This PDF file contains the front matter associated with SPIE Proceedings Volume 7048, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

The reliability of PV modules and systems is critical to the commercial success of Photovoltaics. Financial payback requires PV systems to reliably produce the promised electricity over the warranted time period. This paper will review the present status of PV system reliability using outdoor data from fielded arrays and results from accelerated testing of components.

We discuss the measurement and analysis of current vs. voltage (I-V) characteristics of photovoltaic (PV) cells and modules for reliability determination. We discuss both the error sources in the measurements and the strategies to minimize their influence. These error sources include the sample area, spectral errors, temperature fluctuations, current and voltage response time, contacting, and degradation during testing issues. Information that can be extracted from light and dark I-V includes peak power, open-circuit voltage, short-circuit current, series and shunt resistance, diode quality factor, dark current, and photo-current. The quantum efficiency provides information on photo-current nonlinearities, current generation and recombination mechanisms.

We report a new system for measurement of the spatially resolved quantum efficiency (QE) of the semiconductor solarcells. In our method solar-cell is illuminated by modified liquid crystal display projector scanner. System allows to measure photo-current, and optical properties of the illuminated surface. The same system can be also used to measure surface topography of the wafer, its bow, and warp, and calculate lateral stress in the structure if structure cross-section is known.

Manufacturers of PV-modules usually give a warranty for at least 20 years. There is still only little knowledge about the lifetime of newly developed modules, however. How do they cope with snow, desert-climate or tropical humidity? In order to answer this question the Fraunhofer-Institute for Solar Energy Systems and TUV Rheinland have installed different outdoor exposure sites where modules have to stand extreme climates: high temperatures with high differences between day and night in the Negev desert at Israel, snow, wind and changing irradiation in the German Alps, and high humidity at warm temperatures at Indonesia. Commercial modules from industrial partners as well as innovative modules with different combinations of encapsulants and back-sheets were exposed. UV-irradiation, solar-irradiation, ambient- and module temperatures, ambient humidity and wind speed is measured and collected at a central server in Germany. These data are the basis for the calculation of integral loads for the comparison of different climatic regions and for an estimation of the service life, an exciting field of work since decades. Results from the evaluation of the monitoring during the fist 12 months of exposure are compared. Fluorescent lamps are chosen for accelerated UV-testing, since they simulate the UV-irradiation of the sun well while emitting less thermal radiation than Xenon-lamps. The UV-source is designed for use in climatic cabinets for damp-heat testing with UV.

Advances in photovoltaic technology resulted in increased complexity of device calibration, largely being affected by deviations of test spectrum from natural spectra. While the output spectrum of some solar simulators is adjustable, generally only light intensity and module temperature can be varied. This is due to the light sources used in current simulators. LEDs offer an additional degree of freedom, when using an appropriate combination of wavelengths. This paper presents the advantages of this lighting technology for solar simulation and backs these up through results of the prototype unit developed at the Centre for Renewable Energy Systems Technology. The ability to keep LEDs stable for a long time and dim them with minimal changes in the spectrum allows generation of a spectrum closely matched to AM1.5G standard test spectrum or indeed even realistic variations of the outdoor spectrum. LEDs can be controlled very fast within microseconds or operated continuously, combining a steady state and a flash solar simulator with additional functions such as variable flash frequencies and flash shape. Combined with the life expectancy exceeding 50.000h, LEDs are a strong candidate for solar simulator light sources introducing a significant improvement in calibration lifetime as well as significantly reduced running cost. The usage of LEDs can enhance today's characteristic measurement functions and even opens possibilities to fully characterise solar cells indoors within a much shorter time than is possible today, over a range of conditions previously only available through outdoor characterisation.

The solar-powered LED lighting system has been commercialized for a long time. The system usually consists of a DC to DC converter in order to convert the battery voltage into a fixed voltage or current for the LED lighting luminaire. This will cause energy loss and system reliability due to the failure of DC/DC converter. In the present study, we develop a special technique to drive the LED luminaire directly from battery utilizing PWM technique in order to remove the DC/DC converter. However, instantaneous current overdriven can occur easily due to the variation of battery voltage with the state-of-charge of battery. In the present study, we setup a thermal chamber with temperature variation to within 40±3°C. A LED luminaire was specially designed for the LED reliability test with four different circuits with each circuit connecting three LED lamps serially. A driver is designed to provide 4 kinds of power inputs to LED: (a) 350mA constant current, (b) 700mA,100Hz, duty cycle=50%, (c)700mA, 10K Hz duty cycle=50% and (d) 1050mA, 100Hz, duty cycle=33%. The tests were performed simultaneously to compare light decay between normal drive condition (a) and other PWM driving conditions (b, c, d). The accumulated total test time so far is more then 7,032 hours and has shown no significant light decay in 4 different loops. This reveals that the PWM technique directly driven by battery is feasible and is able to reduce energy loss of DC to DC converter in the solar lighting system.

