Modeling, design and thermal performance of a BIPV/T system thermally coupled with a ventilated concrete slab in a low energy solar house: Part 2, ventilated concrete slab

This paper is the second of two papers that describe the modeling and design of a building-integrated photovoltaic-thermal (BIPV/T) system thermally coupled with a ventilated concrete slab (VCS) adopted in a prefabricated, two-storey detached, low energy solar house and their performance assessment based on monitored data. The VCS concept is based on an integrated thermal-structural design with active storage of solar thermal energy while serving as a structural component - the basement floor slab (∼33 m²). This paper describes the numerical modeling, design, and thermal performance assessment of the VCS. The thermal performance of the VCS during the commissioning of the unoccupied house is presented. Analysis of the monitored data shows that the VCS can store 9-12 kWh of heat from the total thermal energy collected by the BIPV/T system, on a typical clear sunny day with an outdoor temperature of about 0 °C. It can also accumulate thermal energy during a series of clear sunny days without overheating the slab surface or the living space. This research shows that coupling the VCS with the BIPV/T system is a viable method to enhance the utilization of collected solar thermal energy. A method is presented for creating a simplified three-dimensional, control volume finite difference, explicit thermal model of the VCS. The model is created and validated using monitored data. The modeling method is suitable for detailed parametric study of the thermal behavior of the VCS without excessive computational effort.     

Reliability evaluation of the solar power system based on the Markov chain method

Energy shortages and environmental problems associated with nonrenewable energy generation techniques have become increasingly prominent worldwide. Solar photovoltaic power generation is able to supply clean, environmentally friendly, and inexhaustible energy. Together with issues related to the expansion of scale, strong stochastic volatility and unpredictability have posed huge challenges to the stability and reliability of this power generation system. The present study proposed a reliable method to evaluate the stationary distribution probability based on the Markov chain method. First, the solar generation system was modeled based on the solar battery. Second, the stochastic property of the solar energy output power was derived and the simulation experiment adopted to verify the feasibility of results. Third, the energy storage device discharge process was modeled based on the Markov chain method and the evaluation method for the reliability of the solar power generation system obtained. Finally, validity of the method was simulated and verified.     

Study of the photon down‐conversion effect produced by thin silicon‐rich oxide films on silicon solar cells

In the present work, we studied the photon down‐conversion effect produced by thin films of silicon oxide with embedded silicon nanocrystals also called silicon‐rich oxide (SRO). These films have been used to absorb high energy light and the re‐emission of two or more low energy photons (~1.1 eV) with the goal of improving the external quantum efficiency and consequently the conversion efficiency of silicon solar cells. According to our results, the incorporation of a thin SRO film on the solar cell surface increases the short circuit current and the FF of the silicon solar cells; the enhancement of spectral response is due to the high photoluminescence intensity of the SRO in the visible region when irradiated with UV light. An improvement of 38% in the solar cell efficiency has been observed in our particular solar cell fabrication process by the use of an SRO film with high photoluminescence intensity, which replaces the conventional silicon dioxide film. Copyright © 2016 John Wiley & Sons, Ltd.     

Photodegradation of the antibiotics nitroimidazoles in aqueous solution by ultraviolet radiation

The objective of this study was to analyze the efficacy of ultraviolet (UV) radiation in the direct photodegradation of nitroimidazoles. For this purpose, i) a kinetic study was performed, determining the quantum yield of the process; and ii) the influence of the different operational variables was analyzed (initial concentration of antibiotic, pH, presence of natural organic matter compounds, and chemical composition of water), and the time course of total organic carbon (TOC) concentration and toxicity during nitroimidazole photodegradation was studied. The very low quantum yields obtained for the four nitroimidazoles are responsible for the low efficacy of the quantum process during direct photon absorption in nitroimidazole phototransformation. The R₂₅₄ values obtained show that the dose habitually used for water disinfection is not sufficient to remove this type of pharmaceutical; therefore, higher doses of UV irradiation or longer exposure times are required for their removal. The time course of TOC and toxicity during direct photodegradation (in both ultrapure and real water) shows that oxidation by-products are not oxidized to CO₂ to the desired extent, generating oxidation by-products that are more toxic than the initial product. The concentration of nitroimidazoles has a major effect on their photodegradation rate. The study of the influence of pH on the values of parameters ? (molar absorption coefficient) and k′_E (photodegradation rate constant) showed no general trend in the behavior of nitroimidazoles as a function of the solution pH. The components of natural organic matter, gallic acid (GAL), tannic acid (TAN) and humic acid (HUM), may act as promoters and/or inhibitors of OH· radicals via photoproduction of H₂O₂. The effect of GAL on the metronidazole (MNZ) degradation rate markedly differed from that of TAN or HUM, with a higher rate at low GAL concentrations. Differences in MNZ degradation rate among waters with different chemical composition are not very marked, although the rate is slightly lower in wastewaters, mainly due to the UV radiation filter effect of this type of water.     

