Electrical characterization of photovoltaic cell with low‐concentration ratio square aperture concentrator

Improving photovoltaic (PV) system power output is the main target of research in this field. Using concentrators with PV systems should increase the power output and consequently reduce the power production costs. However, using concentrators with PV (CPV) system has a drawback of a higher PV system temperature, which affects the voltage produced by the system leading to lower overall system power output. This paper experimentally investigates the performance of a polycrystalline silicon PV cell with a low‐concentration ratio square aperture concentrator. A 50 × 50 mm cell was tested without concentration and with a range of geometric concentration ratios (GCRs) of 4, 6, 8, and 10. Various cooling methods were studied, including no cooling, passive cooling by using finned heatsink, and active cooling by using finned heatsink and a fan, and the CPV performance was presented in conversion efficiency, the electrical power gain, and the reduction in PV material at various testing conditions. Significant improvement was obtained by using square aperture concentrator at different GCRs with highest power gain of 362.85%, PV cell material reduction of 78.39%, and efficiency increase by 72% at GCR 10 and active cooling. The results do not consider the power needed to extract the heat generated by the concentration and reduce the cell temperature by using air cooling. But the extracted heat enhances the CPV system output if it is harnessed in domestic applications such as water heating applications. These results highlight the potential of the developed CPV system.     

Multiobjective Particle Swarm Optimization for the optimal design of photovoltaic grid-connected systems

Particle Swarm Optimization (PSO) is a highly efficient evolutionary optimization algorithm. In this paper a multiobjective optimization algorithm based on PSO applied to the optimal design of photovoltaic grid-connected systems (PVGCSs) is presented. The proposed methodology intends to suggest the optimal number of system devices and the optimal PV module installation details, such that the economic and environmental benefits achieved during the system’s operational lifetime period are both maximized. The objective function describing the economic benefit of the proposed optimization process is the lifetime system’s total net profit which is calculated according to the method of the Net Present Value (NPV). The second objective function, which corresponds to the environmental benefit, equals to the pollutant gas emissions avoided due to the use of the PVGCS. The optimization’s decision variables are the optimal number of the PV modules, the PV modules optimal tilt angle, the optimal placement of the PV modules within the available installation area and the optimal distribution of the PV modules among the DC/AC converters.     

Synthesis and characterization of partially fluorinated hydrophobic–hydrophilic multiblock copolymers containing sulfonate groups for proton exchange membrane

A new hydrophobic–hydrophilic multiblock copolymer has been successfully synthesized based on the careful coupling of a fluorine terminated poly(arylene ether ketone) (6FK) hydrophobic oligomer and a phenoxide terminated disulfonated poly(arylene ether sulfone) (BPSH) hydrophilic oligomer. ¹⁹F and ¹H NMR spectra were used to characterize the oligomers’ molecular weights and multiblock copolymer's structure. The comparison of the multiblock copolymer ¹³C NMR spectrum with that of the random copolymer showed that the transetherification side reaction was minimized in this synthesis. The morphologies of membranes were investigated by tapping mode atomic force microscopy (AFM), which showed that the multiblock membrane acidified by the high temperature method has sharp phase separation. Membrane properties like protonic conductivity, water uptake, and self-diffusion coefficient of water as a function of temperature and relative humidity (RH) were characterized for the multiblock copolymer and compared with ketone type random copolymers at similar ion exchange capacity value and Nafion^® controls. The multiblock copolymers are promising candidates for proton exchange membranes especially for applications at high temperatures and low relative humidity.     