We describe optical test methods for indoor and outdoor assessment of concentrating photovoltaic (CPV) and concentrating solar power (CSP) plants and modules. Testing may be done in active mode, where the cell is driven in forward-bias mode, and passive mode, where the system or parts of it are illuminated do measure performance and detect errors. An update on the design and development of the concentrating solar simulator is given. A camera may be used to verify optical alignment and tracking sensitivity of the concentrator system. Indoor testing is required for quality assurance. It is a condition for performance guarantees and performance-based pricing.

The concentrator photovoltaic (CPV) industry has created a qualification standard - IEC 62108. This standard applies to receivers and modules - certainly the most appropriate configurations for qualification and safety testing. CPV systems manufacturers expect the solar cells they buy to be qualified and highly reliable. However, the IEC qualification standard does not apply to the configurations offered by multijunction cell manufacturers and there are no accepted reliability test standards. This paper describes how one cell manufacturer adapted IEC 62108 to perform qualification testing on bare cells. Damp heat and high temperature durability qualification/reliability test results are shown for first generation CPV cells (C1MJ). Typical meteorological year data is analyzed for three locations to look at high temperature durability and to propose thermal cycle reliability test conditions. Space qualification testing is shown to envelope terrestrial thermal cycling and a thermal cycling reliability test is proposed. The space heritage of commercially available cells is reviewed to provide some background on reliability of multijunction cells.

For rigid photovoltaic (PV) cell encapsulation, durable adhesion of the polymeric encapsulant to glass is one of the most important considerations in developing a reliable PV module. The great challenge for encapsulant materials is to obtain adhesion that survives humidity stress at high temperature, since all organic polymers are to some degree permeable to water vapor and water molecules can migrate to the interface and degrade the adhesion. Several test methods were used to accelerate the adhesion degradation process for materials screening. Solar grade EVA and several experimental encapsulant materials were used for the study, which included a detailed analysis of the combined role of moisture and temperature in inducing loss of adhesion. The effect of moisture and temperature on adhesion mechanisms and polymer properties will be discussed.

A primary goal of Photovoltaics is to generate electricity while reducing reliance on the world's petroleum supply. However, PV backsheets are produced from petro-based chemicals, which, to a certain extent, defeat the purpose of using solar energy. Materials from three sustainable resources were targeted for PV backsheet development: PLA made from corn, a cellulosic made from cotton, and a type of nylon made from castor beans. Some of these films were coated with various materials to lower the WVTR. Modules produced using these backsheets were subjected to rigorous testing, including the damp heat test and the wet Hypot test as outlined in UL 1703. As cast PLA film tends to be very brittle. This problem is solved with additives or biaxial orientation. PLA film is UV stable and highly transparent which would merit it for consideration as a front glazing as well as for a backsheet. However, its moisture resistance is not robust. A cellulosic film made from cotton was considered which has a continuous duty temperature rating of 105°C. This product had to be modified significantly to convert it from a hydrophilic film to a hydrophobic one. Additionally, this material has an RTI value of 90°C. Nylon 11, produced from castor beans, is very interesting because it is bio-sustainable, but not biodegradable. It has improved moisture properties over the more common nylons, and has an RTI value of 105°C.

