Flexible packages provide several advantages of lightweight, ease of storage, and deployment, and possibility of using roll-to-roll coating in the manufacture. Of the flexible cells that can be used in flexible packages, organic solar cells are very vulnerable to degradation under exposure to humidity, oxygen and other atmospheric gases, and CIGS and CdTe are somewhat vulnerable. CIGS cell vulnerability to moisture and other atmospheric gases is being reduced by chemical treatment. Multiple pairs of organic/inorganic layers termed dyad's that are being developed for providing protection to considerably more vulnerable organic light emitting diodes are being tested successfully with CIGS flexible modules. Multiple layers of extremely dense coatings prepared by atomic layer deposition that are being developed for providing protection to organic light emitting diodes are also being tried with CIGS cells. It would be essential to reduce the overall cost of individual or combined schemes for achieving economic viability.

Concentrating photovoltaic (CPV) technology has recently gained interest based on their expected low levelized cost of electricity, high efficiency, and scalability. Many CPV systems use Fresnel lenses made of poly(methyl methacrylate) (PMMA) to obtain a high optical flux density. The optical and mechanical durability of such components, however, are not well established relative to the desired service life of 30 years. Specific reliability issues may include: reduced optical transmittance, discoloration, hazing, surface erosion, embrittlement, crack growth, physical aging, shape setting (warpage), and soiling. The initial results for contemporary lens- and material-specimens aged cumulatively to 6 months are presented. The study here uses an environmental chamber equipped with a xenon-arc lamp to age specimens at least 8x the nominal field rate. A broad range in the affected characteristics (including optical transmittance, yellowness index, mass loss, and contact angle) has been observed to date, depending on the formulation of PMMA used. The most affected specimens are further examined in terms of their visual appearance, surface roughness (examined via atomic force microscopy), and molecular structure (via Fourier transform infrared spectroscopy).

Complex systems like modules in concentrating photovoltaics (CPV) are designed in a systems approach. The better the components are concerted, the better the performance goals of the system can be fulfilled. Optics are central to the CPV module's reliability and efficiency. Fresnel lens optics provide the module cover, and protect the module against the environment. Fresnel lenses on glass can provide the module's structural integrity. The secondary optical element, used to increase the collection of light, the acceptance half-angle, and the uniformity on the cell, may provide encapsulation for the receiver. This encapsulation function may be provided by some optical designs in sol gel, or silicone. Both materials are unknown in their longevity in this application. We present optical designs fulfilling structural or protective functions, discuss the optical penalties to be paid, and the innovative materials and manufacturing technologies to be tested.

Building applied photovoltaics (BAPV) is a major application sector for photovoltaics (PV). Due to the negative temperature coefficient of power output, the performance of a PV module decreases as the temperature of the module increases. In hot climatic conditions like Arizona, the BAPV module temperature can reach as high as 90-95°C during peak summer. Considering a typical 0.5%/°C power drop for crystalline silicon modules, about 30% performance drop would be expected during peak summer because of the difference between rated temperature (25°C) and operating temperature (~90°C) of the modules. In order to predict the performance of PV modules, it becomes necessary to predict the module temperature. The module temperature is dictated by air gap between module and roof surface, irradiance, ambient temperature, wind speed, and wind direction. Based on the temperature and weather data collected over a year in Arizona, a mathematical thermal model has been developed and presented in this paper to predict module temperature for five different air gaps (0, 1, 2, 3 and 4 inches) as well as modules with a thermally insulated (R30) back. The thermally insulated back is expected to serve as the worst case temperature a BAPV module could ever experience. This paper also provides key technical details on: the specially built simulated rooftop structure; mounting configuration of PV modules on the rooftop structure; LabVIEW program developed for data acquisition; and a data processing program for an easy data analysis.

Photovoltaic modules and systems lifetime and availability are difficult to determine and not really well-known. This information is an important data to insure the installation performance of such a system and to prepare its recycling. The aim of this article is to present a methodology for the availability and lifetime evaluation of a photovoltaic system using the Petri networks method. Each component - module, wires and inverter - is detailed in Petri networks and several laws are used in order to estimate the reliability. Several guides (FIDES, MIL-HDBK-217 ...) allow determining the reliability of electronic components using collections of data. For photovoltaic modules, accelerated life testing are carried out for the evaluation of the lifetime which is described by a Weibull distribution. Results obtained show that Petri networks are very useful to simulate lifetime thanks to its intrinsic modularity.

