Experimental energy yield in 1·5 × and 2 × PV concentrators with conventional modules

Low concentration devices along with standard (one sun) modules represent an attractive option to reduce the cost per kilowatt‐hour in photovoltaic installations. This paper deals with the energy gains obtained over a year by two of such devices: a 2 × V‐trough concentrator and a 1·5 × single flat mirror structure. The experiment was mounted on a two‐axis tracking system located in Arguedas (northern Spain). Due to various optical and electrical phenomena, the energy gain is notably lower than the geometrical concentration. We have conducted a theoretical analysis of these phenomena and quantified the energy loss associated with each. Daily and monthly energy gains show an influence of daylight clearness index on energy output. In view of this effect, and taking into account a possible increase in degradation of the photovoltaic modules due to high working temperatures and hot‐spots, the viability of these concentration devices is far from being clear. Copyright © 2007 John Wiley & Sons, Ltd.     

Dust effects on PV array performance: in‐field observations with non‐uniform patterns

This paper presents the impact of non‐homogeneous deposits of dust on the performance of a PV array. The observations have been made in a 2‐MW PV park in the southeast region of Spain. The results are that inhomogeneous dust leads to more significant consequences than the mere short‐circuit current reduction resulting from transmittance losses. In particular, when the affected PV modules are part of a string together with other cleaned (or less dusty) ones, operation voltage losses arise. These voltage losses can be several times larger than the short‐circuit ones, leading to power losses that can be much larger than what measurements suggest when the PV modules are considered separately. Significant hot‐spot phenomena can also arise leading to cells exhibiting temperature differences of more than 20 degrees and thus representing a threat to the PV modules' lifetime. Copyright © 2013 John Wiley & Sons, Ltd.     

Scale up the collection area of luminescent solar concentrators towards metre‐length flexible waveguiding photovoltaics

Luminescent solar concentrators (LSCs) are cost‐effective components easily integrated in photovoltaics (PV) that can enhance solar cells' performance and promote the integration of PV architectural elements into buildings, with unprecedented possibilities for energy harvesting in façade design, urban furnishings and wearable fabrics. The devices' performance is dominated by the concentration factor (F), which is higher in cylindrical LSCs compared with planar ones (with equivalent collection area and volume). The feasibility of fabricating long‐length LSCs has been essentially limited up to ten of centimetres with F < 1. We use a drawing optical fibre facility to easily scale up large‐area LSCs (length up to 2.5 m) based on bulk and hollow‐core plastic optical fibres (POFs). The active layers used to coat the bulk fibres or fill the hollow‐core ones are Rhodamine 6G‐ or Eu³⁺‐doped organic–inorganic hybrids. For bulk‐coated LSCs, light propagation occurs essentially at the POFs, whereas for hollow‐core device light is also guided within the hybrid. The lower POFs' attenuation (~0.1 m⁻¹) enables light propagation in the total fibre length (2.5 m) for bulk‐coated LSCs with maximum optical conversion efficiency (η_opt) and F of 0.6% and 6.5, respectively. For hollow‐core LSCs, light propagation is confined to shorter distances (6–9 × 10⁻² m) because of the hybrids' attenuation (1–15 m⁻¹). The hollow‐core optimised device displays η_opt = 72.4% and F = 12.3. The F values are larger than the best ones reported in the literature for large‐area LSCs (F = 4.4), illustrating the potential of this approach for the development of lightweight flexible high‐performance waveguiding PV. Copyright © 2016 John Wiley & Sons, Ltd.     

Energy payback time of the high‐concentration PV system FLATCON®

The ecological benefit and sustainability of a new energy technology and its potential to reduce CO₂ emissions depend strongly on the amount of energy embodied in the materials and production processes. The energy payback time is a measure for the amount of time that a renewable energy system has to operate until the energy involved in its complete life‐cycle is regenerated. In this paper, the energy payback time of the high‐concentration photovoltaic system FLATCON® using III–V semiconductor multi‐junction solar cells has been evaluated. Considering the energy demand for the system manufacturing, including transportation, balance of system and system losses, the energy payback time turns out to be as low as 8–10 months for a FLATCON® concentrator built in Germany and operated in Spain. The energy payback time rises slightly to 12 to 16 months for a system installed in Germany. The main energy demand in the production of such a high‐concentration photovoltaic system was found to be the zinced steel for the tracking unit. Copyright © 2005 John Wiley & Sons, Ltd.     