Proton-conducting membranes with high selectivity from cross-linked poly(vinyl alcohol) and poly(vinyl pyrrolidone) for direct methanol fuel cell applications

A series of hydrocarbon membranes consisting of poly(vinyl alcohol) (PVA), sulfosuccinic acid (SSA) and poly(vinyl pyrrolidone) (PVP) were synthesized and characterized for direct methanol fuel cell (DMFC) applications. Fourier transform infrared (FT-IR) spectra confirm a semi-interpenetrating (SIPN) structure based on a cross-linked PVA/SSA network and penetrating PVP molecular chains. A SIPN membrane with 20% PVP (SIPN-20) exhibits a proton conductivity value comparable to Nafion^® 115 (1.0 × 10⁻² S cm⁻¹ for SIPN-20 and 1.4 × 10⁻² S cm⁻¹ for Nafion^® 115). Specifically, SIPN membranes reveal excellent methanol resistance for both sorption and transport properties. The methanol self-diffusion coefficient through a SIPN-20 membrane conducted by pulsed field-gradient nuclear magnetic resonance (PFG-NMR) technology measures 7.67 × 10⁻⁷ cm² s⁻¹, which is about one order of magnitude lower than that of Nafion^® 115. The methanol permeability of SIPN-20 membrane is 5.57 × 10⁻⁸ cm² s⁻¹, which is about one and a half order of magnitude lower than Nafion^® 115. The methanol transport behaviors of SIPN-20 and Nafion^® 115 membranes correlate well with their sorption characteristics. Methanol uptake in a SIPN-20 membrane is only half that of Nafion^® 115. An extended study shows that a membrane-electrode assembly (MEA) made of SIPN-20 membrane exhibits a power density comparable to Nafion^® 115 with a significantly higher open current voltage. Accordingly, SIPN membranes with a suitable PVP content are considered good methanol barriers, and suitable for DMFC applications.     

Direct methanol fuel cell performance of sulfonated poly (2,6-dimethyl-1,4-phenylene oxide)-polybenzimidazole blend proton exchange membranes

Various sulfonated poly (2,6-dimethyl-1,4-phenylene oxide) (SPPO)-polybenzimidazole (PBI) blend membranes were prepared and investigated as proton exchange membranes (PEMs) for direct methanol fuel cell (DMFC) applications. With increasing PBI content water swelling, ion exchange capacity, proton conductivity and methanol permeability of SPPO-PBI membranes were found to be decreased due to acid-base interactions between sulfonate and the amine groups of the blended components. Among various SPPO-PBI blend membranes, 80:20 wt% was found as the optimum composition, which showed the highest membrane selectivity parameter. Direct methanol-air single fuel cell tests revealed a higher cell efficiency of 11.6% for SPPO80-PBI20 than 10.9% for Nafion^®117 at 5 M methanol feed, and also a higher power density of 57.6 mW.cm⁻² compared to 39.4 mW.cm⁻² for Nafion^®117. Transport properties as well as DMFC performance results of SPPO-PBI blend PEMs converge to indicate their potential for DMFC applications.     

Effect of soiling in CPV systems

The effect of soiling in flat PV modules has been already studied, causing a reduction of the electrical output of 4% on average. For CPV’s, as far as soiling produces light scattering at the optical collector surface, the scattered rays should be definitively lost because they cannot be focused onto the receivers again. While the theoretical study becomes difficult because soiling is variable at different sites, it becomes easier to begin the monitoring of the real field performance of concentrators and then raise the following question: how much does the soiling affect to PV concentrators in comparison with flat panels?’ The answers allow to predict the PV concentrator electrical performance and to establish a pattern of cleaning frequency. Some experiments have been conducted at the IES-UPM and CSES-ANU sites, consisting in linear reflective concentration systems, a point focus refractive concentrator and a flat module. All the systems have been measured when soiled and then after cleaning, achieving different increases of I_SC. In general, results show that CPV systems are more sensitive to soiling than flat panels, accumulating losses in I_SC of about 14% on average in three different tests conducted at IES-UPM and CSES-ANU test sites in Madrid (Spain) and Canberra (Australia). Some concentrators can reach losses up to 26% when the system is soiled for 4 months of exposure.     