This paper is dealing with measuring the water ingress to PV-modules under different climatic conditions and simulating it over an expected lifetime of 20 years. Furthermore different kinds of back sheet / encapsulant combinations were considered. For this purpose an own developed high sensitive test device composed of a climate cabinet and a mass spectrometer was used to investigate the temperature dependent permeation and diffusion processes that takes place in the polymers. Furthermore the results - permeation and diffusion coefficient - were used to simulate the mass transport through the back sheet and inside the encapsulant materials. In a second part the amount of absorbed water was analysed by a gravimetric method. For this study encapsulant materials were exposed to different ambient climates to quantify the sorption isotherme. With these results - permeation / diffusion coefficient and absorbed water amount - the mass transport and water concentration were simulated over the lifetime of a PV-module under different climatic conditions. Additional the influence of various tight back sheets on water ingress will be shown.

Photovoltaic modules (PV modules) are supposed to have a lifetime of more than 20 years under various environmental conditions like temperature changes, mechanical loads, etc. Common outdoor exposure may influence efficiency and lifetime which necessitates assessment of PV module performance and detection of output deficits. For this purpose reliable and nondestructive testing methods are desirable. Commercially available PV modules were tested by different analysis methods. The PV module's electrical properties were investigated by thermography and electroluminescence measurements. The combination of these two techniques is well-suited to detect many cell and module defects. A crystalline module showed significant cell breakage after temperature cycle test. To observe the mechanisms of this specific defect type laminated test specimens on smaller scales were produced and analyzed over production process and during temperature cycles derived from the international standards IEC 61215 and IEC 61646. The defect study on small scales allows conclusions about the defect's influence on larger PV modules. Further methods capable for mechanical characterization like Laser Doppler vibrometry, surface geometry scan and digital image correlation are presented briefly. The combination of the methods mentioned above allows a very precise assessment of the mechanical and electrical capability which is essential for reliability and lifetime concepts.

The main object of this paper is to identify solar panel installation configurations to achieve optimum system performance irrespective of installation surface configurations. It is important to mention that the panel installation requirements are strictly dependent on the roof configurations, Northern and Southern hemispherical locations, and the latitudes of the installation locations. Panel installation schemes for flat roof, inclined roof, inverted V-shape roof and other roof configurations are briefly discussed. Potential tracking concepts, tracking algorithms, and controllers are identified.

Silicon solar cells suffer from defects such as microcracks and shunts that limit performance and reliability. We describe a new family of imaging techniques, including lock-in thermoreflectance and mechanoreflectance, which offer much higher spatial resolution and lower cost than current methods for inspection of solar cells. These techniques are based on advanced image processing algorithms for detection of very small variations in optical reflectance, using ordinary visible light CCD cameras. The image data can be merged with conventional techniques such as electroluminescence, in one camera system. Experimental results and comparison with conventional techniques for evaluation of solar cells are presented.

Systematic investigation of aging mechanisms of a glass-clear PVB film interface at the edge of thin film silicon photovoltaic modules has been performed. The modules under study were composed of a front superstrate laminated to a back glass. Different degradation mechanisms responsible for adhesive strengths loss between PVB film and superstrate are discussed. Glass-foil adhesive strength in compressive shear configuration using different glass compositions and module configurations is given. As accelerated aging stress of the modules, standard damp heat test conditions (85° C, 85% relative humidity) have been applied. A chemical analysis of the glass foil interface was performed and the correlation of those results to those coming from wet leakage measurements is also given.

