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Richard E. Smalley, in 2003, defined the Terawatt (TW) Challenge as “Adapting our energy infrastructure to simultaneously address diminishing oil resources and rising levels of atmospheric CO 2.” Smalley, best known for the discovery of C 60, for which he received the 1996 Nobel Prize in Chemistry, continued to address the challenges of anthropomorphic and natural global energy flows until he passed away in 2005. Smalley challenged the world to transform the energy sector. He envisioned electricity transmitted by high-voltage direct current (DC) lines from massively deployed solar plants in sunny areas and remotely sited nuclear plants. He also envisioned using advanced batteries for local storage of energy. To meet the needs of ~10 people in a world with a dwindling oil supply, Smalley asserted that the world would need to transform its fossil-fuel-driven 14-TW (average power) energy used in 2003 to a largely renewable-energy-driven 30–60 TW (average power) in 2050. This would be possible only if solar-electricity costs could be drastically reduced. The challenges associated with this transition have been called the “Terawatt Challenge.” Fifteen years later, solar-module costs have been reduced by tenfold and annual deployment of solar photovoltaic (PV) modules has grown by a factor of 100,from ~1 gigawatt (GW) in 2004 to ~100 GW in 2018, with a total of 500 GW installed worldwide, producing 2% of the planet’s electricity. As global installed solar generating capacity approaches1 TW, we revisit Smalley’s TW challenge to identify what has changed and quantify the TW Challenge for a baseline scenario and for two scenarios designed as upper and lower bounds determined by the degree we implement electrification and storage. In this paper, we show that the energy choices we make today will dramatically affect the magnitude of future global energy requirements.

Today resource adequacy is most often maintained by installing natural gas plants to meet the peak load. In California, the current risk of inadequate electricity supply is highest around sunset in late summer. In a zero-carbon grid, resource adequacy will increasingly require adequate stored energy throughout the entire year. Here we seek to develop an intuition about the times of the year when resource adequacy may be most challenged for a solar-dominant system. We use a simplified approach and show that the month of the biggest challenge occurs in winter and can shift by more than two months depending on the amount of solar and storage that are built.

Summary What role have batteries to play in the transition toward terawatt levels of photovoltaics? In this perspective, we attempt to answer this question by looking at technical, economic, and ecological features of PV-battery systems. We argue that the window of opportunity for batteries lies in the capacities of a few kWh/kWP, the exact amount depending on various factors including battery cost, degradation rate, location, load profile, diversification of renewable energy sources, and interconnections. Using a simple PV plus battery model, we illustrate that such storage capacities efficiently reduce fluctuations in electricity generation, enabling higher PV adoption rates at competitive costs, and with a carbon footprint that is at least five times lower than that of the current energy mixes. Using sensible capacities, batteries are a powerful companion for solar energy, yet technical, economic, and policy innovations are needed to expand adoption. We see longer battery lifetimes and low capacity degradation rates are the most impactful technological parameters. Economic efforts should aim to reduce balance of plant costs and create better market opportunities for stationary storage, whereas policies should provide a strong regulatory framework to facilitate multipurpose usage and sector coupling.

The paper describes a proposed qualification standard for photovoltaic concentrator modules. The standard's purpose is to provide stress tests and procedures to identify any component weakness in photovoltaic concentrator modules intended for power generation applications. If no weaknesses are identified during qualification, both the manufacturer and the customer can expect a more reliable product. The qualification test program for the standard includes thermal cycles, humidity-freeze cycles, water spray, off-axis beam damage, hail impact, hot-spot endurance, as well as electrical tests for performance, ground continuity, isolation, wet insulation resistance, and bypass diodes. Because concentrator module performance can not be verified using solar simulator and reference cell procedures suitable for flat-plate modules, the standard specifies an outdoor I-V test analysis allowing a performance comparison before and after a test procedure. Two options to this complex analysis are the use of a reference concentrator module for side-by-side outdoor comparison with modules undergoing various tests and a dark I-V performance check.

