Electrochemical oxidation behavior of Mg–Li–Al–Ce–Zn and Mg–Li–Al–Ce–Zn–Mn in sodium chloride solution

Mg–Li–Al–Ce–Zn and Mg–Li–Al–Ce–Zn–Mn alloys were prepared using a vacuum induction melting method. Their electrochemical oxidation behavior in 0.7 M NaCl solution was investigated by means of potentiodynamic polarization, potentiostatic oxidation, electrochemical impedance technique and scanning electron microscopy examination. Their utilization efficiencies and performances as anode of metal–hydrogen peroxide semi-fuel cell were determined. The Mg–Li–Al–Ce–Zn–Mn exhibited higher discharge activity and utilization efficiency than Mg–Li–Al–Ce–Zn, and gave improved fuel cell performance. The utilization efficiency of Mg–Li–Al–Ce–Zn–Mn is comparable with that of the state-of-the-art magnesium alloy anode AP65. The magnesium–hydrogen peroxide semi-fuel cell with Mg–Li–Al–Ce–Zn–Mn anode presented a maximum power density of 91 mW cm⁻² at room temperature. Scanning electron microscopy and electrochemical impedance studies indicated that the alloying element Mn prevented the formation of dense oxide film on the alloy surface and facilitated peeling off of the oxidation products.     

Electrical properties of Cu–In–S absorber prepared on Cu tape (CISCuT)

An In precursor on a Cu tape, sulfurized under special transient conditions, shows an internal structure with at least four different semiconducting layers. This structure has a rectifying I–V characteristic also without any buffer layer. The space-charge region is located near the top surface in the upper part of the In-rich layer having a columnar structure, and in the top layer. Deeper-lying layers provide a good contact to the In-rich layer, but show no carrier collection themselves. An EBIC investigation and an original thermopower measurement revealed a pnp-structure with the n-type layer being the In-rich one. The lower part of the film contains a short-circuited p–n junction, switched in series in the opposite direction. One proposal for the band structure of the absorber is presented.     

Elastomer–metal–absorber: development and application

A new principle of a solar collector that consists of appropriately shaped metal form plates as absorbers and clipped in elastomer fluid pipes, the so-called elastomer–metal–absorber, will be presented. The advantages are its freeze resistance, its seawater suitability and new possibilities for simplified collector installation and system techniques. The design parameters including a detailed analysis of the thermal resistance between the absorber and fluid will be discussed, where special regard is given to the development of an appropriate elastomer material with high thermal conductivity as one of the key items. The first development steps have shown that absorbers with a high thermal performance may be constructed. Finally, the idea of application of the principle of the elastomer–metal–absorber to metal roofs and façades will be presented. This idea is followed up within a development project.     

Computer simulation of the effect of phosphorous doping of the i-layer in a thin-film a-Si:H p–i–n solar cell

The simulation RAUPV2 has been used to model a thin-film a-Si:H p–i–n solar cell, fabricated at the Rand Afrikaans University. For a physically acceptable set of input parameters, the simulated J–V curve agrees very well with the empirical J–V curve, under AM1.5 g illumination. The effect of boron- and phosphorous doping of the i-layer (B- and P-profiling) was studied. It was found that boron doping of the i-layer greatly reduced cell performance. On the other hand, there seemed to be an optimal phosphorous concentration in the i-layer, P_opt, for which cell performance, measured in terms of maximum power output, was a maximum. It was observed that as the P concentration in the i-layer was increased towards P_opt, the recombination rate in the front of the i-layer decreased, whilst that in the back part of the i-layer increased. The short-circuit current was seen to decrease under P-profiling. It was seen that as a consequence of P-profiling, the drift field in the back part of the i-layer was relatively insensitive to the effect of an applied voltage, for applied voltages up to about 0.55 V.     

Analysis of photocurrent in the i-layer of GaAs-based n–i–p solar cell

A numerical investigation of the intrinsic layer effect on the improvement of GaAs n–i–p solar cell performances is presented. Solution of Poisson's equation together with continuity equations for electrons and holes allows the determination of carrier's density, electric field and recombination profiles within the i-layer. The analysis examines the effect of i-layer thickness on the electric field, recombination rate and collection efficiency. It is found that increasing the i-layer thickness increases the absorption while it reduces the electric field and increases the recombination rate. The three competing parameters have to be monitored simultaneously so as to obtain an optimal thickness. To achieve this, the variation of the total photocurrent is used as indicator. The photocurrent shows a sharp increase in the domain of very thin i-layers (<0.5 μm) then a saturation is reached for thicker layers (>1 μm), the simulation is performed for thicknesses up to 2 μm.     

