A generalized window energy rating system for typical office buildings

Detailed computer simulation programs require lengthy inputs, and cannot directly provide an insight to relationship between the window energy performance and the key window design parameters. Hence, several window energy rating systems (WERS) for residential houses and small buildings have been developed in different countries. Many studies showed that utilization of daylight through elaborate design and operation of windows leads to significant energy savings in both cooling and lighting in office buildings. However, the current WERSs do not consider daylighting effect, while most of daylighting analyses do not take into account the influence of convective and infiltration heat gains. Therefore, a generalized WERS for typical office buildings has been presented, which takes all primary influence factors into account. The model includes embodied and operation energy uses and savings by a window to fully reflect interactions among the influence parameters. Reference locations selected for artificial lighting and glare control in the current common simulation practice may cause uncompromised conflicts, which could result in over- or under-estimated energy performance. Widely used computer programs, DOE2 and ADELINE, for hourly daylighting and cooling simulations have their own weaknesses, which may result in unrealistic or inaccurate results. An approach is also presented for taking the advantages of the both programs and avoiding their weaknesses. The model and approach have been applied to a typical office building of Hong Kong as an example to demonstrate how a WERS in a particular location can be established and how well the model can work. The energy effect of window properties, window-to-wall ratio (WWR), building orientation and lighting control strategies have been analyzed, and can be indicated by the localized WERS. An application example also demonstrates that the algebraic WERS derived from simulation results can be easily used for the optimal design of windows in buildings similar to the typical buildings.     

Wide optical band gap window layers for solar cells

In this paper, the preparation of amorphous silicon carbide with very wide optical band gap and high conductivity were reported. The films were fabricated under the “silane–plasma starving” and H₂ dilution condition in conventional capacitively coupled reactors. The silane–plasma starving condition and H₂ dilution play important roles in decreasing H content, modulating the material toward the ordered structure and enhancing the doping ratio. This is an easy way to prepare wide optical band gap and highly conductive p-type window layers for a-Si : H-based solar cells.     

Design and fabrication of electrochromic light modulators

The battery-like structure of electrochromic devices warrants the application of a stoichiometric oxidation-reduction model to interpret and to optimize their operation. Of particular significance is the variation of the potential of electrochromic materials with composition, the bleached state absorption coefficients, their electrochemical stability limits and their coloration functionality versus Faradaic charge. Once these input parameters are known, the optical transmission spectrum of electrochromic light modulating devices can be predicted as a function of terminal voltage given certain assumptions about the thickness and redox state of the electrochromic and counter electrode materials on device assembly. The latter is not readily determined directly, but may be derived from properties of the two terminal device. Furthermore, the electro-optical characteristics of the two terminal device can be used to determine the source of any deviation from its optimal dynamic range.     

Chemically deposited CdS by an ammonia-free process for solar cells window layers

Chemically deposited CdS window layers were studied on two different transparent conductive substrates, namely indium tin oxide (ITO) and fluorine doped tin oxide (FTO), to determine the influence of their properties on CdS/CdTe solar cells performance. Three types of CdS films obtained from different chemical bath deposition (CBD) processes were studied. The three CBD processes employed sodium citrate as the complexing agent in partial or full substitution of ammonia. The CdS films were studied by X-ray diffraction, optical transmission spectroscopy and atomic force microscopy. CdS/CdTe devices were completed by depositing 3 μm thick CdTe absorbent layers by means of the close-spaced vapor transport technique (CSVT). Evaporated Cu-Au was used as the back contact in all the solar cells. Dark and under illumination J-V characteristic and quantum efficiency measurements were done on the CdS/CdTe devices to determine their conversion efficiency and spectral response. The efficiency of the cells depended on the window layer and on the transparent contact with values between 5.7% and 8.7%.     

Performance of a multifunctional PV/T hybrid solar window

A building-integrated multifunctional PV/T solar window has been developed and evaluated. It is constructed of PV cells laminated on solar absorbers placed in a window behind the glazing. To reduce the cost of the solar electricity, tiltable reflectors have been introduced in the construction to focus radiation onto the solar cells. The reflectors render the possibility of controlling the amount of radiation transmitted into the building. The insulated reflectors also reduce the thermal losses through the window. A model for simulation of the electric and hot water production was developed. The model can perform yearly energy simulations where different features such as shading of the cells or effects of the glazing can be included or excluded. The simulation can be run with the reflectors in an active, up right, position or in a passive, horizontal, position. The simulation program was calibrated against measurements on a prototype solar window placed in Lund in the south of Sweden and against a solar window built into a single family house, Solgården, in Älvkarleö in the central part of Sweden. The results from the simulation shows that the solar window annually produces about 35% more electric energy per unit cell area compared to a vertical flat PV module.     

