The photovoltaic-alkaline water (PV-AW) electrolysis system offers an appealing approach for large-scale green hydrogen generation. However, current PV-AW systems suffer from low solar-to-hydrogen (STH) conversion efficiencies (e.g., <20%) at practical current densities (e.g., >100 mA cm(-2)), rendering the produced H-2 not economical. Here, we designed and developed a highly efficient PV-AW system that mainly consists of a customized, state-of-the-art AW electrolyzer and concentrator photovoltaic (CPV) receiver. The highly efficient anodic oxygen evolving catalyst, consisting of an iron oxide/nickel (oxy)hydroxide (Fe2O3-NiOxHy) composite, enables the customized AW electrolyzer with unprecedented catalytic performance (e.g., 1 A cm(-2) at 1.8 V and 0.37 kgH(2)/m(-2) hour(-1) at 48 kWh/kgH(2)). Benefiting from the superior water electrolysis performance, the integrated CPV-AW electrolyzer system reaches a very high STH efficiency of up to 29.1% (refer to 30.3% if the lead resistance losses are excluded) at large current densities, surpassing all previously reported PV-electrolysis systems.

Currently, single-layer antireflection coated (SLARC) solar glass has a dominant market share of 95% compared to glass with other coatings or no coating, for Si PV modules. This antireflection coating (ARC) results in an efficiency gain of 2-3%. However, there are issues with these SLARCs: (1) solar cell warming due to increased sub-bandgap light absorption (by +0.4 similar to 1.2 K), counteracting the cell current gain and accelerating the aging of the solar panels, and (2) poor durability due to the coating's porous structure (typically lasting <= 5 years). This paper aims to develop a non-porous multilayer coating (MLC) that is more durable and will act as a spectrally selective filter for solar modules. Studies have been conducted on MLCs in terms of optical, microstructure, mechanical, and durability properties compared with commercial single-layer AR coatings. The MLCs showed superior performance in durability and benefit in reducing parasitic heat absorption in the non-usable wavelength range. Also, a techno-economic analysis model based on the multifunctional coating specifically to evaluate economic benefits has been developed.

Reducing the operation temperature of photovoltaic (PV) modules will allow prolonging their service time and energy output. This work investigated a passive PV module cooling technique by attaching vortex generators (VGs) on the rear surface of PV modules. The rectangular wing VGs of size 2 x 3 cm, are made from aluminium sheet (Al VG) or 3D printed thermally conductive polymer (Poly VG). After ten months of data collection on an open rack system, we have gained insight into the wind speed- and direction-dependent performance of the Al and Poly VGs. The pronounced difference in thermal conductivity of the two materials helps distinguish cooling due to vortex generation, predominant at low wind speeds, from the heat sink effect, prevalent at higher wind speeds. Despite being optimised for free convection, both VGs demonstrated 1.5 degrees C of cooling under low wind and high irradiance, while Al VGs provided 2.5 degrees C of cooling under high module temperature and windy scenarios. Both VGs exhibit equivalent performance with south and west winds, indicating the dominance of the vortex generation mechanism. The module equipped with VGs exhibited an increase in convective heat transfer coefficient as evaluated by the thermal balance model.

The antireflection(AR) coating applied to solar glass in photovoltaic modules has remained largely unchanged for decades, despite its well-documented lack of durability. Traditional porous structured single-layer AR coatings last as little as 5 years in the field. In this paper, we propose a novel 5-layer dense AR coating design that offers improved durability and effectiveness compared to traditional coatings. This paper provides detailed insights into the development and characterization of the novel 5-layer AR coating, providing guidance to the photovoltaic community seeking to improve the efficiency and longevity of solar modules.

The antireflection (AR) coating applied to solar glass in photovoltaic modules has remained largely unchanged for decades, despite its well-documented lack of durability. Traditional porous structured single-layer AR coatings last as little as 5 years in the field. In this paper, we propose a novel five-layer dense AR coating design that offers improved durability and effectiveness compared to traditional coatings. This paper provides detailed insights into the development and characterization of the novel five-layer AR coating, including simulation, optical measurements, and abrasion testing, providing guidance to the photovoltaic community seeking to improve the efficiency and longevity of solar modules.

A technique for calculating etendue from flowlines is proposed for both Lambertian and non-Lambertian light fields. Hyperbolic curve fitting from flowline measurements is proposed as a means of extrapolating flowlines to the far-field for improved calculation of etendue. The technique is applicable to rotationally symmetric light fields, and to specific asymmetric light fields where analytic viewfactor calculations exist.