Application of design space methodology for optimum sizing of wind–battery systems

A methodology for optimum sizing of different components (i.e., rotor diameter, electrical generator rating, and battery capacity) of a standalone wind–battery system is proposed in this paper. On the basis of time series simulation of the system performance along with different design constraints, the entire set of feasible design options, also known as the design space, has been identified on a rotor diameter vs. rated power diagram. The design space of a standalone wind–battery system identifies the entire envelope within which a feasible system may be designed. The optimum configuration of the standalone system is identified on the basis of minimum cost of energy (US$/kWh). It is observed that the cost of energy is sensitive to the magnitude of average demand and the wind regime. Sensitivity of the capital cost on the minimum cost of energy is also studied.     

The importance of control strategies in PV–hydrogen systems

The control strategy for a photovoltaic (PV) system with a hydrogen (H₂) subsystem consisting of an electrolyzer, pressurized hydrogen gas storage, and fuel cell has been investigated. Detailed computer simulation models for TRNSYS have been developed, tested, and verified against a reference system, namely the PHOEBUS plant in Jülich, Germany. The basic control strategy and main logical control variables for a PV–H₂ system are described. System performance indicators, parameters, and constraints that can be used to analyze the performance of PV–H₂ systems have been identified. The results from a time series simulation for a typical year are presented. Finally, the importance of selecting smart control strategies is demonstrated.     

Weather data and probability analysis of hybrid photovoltaic–wind power generation systems in Hong Kong

This paper describes a simulation model for analyzing the probability of power supply failure in hybrid photovoltaic–wind power generation systems incorporating a storage battery bank, and also analyzes the reliability of the systems. An analysis of the complementary characteristics of solar irradiance and wind power for Hong Kong is presented. The analysis of local weather data patterns shows that solar power and wind power can compensate well for one another, and can provide a good utilization factor for renewable energy applications. For the loss of power supply probability (LPSP) analysis, the calculation objective functions and restraints are set up for the design of hybrid systems and to assess their reliability. To demonstrate the use of the model and LPSP functions, a case study of hybrid solar–wind power supply for a telecommunication system is presented. For a hybrid system on the islands surrounding Hong Kong, a battery bank with an energy storage capacity of 3 days is suitable for ensuring the desired LPSP of 1%, and a LPSP of 0% can be achieved with a battery bank of 5 days storage capacity.     

Optical and solar parameters of irradiated lead–alkali–silicate glass

Lead–alkali–silicate glass that is used for a shielding window of hot cells in nuclear technology has been irradiated by a ⁶⁰Co radioisotope source between 0.998 and 35.939 kGray dose levels. Gamma rays can affect glass and change its several optical and solar parameters such as secondary internal heat transfer factor (q_i), direct solar transmittance (τ_e), solar factor (g) and shading coefficient via the absorbed dose. It is aimed to investigate the performance of the glass in terms of the shading coefficient, which is the most important parameter to view clearly inside of the hot cell. Furthermore, a comparative evaluation has been done with respect to the unexposed lead–alkali–silicate glass. Change in the shading coefficient with respect to absorbed dose is extremely important.     

Combined analytical/FEA-based coupled aero structure simulation of a wind turbine with bend–twist adaptive blades

The simulation of wind turbines with bend–twist adaptive blades is a coupled aero-structure (CAS) procedure. The blade twist due to elastic coupling is a required parameter for wind turbine performance evaluation and can be predicted through a finite element (FE) structural analyser. FEA-based codes are far too slow to be useful in the aerodynamic design/optimisation of a blade. This paper presents a combined analytical/FEA-based method for CAS simulation of wind turbines utilising bend–twist adaptive blades. This method of simulation employs the induced twist distribution and the flap bending at the hub of the blade predicted through a FEA-based CAS simulation at a reference wind turbine run condition to determine the wind turbine performance at other wind turbine run conditions. This reduces the computational time significantly and makes the aerodynamic design/optimisation of bend–twist adaptive blades practical. Comparison of the results of a case study which applies both combined analytical/FEA-based and FEA-based CAS simulation shows that when using the combined method the required computational time for generating a power curve reduces to less than 5%, while the relative difference between the predicted powers by two methods is only about 1%.     