Solar material protection factor (SMPF) and solar skin protection factor (SSPF) for window panes and other glass structures in buildings

The two quantities solar material protection factor (SMPF) and solar skin protection factor (SSPF) are introduced in order to measure and calculate the capability of glass to protect indoor materials and human skin from degradation caused by the solar radiation. Comparison of the SMPF and SSPF values for different glass fabrications enables one to select the most appropriate glass material for the specific buildings. Numerical examples are shown with measurements and calculations carried out on various glass materials, including two electrochromic window (ECW) devices, and several two- and three-layer window pane combinations. Visibility levels at various protection degrees are also given.     

Improvement of conversion efficiency by In0.52Al0.48 As window layers for pn InP solar cells

The effects of In_0.52Al_0.48 As window layers on p+n InP cell performances have been experimentally studied. The carrier collection efficiency is improved by introducing the In_0.52Al_0.48 As window layer and the short circuit current density increases. A conversion efficiency of 17.9% is obtained for a heteroface cell with a 50 nm thick window layer, while the efficiency of an InP cell without the window layer is 15.0% under air mass 1.5 condition.     

Design and fabrication of low cost solar water heaters

We designed two types of very low cost solar water heaters which do not need a water supply connection. The first one consisted of two plastic bowls, one inside the other with 5 cm thickness of insulation in between. A transparent plastic cover was tied around the smaller vessel. It was found that water placed inside the smaller vessel had its temperature raised by 18°C from the ambient temperature within four hours when the average insolation was about 600 kWh/m². The second one consisted of two earthen vessels in place of plastic bowls. The water temperature rise was 20°C under the same radiation. If either of the heaters was covered with cotton-wool insulation in the afternoon, the temperature remains 13°C above the ambient early next morning. The cost of the material was around US$ 4.50 for the plastic bowl heater while this is around US$ 3.50 for the earthen vessel water heater.     

Optimal parameters for performant heterojunction InGaP/GaAs solar cell

We demonstrated mainly some of the different parameters effects -as a function of temperature-as window layers, thickness, and doping of the various layers (emitter, base and BSF) on the performances of InGaP/GaAs solar cell. First, we have varied the molar fraction of different layers; their thickness and the doping of both emitters and bases. We have registered the result of each variation until obtaining optimal parameters. In a second stage, we have simulated the InGaP/GaAs cell without window layers which results in η = 12.47% and η = 22.14% for eliminating top and bottom windows respectively. Then, the elimination of layer BSFs(back surface field) on the back face of the considered cell causes a remarkable decrease in open circuit voltage Voc and output η which reached 1.57 V and 11.95% respectively. In a last stage, we optimized and simulated the performances of the InGaP/GaAs dual-junction solar cell for its optimal parameters while varying its operation temperature from 300 K to 375 K with an increment of 25 °C using a virtual wafer fabrication TCAD Silvaco. The optimization at 300 K led to the following results Icc = 15.19 mA/cm^?2, Voc = 2.53 V, FF = 91.32% and η = 25.43% which are close with those found in literature for In_(1?x)Ga_(x)P(x is molar fraction: x = 0.5). Therefore, we could determine the critical parameters of the cell and optimize its main parameters to obtain the highest performance for a dual junction solar cell. This work will pave the way with new prospects in the field of the photovoltaic. The structure simulation will simplify the manufacturing processes of solar cells; will thus reduce the costs while producing high outputs of photovoltaic conversion.     

