Assessing the use of simple dye-sensitized solar cells for drinking water chlorination by communities with limited resources

Dye-sensitized ZnO and TiO₂ photoelectrochemical cells were constructed using recycled waste materials and readily accessible household chemicals to assess whether it would be feasible for low-income communities to utilise solar energy for drinking water chlorination. Prussian Blue sensitized ZnO cells utilising ferro/ferricyanide and iron/copper redox couples for charge transfer produced open circuit potentials of between 0.19 and 0.53 V, and short circuit currents in the range 0.3–1.5 mA cm^?2. Although the power output from these cells was significantly lower than those using the iodide/triiodide redox couple for charge transfer, the significantly lower cost of construction of cells using alternative electrolytes could make these cells accessible to poor communities for producing small amounts of solar electricity for drinking water chlorination.     

An assessment of solar energy potential in Kampuchea

A satellite technique was adopted to assess solar energy potential in Kampuchea. The study aims to explore solar irradiation potential and distribution under the influence of Asian monsoons over land and a large water surface of a lake by using the satellite technique, with a relatively small spatial scale, which have never been accessed before. In this study, the solar irradiation potential over Kampuchea (10°N–14.5° N, 101.5°E–105°E) was estimated at interval of half a degree grid. The seasonal variations of mean daily solar irradiation in Kampuchea were measured during two Asian winter and summer monsoon seasons.The results revealed that the mean solar irradiation depends more on orographic effects than on seasonal changes. During the winter monsoon, the local minimal means of daily solar irradiation were found on the great Lake Tonle Sap and on the northern, windward side of the Elephant Mountain with a range of 13–14 MJ m^?2 day^?1. The local maximal means of daily solar irradiation were found on the northwestern part of Kampuchea, with a value of 18 MJ m^?2 day^?1. In contrast, during the summer monsoon, the local minimal means of daily solar irradiation were, again, found on the same mountainous region of the Elephant Mountain, but the area of minimal means shifted to the southern side where it is the windward side of the mountain during the summer monsoon with a value of 12 MJ m^?2 day^?1. The local maximal means of the daily solar irradiation were found scattered over various areas: south of Lake Tonle Sap and at various places in the north and northwestern parts of the country, with a range of 18–19 MJ m^?2 day^?1. It was also found that a high mean of solar irradiation is generally associated with a low standard deviation, i.e., it is less in temporal variation.     

Potentials of food wastes for power generation and energy conservation in Taiwan

Food waste is approximately 20–30% of the household garbage in Taiwan. There are several ways to use recycled food waste, swine feeding and composting are the two main ways in Taiwan. The objective of this study was to evaluate the potentials of food wastes for power generation and energy conservation in Taiwan. The assessment was conducted by using the related statistics of Taiwan. The results showed that the total amount of food wastes recycled increased from 167,304 to 570,176 Mg y^?1 (+240%) during the period from 2003 to 2006, and increased from 139,614 to 452,550 Mg y^?1 (+224%) and from 22,290 to 112,666 Mg y^?1 (+405%) for swine feeding and composting during the same period, respectively. Potential of food wastes for power generation was 68.0 GWh y^?1, and that excluding swine feeding and composting were 14.0 and 54.5 GWh y^?1 in Taiwan in 2006, respectively. On the other hand, energy conservation potential of food wastes for compost production was 122 MWh y^?1, comparing with energy consumption of chemical fertilizer (ammonium sulfate and calcium superphosphate) production in Taiwan in 2006. The results also suggested that food wastes recycled can not only reduce the amount of the garbage, but also showed the potentials for power generation and energy conservation.     

100 t/a-Scale demonstration of direct dimethyl ether synthesis from corncob-derived syngas

Direct conversion of biomass-derived syngas (bio-syngas) to dimethyl ether (DME) at pilot-scale (100 t/a) was carried out via pyrolysis/gasification of corncob. The yield rate of raw bio-syngas was 40–45 Nm³/h with less than 20 mg/Nm³ of tar content when the feedrate of dried corncob was 45–50 kg/h. After absorption of O₂, S, Cl by a series of absorbers and partial removal of CO₂ by the pressure-swing adsorption (PSA) unit sequentially, the obtained bio-syngas (H₂/CO≈1) was directly synthesized to DME over Cu/Zn/Al/HZSM-5 catalyst in the fixed-bed tubular reactor. CO conversion and DME space-time yield (STY) were 67.7% and 281.2 kg/m_cat³/h respectively at 260 °C, 4.3 MPa and 3000 h^?1(GHSV, syngas hourly space velocity). Synthesis performance would be increased if the tail gas (H₂/CO > 2) was recycled to the reactor when GHSV was 650–3000 h^?1.     

