The risk of power loss in crystalline silicon based photovoltaic modules due to micro-cracks

Micro-cracks in wafer based silicon solar cell modules are nowadays identified by a human observer with the electroluminescence (EL) method. However, the essential question of how the micro-cracks affect the PV module performance has yet to be answered. We experimentally analyze the direct impact of micro-cracks on the module power and the consequences after artificial aging. We show that the immediate effect of micro-cracks on the module power is small, whereas the presence of micro-cracks is potentially crucial for the performance of the module after artificial ageing. This confirms the necessity to develop the means of quantifying the risk of power loss in PV modules with cracked solar cells in their lifetime, in order to enable manufacturers to discard defective modules with high risk of failure while keeping modules with uncritical micro-cracks. As a first step towards risk estimation we develop an upper bound for the potential power loss of PV modules due to micro-cracks in the solar cells. This is done by simulating the impact of inactive solar cell fragments on the power of a common PV module type and PV array. We show that the largest inactive cell area of a double string protected by a bypass diode is most relevant for the power loss of the PV module. A solar cell with micro-cracks, which separate a part of less than 8% of the cell area, results in no power loss in a PV module or a PV module array for all practical cases. In between approximately 12 and 50% of inactive area of a single cell in the PV module the power loss increases nearly linearly from zero to the power of one double string.     

Thermal aspects of c-Si photovoltaic module energy rating

Standard test conditions (STC) of photovoltaic (PV) modules are not representative of field conditions; PV module operating temperature often rises up to 30 °C above STC temperature (25 °C), causing a performance drop of 0.5%/°C for crystalline silicium modules. Normal operating cell temperature (NOCT) provides better estimates of PV module temperature rise. It has nevertheless to be measured; moreover NOCT wind speed conditions do not always fit field conditions. The purpose of this work is to model average PV module temperature at given irradiance levels as a function of meteorological parameters and PV module implementation. Thus, no empirical knowledge of PV module thermal behaviour is required for energy rating basing on irradiation distributions over irradiance levels.     

An approach to the selection of the inverter for architecturally integrated photovoltaic grid-connected systems

An optimal compromise between energy efficiency and aesthetics for PV in the built environment sometimes requires to divide the PV field into sections with different orientation and tile each, which are connected to a single inverter. From the experience and data collected through a year of monitoring the 2-Kwp photovoltaic grid-connected system installed on the flat roof of the High Technical School of the University of Jaen, some charts are presented to help architects, engineers and installers to select the most suitable inverter for two specific architectural solutions addressed to integrating PV in buildings. However, charts for other sites, climates and architectural designs can be easily obtained.     

Simple, fast and accurate two-diode model for photovoltaic modules

This paper proposes an improved modeling approach for the two-diode model of photovoltaic (PV) module. The main contribution of this work is the simplification of the current equation, in which only four parameters are required, compared to six or more in the previously developed two-diode models. Furthermore the values of the series and parallel resistances are computed using a simple and fast iterative method. To validate the accuracy of the proposed model, six PV modules of different types (multi-crystalline, mono-crystalline and thin-film) from various manufacturers are tested. The performance of the model is evaluated against the popular single diode models. It is found that the proposed model is superior when subjected to irradiance and temperature variations. In particular the model matches very accurately for all important points of the I-V curves, i.e. the peak power, short-circuit current and open circuit voltage. The modeling method is useful for PV power converter designers and circuit simulator developers who require simple, fast yet accurate model for the PV module.     

On the temperature dependence of photovoltaic module electrical performance: A review of efficiency/power correlations

A brief discussion is presented regarding the operating temperature of one-sun commercial grade silicon-based solar cells/modules and its effect upon the electrical performance of photovoltaic installations. Suitable tabulations are given for most of the known algebraic forms which express the temperature dependence of solar electrical efficiency and, equivalently, solar power. Finally, the thermal aspects of the major power/energy rating methods are briefly discussed.     

Price development of photovoltaic modules,inverters, and systems in the Netherlands in 2012

Since 2010 the Dutch photovoltaic (PV) market has been growing fast, with around doubling of installed capacity in 2011 and 2012. Four quarterly inventories have been made in 2012 for modules, inverters, and systems that are presently available for purchase in the Netherlands. We have found that the average selling price of modules, inverters, and systems decreased with 44.3, 14, and 7.3–10.2%, respectively: average selling prices are 1.26 €/Wp, 0.41 €/Wp, and 1.46 €/Wp for modules, inverters, and systems on tilted roofs, respectively, at the end of 2012. Average installation costs amount to 0.43 €/Wp. Using an energy yield of 900 kWh/kWp, 25 years system lifetime, 6% discount rate, and 1% operation and maintenance (O&M) cost, a levelized cost of electricity (LCOE) is calculated for a 2.5 kWp system to be 0.194 €/kWh for a system price of 1.98 €/Wp (including installation). Grid parity conditions are apparent, with electricity retail prices of around 0.23 €/kWh.     

