like partial shading. Module cell interconnection topology must demonstrate resilience to such conditions to maximize energy generation without compromising shadow-free performance, manufacturing complexity, or cost. This study presents a modeling tool for VIPV, calculating effective irradiance on the VIPV surface using Light Detection And Ranging (LiDAR) point clouds to estimate the direct component and sky images for the diffuse irradiance. Subsequently, energy generated by the VIPV module is computed using circuit simulation software. Different module topologies regarding cell number, size, interconnections, and bypass diodes have been analysed. Results show significant daily energy production variations under partial shading conditions for different configurations (up to 41%). While integrating a large number of bypass diodes (160) offers optimal performance, this configuration may be impractical due to manufacturing complexity. However, similar results are achievable with appropriate configurations containing parallel branches and only 8 bypass diodes.

Hybrid lighting-CPV, a new efficient concept mixing illumination with CPV.

Hybrid Lighting-CPV concept mixes illumination using low-cost fiber optics for light transmission with conventional Concentrating Photovoltaic (CPV) technology. This approach may offer an important increase in the value of a CPV system. Direct illumination from sunlight with fibers does not require the double light-electricity-light energy conversion allowing for efficient lighting using just a small area of the CPV system, preferably those areas with lower CPV efficiency conversion. Simultaneously the need of concentration and tracking required is completely covered by the infrastructure of the CPV system. In this work, we present a theoretical study of the losses in optical fibers in order to establish the design criteria for the hybrid system. Losses caused by chromatic aberration increase with f-number while transmission losses in the fiber decrease.

Antireflective coatings for multijunction solar cells under wide-angle ray bundles.

Two important aspects must be considered when optimizing antireflection coatings (ARCs) for multijunction solar cells to be used in concentrators: the angular light distribution over the cell created by the particular concentration system and the wide spectral bandwidth the solar cell is sensitive to. In this article, a numerical optimization procedure and its results are presented. The potential efficiency enhancement by means of ARC optimization is calculated for several concentrating PV systems. In addition, two methods for ARCs direct characterization are presented. The results of these show that real ARCs slightly underperform theoretical predictions.

Solar simulator for concentrator photovoltaic systems.

A solar simulator for measuring performance of large area concentrator photovoltaic (CPV) modules is presented. Its illumination system is based on a Xenon flash light and a large area collimator mirror, which simulates natural sun light. Quality requirements imposed by the CPV systems have been characterized: irradiance level and uniformity at the receiver, light collimation and spectral distribution. The simulator allows indoor fast and cost-effective performance characterization and classification of CPV systems at the production line as well as module rating carried out by laboratories.

Indoor Experimental Assessment of the Efficiency and Irradiance Spot of the Achromatic Doublet on Glass (ADG) Fresnel Lens for Concentrating Photovoltaics.

We present a method to characterize achromatic Fresnel lenses for photovoltaic applications. The achromatic doublet on glass (ADG) Fresnel lens is composed of two materials, a plastic and an elastomer, whose dispersion characteristics (refractive index variation with wavelength) are different. We first designed the lens geometry and then used ray-tracing simulation, based on the Monte Carlo method, to analyze its performance from the point of view of both optical efficiency and the maximum attainable concentration. Afterwards, ADG Fresnel lens prototypes were manufactured using a simple and reliable method. It consists of a prior injection of plastic parts and a consecutive lamination, together with the elastomer and a glass substrate to fabricate the parquet of ADG Fresnel lenses. The accuracy of the manufactured lens profile is examined using an optical microscope while its optical performance is evaluated using a solar simulator for concentrator photovoltaic systems. The simulator is composed of a xenon flash lamp whose emitted light is reflected by a parabolic mirror. The collimated light has a spectral distribution and an angular aperture similar to the real Sun. We were able to assess the optical performance of the ADG Fresnel lenses by taking photographs of the irradiance spot cast by the lens using a charge-coupled device (CCD) camera and measuring the photocurrent generated by several types of multi junction (MJ) solar cells, which have been previously characterized at a solar simulator for concentrator solar cells. These measurements have demonstrated the achromatic behavior of ADG Fresnel lenses and, as a consequence, the suitability of the modelling and manufacturing methods.