Band gap optimization of p–i–n layers of a-Si:H by computer aided simulation for development of efficient solar cell

The p-layer band gap and its thickness strongly influence the efficiency of hydrogenated amorphous silicon (a-Si:H) p–i–n solar cell, i and n-layer band gaps also play key role. In the present work, p, i and n layer band gaps as 2.1 eV (at thickness 10 nm), 1.75 eV (at thickness 400 nm) and 1.95 eV (at thickness 30 nm), respectively and acceptor and donor concentrations as 1 × 10¹⁸ cm^?3and 1 × 10²⁰ cm^?3, respectively, are optimized for obtaining efficient a-Si:H p–i–n solar cell by computer aided one-dimensional AFORS-HET software. It is important to mention that when p-layer thickness is changed to 5 nm, maximum efficiency is obtained at p-layer band gap of 2.2 eV. Such an optimized value would further help to prepare efficient a-Si:H p–i–n solar cells experimentally.     

Effect of rotating cylinder on heat transfer in a square enclosure filled with nanofluids

Convective heat transfer in a differentially heated square enclosure with an inner rotating cylinder is studied theoretically. The free space between the cylinder and the enclosure walls is filled with water–Ag, water–Cu, water–Al₂O₃ or water–TiO₂ nanofluids. The governing equations are formulated for velocity, pressure and temperature formulation and are modeled in COMSOL, a partial differential equation (PDE) solver based on the Galerkin finite element method (GFEM). The governing parameters considered are the solid volume fraction, 0.0 ? ? ? 0.05, the cylinder radius, 0 ? R ? 0.3 and the angular rotational velocity, ?1000 ? Ω ? 1000. The results are presented to show the effect of these parameters on the heat transfer and fluid flow characteristics. It is found that the strength of the flow circulation is much stronger for a higher nanoparticle concentration, a better thermal conductivity value and a smaller cylinder with a faster, negative rotation. The maximum heat transfer are obtained at a high nanoparticle concentration with a good conductivity value, a slow positive rotation and a moderate cylinder size located in the center of the enclosure.     

Factorial experimental design applied to Escherichia coli disinfection by Fenton and photo-Fenton processes

The aim of this work is to apply a factorial experimental design in the disinfection of Escherichia coli present in treated urban wastewater by means of Fenton and photo-Fenton processes.As a consequence of the large number of existing variables including the matrix, irradiation (λ = 320–800 nm), and doses of H₂O₂ (20–50 mg L^?1) and Fe³⁺ (2.5–5 mg L^?1), an experimental design methodology has been used in order to study their influence. It is observed that the presence of irradiation is the variable with the greatest influence on the response factor (inactivation of E. coli), although other variables also have a significant influence. By applying photo-Fenton treatment to treated urban wastewater samples, an average value of disinfection of 2.43 log is achieved in the inactivation of E. coli. The influence of the matrix in the inactivation of E. coli is clear, with higher levels of disinfection being obtained in samples prepared by dilution of E. coli in distilled water (5.81 log).Furthermore, a reduced empirical model has been obtained taking into account the influence of variables of E. coli inactivation in treated urban wastewater. The model adequately describes the inactivation of E. coli.     

Mono-ion transport electrolyte based on ionic liquid polymer for all-solid-state dye-sensitized solar cells

Ionic liquid polymers, poly(1-alkyl-3-(acryloyloxy)hexylimidazolium iodide), are synthesized and used as mono-ion transport electrolytes for all-solid-state dye-sensitized solar cells. For these ionic liquid polymers, imidazolium cations are tethered on polymer main chain and only iodide species is mobile. Such a mono-ion transport feature is favorable as solid-state electrolyte in dye-sensitized solar cells. High thermal stability up to 200 °C for these ionic liquid polymers is confirmed by thermogravimetric analysis. Among these ionic liquid polymers, poly(1-ethyl-3-(acryloyloxy)hexylimidazolium iodide) (PEI) exhibits the highest ionic conductivity (3.63 × 10^?4 S cm^?1) at room temperature. The dye-sensitized solar cell based on PEI electrolyte without the addition of iodine exhibits the open-circuit voltage of 838 mV, the short-circuit current density of 9.75 mA cm^?2 and the conversion efficiency of 5.29%, measured at AM 1.5 illumination (100 mW cm^?2). Incorporating iodine into PEI electrolyte results in the decrease of both the open-circuit voltage and the photocurrent density due to the visible light adsorption by iodine and the enhancement of the recombination between conduction band electrons and the triiodide.     