Estimation of photovoltaic module yearly temperature and performance based on Nominal Operation Cell Temperature calculations

The simulation of module temperature from Nominal Operation Cell Temperature (NOCT) is widely used to easily estimate module performance along the year. In this context, it is important to determine this parameter in a reliable way, as it is used to compare the performance of different module designs and can influence system predictions. At present there are several international standards that indicate the method to calculate NOCT in crystalline and thin-film terrestrial photovoltaic modules. This work presents the results obtained when applying these standards to different types of PV modules, including glass–glass and glass–tedlar structures, crystalline and thin-film technologies, and some special module designs for building integration applications. NOCT values so calculated have been used to estimate the yearly module temperature and performance for different orientations and tilted angles, analysing temperature influence in these estimations. Possible error sources that could bring about erroneous values of NOCT are also analysed.     

Equilibrium thermal characteristics of a building integrated photovoltaic tiled roof

Photovoltaic (PV) modules attain high temperatures when exposed to a combination of high radiation levels and elevated ambient temperatures. The temperature rise can be particularly problematic for fully building integrated PV (BIPV) roof tile systems if back ventilation is restricted. PV laminates could suffer yield degradation and accelerated aging in these conditions. This paper presents a laboratory based experimental investigation undertaken to determine the potential for high temperature operation in such a BIPV installation. This is achieved by ascertaining the dependence of the PV roof tile temperature on incident radiation and ambient temperature. A theory based correction was developed to account for the unrealistic sky temperature of the solar simulator used in the experiments. The particular PV roof tiles used are warranted up to an operational temperature of 85 °C, anything above this temperature will void the warranty because of potential damage to the integrity of the encapsulation. As a guide for installers, a map of southern Europe has been generated indicating locations where excessive module temperatures might be expected and thus where installation is inadvisable.     

The effect of tilt angle, air pollution on performance of photovoltaic systems in Tehran

The tilt angle influences the amount of energy collected by a photovoltaic module. However, representations of these effects on the energy yield and the performance of the PV system are commonly based on the theoretical calculations, whereas there is a lack of experimental investigations. To verify the calculations, an experimental setup has been installed at the Department of Electrical and Computer Engineering, University of Tehran. Some results of this test station, from March, 1999 to January, 2000 are represented in this paper.     

Determining optimum tilt angles and orientations of photovoltaic panels in Sanliurfa, Turkey

The performance of a photovoltaic (PV) panel is affected by its orientation and its tilt angle with the horizontal plane. This is because both of these parameters change the amount of solar energy received by the surface of the PV panel. A mathematical model was used to estimate the total solar radiation on the tilted PV surface, and to determine optimum tilt angles for a PV panel installed in Sanliurfa, Turkey. The optimum tilt angles were determined by searching for the values of angles for which the total radiation on the PV surface was maximum for the period studied. The study also investigated the effect of two-axis solar tracking on energy gain compared to a fixed PV panel. This study determined that the monthly optimum tilt angle for a PV panel changes throughout the year with its minimum value as 13° in June and maximum value as 61° in December. The results showed that the gains in the amount of solar radiation throughout the year received by the PV panel mounted at monthly optimum tilt angles with respect to seasonal optimum angles and tilt angel equal to latitude were 1.1% and 3.9%, respectively. Furthermore, daily average of 29.3% gain in total solar radiation results in an daily average of 34.6% gain in generated power with two-axis solar tracking compared to a south facing PV panel fixed at 14° tilt angle on a particular day in July in Sanliurfa, Turkey.     

Estimation of the maximum power and normal operating power of a photovoltaic module by neural networks

This paper presents an application of the neural networks for identification of the maximum power (MP) and the normal operating power (NOP) of a photovoltaic (PV) module. Two neural networks are developed; the first is the maximum power neural network (MPNN) and the second is the normal operating power neural network (NOPNN). The two neural networks receive the solar radiation and the PV module surface temperature as inputs, and estimate the MP and the NOP of a PV module as outputs. The training process for the two neural networks used a series of input/output data pairs. The training inputs are the solar radiation and the PV module surface temperature, while the outputs are the PV module MP for the MPNN and the PV module NOP for the NOPNN. The results showed that, the proposed neural networks introduced a good accurate prediction for the PV module MP and NOP compared with the measured values.     

Analysis of thermal and electrical performance of semi-transparent photovoltaic (PV) module

Building-integrated PhotoVoltaic (BIPV) is one of the most fascinating PV application technologies these days. To apply PV modules in buildings, various factors should be considered, such as the installation angle and orientation of PV module, shading, and temperature. The temperature of PV modules that are attached to building surfaces especially is one of the most important factors, as it affects both the electrical efficiency of a PV module and the energy load in a building. This study investigates the electrical and thermal performance of a semi-transparent PV module that was designed as a glazing component. The study evaluates the effects of the PV module's thermal characteristics on its electrical generation performance. The experiment was performed under both Standard Test Condition (STC) and outdoor conditions. The results showed that the power decreased about 0.48% (in STC with the exception of the temperature condition) and 0.52%(in outdoor conditions, under 500 W/m²) per the 1 °C increase of the PV module temperature. It was also found that the property of the glass used for the module affected the PV module temperature followed by its electrical performance.     