Soiling and other optical losses in solar‐tracking PV plants in navarra

Field data of soiling energy losses on PV plants are scarce. Furthermore, since dirt type and accumulation vary with the location characteristics (climate, surroundings, etc.), the available data on optical losses are, necessarily, site dependent. This paper presents field measurements of dirt energy losses (dust) and irradiance incidence angle losses along 2005 on a solar‐tracking PV plant located south of Navarre (Spain). The paper proposes a method to calculate these losses based on the difference between irradiance measured by calibrated cells on several trackers of the PV plant and irradiance calculated from measurements by two pyranometers (one of them incorporating a shadow ring) regularly cleaned. The equivalent optical energy losses of an installation incorporating fixed horizontal modules at the same location have been calculated as well. The effect of dirt on both types of installations will accordingly be compared. Copyright © 2010 John Wiley & Sons, Ltd.     

Performance analysis for V‐BLAST system using OSIC receiver in correlated channel

Vertical‐Bell Labs Layered Space–Time (V‐BLAST) system is an emerging spatial multiplexing scheme that can achieve high spectral efficiency. Ordered successive interference cancellation (OSIC) detection algorithm is suitable for V‐BLAST system because it can afford a reasonable trade‐off between complexity and performance. However, the correlation of a real‐world wireless channel may result in a substantial degradation of the OSIC performance. In this paper, the performance of OSIC under correlated fading is analyzed. We obtain the closed‐form expression of post‐processing signal‐to‐noise ratio (SNR) for each sub‐stream based on V‐BLAST architecture, and then derive the distribution of post‐processing SNR based on multivariate statistical theory. The upper bound of the average probability of error (APE) is derived by the nearest neighbor union bound theory. From the expression of APE for each sub‐stream, it is shown that the diversity gain at the ith processing step is (N ? M + i), where N and M are the number of receive and transmit antennas, respectively. Correlation can decrease the effective post‐processing SNR rather than the diversity gain, and the decreased amount of the effective post‐processing SNR is accurately measured by the corresponding diagonal element of the inverse of the transmit correlation matrix. The optimal ordering can improve the performance and this advantage vanishes gradually as the scattering angle decreases. Copyright © 2010 John Wiley & Sons, Ltd.     

Silver‐Nanowire‐Based Interferometric Optical Tweezers for Enhanced Optical Trapping and Binding of Nanoparticles

Light‐induced self‐assembly offers a new route to build mesoscale optical matter arrays from nanoparticles (NPs), yet the low stability of optical matter systems limits the assembly of large‐scale NP arrays. Here it is shown that the interferometric optical fields created by illuminating a single Ag nanowire deposited on a coverslip can enhance the electrodynamic interactions among NPs. The Ag nanowire serves as a plasmonic antenna to shape the incident laser beam and guide the optical assembly of colloidal metal (Ag and Au) and dielectric (polystyrene) NPs in solution. By controlling the laser polarization direction, both the mesoscale interactions among multiple NPs and the near‐field coupling between the NPs and nanowire can be tuned, leading to large‐scale and stable optical matter arrays consisting of up to 60 NPs. These results demonstrate that single Ag nanowires can serve as multifunctional antennas to guide the optical trapping and binding of multiple NPs and provide a new strategy to control electrodynamic interactions using hybrid nanostructures.     

Experimental demonstration of high‐concentration photovoltaics on a parabolic trough using tracking secondary optics

A new approach to high‐concentration photovoltaics (HCPV) based on a parabolic trough primary concentrator is presented. The design diverges from the standard HCPV arrangement of a two‐axis tracking point‐focus concentrator, and rather employs a simpler parabolic trough primary concentrator to reduce cost. To break the 2D limit of concentration, and bring the system into the realm of HCPV, the system employs an array of rotating secondary concentrators is arranged along the focal line of the parabolic trough. The resulting line‐to‐point (LTP) focus geometry allows the system to achieve a geometric concentration of 590×, yet still maintains the advantages of having a linear trough primary concentrator, namely manufacturability, economy, and scalability. A full‐scale prototype of the system was constructed in Biasca, Switzerland. During on‐sun tests a flux concentration of 364 suns was measured at the exit of the secondary concentrator, the highest reported concentration for any parabolic‐trough‐based system. Moreover, the system reached a peak efficiency of 20.2%, the highest measured solar‐to‐DC efficiency for a parabolic trough‐based solar collector. Long‐term performance is estimated by means of a coupled optical‐electrical model validated vis‐à‐vis the experimental results. This work serves as an experimental proof‐of‐concept for high‐concentration trough‐based collectors, thereby opening new avenues for reducing the cost of HCPV systems. Copyright © 2016 John Wiley & Sons, Ltd.     