Comparison of numerical and experimental performance criteria of an ammonia–water bubble absorber using plate heat exchangers

A mathematical model for ammonia–water bubble absorbers was developed and compared with experimental data using a plate heat exchanger. The analysis was performed carrying out a sensitive study of selected operation parameters on the absorber thermal load and mass absorption flux. Regarding the experimental data, the values obtained for the solution heat transfer were in the range 0.51–1.21 kW m^?2 K^?1 and those of the mass absorption flux in the range 2.5–5.0 × 10^?3 kg m^?2 s^?1. The comparison between experimental and simulation results was acceptable being the maximum difference of 11.1% and 28.4% for the absorber thermal load and the mass absorption flux, respectively.     

Year round test of a solar adsorption ice maker in Kunming,China

A solar adsorption ice maker with activated carbon–methanol adsorption pair was developed for a practical application. Its main features include utilization of a water cooled condenser and removing all valves in the refrigerant circuit except the one that is necessary for refrigerant charging. Year round performance tests of the solar ice maker were performed in Kunming, Yunnan Province, China. Test results show that the COP (coefficient of performance) of the solar ice maker is about 0.083–0.127, and its daily ice production varies within the range of 3.2–6.5 kg/m² under the climatic conditions of daily solar radiation on the surface of the adsorbent bed being about 15–23 MJ/m² and the daily average ambient temperature being within 7.7–21.1 °C. The suitable daily solar radiation under which the solar ice maker can run effectively in Kunming is above 16 MJ/m².     

Definition of encapsulation barrier requirements: A method applied to organic solar cells

To reach sufficient lifetime for commercial applications, organic solar cells (OPV) require encapsulation with a low permeability barrier material toward atmosphere oxidizing agents, specifically water. Moreover, barrier materials should have the same driving aspects as organic devices like transparency, flexibility and low cost processing techniques such as coating or lamination. The generally admitted value of 10^?6 g m^?2 day^?1 for water vapor transmission rate (WVTR) derived from OLED technology should not be considered as an applicable golden rule and some recent studies demonstrate that OPV cells can be protected with medium barrier materials with a WVTR of around 10^?3 g?m^?2 day^?1. This improved stability is mainly related to the development of new cell architectures. However, a global barrier requirement cannot be defined, but has to be on one hand established in direct relationship between intrinsic stability of the device and on the other hand on the targeted lifetime and operating conditions. In this study, we applied a method to define rapidly the barrier requirement of two OPV cell types named classical and inverted structures. This method combines barrier measurements of encapsulating materials with accelerated lifetime experiments of encapsulated cells and enables to establish the barrier levels necessary to ensure the protection of a given device depending on the intrinsic stability and targeted lifetime.     

Electronic structure and water splitting under visible light irradiation of BiTa1−xCuxO4 (x = 0.00–0.04) photocatalysts

A series of photocatalysts, BiTa_1?xCu_xO₄ (x = 0.00–0.04), were synthesized by the conventional solid-state reaction method and their electronic structures and photocatalytic activities were investigated. The electron microscope observations revealed that the particle sizes of BiTaO₄:Cu crystals were smaller and the surface with many characteristic steps was more obvious than that of the nondoped BiTaO₄, which lead to the increase of photocatalytic activity of water splitting. The UV–vis spectra indicate that the Cu²⁺ ions doping not only enhanced the photocatalytic activity under ultraviolet–visible (λ > 300 nm) light irradiation but also induced the visible light (λ > 400 nm) response. The photocatalyst doped with 2 mol% Cu²⁺ and loaded with 0.3 wt% RuO₂ co-catalyst was found to have the highest activity. New band gap in the visible light range is obtained by copper-doped BiTaO₄, which is attributed to the transition from the donor level resulting from the Cu impurity to the conduction band of BiTaO₄ doped with copper on the basis of the result of DFT calculation.     