Carbon tax for subsidizing photovoltaic power generation systems and its effect on carbon dioxide emissions

This paper proposes a new framework for evaluating quantitatively the effect of carbon taxation. In this study, the tax revenues are supposed to be used only as a subsidy for installing Photovoltaic Power Generation (PV) Systems on houses. The evaluation model developed in this study comprises three sequential modules. The first module is for estimating the demand for the PV system under the subsidy and the carbon taxation policy, the second is the module for life-cycle inventory analysis based on the modified Input–Output table, and the third is the module for calculating the amount of carbon-dioxide emissions from the final-demand vector of the Input–Output table. Major findings of this study are as follows: (1) The amount of CO₂-emission reduction increases by advertising the PV system with subsidy policy even under the same tax-rate. (2) The CO₂-payback time of the PV system reduces by half if the GDP is assumed not to change after the introduction of carbon taxation.     

A multi-operational ventilated photovoltaic and solar air collector: application, simulation and initial monitoring feedback

This paper concerns the application of the first European example of a roof mounted, multi-operational ventilated photovoltaic and solar air collector, development of a detailed simulation methodology for such a system, and gives a brief outline of monitored findings after six months of operation. The aim for this simulation development was to provide a method that can aid future system design and optimize performance in line with energy requirements for specific buildings. This work is discussed in relation to two key investigations into the simulation of building integrated hybrid PV thermal collectors.     

Spatial and orientational distribution of cracks in crystalline photovoltaic modules generated by mechanical load tests

Cracks in crystalline silicon solar cells influence the photovoltaic (PV) module power output in accelerated aging tests. A detailed insight into the formation of cracks offers the potential to optimize the PV module design in order to reduce the risk of power degradation in its lifetime. In this paper we present a statistical analysis on the crack formation in 27 crystalline silicon PV modules caused by a standard mechanical load test according to IEC 61215 10.16. The criticality of cracks depends strongly on the crack orientation, therefore we analyze both the spatial distribution of cracks and its dependence on the orientation of the cracks in the tested PV modules. We find that 50% of the damaged cells are cracked parallel to the busbars, which is a crack orientation with high potential impact on the power output of the PV module. A simplified numerical analysis is used to give an explanation for the statistical data and we propose a strategy for the reduction of the crack criticality.     

并网光伏发电项目的LCOE分析

围绕并网光伏发电系统的度电成本/平准化电力成本(LCOE)水平进行了分析讨论。针对LCOE的评估依据和测算方法,提出一种适用于我国光伏发电项目的 LCOE评估模型。利用该模型对影响LCOE的几个典型因素进行了敏感性分析;测算了我国光伏发电项目的 LCOE水平;预测了光伏发电项目的 LCOE发展。     

贵港供电局光伏建筑一体化项目优化设计研究

对光伏建筑一体化发展应用及需求进行分析,结合贵港供电局办公大楼现有条件进行深入评估,选取最优光伏发电设计方案,充分利用太阳能光电转换技术,解决建筑物的照明、办公等用能需求,为开展节能减排做出带头示范作用,引导全社会共同创造一个科学用电、节能减排、绿色环保的社会环境。     

Estimation of equivalent circuit parameters of PV module and its application to optimal operation of PV system

A method to estimate the equivalent circuit parameters of a PV (photovoltaic) module is presented. The parameters are calculated using a least-squares fitting of the equivalent model current–voltage characteristic with the measured one. For applications of the equivalent circuit model parameters, a quantitative diagnostic method of the PV modules by evaluating the parameters is introduced and examined by simulation. A new maximum peak power tracking (MPPT) method using the model parameters, a solar insolation, and a cell temperature is also shown. Its performance is compared with other MPPT control algorithms by simulations. The performance of the proposed method was better than other MPPT methods.     

光伏系统蓄电池组不均衡性的故障分析及排除

蓄电池组是光伏系统的重要设备,其故障往往导致光伏系统不能正常运行。光伏系统蓄电池组的故障多数因其不均衡所致。文章分析了蓄电池组因不均衡性导致的故障,提出了故障预防措施和故障排除方法。     

Photoreduction of Carbon Dioxide to Formic Acid,Formaldehyde, Methanol,Acetaldehyde and Ethanol Using Aqueous Suspensions of Strontium Titanate with Transition Metal Additives

The photoassisted reduction or aqueous carbon dioxide was carried out in the presence of suspensions of powdered strontium titanate, surface treated with various transition metal oxide additives, using either high-pressure mercury lamps or sunlight as the energy source. The organic products observed included formic acid, formaldehyde, methanol, acetaldehyde and ethanol.