Depositing an antireflection coating on the front surface of solar cells allows a significant reduction in reflection losses. It thus allows an increase in the efficiency of the cells. A modeling of the refractive ind...Depositing an antireflection coating on the front surface of solar cells allows a significant reduction in reflection losses. It thus allows an increase in the efficiency of the cells. A modeling of the refractive indices and the thicknesses of an optimal antireflection coating has been proposed. Thus, the average reflective losses can be reduced to less than 8% and less than 2.4% in a large wavelength range respectively for a single-layer and double-layer anti-reflective coating types. However, the difficulty of finding these model materials (materials with the same refractive index) led us to introduce two notions: the refractive index difference and the thickness difference. These two notions allowed us to compare the reflectivity of the antireflection layer in silicon surface. Thus, the lower the refractive index difference is, the more the material resembles to the ideal material (in refractive index), and thus its reflective losses are minimal. SiNx and SiO2/TiO2 antireflection layers, in the wavelength range between 400 and 1100 nm, have reduced the average reflectivity losses to less than 9% and 2.3% respectively.展开更多
In recent years, photovoltaic (PV) modules are widely used in many applications around the world. However, this renewable energy is plagued by dust, airborne particles, humidity<span style="font-family:Verdana...In recent years, photovoltaic (PV) modules are widely used in many applications around the world. However, this renewable energy is plagued by dust, airborne particles, humidity<span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> and high ambient temperatures. This paper studies the effect of dust soiling on silicon-based photovoltaic panel performance in a mini-solar power plant located in Dakar (Senegal, 14<span style="white-space:nowrap;">°</span>42'N latitude, 17<span style="white-space:nowrap;">°</span>28'W longitude). Results of the current</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">voltage (I - V) characteristics of photovoltaic panels tested under real conditions. We modeled a silicon-based PV cell in a dusty environment as a stack of thin layers of dust, glass and silicon. </span><span style="font-family:Verdana;">The </span><span style="font-family:;" "=""><span style="font-family:Verdana;">silicon layer is modeled as a P-N junction. The study performed under standard laboratory conditions with input data of irradiation at 1000 W/m</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;">, cell temperature at 25<span style="white-space:nowrap;">°</span>C and solar spectrum with Air Mass (AM) at 1.5 for the monocrystalline silicon PV cell (m-Si). The analysis with an ellipsometer of dust samples collected on photovoltaic panels allowed to obtain the refraction indices (real and imaginary) of these particles which will complete the input parameters of the model. Results show that for a photon flux arriving on dust layer of 70 μm (corresponding to dust deposit of 3.3 g/m</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;">) deposited on silicon-based PV cell</span></span><span style="font-family:Verdana;">s</span><span style="font-family:Verdana;">, short circuit current decreases from 54 mA (for a clean cell) to 26 mA. Also, conversion efficiency decreases by 50% compared </span><span style="font-family:Verdana;">to </span><span style="font-family:Verdana;">clean cell and the cell fill factor decreases by 76% - 50% compared to reference PV cell.</span>展开更多
Most manufacturers of solar modules guarantee the minimum performance of their modules for 20 to 25 years, and 30-year warranties have been introduced. The warranty typically guarantees that the modules will perform t...Most manufacturers of solar modules guarantee the minimum performance of their modules for 20 to 25 years, and 30-year warranties have been introduced. The warranty typically guarantees that the modules will perform to at least 90% capacity in the first 10 years and to at least 80% in the following 10 - 15 years. Early degradation resulting from design flaws, materials or processing issues is often apparent from startup to the first few years in service. Importantly, many module failures and performance losses are the result of gradual accumulated damage resulting from long-term outdoor exposure in harsh environments, referred. Many of these processes occur on relatively long time scales and the various degradation processes may be chemical, electrical, thermal or mechanical in nature. These are either initiated or accelerated by the combined stresses of the service environment, in particular solar radiation, temperature and moisture, and other stresses such as salt air, wind and snow. Accelerated Life Testing (ALT) test methodology is normally predicated on first being able to reproduce a specific degradation or failure mode without altering it (correlation);and, second, to produce that result in less than real-time acceleration. Degradation and failure may result when an applied stress exceeds material or product strength. This may be a one-time catastrophic event, the result of cyclic fatigue, or a gradual decline in requisite properties due to ageing mechanisms. Engineers in the manufacturing industries have used accelerated test (AT) experiments for many decades. The purpose of AT experiments is to acquire reliability information quickly. Test units of a material, component, subsystem or entire systems are subjected to higher-than-usual levels of one or more accelerating variables such as temperature or stress. Then the AT results are used to predict life of the units at use conditions. The extrapolation is typically justified (correctly or incorrectly) on the basis of physically motivated models or a combination of empirical model fitting with a sufficient amount of previous experience in testing similar units. The need to extrapolate in both time and the accelerating variables generally necessitates the use of fully parametric models. Statisticians have made important contributions in the development of appropriate stochastic models for AT data [typically a distribution for the response and regression relationships between the parameters of this distribution and the accelerating variable(s)], statistical methods for AT planning (choice of accelerating variable levels and allocation of available test units to those levels) and methods of estimation of suitable reliability metrics. This paper provides a review of many of the AT models that have been used successfully in this area.展开更多