Forecast study of the supply curve of solar and wind technologies in Argentina,Brazil, Chile and Mexico

This paper forecasts the supply curve of non-conventional renewable technologies such as wind and solar generating stations in Argentina, Brazil, Chile and Mexico using technological and economic parameters. It also estimates the additional investment costs in solar and wind generation for reaching the renewable energy target in each of these countries. To assess the power supply profile from 1 axis tracking PV and horizontal axis wind turbine (three blade) stations, two different scenarios are developed for 2014 and 2025. Scenario 1 estimates the PV and wind annual electricity yield by using polycrystalline silicon (cSi poly) as semiconductor material for PV cells and a Vestas 90–3.0 MW turbine for the wind for 2014.Scenario 2 assumes a more efficient technology, such as CPV. In fact, the model employs 45% efficiency triple junction cells using ∼3500 m2 for each 1 MW installed capacity in 2025. Moreover, this scenario also assumes a more powerful type of turbine, i.e. Vestas 112–3.075 MW. The biggest potential for wind power is found to be in Argentina, followed by Brazil, Mexico and Chile. In addition, a 550 MW installed capacity CPV power station, using triple junction cells could generate up to 4 TWh in Chile in 2025.     

Finite element method for computational fluid dynamics to design photovoltaic thermal (PV/T) system configuration

This study focuses on the optimal configuration and suitable flow rate in photovoltaic thermal (PV/T) system. Design and verification were carried out by finite element method (FEM) to solve computational fluid dynamic (CFD) problem and to determine the suitable flow in a collector system. COMSOL MULTIPHYSICS^® software was used for the analysis. The computed results were then comparatively evaluated against a set of result samples obtained from testing data of the 16 modules of PV/T system—a configuration with 4 strings (horizontal-axis) of 4 modules in-series (vertical-axis) (4×4). The redesign of PV/T system was further studied by changing the system configuration from a 4×4 configuration to simulate various configurations consisting of 8×2, 3×4, 4×3 and 6×2. For the same number of PV/T module (16), the 4×4 configuration provided better flow distribution, when compared with an 8×2 configuration. When decreasing to 12 modules, it was shown that the 3×4 configuration resulted in the most suitable flow distribution, compared with the 4×3 and 6×2 configurations. From these results, it can be concluded that the number of strings used was inversely proportional to the flow distribution quality. Experimental results have also shown that the optimized flow rate for the 4×4 configuration was approximately 1-3 L/min.     

Terminally-crosslinked poly(ether sulfone) block copolymer,as a highly selective and stable polymer electrolyte membrane for DMFC applications

The terminally-crosslinked sulfonated poly(ether sulfone) block copolymer (SPES-b) was developed for use as a proton exchange membrane in DMFC applications. The properties of the membrane prepared from SPES-b were compared with those of its non-crosslinked counterpart (SPES-bn) and Nafion^®-117. The membrane displayed a well-defined morphology due to phase separation between the hydrophobic and hydrophilic ionic units in the SPES-b block copolymer. The terminally-crosslinked SPES-b membrane yielded a high proton conductivity of 0.09 S/cm and a low methanol permeability of 5.3 × 10⁻⁸ cm²/s at 20 °C, and the membrane displayed excellent dimensional, mechanical, hydrolytic, and oxidative stabilities.     

Passive DMFCs with PtRu catalyst on poly(3,4-ethylenedioxythiophene)-polystyrene-4-sulphonate support

Passive direct methanol fuel cells (DMFCs) are considered interesting candidates for small-scale power applications. We investigated the performance in passive DMFCs of the PtRu catalyst supported on poly(3,4-ethylenedioxythiophene)-polystyrene-4-sulphonate (pEDOT-pSS), a Nafion^®-free, mixed electronic–protonic conductor that assures electronic transport for methanol oxidation at the anode and provides the proton movement. The DMFCs were assembled with Vulcan XC-72R carbon/Pt (in excess) cathode, Nafion^® 117 membranes and 1 M CH₃OH, and long-time performance data are reported and discussed.     