Quantifying residential PV economics in the US––payback vs cash flow determination of fair energy value

Payback is often used as a measure of profitability by prospective PV owners. Contrasting this measure with another financial gauge––life-cycle cash flow––the paper discusses why payback may not be the most appropriate measure for residential PV applications and why it may hide sound financial opportunities for those deciding to invest in a PV system.In parallel, the paper addresses another aspect of economic feasibility: the value of energy produced. For residential applications, this value is currently set at residential net-metered retail rates. We present preliminary evidence that a higher value, reflective of the local effective capacity of PV ought to be claimed for residential PV applications.     

Thermal–electrical–luminous model of multi-chip polychromatic LED luminaire

This paper proposed a thermal–electrical–luminous dynamic model of red–green–blue (RGB) light-emitting diode (LED) luminaire for lighting control. The thermal–electrical–luminous model consists of three parts, namely, electrical–thermal (E–T), electrical–luminous (E–L), and thermal–luminous (T–L) models. Using step response method, the electrical–thermal (E–T) model G(s) is derived as a first-order bi-proper system. The electrical–luminous (E–L) and thermal–luminous (T–L) models are zeroth order model with a constant gain since the luminous response to electric or thermal input is much faster. The thermal–electrical–luminous model shows that the luminous intensity is proportional to input power and inversely proportional to junction temperature. The dynamic response of luminous intensity is dominated by the electrical–thermal model G(s).The whole thermal–electrical–luminous model can be further divided into a constant gain and a first-order bi-proper system. The constant gain causes the instantaneous response at power switch on; the first-order system represents the luminous variation due to junction temperature change which is mainly related to the heat sink design. The complete model can accurately describe luminous dynamic behavior and be used in control system design of RGB LED lighting luminaire.     

Studies on the temperature dependence of I–V and C–V characteristics of electron irradiated silicon photo-detectors

The current transport mechanisms of n⁺–p silicon (Si) photo-detectors in different temperature and bias regions before and after irradiation with a dose of 350 kGy has been investigated and presented in this article. Temperature-dependent dark current–voltage (I–V) studies under forward and reverse bias were carried out for this purpose. In the temperature range studied, the dark current contribution in the low bias range is believed to be due to the generation-recombination of minority carriers in the space-charge region. Electron irradiation does not seem to have altered the dark current conduction mechanism. Capacitance–voltage (C–V) at various temperatures was measured to identify the presence of deep levels in the device.     

Preparation of microcrystalline silicon–carbon films

The effects of discharge parameters on the properties of hydrogenated silicon–carbon films deposited by PECVD system have been investigated. Hydrogenated microcrystalline silicon–carbon films have been grown at low RF power. The increase in RF power from 5 to 25 W leads to a decrease of the crystallinity degree and an enhancement of the carbon content from 0.025 to 0.10. The optical energy gap can be tuned in the 1.86–1.96 eV range and the dark conductivity decreases by about three orders of magnitude. In the investigated pressure range (1.7–2.9 Torr) microcrystalline samples show approximately the same optical and electrical properties. Microcrystalline films with high dark conductivity present an n-type character and the micro-mono crystalline silicon heterostuctures fabricated with these materials reveal a rectifying behaviour of the junctions.     

Spectral response of a-Si:H p–i–n solar cells

The spectral response of a typical thin-film a-Si:H p–i–n solar cell has been investigated using the simulation RAUPV2. The peak in the external quantum efficiency has been observed to shift towards the violet part of the spectrum on decreasing the cell thickness. Moreover, the height of the peak increases as cell thickness is decreased. This is correlated with an enhancement in cell performance for thinner cells, due to a general increase in the drift field within the cell. The external quantum efficiency of a cell with an optimal concentration of phosphorous in the intrinsic layer has also been investigated. The external quantum efficiency for this cell is similar to that of the thinner cell, and is associated with the enhancement of the drift field near the p/i interface that is brought about by the phosphorous doping of the intrinsic layer. However, the integrated recombination for the thinner cell and the phosphorous-profiled cell differ significantly at long wavelengths, despite their similarity at shorter wavelengths. This effect is due to the weakening of the drift field near the n/i interface in the phosphorous-profiled cell.     