Ethylene propylene diene monomer (EPDM) based polymers have been formulated for specific use in photovoltaic modules to produce better performance and longer term stability at a lower cost than standard materials. EPDM formulations are advantageous over ethylene vinyl-acetate (EVA) because they can use the same lamination/cure cycle as EVA, they do not need a second back-sheet protective material (e.g. PET/Tedlar), they have a lower glass transition temperature, no melting transition, more constant mechanical moduli as a function of temperature, they are less polar than EVA (provides better corrosion protection), and they have excellent damp heat (85°C/85% relative humidity) resistance against delamination. Module designs typically use EVA on the back side of cells despite the fact that transparency is not advantageous. We have developed a single encapsulant layer that will replace standard module back-sheet constructions consisting of EVA/PET/Tedlar. Because a single low-cost material layer is used, it will provide a significant materials cost savings of about $6 to $8/m² as compared to traditional back-sheets. Electrical insulation tests were conducted using 0.85 mm thick stainless steel sheets as a model for a cell. It was found that a polymer layer thickness of about 0.33mm provided better high voltage electrical insulation than a combined film of Tedla (0.038 mm) / PET (0.051 mm) / EVA (0.55 mm). When formulated with a white pigment, reflectivity was comparable to Tedlar^TM. Upon accelerated exposure to light at 60C and 60% RH it was found that an EVA layer in front of these materials would decompose before significant yellowing and delamination of the back EPDM layer occurs.

The estimation of PV-modules lifetime facilitates the further development and helps to lower risks for producers and investors. One base for this extensive testing and simulation work is the knowledge of the chemical degradation processes and their kinetics, as well as of the permeation of water and oxygen into the module, especially of the encapsulant. Besides ethylen-vinylacetate copolymer (EVA), which is the dominant material for encapsulation, new materials become available and need the assessment of their properties and the durability impact. Accelerated durability tests were performed on different EVA materials. The paper reports on several measurement methods for analysis of the polymers that were used, FT-IR with attenuated total reflection (ATR), and Raman microscopy, e.g. It is very important to identify degradation products and intermediates in order to identify the leading degradation processes and their kinetics as well as potential interactions between different processes. Another important factor for the degradation of the PV-modules and the concerned polymers in particular is the permeation of reactive substances, especially of water vapor, into and inside the modules. The paper shows results of permeation measurements of the new materials, as well as FEM-based numerical simulations of the humidity diffusion within a PV-module what is an important step towards the calculation of the chemical degradation using numerical simulation tools in the future.

The estimation of PV-modules lifetime facilitates the further development and helps to lower risks for producers and investors. One base for this extensive testing work is the knowledge of the degradation kinetics of encapsulating polymer materials. Besides ethylen-vinylacetate copolymer (EVA), which is the prevalent material for encapsulation, new materials like Poly-Vinyl-Butyral (PVB), and thermoplastic Poly-Urethan (TPU) become available and need the assessment of their properties and the durability impact. In this context is it very important to identify the extent of degradation caused by different parameters in order to identify the determining factor of polymer degradation as well as potential interactions between different degradation processes. To simulate long time degeneration processes accelerated aging under damp-heat and high-UV conditions was performed on different EVA, TPU, and PVB samples. In this paper we report first results on measuring fluorescence spectra from different encapsulation materials after accelerated ageing in dependence on time and aging procedure. Our investigations clearly demonstrate that it is possible to follow damp-heat and UV induced aging processes of different polymers used in PV-modules as encapsulation materials by luminescence detection.

The polyvinyl butyral (PVB) encapsulant material is being evaluated as a candidate for use in photovoltaic solar cells encapsulation process due to high stability against UV radiation and the high adhesive force to glass. This material is used for a long time in automotive technology, building integrated vitrification and security glazing. The long experience in this sector can direct be carried over to the photovoltaic industry. The purpose of this experimental investigation is to better understand the electrical properties and thermal stability of PVB based encapsulant material and their dependence on temperature will be presented. An overview of some main electrical and thermal properties of PVB is compared to EVA.

Glass is a proven, excellent substrate and cover for photovoltaic applications. But glass can be a source of module reliability problems if not properly fabricated. Glass reliability issues can include brittle failure due to mechanical and thermal stresses, surface weathering, lamination adhesion, TCO adhesion, moisture ingress, and anti-reflective coating durability. A synopsis of typical problems and how to prevent them is provided for both new and current module manufacturers.

Hot-spot heating occurs in a photovoltaic (PV) module when its operating current exceeds the short-circuit current of a shadowed or faulty cell in a cell-string. This shadowed/faulty cell could overheat due to reverse bias and become a fire or electrical hazard. Currently, there are three different test methods used in the industry to identify and address this issue. These three methods are based on the UL 1703 (intrusive) standard, ASTM E2481-06 (non-intrusive) standard and IEC 61215 (non-intrusive) standard. Comparing and identifying the best test method [in terms of time, cost and complexity] is of great value to the consumers, PV module manufacturers and test laboratories such as ASU-PTL. The objective of this paper is to compare these three methods in order to identify the best test method for the modules composed of low and/or high shunt resistance cells. In this work, 18 modules composed of low and high shunt resistance cells were investigated in each of the test methods. Out of eighteen (9 mono-Si and 9 poly-Si) modules tested, sixteen modules (9 poly-Si and 7 mono-Si) passed the hotspot tests of all the three standards. The other two modules (mono-Si with voltage limited cells) passed in the ASTM and IEC methods, but failed in the UL method. These two failures in the UL method may be explained in terms of standard's worst-case assumption (open-circuited diodes) of non-sharing of the stress current by the installed bypass diodes of the modules and/or the extended test duration required in this standard.