A study on fabrication of sulfonated poly(ether ether ketone)-based membrane-electrode assemblies for polymer electrolyte membrane fuel cells

The porosity effect of catalyst electrodes in membrane-electrode assemblies (MEAs) using a hydrocarbon-based polymer as electrolyte and ionomer was investigated on physical and electrochemical properties by varying the content of ionomer binder (dry condition) in the catalyst electrodes. The MEAs were compared with the Nafion^®-based MEA using Nafion^® 112 and 5 wt.% ionomer solution (EW = 1100) in terms of porosity values, scanning electron microscopic images, Nyquist plots, dielectric spectra and I–V polarization curves. In this study, sulfonated poly(ether ether ketone) (SPEEK) membranes with 25 ± 5 μm of thickness and 5 wt.% ionomer solutions have been prepared. The prepared membranes were characterized in terms of FT-IR, DSC and proton conductivity. Proton conductivity of the SPEEK membranes was compared with one of the Nafion^® membranes with relative humidity. The porosity of the catalyst electrodes was calculated using the properties of catalyst, ionomer solution and solvent. As a result, the performance of the new type polymer (i.e., SPEEK in this study)-based MEA with the similar membrane conductivity and porosity of the catalyst electrode in the Nafion^® MEA was similar to that of the Nafion^® MEA.     

A high-performance chitosan-based double layer proton exchange membrane with reduced methanol crossover

A novel double layer proton exchange membrane (PEM) comprising a layer of structurally modified chitosan, as a methanol barrier layer, coated on Nafion^®112 was prepared and assessed for direct methanol fuel cell (DMFC) applications. Scanning electron microscope (SEM) micrographs of the designed membrane revealed a tight adherence between layers, which indicate the high affinity of opposite charged polyelectrolyte layers. Proton conductivity and methanol permeability measurements showed improved transport properties of the designed membrane compared to Nafion^®117. Moreover, DMFC performance tests revealed a higher open circuit voltage and power density, as well as overall fuel cell efficiency for the double layer membrane in comparison with Nafion^®117, especially at elevated methanol solution feed. The obtained results indicate the designed double layer membrane as a promising PEM for high-performance DMFC applications.     

Water and proton transport properties of hexafluorinated sulfonated poly(arylenethioethersulfone) copolymers for applications to proton exchange membrane fuel cells

In the present study, we examine the water and proton transport properties of hexafluorinated sulfonated poly(arylenethioethersulfone) (6F-SPTES) copolymer membranes for applications to proton exchange membrane fuel cells (PEMFCs). The 6F-SPTES copolymer membranes build upon the structures of previously studied sulfonated poly(arylenethioethersulfone) (SPTES) copolymer membranes to include CF₃ functional groups in efforts to strengthen water retention and extend membrane performance at elevated temperatures (above 120 °C). The 6F-SPTES copolymer membranes sustain higher water self-diffusion and greater proton conductivities than the commercial Nafion^® membrane. Water diffusion studies of the 6F-SPTES copolymer membranes using the pulsed-field gradient spin-echo NMR technique reveal, however, the fluorinated membranes to be somewhat unfavorable over their non-fluorinated counterparts as high temperature membranes. In addition, proton conductivity measurements of the fluorinated membranes up to 85 °C show comparable results with the non-fluorinated SPTES membranes.     

Effects and properties of various molecular weights of poly(propylene oxide) oligomers/Nafion acid–base blend membranes for direct methanol fuel cells

Various molecular weights of poly(propylene oxide) diamines oligomers/Nafion^® acid–base blend membranes were prepared to improve the performance of Nafion^® membranes in direct methanol fuel cells (DMFCs). The acid–base interactions were studied by Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). The performance of the blend membranes was evaluated in terms of methanol permeability, proton conductivity and cell performance. The proton conductivity was slightly reduced by acid–base interaction. The methanol permeability of the blend D2000/Nafion^® was 8.61 × 10⁻⁷ cm² S⁻¹, which was reduced 60% compared to that of pristine Nafion^®. The cell performance of D2000/Nafion^® blend membranes was enhanced significantly compared to pristine Nafion^®. The current densities that were measured with Nafion^® and 3.5 wt% D2000/Nafion^® blend membranes were 62.5 and 103.5 mA cm⁻², respectively, at a potential of 0.2 V. Consequently, the blend poly(propylene oxide) diamines oligomers/Nafion^® membranes critically improved the single-cell performance of DMFC.     