The aim of these investigations was to determine the influence of the relevant load parameters temperature and humidity on the degradation behavior of selected polymeric PV encapsulation materials. A test program concerning three accelerated artificial ageing tests was set up and a comprehensive study of the selected candidate materials and its degradation behavior was done. To assess the long term performance and durability of materials, it was necessary not only to measure the deterioration of macroscopic physical properties, but also to gain information about degradation processes taking place at a molecular level. Therefore, the material properties and the aging behaviour were characterized by infrared spectroscopy, by UV/VIS spectroscopy, by differential scanning calorimetry, by dynamical mechanical analysis and by tensile tests. By IR spectroscopy no significant thermal oxidation was detected for all investigated materials. But UV/VIS spectroscopy showed a significant drop in solar transmittance and reflectance values. Yellowing was observed due to the formation of chromophoric degradation products. For all materials a significant decrease in ultimate mechanical properties due to chemical aging was measured. For both backsheet materials the changes in ultimate mechanical properties can be attributed nearly exclusiveley to the polyester layer. On the other hand, a stiffening of all materials due to physical aging was observed within the first 1000h of damp heat testing. For the backsheet laminates, delamination at the edges was observed. Generally, higher temperature levels during exposure induced faster rate of chemical and physical aging. High humidity levels showed to be less influential on polymer degradation than temperature.

PV modules have to have a service lifetime of more than 20 years. It is hard to follow suitable degradation indicators during service life testing with sufficient accuracy for reliable service life estimation. Often the polymeric encapsulation material, mostly ethylene vinyl acetate, shows degradation effects. The detection of small changes of the material in a non-destructive manner helps to follow the changes over time during indoor testing. PV modules with crystalline Si-cells of seven German manufacturers were analyzed after accelerated ageing tests with Raman spectroscopy. This technology allows non-destructive measurements of the encapsulation material through the glazing so that the degradation of the samples can be followed by measuring after different exposure times. Samples had been exposed to damp-heat conditions for up to 4000 h. The results show significant differences in the materials degradation above the edges and the center of the cell. With increasing exposure times, it becomes apparent that the degradation process starts near the edges of the cells and propagates towards the center, indicating the impact of diffusion processes.

Within the following work mechanical and thermo-mechanical studies on embedded solar cells were carried out. Temperature dependant material properties such as shear modulus and coefficient of thermal expansion of an EVA encapsulant were determined by dynamic mechanical analysis (DMA) and thermo mechanical analysis (TMA). Those parameters were integrated into various simulation models such as the lamination process starting from the curing temperature at 150 °C and thermo cycling. Parameter studies were carried out concerning the cell thickness to assess the thermo-mechanical behavior of the cell string and the stress distribution in the silicon. Within a second study the mechanical behavior of the laminate was investigated. As a result it is shown that the solar cells have a significant impact on the deflection of the laminate, whose behavior over a temperature range is dominated by the stiffness properties of the encapsulant. By means of a combination of global models and submodels it was possible to assess the stress distribution in the solar cells with particular interest in the interconnection region between the cells. The magnitude of the stress depends strongly on the stiffness of the encapsulant. Especially for thin cells the stress can increase critically.

Concentrating solar applications utilize direct normal irradiance (DNI) radiation, a measurement rarely available. The solar concentrator industry has begun to deploy numerous measurement stations to prospect for suitable system deployment sites. Rotating shadowband radiometers (RSR) using silicon photodiodes as detectors are typically deployed. This paper compares direct beam estimates from RSR to a total hemispherical measuring radiometer (SPN1) multiple fast thermopiles. These detectors simultaneously measure total and diffuse radiation from which DNI can be computed. Both the SPN1 and RSR-derived DNI are compared to DNI measured with thermopile pyrheliometers. Our comparison shows that the SPN1 radiometer DNI estimated uncertainty is somewhat greater than, and on the same order as, the RSR DNI estimates for DNI magnitudes useful to concentrator technologies.

When an Eppley Normal Incident Pyrheliometer is calibrated against an Eppley Hickey Frieden Absolute Cavity Radiometer, the instrument systematically deviates from the absolute cavity readings. The reason for this deviation is not understood. Comparisons are made between one pyrheliometer and an absolute cavity radiometer on selected clear days over a period of 8 months in Eugene, Oregon. The ratios of the readings from the two instruments are correlated against wind speed, pressure, temperature, relative humidity, beam intensity, and zenith angle to determine if any of these parameters statistically influence the calibration process. Wind speed, pressure, beam intensity, and air mass are shown to be statistically significant factors in determining the responsivity of the normal incident pyrheliometer. The results of these tests are evaluated and discussed. Use of air mass instead of zenith angle is proposed for calibration reports.