On Mauritania’s northern coast, wind and solar resources are abundant and must be used effectively. These resources have the potential to completely or partially replace the existing or projected diesel generators. T...On Mauritania’s northern coast, wind and solar resources are abundant and must be used effectively. These resources have the potential to completely or partially replace the existing or projected diesel generators. The main objective of this case study is to study the possibility of using a hybrid system (HS) of the type (diesel, wind and storage). The most important part of this case study intended for this area will be to add the solar in a first phase and then the incorporation of an interconnection with the nearby network in a second phase. This interconnection will be secured by mean of medium voltage lines of 33 kV, where the nearest point is located 35 km away. Indeed, the study of the optimization model is carried out through Homer, which was developed by National Renewable Energy Laboratory [NREL]. Thus, it should be noted that the HS is analyzed on the basis of costs ($/kW) and price ($/kWh) and greenhouse gas emissions. Therefore, in order to achieve these techno-economic optimization objectives, this paper introduces a sensitivity analysis that has been proposed to determine the effect of costs on each HS configuration. In the end, HSs are needed for maximum use of renewable resources at the studied site for an uninterrupted power supply.展开更多
The catalytic dehydrocyclization of n-hexane was studied here for the first time using a number of compounds based on H3PMo12O40. The described catalysts were prepared by either replacing the acidic proton with counte...The catalytic dehydrocyclization of n-hexane was studied here for the first time using a number of compounds based on H3PMo12O40. The described catalysts were prepared by either replacing the acidic proton with counter-ions such as ammonium or transition metal cations (NH4+, Fe3+, K+), or by replacing Mo6+ with (Ni3+, Co3+, Mn3+) in the polyoxometalate framework, as reported earlier. For comparison purposes, the known (TBA)7PW11O39 catalyst system was used. All reactions were conducted at different temperatures in the range 200 - 450. The Keggin structure of these heteropolycompounds was ascertained by XRD, UV and IR measurements. 31P NMR measurements and thermal behaviour of the prepared catalysts were also studied. These modified polyoxometalates exhibited heterogeneous superacidic catalytic activities in dehydrocyclization of n-hexane into benzene, cyclohexane, cyclohexene and cyclohexadiene. The catalysts obtained by substituting the acidic proton or coordination atom exhibited higher selectivity and stability than the parent compound H3PMo12O40. Catalytic activity and selectivity were heavily dependent on the composition of the catalyst and on the reaction conditions. At higher temperatures, the catalyst exhibited higher conversion efficiency at the expense of selectivity. Using higher temperatures (>400) in the presence of hydrogen carrier gas, selectivity towards dehydrocyclization ceased and methane dominated. To explain the results, a plausible mechanism is presented, based on super-acidic nature of the catalyst systems.展开更多
The use of renewable energy is growing significantly in the world. In front of the growing demand for electric energy, essentially for the needs of remote, isolated and mountainous regions, photovoltaic systems, espec...The use of renewable energy is growing significantly in the world. In front of the growing demand for electric energy, essentially for the needs of remote, isolated and mountainous regions, photovoltaic systems, especially water pumping systems, are beginning to emerge in large applications. In this sense, the proposed study deals with the problem of the water level regulation in the photovoltaic pumping system. It is in this context that the interest in this paper is dictated by the need to use an existing energy source on the site. Still in this light, it is important to note that, often, the calculation of the size of the GPV that feeds the pumping system and the pump involves a certain degree of uncertainty, mainly due to two main reasons: the first is related to randomness of solar radiation which is often little known and the second is related to the difficulty to estimate the water needs. This is why, on the one hand, the realization of such a system has made it possible to show the possibility of determining the projected quantity for water storage. Similarly, it has shown that the prediction of this quantity of water can be calculated by a simple analytical method based on numerical computation. Thus, it was also shown for this pumping system, thanks to graphical analysis methods, developing autonomy, reliability and good performance. In this sense, this experience opens the door for a practical and economical solution to the problem of lack of water, especially in our regions. Measurements made on the studied system prove that the designed approach improves the efficiency. Finally, it is also expected to draw further conclusions for the operation of these systems in similar sites.展开更多