For PV modules to fulfill their intended purpose, they must generate sufficient economic return over their lifetime to justify their initial cost. Not only must modules be manufactured at a low cost/Wp with a high energy yield (kWh/kWp), they must also be designed to withstand the significant environmental stresses experienced throughout their 25+ year lifetime. Based on field experience, the most common factors affecting the lifetime energy yield of glass-based amorphous silicon (a-Si) modules have been identified; these include: 1) light-induced degradation; 2) moisture ingress and thin film corrosion; 3) transparent conductive oxide (TCO) delamination; and 4) glass breakage. The current approaches to mitigating the effect of these degradation mechanisms are discussed and the accelerated tests designed to simulate some of the field failures are described. In some cases, novel accelerated tests have been created to facilitate the development of improved manufacturing processes, including a unique test to screen for TCO delamination. Modules using the most reliable designs are tested in high voltage arrays at customer and internal test sites, as well as at independent laboratories. Data from tests at the Florida Solar Energy Center has shown that a-Si tandem modules can demonstrate an energy yield exceeding 1200 kWh/kWp/yr in a subtropical climate. In the same study, the test arrays demonstrated low long-term power loss over two years of data collection, after initial stabilization. The absolute power produced by the test arrays varied seasonally by approximately ±7%, as expected.

Solar cell module reliability is inextricably linked to cell-level reliability. This is particularly so with thin-film technologies. In CdTe, reliability issues historically associate with back contact stability and the use of Cu as an extrinsic dopant. Using a simple approach by which identical cells are heated under open-circuit bias and 1-sun illumination, degradation activation energies of 0.63 and 2.94 eV in laboratory-scale CdS/CdTe devices were identified in the accelerated stress temperature range of 60 to 120 °C. At lower stress temperatures, cell performance changes were linearly correlated with changes in both fill factor (FF) and short-circuit current (J_sc). At higher stress temperatures, changes in efficiency were correlated with changes in FF and open-circuit voltage (V_oc). The measured activation energy of 0.63 is associated with Cu-diffusion. During the early stage of stress testing, which may provide additional back contact annealing, improvements in FF were due to Cu-diffusion. Decreased performance observed at longer stress times (decreased FF and V_oc), according to a two-diode Pspice model, were due to both increased space-charge recombination (near the junction) and decreased recombination in the bulk. Kirkendall void formation (S-outdiffusion) at the CdS/CdTe interface is given as responsible for the 2.9 eV degradation mechanism.

Thin-film solar cells based on CIGS are being considered for large scale power plants as well as building integrated photovoltaic (BIPV) applications. Past studies indicate that CIGS cells degrade rapidly when exposed to moisture. As a result, an effective approach to encapsulation is required for CIGS cells to satisfy the international standard IEC 61646. CIGS modules fabricated for use in large power plants can be encapsulated with glass sheets on the top and bottom surfaces and can be effectively sealed around the edges. In the case of BIPV applications, however, it is desirable to utilize CIGS cells grown on flexible substrates, both for purposes of achieving reduced weight and for cases involving non-flat surfaces. For these cases, approaches to encapsulation must be compatible with the flexible substrate requirement. Even in the case of large power plants, the glass-to-glass approach to encapsulation may eventually be considered too costly. We are investigating encapsulation of flexible CIGS cells by lamination. Sheets of PET or PEN coated with multilayer barrier coatings are used to laminate the flexible cells. Results are discussed for laminated cells from two CIGS manufacturers. In both cases, the cell efficiency decreases less than 10% after 1000 hours of exposure to an environment of 85°C/85%RH. This paper discusses these two approaches, and reviews results for uncoated cells and mini-modules fabricated by the former Shell Solar Industries (SSI).