Nowadays, as a standard practice, the cover glasses for commercial photovoltaic (PV) modules are coated with antireflection coatings (ARCs). The most used ARC in the market consists of single-layer inner-pore silica (SiO 2 ) where hollow silica beads are incorporated into the coating. To match the lifespan of installed modules, ARCs are expected to resist the harsh abrasion from brush cleaning and withstand severe environments. With the exponential growth of worldwide solar module deployment, understanding the outdoor performance and reliability of these ARCs is imperative. In this work, multiple typical AR coated commercial solar glass specimens from various manufacturers were characterized in terms of their optical property, abrasion resistance and outdoor reliability. Open-pore and dense silica samples were also fabricated and characterized for parallel comparison. It was found that dense ARCs present much better durability compared to inner-pore and open-pore ARCs, enabling a much longer lifespan although optical benefits were reduced. Furthermore, double-layer dense ARCs were investigated for boosting durability as well as maintaining a reasonable optical enhancement compared to single-layer ARC. These findings provide substantial guidance on the optimization of sustainable future commercial ARCs.

High operating temperatures have a negative impact on photovoltaic (PV) modules. Hence, lowering the temperature of commercial crystalline silicon modules during their operation becomes increasingly interesting, as it increases the system's energy yield and prolongs the module's lifespan. In this work, we experimentally and numerically investigated a potentially cost-effective passive cooling method for PV modules, using vortex generators (VGs) optimised for free convection conditions (in the absence of wind). The VGs are attached to the rear surface of the module and arranged in an array. Infrared thermography was employed to assess the cooling ability of the VGs with different spacing. It is found that the thermally non-conductive VGs can reduce the operating temperatures of a module by up to 2 degrees C under free convection and by 3 degrees C with the use of conductive materials. To better understand the flow behaviour around the VGs, computational fluid dynamics simulations were undertaken, along with particle image velocimetry (PIV) measurements. The VG-induced mixing in the boundary layer is responsible for enhancing the convective flux on the rear module surface. We observed both that the formation of vortices is strongly dependent on the aerodynamic shape of the VG and that the placement of the VGs is crucial.

Textured glass is a possible means for reflection reduction of a photovoltaic module. Texturing not only increases the energy yield of the system through reduced reflection losses, but also can play a role in dissipating waste heat through enhancing convective and radiative heat loss. In this work, we describe three textured glass surfaces analytically and model them numerically at optical (400-1050 nm) and mid-infrared (MIR, 5-30 μm) wavelengths. Spectral and directional results are processed with a series of weight functions to evaluate the total transmission to determine the optical performance and the total MIR hemispherical emissivity for the thermal performance. It is found that the proposed textured surfaces could improve the total optical transmission by 3.3%-4.6% relative to planar glass for direct solar radiance and 4.9%-6.7% for diffuse component, whereas the total MIR hemispherical emissivity is boosted by 6.6%-9.3% relative. The current most commercially favored inverted pyramid pattern may not be the most effective glass surface texturing scheme based on optical and radiative enhancement or self-cleaning properties.

We investigate the use of distributed Bragg reflectors (DBRs) within triple-junction solar cells (TJSC) for spectrum splitting photovoltaics. An optical model of a lattice-matched (LM) GaInP/GaInAs/Ge TJSC with intermediate DBR is developed, in good agreement with measured reflectance. By modifying the DBR layer number, composition and thickness to broaden the reflectance band, we show that a DBR can provide suitable 900-1050 nm reflectance for spectrum splitting from the LM TJSC to a Si cell, resulting in a more efficient 4 junction receiver. For better practicality and cost effectiveness, we propose that the buffer layers in metamorphic (MM) TJSCs could additionally function as a DBR for spectrum splitting applications. We propose several DBR designs to achieve a suitable spectrum-splitting reflectance band from MM TJSCs to a Si cell, again resulting in a more efficient 4-junction receiver. Finally, we show that our intermediate DBR approach to spectrum splitting has the advantage of a greatly reduced angle-of-incidence dependence compared to a discrete dielectric filter.