The following footnote should be included in this article [1]: This paper was commissioned for publication by David Cahen, who served as Editor-in-Chief of this journal from 2014-2018.

In "The 100 Percent Clean Energy Act of 2018" the California legislature set a target of 100\% of California's electricity generated from renewable and zero-carbon sources by 2045. The California Public Utility Commission (CPUC) and other state entities now have the task of planning to meet that target. The California Energy Commission (CEC) has sponsored multiple studies and sought public input on the pathways that they are exploring. A key result of that planning process is a Reference System Portfolio (RSP) based on existing and planned electricity generating capabilities, and modeled grid build out to meet the planned targets by 2045 at the lowest cost. Although this RSP has been discussed by the CEC in a public forum, to our knowledge, it has not been presented to the photovoltaic community.Here we document the CEC’s current RSP, with emphasis on understanding their expectations for build out of solar as well as the associated need for storage and curtailment.

Optimization models can be quite powerful in identifying a pathway to lowest cost zero-carbon energy systems. However, it is less obvious how to invert the models to calculate the target cost and duration of storage needed for that storage to be a significant solution. Storage is a dispatchable and flexible resource with the ability to perform many functions of grid support, further complicating the analysis. This paper complements existing papers by presenting an academic study of a simplified energy system, demonstrating a method for quantifying cost and duration targets for storage. The simplified analysis also helps to gain intuition about the synergistic relationship between storage and solar energy in a location like the state of California.

The standardization of VIPV (Vehicle-integrated photovoltaic) has been driven by the international discussion among scientists and engineers, from photovoltaic research, photovoltaic industries, automobile and other industries, and testing laboratories. Since the VIPV is not flat and fixed installation, as well as a wide variety of designs, the knowledge of CPV (Concentrator Photovoltaic) technology, has been useful for developing testing technologies. This paper took two examples in the performance testing and the test for the tolerance for the partial/dynamic shading, utilizing various techniques exclusively used in CPV technologies.

The degradation rate plays an important role in predicting and assessing the long-term energy generation of photovoltaics (PV) systems. Many methods have been proposed for extracting the degradation rate from operational data of PV systems, but most of the published approaches are susceptible to bias due to inverter clipping, module soiling, temporary outages, seasonality, and sensor degradation. In this paper, we propose a methodology for determining PV degradation leveraging available modeled clear-sky irradiance data rather than site sensor data, and a robust year-over-year rate calculation. We show the method to provide reliable degradation rate estimates even in the case of sensor drift, data shifts, and soiling. Compared with alternate methods, we demonstrate that the proposed method delivers the lowest uncertainty in degradation rate estimates for a fleet of 486 PV systems.

Champion photovoltaic (PV) cell and module efficiencies have been reported in Progress in PV since 1993. Following the evolution of these efficiencies enables researchers to track the progress of various technologies. National Renewable Energy Laboratory has maintained a historical chart of the champion cell efficiencies, but has not published a similar chart of champion module efficiencies. Here, we analyze champion module efficiencies and compare them to champion cell efficiencies to better understand technology trends over the last three decades, highlighting that, in some cases, module efficiencies exceed 90% of cell efficiencies. Recommendations are provided on how to change the data collection and reporting for champion efficiencies to increase the value of these records.

A silicon heterostructure photovoltaic system fielded for 10 years has been investigated in detail. The system has shown degradation, but at a rate similar to an average Si system, and still within the module warranty level. The power decline is dominated by a nonlinear V oc loss rather than more typical changes in I sc or Fill Factor. Modules have been evaluated using multiple techniques including: dark and light I – V measurement, Suns- V oc, thermal imaging, and quantitative electroluminescence. All techniques indicate that recombination and series resistance in the cells have increased along with a decrease of factor 2 in minority carrier lifetime. Performance changes are fairly uniform across the module, indicating changes occur primarily within the cells.