The reliability of ZnO-based window layer for CuInGaSe₂ (CIGS) solar cells was investigated. Samples of RF magnetron-sputtered, single-layer intrinsic and Al-doped ZnO and their combined bilayer on glass substrates were exposed in a weatherometer (WOM) and damp heat (DH) conditions with or without acetic acid vapor. Some preliminary samples of single-layer Al-doped Zn_1-xMg_xO (ZMO) alloy, a potential replacement for Al:ZnO with a wider bandgap, were also evaluated in the DH. The Al-doped ZnO and ZMO films showed irreversible loss in the conducting properties, free carrier mobility, and characteristic absorption band feature after <500-h DH exposure, with the originally clear transparent films turned into white hazy insulating films and the degradation rate follows the trend of (DH + acetic acid) > DH > WOM. The degradation rate was also reduced by higher film thickness, higher deposition substrate temperature, and dry-out intervals. The results of X-ray diffraction analysis indicate that the ZnO-based films underwent structural degeneration by losing their highly (002) preferential orientation with possible transformation from hexagonal into cubic and formation of Zn(OH)₂. Periodic optical micro-imaging observations suggested a temporal process that involves initial hydrolysis of the oxides at sporadic weak spots, swelling and popping of the hydrolyzed spots due to volume increase, segregation of hydrolyzed regions causing discontinuity of electrical path, hydrolysis of the oxide-glass interface, and finally, formation of insulating oxides/hydroxides with visible delamination over larger areas.

This paper summarizes the electrical and thermal characterizations of thin film PV modules based on amorphous triple junctions (3J: a-Si) and Copper Indium Selenide (CIS) thin film solar cells. Tests are operated in outdoor exposure and under natural sunlight of Ghardaia (Algeria) as specific desert climate environment, characterized by high irradiation and temperature levels. Data acquired from Environmental Operating Conditions (EOC) was converted into solar module output characteristics at Standard Test Conditions (STC) by using three method suggested by Anderson and Mermoud as well as the equations already standardized as IEC 60891. Then, based on the investigation results of the conversion equations, differences among the converting methods (range of application, specificity of solar cell material, and experimental test conditions) were studied.

Economic, flexible packages that provide needed level of protection to organic and some other PV cells over >25-years have not yet been developed. However, flexible packaging is essential in niche large-scale applications. Typical configuration used in flexible photovoltaic (PV) module packaging is transparent frontsheet/encapsulant/PV cells/flexible substrate. Besides flexibility of various components, the solder bonds should also be flexible and resistant to fatigue due to cyclic loading. Flexible front sheets should provide optical transparency, mechanical protection, scratch resistance, dielectric isolation, water resistance, UV stability and adhesion to encapsulant. Examples are Tefzel, Tedlar and Silicone. Dirt can get embedded in soft layers such as silicone and obscure light. Water vapor transmittance rate (WVTR) of polymer films used in the food packaging industry as moisture barriers are ~0.05 g/(m².day) under ambient conditions. In comparison, light emitting diodes employ packaging components that have WVTR of ~10^-6 g/(m².day). WVTR of polymer sheets can be improved by coating them with dense inorganic/organic multilayers. Ethylene vinyl acetate, an amorphous copolymer used predominantly by the PV industry has very high O₂ and H₂O diffusivity. Quaternary carbon chains (such as acetate) in a polymer lead to cleavage and loss of adhesional strength at relatively low exposures. Reactivity of PV module components increases in presence of O₂ and H₂O. Adhesional strength degrades due to the breakdown of structure of polymer by reactive, free radicals formed by high-energy radiation. Free radical formation in polymers is reduced when the aromatic rings are attached at regular intervals. This paper will review flexible packaging for PV modules.

The reliability of Uni-Solar triple-junction amorphous silicon thin-film PV modules is very important to their success in an increasingly competitive PV market. Modules must show useful operating lifetimes on the order of 20 to 30 years, and although module efficiency is very important, the total energy a module will produce is largely dependent on its operating lifetime. Thus, it is essential to evaluate module reliability in order to estimate module lifetime and establish customer warranty periods. While real world outdoor exposure testing is necessary and important, it is essential that accelerated environmental test methods are utilized to provide more rapid feedback regarding failure modes, design flaws and degradation mechanisms. The following paper gives an overview of the methodology used to ensure long-term reliability of Uni-Solar flexible thin-film modules. The applied test methods are primarily based upon accepted industry test standards such as IEC-61646, UL-1703, and ASTM. The design, screening, and qualification process to ensure the robustness of new designs is described as well as subsequent module validation testing and manufacturing process control. Test methods important for flexible module laminates are briefly discussed and examples of reliability tests are given. Upon successful design validation and certification, the quality and reliability of manufactured modules is maintained through supplier and product quality assurance programs.