A modified rain attenuation prediction model for tropical V‐band satellite earth link

Radio wave propagation plays a very important part in the design and eventually dictates performance of space communication systems. Over time, the requirements of satellite communication have grown extensively where higher capacity communications systems are needed. Escalating demands of microwave and millimetre wave communications are causing frequency spectrum congestion. Hence, existing and future satellite system operators are planning to employ frequency bands well above 10 GHz. The challenge in operating at such high frequencies for communication purposes is that there exists stronger electromagnetic interaction between the radio signals and atmospheric hydrometeors. Such instances will degrade the performance of such high frequency satellite communication systems. The development of a revised model for a better‐improved rain fade prediction of signal propagations in tropical region is considered very important. Researchers and engineers can employ the model to accurately plan the future high frequencies satellite services. Copyright © 2014 John Wiley & Sons, Ltd.     

The performance of uplink LDPC‐coded multirelay cooperation based on virtual V‐BLAST processing

This paper proposes an efficient uplink low‐density parity‐check (LDPC)‐coded multirelay cooperation architecture based on virtual Vertical‐Bell Labs Layered Space–Time (V‐BLAST) processing over a Rayleigh fading channel, where minimum mean square error in combination with a successive interference canceller and belief propagation‐based joint iterative decoder based on the introduced multilayer Tanner graph are effectively designed to detect and decode the corrupted received sequence at the destination. By introducing V‐BLAST transmission to coded multirelay cooperation, relays send their symbol streams simultaneously, which significantly reduce the transmission delay and provide higher transmission efficiency. The theoretical analysis and numerical results show that the proposed LDPC‐coded cooperation scheme outperforms the coded noncooperation under the same code rate and achieves a better compromise, with respect to the performance, signal delay, and encoding complexity associated to the number of relays, than the conventional LDPC‐coded cooperations without V‐BLAST transmission. This performance gain can be credited to the proposed V‐BLAST processing architecture and belief propagation‐based joint iterative decoding by the introduced multilayer Tanner graph at a receiver side. Copyright © 2013 John Wiley & Sons, Ltd.     

Technical and economic performance analysis of large‐scale ground‐mounted PV plants in Italian context

During the last decade, the market penetration of photovoltaic (PV) technology has been increased tremendously worldwide. In the EU context, following the quick development in German and Spanish PV sector, Italy is currently one of the most interesting market. In view of these facts, it is strategic to perform detailed technical and economic analyses to establish energy performances and profitability of the PV plants, depending on their configurations. In particular, in addition to the selection of main components, such as inverters and modules, which are now characterized, on average, by good performance levels, the debate on the support structures is still open. In detail, the choice may fall, for example, on traditional fixed structures or on one/two axis tracking systems, that could ensure best productivity per unit of power, but also are typically characterized by higher complexity and land‐occupation factors than the first ones. The purpose of this work is to carry out performance analyses on the most widespread plant configurations, taking into account different Italian climatic contexts, considering technical, energetic, and economic points of view. With this aim, different types of components (modules and inverters) and ground‐mounting structures (fixed, one‐axis, two‐axis) have been evaluated. Subsequently, their obtainable performances have been estimated in three different locations (Milano, Roma, Palermo) that have been considered representative of average irradiation levels available in Italy. Analyses have been carried out by computer simulations, through two consequent levels of detail, highlighting the main performance influence‐factors. In conclusion, the final profitability of each analyzed configuration has been evaluated, giving a reliable indication on their effective economic advantages. Copyright © 2010 John Wiley & Sons, Ltd.     

New Path‐Setup Method for Optical Network‐on‐Chip

With high bandwidth, low interference, and low power consumption, optical network‐on‐chip (ONoC) has emerged as a highly efficient interconnection for the future generation of multicore system on chips. In this paper, we propose a new path‐setup method for ONoC to mitigate contentions, such as packets, by recycling the setup packet halfway to the destination. A new, strictly non‐blocking optical router is designed to support the new method. The simulation results show the new path‐setup method increases the throughput by 52.03%, 41.94%, and 36.47% under uniform, hotspot‐I, and hotspot‐II traffic patterns, respectively. The end‐to‐end delay performance is also improved.     