Investigation of a novel combined cycle of solar powered adsorption–ejection refrigeration system

A novel model of the combined cycle of a solar-powered adsorption–ejection refrigeration system (CCSPAERS) is established. By analyzing the theory of this system and its thermodynamics, together with numerical simulation, it is found that it is a feasible method to overcome the intermittent character of a single bed solar adsorption refrigeration system. The estimated coefficient of performance for this combined cycle is about 0.4 under the following operating conditions: condensing temperature 313 K, evaporating temperature 283 K, regenerating temperature 393 K and desorbing temperature 473 K, using zeolite 13X–water as the pair. The higher desorbing temperature can be obtained when a vacuumed tube adsorber or a CPC adsorber is used.     

Modelling of stratified gas–liquid two-phase flow in horizontal circular pipes

This paper reports numerical and experimental investigation of stratified gas–liquid two-phase flow in horizontal circular pipes. The Reynolds averaged Navier–Stokes equations (RANS) with the k–ω turbulence model for a fully developed stratified gas–liquid two-phase flow are solved by using the finite element method. A smooth interface surface is assumed without considering the effects of the interfacial waves. The continuity of the shear stress across the interface is enforced with the continuity of the velocity being automatically satisfied by the variational formulation. For each given interface position and longitudinal pressure gradient, an inner iteration loop runs to solve the non-linear equations. The Newton–Raphson scheme is used to solve the transcendental equations by an outer iteration to determine the interface position and pressure gradient for a given pair of volumetric flow rates. Favorable comparison of the numerical results with available experimental results indicates that the k–ω model can be applied for the numerical simulation of stratified gas–liquid two-phase flow.     

An optimum dispatch strategy using set points for a photovoltaic (PV)–diesel–battery hybrid power system

This paper presents dispatch strategies for the operation of a solar photovoltaic (PV)–diesel–battery hybrid power system using ‘set points’. This includes determination of the optimum values of set points for the starting and stopping of the diesel generator to minimise the overall system costs. A computer program for a typical dispatch strategy has been developed to predict the long-term energy performance and the lifecycle cost of the system.     

Synthesis of cobalt–silicon oxide thin films

Silicon–cobalt oxide thin films were prepared by the dipping sol–gel process. Samples with different number of dipping–annealing cycles were prepared. Some data regarding the precursor sol are given from small angle X-ray scattering characterization. Composition, structure, surface morphology and optical properties are obtained from X-ray diffraction, reflectance, transmittance, FTIR, scanning electron microscopy and EDX spectroscopy measurements. The silicon–cobalt oxide thin films prepared in this work are mostly amorphous. They have a high absorption coefficient in the visible and infrared regions. A refractive index from 2.15 to 1.79 (at 1200 nm wavelength), and a band gap between 3.73 and 3.68 eV with increasing film thickness were measured in the films. Sol–gel prepared Si–Co oxide thin films could be well suited for use in photothermal solar collectors.     

Optimal optical generation profiles in a-Si:H p–i–n solar cells

The dependence of the maximum power output P_M and short-circuit current J_SC on the form (relative variation with position) of the optical generation rate profile in an a-Si:H p–i–n solar cell has been investigated computationally. It was found that there was an optimal form for the generation profile, and that P_M increased from 4.64 to 5.29 mWcm⁻², an increase of about 14%, when this optimal generation profile was used in the simulation. Optimal doping of the i-layer of the cell with phosphorous led to a P_M of 5.60 mWcm⁻², and when the optimal generation profile for this P-profiled cell was found, it yielded a P_M of 7.86 mWcm⁻², an increase of about 40%. This suggests that the combination of P-profiling and optimal generation could lead to significant improvements in cell performance. Moreover, it was found that for both cells the form of the optimal generation profile could be associated with the position of the peak in the external quantum efficiency, obtained from the spectral response. The possibility of using band-gap grading to achieve an optimal generation rate profile has been suggested.