聚光式太阳灶的设计与制作(Ⅶ)--太阳灶模具的制作

（三）反光材料 聚光太阳灶实用效果的优劣，除了设计和制作工艺对太阳灶的影响之外，在很大程度上取决于反光材料的性能。选用反射率高、寿命长的反光材料，能提高太阳灶的热效率。在功率相等的情况下可以使反光面做得小一些，从而有利于操作，也有利于降低成本。     

聚光式太阳灶的设计与制作(Ⅷ)--太阳灶技术要求和测试方法

作为一种产品,我们需要采用科学的方法对它进行检测,以评价它的各项技术指标的优劣.聚光型太阳灶行业标准(NY219-2003),系统地归纳了我国十余年来在聚光型太阳灶方面的科研成果和生产推广经验,提出了太阳灶的设计、型号、规格和测试方法,规定了太阳灶的技术要求、结构检测和性能试验方法,是世界上首次提出的太阳灶标准.为方便读者掌握和应用,我们把标准的主要内容介绍如下.     

Performance of p-type silicon-oxide windows in amorphous silicon solar cell

a-SiO_x films have been prepared using silane and pure oxygen as reactive gases in plasma CVD system. Diborane was introduced as a doping gas to obtain p-type conduction silicon oxide. Infrared absorption spectra show the incorporation of Si–O stretch mode around 1000 cm⁻¹. The optical bandgap increases with the oxygen to silane gas ratio, while the electrical conductivity decreases. Hydrogenated amorphous silicon solar cells have been fabricated using p-type a-SiO_x with around 1.85 eV optical bandgap and conductivity greater than 10⁻⁷ S/cm. The measured current–voltage characteristics of the solar cells under 100 mW/cm² artificial light are V_oc=0.84 V, J_sc=14.7 mA/cm², FF=0.635 with a conversion efficiency of 7.84%.     

How front side plasmonic nanostructures enhance solar cell efficiency

Dielectric roughness on the front surface enhances significantly solar cell efficiency by light trapping in the absorbing layer. However in plasmonic assisted thin silicon solar cells we show, by a detailed analysis of the various mechanisms, that front-surface plasmonic structures enhance the efficiency by a different mechanism—namely the effective broadband forward scattering into the silicon, while trapping (path length enhancement) is relatively small for these structures. The plasmonic local field enhancement contribution is even smaller in this configuration. Based on our study we optimized this “anti-reflection mechanism” by tuning the plasmonic structure such that the spectral location of the more efficiently scattering dipole and quadrupole resonances fit correctly the visible and NIR sun spectrum.     

Theoretical analysis of the effect of conduction band offset of window/CIS layers on performance of CIS solar cells using device simulation

One of the most important factors of CdS leading to high performance in Cu(In,Ga)Se₂ (CIGS) solar cells is appropriation of the conduction band offset of CdS/CIGS layers. However, it is not clearly explained. In this study, device modeling and simulation were conducted to explain the effect of conduction band offset of window/CIGS layers on performance of CIGS solar cells. As a result of calculation, excellent performance can be obtained when the conduction band of window layer positions higher by 0–0.4 eV than that of CIGS.     

Recycling silicon solar cell waste in cement-based systems

This is a study of the recycling of crystalline solar cells by incorporating them in cement matrices. The hydration process of a mixture of calcium aluminate cement (CAC) and solar photovoltaic cell waste was researched and analyzed. The nature of the hydration products of various compositions of these mixtures was evaluated at a temperature of 20 °C by analyzing the samples through X-ray diffraction, infrared spectroscopy and scanning electron microscopy. The total porosity and mechanical strength development of these materials were also determined. It was revealed that the presence of a solar cell residue of up to 5% in the cement matrices does not result in new hydration products that are different from those derived from the normal hydration of the CAC cement. Moreover, the material developed can be considered as an expansive cement blend because it releases H₂ at early stages. The presence of waste causes a decrease in the mechanical strength and an increase in the total porosity of this material, but it can be used for applications such as thermal insulation.     

Variation of discomfort with south window area and insulation on walls/roof

Dependence of the discomfort index on the south window area and the cost of optimally distributed insulation over the walls and roof (corresponding to different available investments) of a non-air-conditioned one room building is investigated. It is assumed that, in the winter, the wooden shutters provided in the window are opened during the day and are closed during the night, and that, in the summer, the shutters are closed during the day and are opened during the night. It is seen that the discomfort decreases with increasing window area and an increasing amount of insulation.     