Exergetic optimization of a solar photovoltaic thermal (PV/T) air collector

In this paper, an exergetic optimization has been developed to determine the optimal performance and design parameters of a solar photovoltaic thermal (PV/T) air collector. A detailed energy and exergy analysis has been carried out to calculate the thermal and electrical parameters, exergy components, and exergy efficiency of a typical PV/T air collector. The thermal and electrical parameters of a PV/T air collector include solar cell temperature, back surface temperature, outlet air temperature, open‐circuit voltage, short‐circuit current, maximum power point voltage, maximum power point current, etc. An improved electrical model has been used to estimate the electrical parameters of a PV/T air collector. Furthermore, a new equation for the exergy efficiency of a PV/T air collector has been derived in terms of design and climatic parameters. A computer simulation program has been also developed to calculate the thermal and electrical parameters of a PV/T air collector. The results of numerical simulation are in good agreement with the experimental measurements noted in the previous literature. Moreover, the simulation results obtained in this paper are more precise than the one given by the previous literature, and the new exergy efficiency obtained in this paper is in good agreement with the one given by the previous literature. Finally, exergetic optimization has been carried out under given climatic, operating, and design parameters. The optimized values of inlet air velocity, duct length, and the maximum exergy efficiency have been found. Parametric studies have been also carried out. Copyright © 2010 John Wiley & Sons, Ltd.     

太阳能富集地区住宅建筑非平衡保温研究——拉萨市供暖期太阳辐射分析与室内热环境测试

在有供暖需求的太阳能资源富集地区,由于太阳辐射强烈,住宅建筑各个朝向外墙,尤其是南北向的外墙所接收的太阳辐射量差异很大,为了更有效地利用太阳能并降低保温成本,这种差异应表现在建筑围护结构保温性能的设计中.本文通过对拉萨市标准年气象数据库的分析得到了其住宅建筑各朝向外墙供暖季内获得的太阳辐射量.与内地城市相比,拉萨市太阳能资源丰富且朝向差异很大,非平衡保温具有一定的实际意义.另外,冬季现场测试表明无供暖建筑的南北朝向房间热环境有所不同,南向房间测试周期内基本处于人体舒适范围内,而北向房间始终偏冷,远离人体热舒适区域,有供暖需求.     

Solar Light Photocatalytic CO2 Reduction: General Considerations and Selected Bench-Mark Photocatalysts

The reduction of carbon dioxide to useful chemicals has received a great deal of attention as an alternative to the depletion of fossil resources without altering the atmospheric CO₂ balance. As the chemical reduction of CO₂ is energetically uphill due to its remarkable thermodynamic stability, this process requires a significant transfer of energy. Achievements in the fields of photocatalysis during the last decade sparked increased interest in the possibility of using sunlight to reduce CO₂. In this review we discuss some general features associated with the photocatalytic reduction of CO₂ for the production of solar fuels, with considerations to be taken into account of the photocatalyst design, of the limitations arising from the lack of visible light response of titania, of the use of co-catalysts to overcome this shortcoming, together with several strategies that have been applied to enhance the photocatalytic efficiency of CO₂ reduction. The aim is not to provide an exhaustive review of the area, but to present general aspects to be considered, and then to outline which are currently the most efficient photocatalytic systems.     

Photovoltaic technology in Malaysia: past,present, and future plan

This article presents solar energy or specifically the solar photovoltaic (PV) development outlook in Malaysia. The paper first introduces the massive potential of solar energy in the country, the key players in the solar energy development and the early solar energy policies, and programmes in the country. The most important to the PV development is the Malaysia Building Integrated Photovoltaic initiative, which is presented in this paper followed by an explanation on the Feed-in Tariff recently introduced in the country to encourage new solar PV projects. The outlook for solar PV in Malaysia is optimistic and as the uptake of solar PV increases, the unit cost is coming down rapidly. Solar PV is expected to be the most competitive Renewable Energy (RE) source, with the potential to achieve grid parity for electrical power in the country in the near future, and surpassing all other REs combined by 2050.     

The novel usage of spectroscopic ellipsometry for the development of amorphous Si solar cells

We present the novel use of spectroscopic ellipsometry (SE) for the development of a-Si:H solar cell. SE is a very fast and useful tool to measure various optical properties of thin film. In the case of a-Si:H thin film analysis, generally, SE is used to estimate the film thickness, roughness, void fraction, optical constants such as (n,k), and so forth. In this study, optical parameters from SE measurements were analyzed with relation to structural and electrical properties of a-Si:H thin film for solar cell. By analyzing IR absorption spectra and conductivity measurements, it was affirmed that <ε₂> and parameter A by Tauc-Lorentz model fitting of SE data are representative parameters qualifying a-Si:H thin film, and that they have close relationships with FF and light induced degradation property of solar cells. Based on the analysis, solar cells that have i-layers with various E_g were optimized. By this research, easier and faster methodology to develop a-Si:H thin film for thin film Si solar cells using SE measurements was established.