The width-tapered cantilever beam method is used to quantify the debond energy (adhesion) of encapsulant and backsheet structures of 32 modules collected from the field. The collected population of modules contains both those that have remained intact and those with instances of either or both encapsulant and backsheet delamination. From this survey, initial threshold values (an adhesion value above which a module should remain intact throughout its lifetime) for encapsulant and backsheet interfaces are proposed. For encapsulants this value is ∼ $160\,{\text{J}\text{/}\text{m}}^{2}$ and for backsheets ∼ $10\,{\text{J}\text{/}\text{m}}^{2}$ . It is expected that these values will continue to be refined and evolve as the width-tapered cantilever beam method gets adopted by the PV industry, and that they may aid in the future improvement of accelerated lifetime tests and the development of new, low-cost materials.

The extensive photovoltaic field reliability literature was analyzed and reviewed. Future work is prioritized based upon information assembled from recent installations, and inconsistencies in degradation mode identification are discussed to help guide future publication on this subject. Reported failure rates of photovoltaic modules fall mostly in the range of other consumer products; however, the long expected useful life of modules may not allow for direct comparison. In general, degradation percentages are reported to decrease appreciably in newer installations that are deployed after the year 2000. However, these trends may be convoluted with varying manufacturing and installation quality world-wide. Modules in hot and humid climates show considerably higher degradation modes than those in desert and moderate climates, which warrants further investigation. Delamination and diode/j-box issues are also more frequent in hot and humid climates than in other climates. The highest concerns of systems installed in the last 10 years appear to be hot spots followed by internal circuitry discoloration. Encapsulant discoloration was the most common degradation mode, particularly in older systems. In newer systems, encapsulant discoloration appears in hotter climates, but to a lesser degree. Thin-film degradation modes are dominated by glass breakage and absorber corrosion, although the breadth of information for thin-film modules is much smaller than for x-Si. Copyright © 2017 John Wiley & Sons, Ltd.

In this issue of Joule, Steffen et al. tackle a challenging topic to quantify and project costs for operation and maintenance (O&M) of solar and wind power plants in Germany. They note that O&M costs can be 20%–25% of overall costs and find that such costs have decreased, resulting in common overestimates of O&M costs.

Solar energy has the potential to play a central role in the future global energy system because of the scale of the solar resource, its predictability, and its ubiquitous nature. Global installed solar photovoltaic (PV) capacity exceeded 500 GW at the end of 2018, and an estimated additional 500 GW of PV capacity is projected to be installed by 2022–2023, bringing us into the era of TW-scale PV. Given the speed of change in the PV industry, both in terms of continued dramatic cost decreases and manufacturing-scale increases, the growth toward TW-scale PV has caught many observers, including many of us (1), by surprise. Two years ago, we focused on the challenges of achieving 3 to 10 TW of PV by 2030. Here, we envision a future with ∼10 TW of PV by 2030 and 30 to 70 TW by 2050, providing a majority of global energy. PV would be not just a key contributor to electricity generation but also a central contributor to all segments of the global energy system. We discuss ramifications and challenges for complementary technologies (e.g., energy storage, power to gas/liquid fuels/chemicals, grid integration, and multiple sector electrification) and summarize what is needed in research in PV performance, reliability, manufacturing, and recycling.

A technical basis for measurement of the operating temperatures of PV modules in vehicle-integrated applications is explored. Convective and radiative heat transfer are modeled to elucidate the methodology. Data reported for sister modules mounted in an experimental black box and in the sun roof of a car show very similar temperatures. The box provides a uniform environment in the closed configuration, but can be adjusted to explore a wider range of operating environments by opening or closing the sides and by insulating the back.

This paper presents a model for evaluating the heat-sink and component temperatures of open-rack installed photovoltaic inverters. These temperatures can be used for predicting inverter reliability. Inverter heat-sink temperatures were measured for inverters connected to three grid-connected PV (photovoltaic) test systems in Golden, Colorado, US. A model is proposed for calculating the inverter heat-sink temperature based on the ambient temperature, the ratio of the consumed power to the rated power of the inverter, and the measured wind speed. To verify and study this model, more than one year of inverter DC/AC power, irradiance, wind speed, and heat sink temperature rise data were collected and analyzed. The model is shown to be accurate in predicting average inverter temperatures, but will require further refinement for prediction of transient temperatures.