Ruthenium (II) complexes with π expanded ligand having phenylene–ethynylene moiety as sensitizers for dye-sensitized solar cells

Ruthenium(II) complexes by introducing phenylene–ethynylene subunit into a tpy (tpy=2,2′:6′,2″-terpyridine) ligand were newly synthesized, and their photophysical and photochemical properties were characterized. The molar extinction coefficients of these dyes were larger than that of black dye. The photovoltaic performances of the solar cells based on these synthesizing dyes were investigated under AM 1.5 irradiation (100 mW cm^?2). The conversion efficiencies of 1a and 1b were 5.7% and 2.4%, respectively.     

A novel Al and Y codoped ZnO/n-Si heterojunction solar cells fabricated by pulsed laser deposition

Al and Y codoped ZnO (AZOY) transparent conducting oxide (TCO) thin films were first deposited on n-Si substrates by pulsed laser deposition (PLD) to form AZOY/n-Si heterojunction solar cells. However, the properties of the AZOY emitter layers are critical to the performance of AZOY/n-Si heterojunction solar cells. To estimate the properties of AZOY thin films, films deposited on glass substrates with various substrate temperatures (T_s) were analyzed. Based on the experimental results, optimal electrical properties (resistivity of 2.8 ± 0.14 × 10^?4 Ω cm, carrier mobility of 27.5 ± 0.55 cm²/Vs, and carrier concentration of 8.0 ± 0.24 × 10²⁰ cm^?3) of the AZOY thin films can be achieved at a T_s of 400 °C, and a high optical transmittance of AZOY is estimated to be >80% (with glass substrate) in the visible region under the same T_s. For the AZOY/n-Si heterojunction solar cells, the AZOY thin films acted not only as an emitter layer material, but also as an anti-reflected coating thin film. Thus, a notably high short-circuit current density (J_sc) of 31.51 ± 0.186 mA/cm² was achieved for the AZOY/n-Si heterojunction solar cells. Under an AM1.5 illumination condition, the conversion efficiency of the cells is estimated at only approximately 4% (a very low open-circuit voltage (V_oc) of 0.24 ± 0.001 V and a fill factor (FF) of 0.51 ± 0.011) without any optimization of the device structure.     

Annealing-induced changes in composition and optoelectronic properties of cadmium sulfide films used in copper–indium–gallium–diselenide solar cells

Owing to its wide band gap, cadmium sulfide film is an effective material for coating on windows when it is used with copper–indium–gallium–diselenide film. Optimizing the annealing temperature and holding time can greatly improve the composition and optical and electrical properties of cadmium sulfide film. Studies of the photoluminescence peak intensity with both a low band gap and a high band gap reveal that a higher S/Cd ratio corresponds to higher crystalline quality. This investigation analyzed two bands in the photoluminescence spectrum – one localized at 2.35–2.51 eV and the other at 1.81–1.86 eV. A cadmium sulfide sample with a highly crystalline structure was obtained by annealing at 100 °C for 20 min. The sheet carrier concentration, mobility, band gap, S/Cd ratio, and sheet resistance of the cadmium sulfide sample are ?4.56 × 10¹⁶ cm^?2, 20.5 cm²/V s, 2.412 eV, 0.99, and 6.67 Ω/cm², respectively. Analysis of a performance of the obtained solar cell under standard air mass 1.5 global illumination revealed a conversion efficiency of 2.392%.     

Effect of ultra-thin polymer membrane electrolytes on dye-sensitized solar cells

In-situ ultra-thin porous poly(vinylidene fluoride-co-hexafluoropropylene) P(VDF–HFP) membranes were prepared by a phase inversion method on TiO₂ electrodes coated with Ru N-719 dye. These membranes were then soaked in the organic liquid electrolyte to form the in-situ ultra-thin porous P(VDF–HFP) membrane electrolytes. Dye-sensitized solar cell (DSC) using the membrane electrolyte exhibited an open-circuit voltage (V_oc) of 0.751 V, a short-circuit current (J_sc) of 16.260 mA cm^?2 and a fill factor (FF) of 0.684 under an incident light intensity of 1000 W m^?2 yielding an energy conversion efficiency (η) of 8.35%. The V_oc, FF and η of the solar cell using the membrane electrolyte increased by about 5.8%, 2.2% and 5.7%, respectively, when compared with the corresponding values of a cell using liquid electrolyte. However, the J_sc decreased by about 2.1%.     