Design and fabrication of a cost effective solar air heater for Bangladesh

In this research, a solar air heater is designed, fabricated and its performance is assessed in the perspective of an emerging/developing country with a huge energy demand like Bangladesh. The winter season (mid-November–mid-February) of the country characterizes by low temperatures, cool air blowing from the west or northwest, clear sky and meager rainfall. Minimum temperature in the extreme northwest in late December and early January sometimes reaches 3 °C and day length is about 10 h. The shortness of winter days can be compensated by reducing the heat loss during long nights. The solar air heater is constructed to prevent as much heat loss as possible. In other words, the heating of air is accomplished by maximizing light gain and minimizing heat loss. It is observed that the fabricated solar air heater is working efficiently. The maximum room temperature and the temperature difference from ambient are 45.5 °C and 12.25 °C for forced circulation and 41.75 °C and 8.5 °C for natural circulation respectively. The experimental outlet temperatures have been compared with that of theoretical values. Due to its low-cost and simple technology, it is affordable in all aspects, viz. of cost, operation and maintenance by the typical people of Bangladesh.     

Numerical analysis of convective and diffusive fuel transports in high-temperature proton-exchange membrane fuel cells

The fuel transports in high-temperature proton-exchange membrane fuel cells have been numerically examined. Both convective and diffusive fuel transports are analyzed in detail. The former is often neglected in straight flow channel configurations while it has been reported to become important for serpentine or interdigitated flow channel configurations. By using a two-dimensional isothermal model, we have performed numerical simulations of a high-temperature proton-exchange membrane fuel cell with a straight flow channel configuration. The present results show that even in a straight flow channel configuration, the convection can play a significant role in fuel transports for the anode side. Examination of the flow field data reveals that the anode gas mixture is transported toward the catalyst layer (CL) whereas the gas mixture in the cathode channel moves away from the reaction site. It is also observed that as the flow moves downstream, the flow rate decreases in the anode channel but increases in the cathode channel. Species transport data are examined in detail by splitting the total flux of fuel transport into convective and diffusive flux components. For oxygen transport in the cathode gas diffusion layer (GDL), diffusion is dominant; in addition, the convective flux has a negative contribution to the total oxygen flux and is negligible compared to the diffusion flux. However, for hydrogen transport to the reaction site, both convection and diffusion are shown to be important processes in the anode GDL. At high cell voltages (i.e., low current densities), it is even observed that the convective contribution to the total hydrogen flux is larger than the diffusive one.     

Advances in a-Si:H/c-Si heterojunction solar cell fabrication and characterization

Our progress in amorphous/crystalline silicon (a-Si:H/c-Si) heterojunction solar cell technology and current understanding of fundamental device physics are presented. In a-Si:H/c-Si cells, device performance is strongly dependent on the quality of the a-Si:H/c-Si heterojunction. Four topics are crucial to minimize recombination at the junction and thereby maximize cell efficiency: wet-chemical pre-treatment of the c-Si surface prior to a-Si:H deposition; optimum a-Si:H doping; thermal and plasma post-treatments of the a-Si:H/c-Si structure. By optimizing these aspects using specifically developed characterization methods, we were able to realize (n)a-Si:H/(p)c-Si and (p)a-Si:H/(n)c-Si cells with up to 18.5% and 19.8% efficiency, respectively.     

Progress in emitter wrap-through solar cell fabrication on boron doped Czochralski-grown silicon

We report on RISE-EWT (Rear Interdigitated Single Evaporation-Emitter Wrap-Through) solar cells on full area (12.5×12.5 cm²) pseudo square boron doped Czochralski-grown silicon wafers. We investigate the main efficiency optimisation factors of these cells by investigating the dependence of RISE-EWT cell parameters on the base dopant concentration N_A. We furthermore detail the effects of large feature sizes in base and emitter regions at the rear of the solar cell and investigate these effects with particular attention to the edge regions. EWT solar cells typically exhibit rather low fill factors. However, our results show that the improved fill factors can be achieved by increasing N_A, which in return leads to optimised efficiency values. For our RISE-EWT solar cells made from boron doped Cz-Si wafers, this benefit is maintained even after light-induced degradation. Our investigation of edge area related effects shows the importance of proper cell design in these areas, leading to a further 2.8% absolute improvement in the fill factor. Combining increased base dopant concentration with optimised edge design, we achieve 19.0% efficiency on (12.5×12.5 cm²) boron doped Cz silicon wafers before light-induced degradation, resulting in 18.1% efficiency in the light-degraded state.