Direct measurement and simulation techniques for analysis of radiation flux on a linear PV concentrator

For a linear reflective photovoltaic concentrator, small regions of low radiation flux can significantly reduce the output current of an entire array. Therefore, understanding the causes of light non‐uniformities along the focal line is crucial in the design of a trough concentrator. Typically, the flux profile is dependent on factors such as the mirror shape accuracy, gaps between mirrors and shading due to receiver supports. Radiation flux profiles have been measured on the combined heat and power solar (CHAPS) collectors developed at the Australian National University (ANU). The results for the first prototype showed significant variation in the radiation flux intensity along the length. The effect of imperfections in the mirror shape has been studied using ray tracing techniques and the software package Opticad. The simulations allowed the individual effects of mirror shape imperfections, gaps between mirrors and shading to be examined. It was found that small variations from the ideal mirror shape could cause large variation in the longitudinal radiation flux profile. Finally, techniques to minimise the drop in performance of a PV concentrator due to flux non‐uniformities are discussed, including use of bypass diodes and choice of solar cells. Copyright © 2006 John Wiley & Sons, Ltd.     

Soft‐output MMSE V‐BLAST receiver with MMSE channel estimation under correlated Rician fading MIMO channels

For wireless multiple‐input multiple‐output (MIMO) communications systems, both channel estimation error and spatial channel correlation should be considered when designing an effective signal detection system. In this paper, we propose a new soft‐output MMSE based Vertical Bell Laboratories Layered Space‐Time (V‐BLAST) receiver for spatially‐correlated Rician fading MIMO channels. In this novel receiver, not only the channel estimation errors and channel correlation but also the residual interference cancellation errors are taken into consideration in the computation of the MMSE filter and the log‐likelihood ratio (LLR) of each coded bit. More importantly, our proposed receiver generalizes all existing soft‐output MMSE V‐BLAST receivers, in the sense that, previously proposed soft‐output MMSE V‐BLAST receivers can be derived as the reduced forms of our receiver when the above three considered factors are partially or fully simplified. Simulation results show that the proposed soft‐output MMSE V‐BLAST receiver outperforms the existing receivers with a considerable gain in terms of bit‐error‐rate (BER) performance. Copyright © 2011 John Wiley & Sons, Ltd.     

Metal‐Organic‐Framework‐Coated Optical Fibers as Light‐Triggered Drug Delivery Vehicles

Physical delivery of anticancer drugs in controlled anatomic locations can complement the advances being made in chemo‐selective therapies. To this end, an optical fiber catheter is coated in a thin layer of metal organic framework UiO‐66 and the anticancer drug 5‐Fluorouracil (5‐FU) is deposited within the pores. Delivery of light of appropriate wavelength through the fiber catheter is found to trigger the release of 5‐FU on demand, offering a new route to localized drug administration. The system exhibits great potential with as much as 110 × 10^?6 m of 5‐FU delivered within 1 min from one fiber.     

A 500‐kW PV generator I–V curve

This paper presents the measurement of the I–V curve of a 500‐kW PV generator by means of an own‐made capacitive load. It is shown that I–V curve analysis can also be applied to big PV generators and that when measuring the operation conditions with reference modules and taking some precautions (especially regarding the operation cell temperature), it is still a useful tool for characterizing them and therefore can be incorporated into maintenance procedures. As far as we know, this is the largest I–V curve measured so far. Copyright © 2013 John Wiley & Sons, Ltd.     

An All‐Optical Gain‐Controlled Amplifier for Bidirectional Transmission

A novel all‐optical gain‐controlled (AOGC) bidirectional amplifier is proposed and demonstrated in a compact structure. The AOGC function using fiber Bragg grating (FBG) pairs controls both directional signals independently, and combinations of optical interleavers and isolators suppress Rayleigh backscattering (RB) noise. The amplifier achieves high and constant gain with a wide dynamic input signal range and low noise figure. The performance does not depend on the input signal conditions, whether static‐state or transient signals, or whether there is symmetric or asymmetric data traffic on bidirectional transmission. Transmission comparison experiments between invariable symmetrical and random variable asymmetric bidirectional data traffic verify that the all‐optical gain control and bidirectional amplification functions are successfully combined into this proposed amplifier.     

Analysis of temperature coefficients for III–V multi‐junction concentrator cells

The temperature dependence of the I–V parameters of different III–V multi‐junction concentrator cells at several concentration levels was investigated. Moreover, the influence of spectral changes on the temperature coefficients of multi‐junction solar cells was examined. Complete sets of temperature coefficients of a metamorphic Ga_0.35In_0.65P/Ga_0.83In_0.17As dual‐junction cell, a metamorphic Ga_0.35In_0.65P/Ga_0.83In_0.17As/Ge triple‐junction cell and a lattice‐matched Ga_0.50In_0.50P/Ga_0.99In_0.01As/Ge triple‐junction cell determined under well‐controlled laboratory conditions are reported. Copyright © 2012 John Wiley & Sons, Ltd.