A progression of potential-induced degradation (PID) mechanisms is observed in CdTe modules, which are dependent on the stress level and moisture ingress. This includes shunting, junction degradation, and two different manifestations of series resistance. The dark I–V method for in situ characterization of P max based on superposition was adapted for the thin-film modules undergoing PID in view of the degradation mechanisms observed. An exponential model based on module temperature and relative humidity (RH) was fit to the PID rate for multiple stress levels in chamber tests and validated by predicting the observed degradation of the module type in the field.

Photovoltaic (PV) reliability and durability have seen increased interest in recent years. Historically, and as a preliminarily reasonable approximation, linear degradation rates have been used to quantify long-term module and system performance. The underlying assumption of linearity can be violated at the beginning of the life, as has been well documented, especially for thin-film technology. Additionally, non-linearities in the wear-out phase can have significant economic impact and appear to be linked to different failure modes. In addition, associating specific degradation and failure modes with specific time series behavior will aid in duplicating these degradation modes in accelerated tests and, eventually, in service life prediction. In this paper, we discuss different degradation modes and how some of these may cause approximately linear degradation within the measurement uncertainty (e.g., modules that were mainly affected by encapsulant discoloration) while other degradation modes lead to distinctly non-linear degradation (e.g., hot spots caused by cracked cells or solder bond failures and corrosion). The various behaviors are summarized with the goal of aiding in predictions of what may be seen in other systems. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

The durability of polymeric encapsulation materials was examined using outdoor exposure at the nominal geometric concentration of 500 suns. The results for 36 months cumulative field deployment are presented for materials including: poly(ethylene-co-vinyl acetate), (EVA); polyvinyl butyral (PVB); ionomer; polyethylene/ polyoctene copolymer (PO); thermoplastic polyurethane (TPU); poly(dimethylsiloxane) (PDMS); poly(diphenyl dimethyl siloxane) (PDPDMS); and poly(phenyl-methyl siloxane) (PPMS). Measurements of the field conditions including ambient temperature and ultraviolet (UV) dose were recorded at the test site during the experiment. Measurements for the experiment included optical transmittance (with subsequent analysis of solar-weighted transmittance, UV cut-off wavelength, and yellowness index), mass, visual photography, photoelastic imaging, and fluorescence spectroscopy. While the results to date for EVA are presented and discussed, examination here focuses more on the siloxane materials. A specimen recently observed to fail by thermal decomposition is discussed in terms of the implementation of the experiment as well as its fluorescence signature, which was observed to become more pronounced with age. Modulated thermogravimetry (allowing determination of the activation energy of thermal decomposition) was performed on a subset of the siloxanes to quantify the propensity for decomposition at elevated temperatures. Supplemental, Pt-catalyst- and primer-solutions as well as peroxide-cured PDMS specimens were examined to assess themore » source of the luminescence. The results of the study including the change in optical transmittance, observed failure modes, and subsequent analyses of the failure modes are described in the conclusions.« less

FEM simulations of PbSn solder fatigue damage are used to evaluate seven cities that represent a variety of climatic zones. It is shown that the rate of solder fatigue damage is not ranked with the cities' climate designations. For an accurate ranking, the mean maximum daily temperature, daily temperature change and a characteristic of clouding events are all required. A physics-based empirical equation is presented that accurately calculates solder fatigue damage according to these three factors. An FEM comparison of solder damage accumulated through service and thermal cycling demonstrates the number of cycles required for an equivalent exposure. For an equivalent 25-year exposure, the number of thermal cycles (− 40 °C to 85 °C) required ranged from roughly 100 to 630 for the cities examined. It is demonstrated that increasing the maximum cycle temperature may significantly reduce the number of thermal cycles required for an equivalent exposure.