文摘Depositing an antireflection coating on the front surface of solar cells allows a significant reduction in reflection losses. It thus allows an increase in the efficiency of the cells. A modeling of the refractive indices and the thicknesses of an optimal antireflection coating has been proposed. Thus, the average reflective losses can be reduced to less than 8% and less than 2.4% in a large wavelength range respectively for a single-layer and double-layer anti-reflective coating types. However, the difficulty of finding these model materials (materials with the same refractive index) led us to introduce two notions: the refractive index difference and the thickness difference. These two notions allowed us to compare the reflectivity of the antireflection layer in silicon surface. Thus, the lower the refractive index difference is, the more the material resembles to the ideal material (in refractive index), and thus its reflective losses are minimal. SiNx and SiO2/TiO2 antireflection layers, in the wavelength range between 400 and 1100 nm, have reduced the average reflectivity losses to less than 9% and 2.3% respectively.
文摘In recent years, photovoltaic (PV) modules are widely used in many applications around the world. However, this renewable energy is plagued by dust, airborne particles, humidity<span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> and high ambient temperatures. This paper studies the effect of dust soiling on silicon-based photovoltaic panel performance in a mini-solar power plant located in Dakar (Senegal, 14<span style="white-space:nowrap;">°</span>42'N latitude, 17<span style="white-space:nowrap;">°</span>28'W longitude). Results of the current</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">voltage (I - V) characteristics of photovoltaic panels tested under real conditions. We modeled a silicon-based PV cell in a dusty environment as a stack of thin layers of dust, glass and silicon. </span><span style="font-family:Verdana;">The </span><span style="font-family:;" "=""><span style="font-family:Verdana;">silicon layer is modeled as a P-N junction. The study performed under standard laboratory conditions with input data of irradiation at 1000 W/m</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;">, cell temperature at 25<span style="white-space:nowrap;">°</span>C and solar spectrum with Air Mass (AM) at 1.5 for the monocrystalline silicon PV cell (m-Si). The analysis with an ellipsometer of dust samples collected on photovoltaic panels allowed to obtain the refraction indices (real and imaginary) of these particles which will complete the input parameters of the model. Results show that for a photon flux arriving on dust layer of 70 μm (corresponding to dust deposit of 3.3 g/m</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;">) deposited on silicon-based PV cell</span></span><span style="font-family:Verdana;">s</span><span style="font-family:Verdana;">, short circuit current decreases from 54 mA (for a clean cell) to 26 mA. Also, conversion efficiency decreases by 50% compared </span><span style="font-family:Verdana;">to </span><span style="font-family:Verdana;">clean cell and the cell fill factor decreases by 76% - 50% compared to reference PV cell.</span>
文摘Most manufacturers of solar modules guarantee the minimum performance of their modules for 20 to 25 years, and 30-year warranties have been introduced. The warranty typically guarantees that the modules will perform to at least 90% capacity in the first 10 years and to at least 80% in the following 10 - 15 years. Early degradation resulting from design flaws, materials or processing issues is often apparent from startup to the first few years in service. Importantly, many module failures and performance losses are the result of gradual accumulated damage resulting from long-term outdoor exposure in harsh environments, referred. Many of these processes occur on relatively long time scales and the various degradation processes may be chemical, electrical, thermal or mechanical in nature. These are either initiated or accelerated by the combined stresses of the service environment, in particular solar radiation, temperature and moisture, and other stresses such as salt air, wind and snow. Accelerated Life Testing (ALT) test methodology is normally predicated on first being able to reproduce a specific degradation or failure mode without altering it (correlation);and, second, to produce that result in less than real-time acceleration. Degradation and failure may result when an applied stress exceeds material or product strength. This may be a one-time catastrophic event, the result of cyclic fatigue, or a gradual decline in requisite properties due to ageing mechanisms. Engineers in the manufacturing industries have used accelerated test (AT) experiments for many decades. The purpose of AT experiments is to acquire reliability information quickly. Test units of a material, component, subsystem or entire systems are subjected to higher-than-usual levels of one or more accelerating variables such as temperature or stress. Then the AT results are used to predict life of the units at use conditions. The extrapolation is typically justified (correctly or incorrectly) on the basis of physically motivated models or a combination of empirical model fitting with a sufficient amount of previous experience in testing similar units. The need to extrapolate in both time and the accelerating variables generally necessitates the use of fully parametric models. Statisticians have made important contributions in the development of appropriate stochastic models for AT data [typically a distribution for the response and regression relationships between the parameters of this distribution and the accelerating variable(s)], statistical methods for AT planning (choice of accelerating variable levels and allocation of available test units to those levels) and methods of estimation of suitable reliability metrics. This paper provides a review of many of the AT models that have been used successfully in this area.