Temperature cycling tests are part of the IEC 61215 qualification testing of crystalline silicon (c-Si) PV modules for evaluating PV module degradation caused by the impact of thermo-mechanically induced stresses. The defined temperature gradient and the cycle time by far exceed the actual impact of natural weathering, however. As a contribution to comparisons between laboratory testing and natural weathering our work provides data from standard temperature cycling tests as defined in IEC 61215 and extended from 200 (standard) to 800 cycles. The results of these tests for seven commercial c-Si PV modules from various manufacturers are compared with results from identical module types exposed outdoors in different climates for a period of 3 years. Degradation effects are evaluated with respect to changes in output power, changes in insulation properties and with respect to interruptions in the electrical interconnection circuits such as cell interconnects. Temperature gradients obtained at the different exposure locations are used to model the thermo-mechanical stress arising from the mismatches of the thermal expansion coefficients of the employed materials.

The degradation in performance for eight photovoltaic (PV) modules stressed at high voltage (HV) is presented. Four types of modules—tandem-junction and triple-junction amorphous thin-film silicon, plus crystalline and polycrystalline silicon modules—were tested, with a pair of each biased at opposite polarities. They were deployed outdoors between 2001 and 2009 with their respective HV leakage currents through the module encapsulation continuously monitored with a data acquisition system, along with air temperature and relative humidity. For the first 5 years, all modules were biased continuously at fixed 600 VDC, day and night. In the last 2 years, the modules were step-bias stressed cyclically up and down in voltage between 10 and 600 VDC, in steps of tens to hundreds of volts. This allowed characterization of leakage current versus voltage under a large range of temperature and moisture conditions, facilitating determination of leakage paths. An analysis of the degradation is presented, along with integrated leakage charge. In HV operation: the bulk silicon modules degraded either insignificantly or at rates of 0.1%/yr higher than modules not biased at HV; for the thinfilm silicon modules, the added loss rates are insignificant for one type, or 0.2%/yr-0.6%/yr larger for the other type.

During the past 3 years crystalline PV modules fabricated by various German manufacturers have been exposed to outdoor conditions in four different climates: warm moderate climate (Cologne, Germany), tropical climate (Serpong, Indonesia), cold high mountain climate (Zugspitze, Germany) and arid conditions (Sede Boqer, Israel). Annual inspections and measurements examined the degradation of these modules with respect to electrical performance, mechanical condition and visible alterations. We give a detailed report of the results after 3 years of weathering, along with the outlook for an extension to new worldwide test locations and for the enhancement of measurement options for long-term characterizations.

Transient or hysteresis effects in polycrystalline thin film CdS/CdTe cells are a function of pre-measurement voltage bias and whether Cu is introduced as an intentional dopant during back contact fabrication. When Cu is added, the current-density (J) vs. voltage (V) measurements performed in a reverse-to-forward voltage direction will yield higher open-circuit voltage (V_oc), up to 10 mV, and smaller short-circuit current density (J_sc), by up to 2 mA/cm², relative to scanning voltage in a forward-to-reverse direction. The variation at the maximum power point, P_max, is however small. The resulting variation in FF can be as large as 3%. When Cu is not added, hysteresis in both V_oc and J_sc is negligible however Pmax hysteresis is considerably greater. This behavior corroborates observed changes in depletion width, W_d, derived from capacitance (C) vs voltage (V) scans. Measured values of W_d are always smaller in reverse-to-forward voltage scans, and conversely, larger in the forward-to-reverse voltage direction. Transient ion drift (TID) measurements performed on Cu-containing cells do not show ionic behavior suggesting that capacitance transients are more likely due to electronic capture-emission processes. J-V curve simulation using Pspice shows that increased transient capacitance during light-soak stress at 100 °C correlates with increased space-charge recombination. Voltagedependent collection however was not observed to increase with stress in these cells.

Due to the system voltage, solar modules in power plants have to withstand continuous high bias voltages between the absorber/conductive layers of the solar module and the grounded mounting structure. Mon et al.^{1, 2} showed in several publications during the 1980s that the charge transferred by this electrical field is leading to strong electrochemical degradation effects in the modules, both crystalline and thin-film. The bias voltage, especially for thin film modules, can cause transparent conductive oxide (TCO) corrosion via sodium diffusion through the glass together with the presence of water molecules in the TCO/glass interface.^{3, 4} Based on these previous works, we analyzed the accelerated degradation effects as well as the end of life conditions of different module technologies and module designs. By means of indoor climate chamber and outdoor experiments and based on a simple model we give an example of service life time in terms of electrochemical damage due to high bias voltages caused by the PV system voltage.