A side-by-side comparison is made between concentrator photovoltaic module and system direct current aperture efficiency data with a focus on quantifying system performance losses. The individual losses measured/calculated, when combined, are in good agreement with the total loss seen between the module and the system. Results indicate that for the given test period, the largest individual loss of 3.7% relative is due to the baseline performance difference between the individual module and the average for the 200 modules in the system. A basic empirical model is derived based on module spectral performance data and the tabulated losses between the module and the system. The model predicts instantaneous system direct current aperture efficiency with a root mean square error of 2.3% relative.

Published data on photovoltaic (PV) degradation measurements were aggregated and re-examined. The subject has seen an increased interest in recent years resulting in more than 11 000 degradation rates in almost 200 studies from 40 different countries. As studies have grown in number and size, we found an impact from sampling bias attributable to size and accuracy. Because of the correlational nature of this study we examined the data in several ways to minimize this bias. We found median degradation for x-Si technologies in the 0.5–0.6%/year range with the mean in the 0.8–0.9%/year range. Hetero-interface technology (HIT) and microcrystalline silicon (µc-Si) technologies, although not as plentiful, exhibit degradation around 1%/year and resemble thin-film products more closely than x-Si. Several studies showing low degradation for copper indium gallium selenide (CIGS) have emerged. Higher degradation for cadmium telluride (CdTe) has been reported, but these findings could reflect a convolution of less accurate studies and longer stabilization periods for some products. Significant deviations for beginning-of-life measurements with respect to nameplate rating have been documented over the last 35 years. Therefore, degradation rates that use nameplate rating as reference may be significantly impacted. Studies that used nameplate rating as reference but used solar simulators showed less variation than similar studies using outdoor measurements, even when accounting for different climates. This could be associated with confounding effects of measurement uncertainty and soiling that take place outdoors. Hotter climates and mounting configurations that lead to sustained higher temperatures may lead to higher degradation in some, but not all, products. Wear-out non-linearities for the worst performing modules have been documented in a few select studies that took multiple measurements of an ensemble of modules during the lifetime of the system. However, the majority of these modules exhibit a fairly linear decline. Modeling these non-linearities, whether they occur at the beginning-of-life or end-of-life in the PV life cycle, has an important impact on the levelized cost of energy. Copyright © 2016 John Wiley & Sons, Ltd.

The field of photovoltaics has grown tremendously over the past decade and in 2015 solar cell deployments accounted for 20% of the expansion of global electricity capacity.

Recently there has been increased interest in using thermoplastic encapsulant materials in photovoltaic modules, but concerns have been raised about whether these would be mechanically stable at high temperatures in the field. Recently, this has become a significant topic of discussion in the development of IEC 61730 and IEC 61215. We constructed eight pairs of crystalline-silicon modules and eight pairs of glass/encapsulation/glass thin-film mock modules using different encapsulant materials, of which only two were formulated to chemically crosslink. One module set was exposed outdoors with thermal insulation on the back side in Mesa, Arizona, in the summer (hot-dry), and an identical module set was exposed in environmental chambers. High-precision creep measurements (±20 μm) and electrical performance measurements indicate that despite many of these polymeric materials operating in the melt or rubbery state during outdoor deployment, no significant creep was seen because of their high viscosity, lower operating temperature at the edges, and/or the formation of chemical crosslinks in many of the encapsulants with age despite the absence of a crosslinking agent. Only an ethylene-vinyl acetate (EVA) encapsulant formulated without a peroxide crosslinking agent crept significantly. In the case of the crystalline-silicon modules, the physical restraint of the backsheet reduced creep further and was not detectable even for the EVA without peroxide. Because of the propensity of some polymeric materials to crosslink as they age, typical thermoplastic encapsulants would be unlikely to result in creep in the vast majority of installations.