Current accelerated tests of photovoltaic (PV) modules mostly prevent infant mortality but cannot duplicate changes occurring in the field nor can predict useful lifetime. Therefore, monitoring of field-deployed PV modules was undertaken at FSEC with goals to assess their performance in hot and humid climate under high voltage operation and to correlate the PV performance with the meteorological parameters. This paper presents performance analysis of U.S. Company manufactured thin film a-Si:H PV modules that are encapsulated using flexible front sheets and framed to be outdoor tested. Statistical data analysis of PV parameters along with meteorological parameters, monitored continuously, is carried out on regular basis with PVUSA type regression analysis. Current-voltage (I-V) characteristic of module arrays that are obtained periodically complement the continuous data monitoring. Moreover, effect of high voltage bias and ambient parameters on leakage current in PV modules on individual modules is studied. Any degradation occurring during initial 18 months could not be assessed due to data acquisition and hurricane problems. No significant degradation was observed in the performance of PV modules during the subsequent 30-months. It is planned to continue this study for a prolonged period so as to serve as basis for their long-term warranties.

This article describes a method to have a better knowledge of barrier performances needed for encapsulating materials, particularly in the case of organic solar cells devices. We have developed a high sensitivity permeameter which enables simultaneous measurements of water and oxygen permeation. Various polymers and inorganic coatings on polymer substrates have been measured. Experimental barrier parameters have been plotted considering the steady and transient states of permeation curves and compared to theoretical values. In addition, we have performed ageing experiments on encapsulated organic solar cells to establish a barrier requirement directly related to the device. Finally, we have performed such experiments using different cathode materials and encapsulating materials.

Prediction of energy production is crucial to the design and installation of the building integrated photovoltaic systems. This prediction should be attainable based on the commonly available parameters such as system size, orientation and tilt angle. Several commercially available as well as free downloadable software tools exist to predict energy production. Six software models have been evaluated in this study and they are: PV Watts, PVsyst, MAUI, Clean Power Estimator, Solar Advisor Model (SAM) and RETScreen. This evaluation has been done by comparing the monthly, seasonaly and annually predicted data with the actual, field data obtained over a year period on a large number of residential PV systems ranging between 2 and 3 kW_dc. All the systems are located in Arizona, within the Phoenix metropolitan area which lies at latitude 33° North, and longitude 112 West, and are all connected to the electrical grid.

Outdoor monitoring of glass to glass a-Si:H thin film photovoltaic (PV) modules by a US manufacturer is carried out in the hot and humid climate of Florida. The modules are monitored under fixed load conditions. Moreover, periodic current-voltage (I-V) characteristics are carried out to validate the performance of PV modules. The data was normalized at standard conditions and compared over a three year period. Two of the modules are biased to ±600 V to study the leakage current. An extensive study of this nature needs to be carried out for prolonged period to accurately predict the useful lifetime of PV modules.

The market demand for commercialization of Photovoltaic (PV) systems depends a lot on the reliability, efficiency and performance of various components within the system. PV panels produce DC power when exposed to sunlight, and an inverter converts this to AC power in a typical solar powered building. Though, PV lighting has existed for a long time it hasn't been very effective, as incandescent light sources were commonly used which are inefficient. Today fluorescent fixtures are mostly used with PV's due to its high efficacy. Light-emitting diodes present a new vision to energy efficiency in lighting design with their low energy consumption. Current research predicts improved efficiencies of LED light fixtures and their commercial use is a few years away. LEDs which operate on DC voltages when coupled with photovoltaics can be a simple PV lighting application and a sustainable solution with potential for payback. This research evaluates the design and construction of a photovoltaic DC LED lighting system for a solar house at Pennsylvania State University. A detailed cost and payback analysis of a PV DC LED lighting system is presented in this research. PV output simulations for the solar house are presented. Results presented in this research indicate that the Solid state lighting market is evolving rapidly and that LED's are a choice in stand-alone photovoltaic DC lighting systems. The efficiency and the cost-effectiveness of such systems would however improve in the coming years with research and development now focused on PV systems and on Solid state lighting technologies.