We observed a large variation in the damp heat (DH) durability of many of the unencapsulated CIGS devices fabricated at NREL. Some devices failed within the first few hours of DH exposure; others failed within a few hundred hours while some lasted for 1000 h. The initial degradation often showed a 50% decrease in efficiency in the first few hundred hours; The premature device failures often correspond to the degradation of the ZnO window layer, the peeling of molybdenum (Mo) from the soda-lime glass (SLG), or both. Repeated J-V measurements lead to significant damage of the contact pads, which provide additional path for moisture ingress. To better understand the onset of degradation and the cause of initial decrease in performance and to minimize the damage caused to the contact pads, we designed an encapsulation scheme to control the moisture ingress by laminating the CIGS devices with a combination of different backsheets having different water vapor transmission rates. The encapsulation provided external contacts which solved the damage caused to the pads. This approach facilitates a way to slow down DH-induced degradation of the CIGS device for a more detailed study.

This paper presents our recent observations on variations in properties and damp heat (DH)-induced degradation behavior for single-layer 2%Al-doped ZnO (AZO) and bilayer ZnO (BZO), which comprises 0.1-μm intrinsic ZnO (i-ZnO) and AZO, deposited on glass substrates using the same sputtering system and essentially identical deposition conditions. BZO films with 0.12-μm AZO have been used on the National Renewable Energy Laboratory's (NREL's) high-efficiency CuInGaSe₂ (CIGS) solar cells for years. For the as-deposited BZO films, the most apparent variations appeared in notable peak shift in transmittance and reflectance spectra and ZnO (002) peak intensity and peak position in X-ray diffraction. Location of substrates placed on the substrate holder platform contributed partly to the variations. For the DH-degraded AZO and BZO, earlier films became highly resistive, porous, and 10~20 X thicker and showed flattened transmittance spectra caused by a loss of free-carrier absorption. However, recent DH-exposed AZO and BZO films also became highly resistive but exhibited only small changes in transmittance spectra, while the columnar grain structure and film thickness remained nearly unchanged without porous features, but with granular particles formed on the surfaces that increased in size with lengthening DH exposure time.

PV modules were fabricated that incorporated various methods to increase the amount of light which is ultimately transmitted to the solar cell in order to improve energy yield. The techniques employed included diffuse scattering and reflection to minimize shading losses, as well as using structured glass to increase the probability of incident light capture. In the first technology, a laser is used to create a scattering pattern on the front-side glass of the module. This pattern directed light away from the bus bars and grid fingers, resulting in an increase in short circuit current (I_SC) of up to 3.3%. In the second technology, the bus wires were coated with a diffuse reflective coating. A part of the incident sunlight is reflected from this coating at such angles that internal reflection at the front surface of the front-side glass occurs. The light is reflected back to the active area of the solar cell and contributes to the generated photocurrent resulting in an average increase of 0.9% in I_SC. Finally, four different types of commercially available structured glass were investigated: grooves, pyramids, inverted pyramids, and a very lightly textured glass with only 5% increased surface area. Results showed an increase in I_SC of up to 3.2% for pyramid structures using normally incident light, with the effect increasing at higher angles of incidence. The results demonstrated the possibility of improving PV module energy yield by taking advantage of basic optical principles and straightforward processing methods.

Models to compute global horizontal irradiance (GHI) and direct normal irradiance (DNI) have been in development over the last three decades. These models can be classified as empirical or physical based on the approach. Empirical models relate ground-based observations with satellite measurements and use these relations to compute surface radiation. Physical models consider the physics behind the radiation received at the satellite and create retrievals to estimate surface radiation. While empirical methods have been traditionally used for computing surface radiation for the solar energy industry, the advent of faster computing has made operational physical models viable. The Global Solar Insolation Project (GSIP) is a physical model that computes DNI and GHI using the visible and infrared channel measurements from a weather satellite. GSIP uses a two-stage scheme that first retrieves cloud properties and uses those properties in a radiative transfer model to calculate GHI and DNI. Developed for polar orbiting satellites, GSIP has been adapted to NOAA's Geostationary Operation Environmental Satellite series and can run operationally at high spatial resolutions. This method holds the possibility of creating high quality datasets of GHI and DNI for use by the solar energy industry. We present an outline of the methodology and results from running the model as well as a validation study using ground-based instruments.