A complete procedure is presented for translating outdoor concentrator photovoltaic (CPV) I–V measurements to the Concentrator Standard Test Conditions (CTSC) (1000 W/m2 and 25 °C cell temperature). Methods are demonstrated for measuring all the necessary input parameters for the translation, including outdoor thermal transient measurements and indoor dark I–V curves. Four modules are subjected to the translation method based on multiple months of outdoor data, one module measured at National Renewable Energy Laboratory and three at Fraunhofer ISE. The modules are also characterized under a sun simulator to provide a comparison to the translation approach. The results show that translated CSTC efficiencies are in good agreement with the efficiencies from the solar simulator. Two of the modules agreed within 1%, whereas the other two modules agree within approximately 4%. An uncertainty analysis of the input parameters is discussed in the context of the total uncertainty associated with the translation to CSTC. The reference voltage and efficiency temperature coefficient are the key parameters impacting the translation uncertainty, whereas uncertainty in the outdoor data is driven by spectral and meteorological parameters. Copyright © 2015 John Wiley & Sons, Ltd.

Current density–voltage ( JV ) curves of a CdTe photovoltaic module measured during 2.5 years of outdoor operation are analyzed using a phenomenological four-parameter equation. This approach is shown to be more accurate than fitting the same data set to the conventional five parameter diode equation. The four extracted parameters are the short-circuit current density J sc , open-circuit voltage V oc , and the differential resistances R sc and R oc , i.e., the reciprocal slopes of the JV curves at short circuit and open circuit, respectively. The dependencies of all four parameters on module temperature and irradiation intensities are analyzed in terms of physically motivated models. The coefficients derived from these models are then used to transform the photovoltaic parameters to reference conditions and to investigate the degradation of the module. The models for R sc and R oc involve voltage-dependent carrier collection. This feature appears prominent already in the initial JV curves, but becomes even more dominant with increasing exposure time. Voltage-dependent carrier collection also explains that the diode ideality factor determined from V oc vs. J sc curves is different from that determined using R oc vs. 1/ J sc plots. The degradation of the module is essentially reflected in fill factor losses caused by a decrease of R sc and an increase of R oc . Additionally, the V oc vs. log( J sc ) curves of the module behavior at low irradiation unveil an increasing influence of a double-exponential diode behavior.

The purpose of this study is to investigate concentrator photovoltaic (CPV) system performance. The performance of the CPV system depends on the climate and the environment condition more than the conventional flat-plate photovoltaic (PV) system. Moreover, the characteristic due to the angle of incidence (AOI) solar irradiance is extremely important. Therefore, the grid-connected PV and CPV systems installed in Japan are investigated to clarify these performance issues in this paper. The performance analysis results including performance ratio and alignment and tracking error data from one year of operation are presented and discussed.

As creep of polymeric materials is potentially a safety concern for photovoltaic modules, the potential for module creep has become a significant topic of discussion in the development of IEC 61730 and IEC 61215. To investigate the possibility of creep, modules were constructed, using several thermoplastic encapsulant materials, into thin-film mock modules and deployed in Mesa, Arizona. The materials examined included poly(ethylene)-co-vinyl acetate (EVA, including formulations both cross-linked and with no curing agent), polyethylene/polyoctene copolymer (PO), poly(dimethylsiloxane) (PDMS), polyvinyl butyral (PVB), and thermoplastic polyurethane (TPU). The absence of creep in this experiment is attributable to several factors of which the most notable one was the unexpected cross-linking of an EVA formulation without a cross-linking agent. It was also found that some materials experienced both chain scission and cross-linking reactions, sometimes with a significant dependence on location within a module. The TPU and EVA samples were found to degrade with cross-linking reactions dominating over chain scission. In contrast, the PO materials degraded with chain scission dominating over cross-linking reactions. Although we found no significant indications that viscous creep is likely to occur in fielded modules capable of passing the qualification tests, we note that one should consider how a polymer degrades, chain scission or cross-linking, in assessing the suitability of a thermoplastic polymer in terrestrial photovoltaic applications.

The annual potential of solar energy far exceeds the world's total energy consumption. However, the vision of photovoltaics (PVs) providing a substantial fraction of global electricity generation and total energy demand is far from being realized. What technical, infrastructure, economic, and policy barriers need to be overcome for PVs to grow to the multiple terawatt (TW) scale? We assess realistic future scenarios and make suggestions for a global agenda to move toward PVs at a multi-TW scale.