Freeform optics has great potential for delivering highly effective solar concentrators and lighting systems, but in some cases it can be challenging to implement. A numerical method is described for calculating 3D flowline concentrator shapes in a way that provides complete freedom over the specification of arbitrary source and receiver objects. This lends the approach to a range of practical design problems involving asymmetric systems, non-lambertian and extended light sources. The method reproduces the hyperbolic and hyperparabolic concentrator geometries identified in the literature, operating close to the thermodynamic limit of concentration. A practical example is given in the optimisation of a secondary concentrator for a concentrator photovoltaic array receiving light from a field of heliostats. The secondary improves the overall capture efficiency of the photovoltaic receiver at noon, and is expected to deliver further improvement at other times of day.

The use of intermediate distributed Bragg reflectors (DBRs) for spectrum splitting photovoltaics is investigated. Optical models for both commercial lattice-matched (LM) and metamorphic (MM) GaInP/GaInAs/Ge triple-junction solar cells (TJSCs) are developed, in good agreement with measured reflectance. Integrating a suitable DBR structure into a TJSC has the potential to provide the required IR reflectance for spectrum splitting from the LM and MM TJSC to a Si cell. We show that the intermediate DBR approach to spectrum splitting has the advantage of a greatly reduced angle-of-incidence dependence compared to a discrete dielectric filter.

The use of intermediate distributed Bragg reflectors (DBRs) for spectrum splitting photovoltaics is investigated. An optical model of a lattice-matched (LM) GaInP/GaInAs/Ge triple-junction solar cell (TJSC) with intermediate DBR is developed, in good agreement with measured reflectance. By modifying the composition and thickness of the DBR layers to broaden the reflectance band, we show that a DBR has the potential to provide suitable reflectance for spectrum splitting from the III-V LM TJSC to a Si cell. The DBR approach to spectrum splitting has the advantage of a much reduced angle-of-incidence dependence than the use of a separate dielectric filter.

High efficiency solar conversion requires collection of a broad spectrum of wavelengths from the ultra-violet into the infrared. Solar collector mirrors must provide high reflection across this spectral band without degrading over time. This work presents the results of a high-performance 200 mm parabolic mirror coated with an ultra-wide broadband dielectric reflector. The mirror was developed to demonstrate high efficiency broadband solar collection and power conversion. Mirror reflection was measured within the limits of NIST capabilities, and averaged over 99.65% from 400 to 1800 nm with an acceptance angle of 30 degrees. Plasma-assisted reactive magnetron sputtering was used to produce these high density and environmentally stable films. These hard oxide films can be repeatedly cleaned in the field. Salt spray, humidity and angle performance results are presented.

Metal halide perovskite solar cells (PSCs) have undergone rapid progress. However, unstable performance caused by sensitivity to environmental moisture and high temperature is a major impediment to commercialization of PSCs. In the present work, a low-temperature, glass-glass encapsulation technique using high performance polyisobutylene (PIB) as the moisture barrier is investigated on planar glass/FTO/TiO2/FAPbI3/PTAA/gold perovskite solar cells. PIB was applied as either an edge seal or blanket layer. Electrical connections to the encapsulated PSCs were provided by either the FTO or Au layers. Results of a "calcium test" demonstrated that a PIB edge-seal effectively prevents moisture ingress. A shelf life test was performed and the PIB-sealed PSC was stable for at least 200 days. Damp heat and thermal cycling tests, in compliance with IEC61215:2016, were used to evaluate different encapsulation methods. Current-voltage measurements were performed regularly under simulated AM1.5G sunlight to monitor changes in PCE. The best results we have achieved to date maintained the initial efficiency after 540 h of damp heat testing and 200 thermal cycles. To the best of the authors' knowledge, these are among the best damp heat and thermal cycle test results for perovskite solar cells published to date. Given the modest performance of the cells (8% averaged from forward and reverse scans) especially with the more challenging FAPbI3 perovskite material tested in this work, it is envisaged that better stability results can be further achieved when higher performance perovskite solar cells are encapsulated using the PIB packaging techniques developed in this work. We propose that heat rather than moisture was the main cause of our PSC degradation. Furthermore, we propose that preventing the escape of volatile decomposition products from the perovskite solar cell materials is the key for stability. PIB encapsulation is a very promising packaging solution for perovskite solar cells, given its demonstrated effectiveness, ease of application, low application temperature, and low cost.