Recent technological advancements have made CCD spectrometers an increasingly suitable alternative to traditional monochromator-based instrumentation. The authors have developed instrumentation for the near instantaneous measurement of spectral global, direct, diffuse, reflected and southward-tilted irradiances. The system uses an AvaSpec2048TEC-2 - a dual channel thermo-electric-cooled fiber optic spectrometer from Avantes Inc. Each channel has a 2048-pixel linear array detector and the system achieves a spectral resolution of 0.0007 μm (FWHM) over the range 0.241-1.1 μm. The system also includes sensor heads, fiber optic cables and a multiplexer. Two types of sensor heads have been developed: a pyrheliometer configuration for direct beam, and a pyranometer configuration for global, diffuse, reflected and tilted measurements. Calibration uses a system of standard light sources. Cosine errors inherent to the spectralon diffusers have been characterized and corrections are applied to data from each sensor head. Accuracy of global irradiance is examined by comparing measurements against global photosynthetically active radiation (PAR) (0.395 - 0.695 μm) from Eppley red and green dome pyranometers. PAR daily totals (MJ/m²/day) and one minute averages (W/m²) are compared for 35 days in 2009 and daily totals are within ± 10% from June to October.

Relationship between sky cloud cover and solar radiation is presented in order to give information about solar radiation attitude varying with cloudiness, useful to optimize solar devices. Meteorological and solar data were recorded by Environmental Technical Physic Laboratories, at University of Rome Tor Vergata from April 15th 2009 to May 31th 2010. Those data were associated to hourly cloud observation recorded in the same site in order to calculate the ratio of global radiation at total cloud amount (N okta) G(N) to global radiation at cloudless sky G(0). The comparison between Kimura and Stephenson (1967) work, and Kasten and Czeplak (1980) parameterization were evaluated to characterize Tor Vergata's site. The model of clear sky condition proposed by Duffie and Beckman (1980), Spena (1996), and Duchon and O'Malley (1998) were used to determinate the transmission coefficient for global radiation at cloudless sky. Monthly and seasonal formulas has been developed using power and polynomial functions: correlation coefficients were shown for each trend. The correlation coefficient R²=0,9 showed that the best approximation is given by polynomial function. The results has indicated that the curve shape of G(N)/G(0) ratio has a maximum for N=3, almost half cloud cover condition, for Rome's latitude. The meaning for this behavior is that global radiation grow with scattered radiation growth. This correlation represent a new element useful to characterize Rome's site and to compare radiation trend with others of different latitudes site, and climate.

A preliminary assessment of perforated shadow band performance is given under partly cloudy and overcast conditions. Decomposition of daily 1-minute pyranometer data into diffuse and global values and subsequent reconstitution of the separate curves is achieved using an interpolating algorithm and a ray trace model of pyranometer exposure. Accuracy of the reconstituted curves relative to reference data is a strong function of clearness index, K_T, with a reduction in relative error for K_T < 0.3 and K_T > 0.7. As expected, algorithm performance degrades under highly variable conditions, when interpolation fails to capture the instantaneous fluctuations in irradiance associated with clouds drifting into the sun path.

Imec has developed a new technology to integrate and interconnect back-contact solar cells into modules, based on embedding cells in silicone on top of a glass substrate. This technology aims at an improved optical performance and reliability (through the use of silicones and low-temperature metallization). One of the additional advantages is that the technology is suitable for integrating very thin cells into modules: whereas standalone interconnection of such fragile thin cells, e.g. tabbing and stringing, would significantly lower the throughput yield due to breakage, the cells are better protected if they are embedded inside silicone. The paper will first elaborate on the process flow, the background and motivation, advantages, drawbacks and limitations, and technical aspects of the developed technology. Then it will present the results of the measurements on the performance of functional solar cells processed into modules using this technology, discussing losses and loss mechanisms. Then, the approach towards determining the reliability of the module will be presented, indicating how imec aims at building up an ageing model, and elaborating the results on the failure mode and effect analysis, modeling, characterization and reliability testing.