Blended Nafion/SPEEK direct methanol fuel cell membranes for reduced methanol permeability

Sulfonated poly(ether ether ketone)s (SPEEKs) were substituted on a polymer main chain that had previously been prepared by sulfonation of poly(ether ether ketone)s in concentrated sulfuric acid for a specified time. The product was then blended with Nafion^® to create composite membranes. The blended SPEEK-containing membranes featured flaky domains dispersed in the Nafion^® matrix. These blends possessed a high thermal decomposition temperature. Additionally, owing to the more crystalline, the blended membranes had a lower water uptake compared to recast Nafion^®, the methanol permeability was reduced to 1.70 × 10⁻⁶ to 9.09 × 10⁻⁷ cm² s⁻¹ for various SPEEK concentrations, and a maximum proton conductivity of ∼0.050 S cm⁻¹ was observed at 30 °C. The single-cell performances of the Nafion^®/SPEEK membranes, with various SPEEK concentrations and a certain degree of sulfonation, were 15–25 mW cm⁻² for SPEEK53 and 19–27 mW cm⁻² for SPEEK63, at 80 °C. The power density and open circuit voltage were higher than those of Nafion^® 115 (power density = 22 mW cm⁻²). The blended membranes satisfy the requirements of proton exchange membranes for direct methanol fuel cell (DMFC) applications.     

Fluorinated carboxylic membranes deposited by plasma enhanced chemical vapour deposition for fuel cell applications

Among the fuel cell technologies, the polymer electrolyte membrane fuel cells (PEMFCs) are particularly promising because they are energy-efficient, clean, and fuel-flexible (i.e., can use hydrogen or methanol). The great majority of PEM fuel cells rely on a polymer electrolyte from the family of perfluorosulfonic acid membranes, nevertheless alternative materials are currently being developed, mainly to offer the alternative workout techniques which are required for the portable energy sources. Plasma polymerization represents a good solution, as it offers the possibility to deposit thin layer with an accurate and homogeneous thickness, even on 3D surfaces. In this paper, we present the results for the growth of proton conductive fluoro carboxylic membranes elaborated by plasma enhanced chemical vapour deposition. These membranes present conductivity values of the same order than the one of Nafion^®. The properties of the membrane, such as the chemical composition, the ionic conductivity, the swelling behaviour and the permeability were correlated to the plasma process parameters. The membranes were integrated in fuel cells on porous substrates and we present here the results regarding the barrier effect and the power output. Barrier effect similar to those of 40 μm Nafion^® layers was reached for 10 μm thick carboxylic membranes. Power outputs around 3 mW cm⁻² were measured. We discuss the results regarding the gas barrier effect and the power outputs.     

Efficient STEP (solar thermal electrochemical photo) production of hydrogen – an economic assessment

A consideration of the economic viability of hydrogen fuel production is important in the STEP (Solar Thermal Electrochemical Photo) production of hydrogen fuel. STEP is an innovative way to decrease costs and increase the efficiency of hydrogen fuel production, which is a synergistic process that can use concentrating photovoltaics (CPV) and solar thermal energy to drive a high temperature, low voltage, electrolysis (water-splitting), resulting in H₂ at decreased energy and higher solar efficiency. This study provides evidence that the STEP system is an economically viable solution for the production of hydrogen. STEP occurs at both higher electrolysis and solar conversion efficiencies than conventional room temperature photovoltaic (PV) generation of hydrogen. This paper probes the economic viability of this process, by comparing four different systems: (1) 10% or (2) 14% flat plate PV driven aqueous alkaline electrolysis H₂ production, (3) 25% CPV driven molten electrolysis H₂ production, and (4) 35% CPV driven solid oxide electrolysis H₂ production. The molten and solid oxide electrolysers are high temperature systems that can make use of light, normally discarded, for heating. This significantly increases system efficiency. Using levelized cost analysis, this study shows significant cost reduction using the STEP system. The total price per kg of hydrogen is shown to decrease from $5.74 to $4.96 to $3.01 to $2.61 with the four alternative systems. The advanced STEP plant requires less than one seventh of the land area of the 10% flat cell plant. To generate the 216 million kg H₂/year required by 1 million fuel cell vehicles, the 35% CPV driven solid oxide electrolysis requires a plant only 9.6 mi² in area. While PV and electrolysis components dominate the cost of conventional PV generated hydrogen, they do not dominate the cost of the STEP-generated hydrogen. The lower cost of STEP hydrogen is driven by residual distribution and gate costs.     