Unsteady conjugate natural convection in a square enclosure filled with a porous medium

Mathematical simulation of unsteady natural convection modes in a square cavity filled with a porous medium having finite thickness heat-conducting walls with local heat source in conditions of heterogeneous heat exchange with an environment at one of the external boundaries has been carried out. Numerical analysis was based on Darcy–Forchheimer model in dimensionless variables such as a stream function, a vorticity vector and a temperature. The special attention was given to analysis of Rayleigh number effect Ra = 10⁴, 10⁵, 10⁶, of Darcy number effect Da = 10^?5, 10^?4, 10^?3, ∞, of the transient factor effect 0 < τ < 1000 and of the heat conductivity ratio k_2,1 = 3.7 × 10^?2, 5.7 × 10^?4, 6.8 × 10^?5 on the velocity and temperature fields. The influence scales of the defining parameters on the average Nusselt number have been detected.     

The economical and environmental performance of miscanthus and switchgrass production and supply chains in a European setting

The purpose of this study is to analyse the economical and environmental performance of switchgrass and miscanthus production and supply chains in the European Union (EU25), for the years 2004 and 2030. The environmental performance refers to the greenhouse gas (GHG) emissions, the primary fossil energy use and to the impact on fresh water reserves, soil erosion and biodiversity. Analyses are carried out for regions in five countries. The lowest costs of producing (including storing and transporting across 100 km) in the year 2004 are calculated for Poland, Hungary and Lithuania at 43–64 € per oven dry tonne (odt) or 2.4–3.6 € GJ^?1 higher heating value. This cost level is roughly equivalent to the price of natural gas (3.1 € GJ^?1) and lower than the price of crude oil (4.6 € GJ^?1) in 2004, but higher than the price of coal (1.7 € GJ^?1) in 2004. The costs of biomass in Italy and the United Kingdom are somewhat higher (65–105 € odt^?1 or 3.6–5.8 € GJ^?1). The doubling of the price of crude oil and natural gas that is projected for the period 2004–2030, combined with nearly stable biomass production costs, makes the production of perennial grasses competitive with natural gas and fossil oil. The results also show that the substitution of fossil fuels by biomass from perennial grasses is a robust strategy to reduce fossil energy use and curb GHG emissions, provided that perennial grasses are grown on agricultural land (cropland or pastures). However, in such case deep percolation and runoff of water are reduced, which can lead to overexploitation of fresh water reservoirs. This can be avoided by selecting suitable locations (away from direct accessible fresh water reservoirs) and by limiting the size of the plantations. The impacts on biodiversity are generally favourable compared to conventional crops, but the location of the plantation compared to other vegetation types and the size and harvesting regime of the plantation are important variables.     

An analysis of energy use and relation between energy inputs and yield in tangerine production

The objective of this study is to determine energy balance between inputs and output for tangerine production in Mazandaran province, one of the most important citrus production centers in Iran. Data is collected by administering a questionnaire in face-to-face interviews. The results show that the highest share of energy was utilized by application of chemical fertilizers and chemicals. Average yield and energy consumption are calculated as 26862.5 kg ha^?1 and 62260.9 MJ ha^?1, respectively. The energy productivity and net energy value are estimated as 0.43 kg MJ^?1 and ?8201.4 MJ ha^?1, respectively. The ratio of energy outputs to energy inputs is approximately 0.87. In addition, the Cobb–Douglas production function is applied to estimate the econometric relationship among different forms of energy consumption. The findings suggest that tangerine producers must optimize their use of indirect and non-renewable energy resources; they apply an excess use of some energy inputs, resulting in an inverse effect on yield as well as imposing risks to natural resources and human health.     

Correlation of critical heat flux and two-phase friction factor for subcooled convective boiling in structured surface microchannels

Critical heat flux (CHF) and pressure drop of subcooled flow boiling are measured for a microchannel heat sink containing 75 parallel 100 μm × 200 μm structured surface channels. The heated surface is made of a Cu metal sheet with/without 2 μm thickness diamond film. Tests and measurements are conducted with de-ionized water, de-ionized water +1 vol.% MCNT additive solution, and FC-72 fluids over a mass velocity range of 820–1600 kg/m² s, with inlet temperatures of 15(8.6)°C, 25(13.6)°C, 44(24.6)°C, and 64(36.6)°C for DI water (FC-72), and heat fluxes up to 600 W/cm². The CHF of subcooled flow boiling of the test fluids in the microchannels is measured parametrically. The two-phase pressure drop is also measured. Both CHF and the two-phase friction factor correlation for one-side heating with two other side-structured surface microchannels are proposed and developed in terms of the relevant parameters.