A commercial HCPV/T system, developed by Solergy, is installed at the airport of Rome, in Italy, as part of a prototype smart grid. The system is rated at 15 kW AC electric and 20 kW thermal and is used to provide both electricity for charging electric vehicles and heat for a conventional thermal power plant. This paper presents an analysis of the performance of the system, operating since March 2017, which achieves a combined peak efficiency of 48%. This study incorporates also an investigation on the improvements that can benefit the system, including a new type of receiver with improved heat dissipation.

Quantitative analysis of two 30-year-old PV modules is performed by a combination of the equivalent-circuit model and optoelectronic characterization methods. The two modules under analysis were manufactured in 1984 with the nameplate power of 41.0 W, but degraded under two different conditions; one was operated in the field in Northern California for about 30 years, and the other was stored in a warehouse for the same period. The power outputs of the two modules measured in 2016 are as 28.4W for the field-exposed one and 35.9 W for the warehoused one. We further break down this power difference of 7.5 W ± 0.3 W to specific physical mechanisms. Through the encapsulant transmittance measurements and the circuit modeling of module I-V curves, the power degradation due to encapsulant discoloration is found as 59% ± 4% of the total difference. With the bias-dependent electroluminescence imaging and the dark I-V measurement of solar cells (via the additionally-attached probe wires), the series-resistance increase is attributed to 33% ± 1%, with the split of 13% ± 4% due to interconnection resistance and 20% ± 4% due to cell resistance. In addition, the synergistic effect of all the physical mechanisms makes up the remaining 8% ± 4%. This case study presents an example of analyzing multiple degradation mechanisms of the PV modules. With more characterization data being collected for today's modules, the same analysis framework can be broadly applied, yield great insights module power degradation attributed to multiple loss mechanisms.

The National Renewable Energy Laboratory (NREL) and National Institute of Solar Energy (NISE), located in the United States and India, respectively, have partnered to deploy and monitor modules of three different thin film technologies, to compare the performance and/or degradation between the two sites. This report analyzes a single year of performance data (May 2014 -- May 2015) for the three thin film technologies, exploring the modules' performance under standard test conditions and monthly performance ratios, as well as fill factors varying season, light level, and temperature.

We present a method for analyzing time series production data from photovoltaic systems to extract the rate at which energy yield is affected by the accumulation of dust, dirt, and other forms of soiling. We describe an approach that is based on prevailing methods, which consider the change in energy production during dry periods. The method described here builds upon these methods by considering a statistical sample of soiling intervals from each site under consideration and utilizing the robust Theil-Sen estimator for slope extraction from these intervals. The method enables straightforward application to a large number of sites with minimal parameterization or data-filtering requirements. Furthermore, it enables statistical confidence intervals and comparisons between sites.

Absorbed sunlight in a solar cell produces electrons and holes. However, at the open-circuit condition, the carriers have no place to go. They build up in density, and ideally, they emit external luminescence that exactly balances the incoming sunlight. Any additional nonradiative recombination impairs the carrier density buildup, limiting the open-circuit voltage. At open circuit, efficient external luminescence is an indicator of low internal optical losses. Thus, efficient external luminescence is, counterintuitively, a necessity for approaching the Shockley–Queisser (SQ) efficiency limit. A great solar cell also needs to be a great light-emitting diode. Owing to the narrow escape cone for light, efficient external emission requires repeated attempts and demands an internal luminescence efficiency 90%.

As photovoltaic penetration of the power grid increases, accurate predictions of return on investment require accurate prediction of decreased power output over time. Degradation rates must be known in order to predict power delivery. This article reviews degradation rates of flat-plate terrestrial modules and systems reported in published literature from field testing throughout the last 40 years. Nearly 2000 degradation rates, measured on individual modules or entire systems, have been assembled from the literature, showing a median value of 0·5%/year. The review consists of three parts: a brief historical outline, an analytical summary of degradation rates, and a detailed bibliography partitioned by technology. Copyright © 2011 John Wiley & Sons, Ltd.