Metal halide perovskite solar cells (PSCs) have undergone rapid progress. However, unstable performance caused by sensitivity to environmental moisture and high temperature is a major impediment to commercialisation of PSCs. In the present work, a low temperature, glass-glass encapsulation technique using high performance polyisobutylene based edge sealant (PIB) as the moisture barrier is investigated on planar glass/FTO/TiO2/FAPbI3/PTAA/gold perovskite solar cells. PIB was applied as either an edge seal or blanket layer. Electrical connections to the encapsulated PSCs were provided by either the FTO or Au layers. Results of a “Calcium Test” demonstrated that a PIB edge-seal effectively prevents moisture ingress. A shelf-life test was performed and the PIB-sealed PSC was stable for at least 200 days. Damp Heat (85 °C/85% RH) and Thermal Cycling (-40 °C 85 °C) tests, in compliance with IEC61215:2016, were used to evaluate different encapsulation methods. Ex-situ current-voltage measurements were performed regularly under simulated AM1.5G sunlight to monitor changes in PCE. We propose that heat rather than moisture was the main cause of our PSC degradation. Furthermore, we propose that preventing the escape of volatile decomposition products from the perovskite solar cell materials is the key for thermal stability. The best results we have achieved to date maintained the initial efficiency after 540 hours of Damp Heat testing and 200 Thermal Cycles (Figure 1). No non-perovskite phase of PSC was detected after the tests. To the authors’ knowledge, these are among the best Damp Heat and Thermal Cycle test results for perovskite solar cells published to date. Given the intrinsic instability of the more challenging FAPbI3 perovskite material tested in this work, it is envisaged that better stability results can be further achieved when higher performance perovskite solar cells are encapsulated using the PIB packaging techniques developed in this work. The efficiency and hysteresis of PSCs are found and reported to improve during storage after fabrication, which indicates that a proper post annealing process may accelerate such an improvement. However, due to poor thermal stability of the perovskite materials, post annealing that is widely applied on c-Si solar cells to improve the efficiency generally cannot be applied on PSCs. With the help of improved thermal stability by PIB encapsulation, we demonstrated that post annealing at 85 °C increased the efficiency and reduced hysteresis, primarily owing to decreased serious resistance and increased Voc (Figure 2). We believe the deeper mechanism is related to the improvement of Schottky barrier as well as the build-in voltage of the metal contacts and charge selective contacts. We also investigated other common encapsulants/sealants such as EVA and UV-epoxy and found to underperform PIB. PIB encapsulation is a very promising packaging solution for perovskite solar cells, given its demonstrated effectiveness, ease of application, low application temperature and low cost.

In this work, the use of a high bandgap perovskite solar cell in a spectrum splitting system is demonstrated. A remarkable energy conversion efficiency of 23.4% is achieved when a CH3NH3PbBr3 solar cell is coupled with a 22.7% efficient silicon passivated emitter rear locally diffused solar cell. Relative enhancements of >10% are demonstrated by CH3NH3PbBr3/CH3NH3PbI3 and CH3NH3PbBr3/multicrystalline-screen-printed-Si spectral splitting systems with tandem efficiencies of 13.4% and 18.8%, respectively. The former is the first demonstration of an all perovskite split spectrum system. The CH3NH3PbBr3 cell on a mesoporous structure was fabricated by the vapor-assisted method while the planar CH3NH3PbI3 cell was fabricated by the gas-assisted method. This work demonstrates the advantage of the higher voltage output from the high bandgap CH3NH3PbBr3 cell and its suitability in a tandem system.

Increasing sunlight conversion efficiency is a key driver for on-going solar electricity cost reduction. For photovoltaic conversion, the approach most successful in increasing conversion efficiency is to split sunlight into spectral bands and direct each band to a dedicated solar cell of an appropriate energy bandgap to convert this band efficiently. In this work, we demonstrate conversion of sunlight to electricity in a solar collector with an efficiency value above 40% for the first time, using a small 287-cm(2) aperture area test stand, notably equipped with commercial concentrator solar cells. We use optical band-pass filtering to capture energy that is normally wasted by commercial GaInP/GaInAs/Ge triple junction cells and convert this normally wasted energy using a separate Si cell with higher efficiency than physically possible in the original device. The 287-cm(2) aperture area sunlight-concentrating converter demonstrating this independently confirmed efficiency is a prototype for a large photovoltaic power tower system, where sunlight is reflected from a field of sun-tracking heliostats to a dense photovoltaic array mounted on a central tower. In such systems, improved efficiency not only reduces costs by increasing energy output for a given investment in heliostats and towers but also reduces unwanted heat generation at the central tower. Copyright (c) 2015 John Wiley & Sons, Ltd.