文摘On Mauritania’s northern coast, wind and solar resources are abundant and must be used effectively. These resources have the potential to completely or partially replace the existing or projected diesel generators. The main objective of this case study is to study the possibility of using a hybrid system (HS) of the type (diesel, wind and storage). The most important part of this case study intended for this area will be to add the solar in a first phase and then the incorporation of an interconnection with the nearby network in a second phase. This interconnection will be secured by mean of medium voltage lines of 33 kV, where the nearest point is located 35 km away. Indeed, the study of the optimization model is carried out through Homer, which was developed by National Renewable Energy Laboratory [NREL]. Thus, it should be noted that the HS is analyzed on the basis of costs ($/kW) and price ($/kWh) and greenhouse gas emissions. Therefore, in order to achieve these techno-economic optimization objectives, this paper introduces a sensitivity analysis that has been proposed to determine the effect of costs on each HS configuration. In the end, HSs are needed for maximum use of renewable resources at the studied site for an uninterrupted power supply.
文摘The catalytic dehydrocyclization of n-hexane was studied here for the first time using a number of compounds based on H3PMo12O40. The described catalysts were prepared by either replacing the acidic proton with counter-ions such as ammonium or transition metal cations (NH4+, Fe3+, K+), or by replacing Mo6+ with (Ni3+, Co3+, Mn3+) in the polyoxometalate framework, as reported earlier. For comparison purposes, the known (TBA)7PW11O39 catalyst system was used. All reactions were conducted at different temperatures in the range 200 - 450. The Keggin structure of these heteropolycompounds was ascertained by XRD, UV and IR measurements. 31P NMR measurements and thermal behaviour of the prepared catalysts were also studied. These modified polyoxometalates exhibited heterogeneous superacidic catalytic activities in dehydrocyclization of n-hexane into benzene, cyclohexane, cyclohexene and cyclohexadiene. The catalysts obtained by substituting the acidic proton or coordination atom exhibited higher selectivity and stability than the parent compound H3PMo12O40. Catalytic activity and selectivity were heavily dependent on the composition of the catalyst and on the reaction conditions. At higher temperatures, the catalyst exhibited higher conversion efficiency at the expense of selectivity. Using higher temperatures (>400) in the presence of hydrogen carrier gas, selectivity towards dehydrocyclization ceased and methane dominated. To explain the results, a plausible mechanism is presented, based on super-acidic nature of the catalyst systems.
文摘The use of renewable energy is growing significantly in the world. In front of the growing demand for electric energy, essentially for the needs of remote, isolated and mountainous regions, photovoltaic systems, especially water pumping systems, are beginning to emerge in large applications. In this sense, the proposed study deals with the problem of the water level regulation in the photovoltaic pumping system. It is in this context that the interest in this paper is dictated by the need to use an existing energy source on the site. Still in this light, it is important to note that, often, the calculation of the size of the GPV that feeds the pumping system and the pump involves a certain degree of uncertainty, mainly due to two main reasons: the first is related to randomness of solar radiation which is often little known and the second is related to the difficulty to estimate the water needs. This is why, on the one hand, the realization of such a system has made it possible to show the possibility of determining the projected quantity for water storage. Similarly, it has shown that the prediction of this quantity of water can be calculated by a simple analytical method based on numerical computation. Thus, it was also shown for this pumping system, thanks to graphical analysis methods, developing autonomy, reliability and good performance. In this sense, this experience opens the door for a practical and economical solution to the problem of lack of water, especially in our regions. Measurements made on the studied system prove that the designed approach improves the efficiency. Finally, it is also expected to draw further conclusions for the operation of these systems in similar sites.