Preparation and properties of crosslinked sulphonated poly(arylene ether sulphone) blend s for direct methanol fuel cell applications

HMS-based sulphonated poly(arylene ether sulphone) (HMSSH) is synthesised using 4,4′-dihydroxy-α-methylstilbene (HMS) monomer to introduce an interesting stilbene core as crosslinkable group. Crosslinked blend membranes are obtained by blending the BPA-based sulphonated poly(arylene ether sulphone) (BPASH) with crosslinkable HMS-based sulphonated poly(arylene ether sulphone) by UV irradiation of the blend membrane. Compared to the native BPASH with crosslinked BPASH/HMSSH blend membranes, the crosslinked blend membranes greatly reduce the water uptake and methanol permeability with only a slight reduction in proton conductivity. The crosslinked blend membrane, which has a 6% HMSSH content, has a water uptake of 59%, methanol permeability of 0.75 × 10⁻⁶ cm² s⁻¹, and proton conductivity of 0.08 S cm⁻¹. A membrane-electrode assembly is used to investigate single-cell performance and durability test for DMFC applications. Both the power density and open circuit voltage are higher than those of Nafion^® 117. A maximum power density of 32 mW cm⁻² at 0.2 V is obtained at 80 °C, which is higher than that of Nafion^® 117 (25 mW cm⁻²).     

Investigation of the effects of AMPS-modified nanoclay on fuel cell performance of sulfonated aromatic proton exchange membranes

Here we describe preparation and characterization of a series of nanocomposite polyelectrolytes based on partially sulfonated poly (ether ether ketone) (SPEEK) and organically modified montmorillonite (MMT). Optimum degree of sulfonation for SPEEK is selected based on its transport properties. MMT is modified via ion exchange reaction using a 2-acrylamido-2-methylpropanesulfonic acid (AMPS) as a functional modifier. AMPS-MMT at different loadings is introduced into the SPEEK matrices via the solution intercalation technique. Also, the nanocomposite membranes are fabricated using SPEEK and commercially available nanoclays like Cloisite Na (Na-MMT) and Cloisite 15A. Transport properties, proton conductivity and methanol permeability of the fabricated composite membranes are evaluated. Presence of AMPS-MMT significantly decreases the activation energy needed for proton conductivity. A membrane based on SPEEK/AMPS-MMT-3 wt% is selected as an optimum formulation which exhibits a high selectivity and power density at the elevated methanol concentrations. Moreover, it is found that the optimum nanocomposite membrane not only provides higher power output compared to the neat SPEEK and Nafion^®117 membranes, but also exhibits a higher open circuit voltage (OCV) in comparison with pristine SPEEK and commercial Nafion^® 117 membranes. Owing to the desirable transport and electrochemical properties SPEEK/AMPS-MMT nanocomposite can be considered as an alternative membrane for direct methanol fuel cell applications.     

Hybrid membranes of PVA for direct ethanol fuel cells (DEFCs) applications

Proton-conducting hybrid membranes composed of poly(vinyl alcohol) (PVA), phosphotungstic acid (HPW) and (diethylenetriamine)pentaacetic acid (DTPA) where prepared. The effect of HPW doping and crosslink with DTPA on the membranes properties such as uptake, pervaporation and proton conductivity was investigated. Uptake and permeated flux decreases with increasing content of HPW and DTPA. Ethanol permeabilities obtained was about two orders of magnitude smaller than Nafion^® 117. FTIR spectra indicated that HPW was incorporated into the polymer matrix and DTPA acted as crosslink agent. The proton conductivity was in the order of 10⁻³ S cm⁻¹ with added 4 wt.% of DTPA and generally increases with the addition of HPW.