Several proposals for increasing the output of photovoltaic (PV) module were conducted. For instance, there are a few attempts for applying hydrophilic or hydrophobic coating on the glass surface of PV module to avoid dust accumulation and applying anti-reflective coating on it to increase transmittance of solar radiation. However it is rare to report the results of durability in consideration of severe outdoor exposure condition, such as desert area. We have developed a new power-enhancement coating being anti-reflective and self-cleaning properties with simple coating methods like spray or dip. The fundamental characteristics of the power-enhancement coating have been reported. In this paper, we discuss the result of several durability tests. The transmittance and water contact angle of the power-enhancement coating were kept under several durability tests such as UV test, weathering test, heat test, heat cycle test and dust test. Due to the acceleration tests, it was estimated the durability of the coating was reached to 30 years in terms of transparency and hydrophilicity.

The ability to optimize and consistently control the properties of the polymer-glass interface in thin film PV laminates in an important aspect of module reliability. Using variable rate peel delamination methods developed to isolate the encapsulant/glass interface, ion migration and interfacial chemistry have been studied following temperature and humidity exposure. In this presentation we will review quantitative AFM (Atomic Force Microscopy) and XPS (X-ray Photoelectron Spectroscopy) analyses linking failure modes with interfacial chemistry.

Solar module lifetime is limited by the fatigue behavior of its cell interconnectors: the copper-ribbons. Every change in temperature induces thermo-mechanical stresses in the module components due to their thermo-mechanical mismatch. The purpose of this work is to quantify this load on the copper-ribbons between the individual cells of a cell string during a thermal cycling test by measuring cell displacement using digital image correlation and to compare the results to finite element analysis (FEM). Furthermore with help of FEM the influences of different materials were investigated, allowing material and layout optimizations with respect to copper-ribbon loading.

Transparent PVB lamination foils are widely used in thin-film solar modules. The application of a pigmented load composed by TiO₂ particles in the foil formulation does not only influence the reflectance properties of this material, it has also a remarkable impact on other material parameters like resistivity and adhesion. The main objective of this study is to illustrate the properties of white lamination films based on polyvinyl butyral materials. A special insight will be on adhesion, foil resistivity and activation energies. Some performance results on modules will be also presented.

Measurement stations for solar radiation resource assessment data are expensive and labor intensive. For this reason, long-term solar radiation measurements are not widely available. Growing interest in solar renewable energy systems has generated a great number of questions about the quality of data obtained from inexpensive silicon photodiode radiometers versus costly thermopile radiometers. We analyze a year of daily total and monthly mean global horizontal irradiance measurements derived from 1-minute averages of 3-second samples of pyranometer signals. The data were collected simultaneously from both types of radiometers at the Solar Radiation Research Laboratory (SRRL) operated by the National Renewable Energy Laboratory in Golden, Colorado. All broadband radiometers in service at SRRL are calibrated annually using an outdoor method with reference radiometers traceable to the World Radiometric Reference. We summarized the data by daily total and monthly mean daily total amounts of solar radiation. Our results show that systematic and random errors (identified in our outdoor calibration process) in each type of radiometer cancel out over periods of one day or more. Daily total and mean monthly daily total solar energy measured by the two pyranometer types compare within 1% to 2%. The individual daily variations among different models of thermopile radiometers may be up to twice as large, up to ±5%, being highest in the winter (higher average solar zenith angle conditions) and lowest in summer, consistent with the lower solar zenith angle conditions.

Integral to photovoltaics is the need to provide improved economic viability. To achieve this goal, photovoltaic technology has to be able to harness more light at less cost. A large variety of concentrating photovoltaic concepts has provided cause for pursuit. To obtain a detailed profitability analysis, a flexible evaluation is crucial for benchmarking the cost-performance of this variety of concentrating photovoltaic concepts. To save time and capital, a way to estimate the cost-performance of a complete solar energy system is to use computer aided modeling. In this work a benchmark tool is introduced based on a modular programming concept. The overall implementation is done in MATLAB whereas Advanced Systems Analysis Program (ASAP) is used for ray tracing calculations. This allows for a flexible and extendable structuring of all important modules, namely an advanced source modeling including time and local dependence, and an advanced optical system analysis of various optical designs to obtain an evaluation of the figure of merit. An important figure of merit: the energy yield for a given photovoltaic system at a geographical position over a specific period, can be calculated.