@font-face {font-family: "Arial";}p.MsoNormal, li.MsoNormal, div. MsoNormal {margin: 0in 0in 0.0001pt; font-size: 12pt; font-family: "Times New Roman";}div. Section1 {page: Section1;} A finite element model has been created to quantify the thermal fatigue damage of the CPV die attach. Simulations are used to compare to results of empirical thermal fatigue equations originally developed for accelerated chamber cycling. While the empirical equations show promise when extrapolated to the lower temperature cycles characterisitic of weather-induced temperature changes in the CPV die attach, it is demonstrated that their damage does not accumulate linearly: the damage a particular cycle contributes depends on the preceding cycles. Simulations of modeled CPV cell temperature histories provided for direct comparison of the FEM and empirical methods, and for calculation of equivalent times provided by standard accelerated test sequences.

Photovoltaic (PV) modules operate at temperatures above ambient owing to the thermal energy of sunlight. The operating temperature primarily depends on the ambient temperature, incident sunlight, mounting configuration, packaging configuration, and wind speed. In this paper, the cumulative thermal degradation is modeled to follow Arrhenius behavior. The data are analyzed to determine the constant temperature that would give average aging equivalent to the variable temperatures observed in the field. These equivalent temperatures are calculated for various locations using six configurations, providing a technical basis for defining accelerated thermal-endurance and -degradation testing. This data may also be useful as a starting point for studies of the combined effects of elevated temperature and other factors such as UV, moisture, and mechanical stress. Copyright © 2011 John Wiley & Sons, Ltd.

The Very High Efficiency Solar Cell (VHESC) program is developing integrated optical system–PV modules for portable applications that operate at greater than 50% efficiency. We are integrating the optical design with the solar cell design, and have entered previously unoccupied design space. Our approach is driven by proven quantitative models for the solar cell design, the optical design, and the integration of these designs. Optical systems efficiency with an optical efficiency of 93% and solar cell device results under ideal dichroic splitting optics summing to 42·7 ± 2·5% are described. Copyright © 2008 John Wiley & Sons, Ltd.

Champion concentrator cell efficiencies have surpassed 40% and now many are asking whether the efficiencies will surpass 50%. Theoretical efficiencies of >60% are described for many approaches, but there is often confusion about “the” theoretical efficiency for a specific structure. The detailed balance approach to calculating theoretical efficiency gives an upper bound that can be independent of material parameters and device design. Other models predict efficiencies that are closer to those that have been achieved. Changing reference spectra and the choice of concentration further complicate comparison of theoretical efficiencies. This paper provides a side-by-side comparison of theoretical efficiencies of multi-junction solar cells calculated with the detailed balance approach and a common one-dimensional-transport model for different spectral and irradiance conditions. Also, historical experimental champion efficiencies are compared with the theoretical efficiencies. Copyright © 2008 John Wiley & Sons, Ltd.

Some may say that PV modules are moving toward being a simple commodity, but most major PV customers ask: “How can I minimize chances of a module recall?” Or, “How can I quantify the added value of a ‘premium’ module?” Or, “How can I assess the value of an old PV system that I'm thinking of purchasing?” These are all questions that PVQAT (the International PV Quality Assurance Task Force) and partner organizations are working to answer. Defining standard methods for ensuring minimal acceptable quality of PV modules, differentiating modules that provide added value in the toughest of environments, and creating a process (e.g. through IECRE [1]) that can follow a PV system from design through installation and operation are tough tasks, but having standard approaches for these will increase confidence, reduce costs, and be a critical foundation of a mature PV industry. This paper summarizes current needs for new tests, some challenges for defining those tests, and some of the key efforts toward development of international standards, emphasizing that meaningful quantification of reliability (as in defining a service life prediction) must be done in the context of a specific product with design parameters defined through a quality management system.