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The impact of retail rate structures on the economics of commercial photovoltaic systems in California

Description: This article examines the impact of retail electricity rate design on the economic value of grid-connected photovoltaic (PV) systems, focusing on commercial customers in California. Using 15-min interval building load and PV production data from a sample of 24 actual commercial PV installations, we compare the value of the bill savings across 20 commercial-customer retail electricity rates currently offered in the state. Across all combinations of customers and rates, we find that the annual bill savings from PV, per kWh generated, ranges from $0.05 to $0.24/kWh. This sizable range in rate-reduction value reflects differences in rate structures, revenue requirements, the size of the PV system relative to building load, and customer load shape. The most significant rate design issue for the value of commercial PV is found to be the percentage of total utility bills recovered through demand charges, though a variety of other factors are also found to be of importance. The value of net metering is found to be substantial, but only when energy from commercial PV systems represents a sizable portion of annual customer load. Though the analysis presented here is specific to California, our general results demonstrate the fundamental importance of retail rate design for the customer-economics of grid-connected, customer-sited PV.
Date: June 24, 2008
Creator: Mills, Andrew D.; Wiser, Ryan; Barbose, Galen & Golove, William
Partner: UNT Libraries Government Documents Department

Electrowetting Solar Cell

Description: This paper discusses the electrowetting solar cell. In comparison with traditional silicon-based PV solar cells, the electrowetting-based self-tracking technology will generate ~70% more green energy with a 50% cost reduction.
Date: April 19, 2012
Creator: Reilly, David & Cheng, Jiangtao
Partner: UNT Honors College

Photovoltaic Mechanisms in Polycrystalline Thin Film Silicon Solar Cells: Quarterly Technical Progress Report No. 1, July 30 - October 31, 1980

Description: Objectives of the program: 1) Development of the surface preparation techniques to aid in the unequivocal interpretation of grain boundary (G.B.) data, 2) Characterization of G.B.s in terms of chemical, physical, electrical and optical parameters, and correlation to solar cell performance. 3) Identification of the effects of intra grain crystal defects and 4) Determination of effects of solar cell processing on G.B. parameters and bulk defects.
Date: January 1, 1980
Creator: Sopori, B.
Partner: UNT Libraries Government Documents Department

Photovoltaic Mechanisms in Polycrystalline Thin Film Silicon Solar Cells: Quarterly Technical Progress Report No. 3, February 1 - April 30, 1981

Description: This report describes two areas of research carried out during this contract period. Results of Cu decoration for defect analysis are given and also the design of an AR coating for optimizing performance of a textured cell. Basic optical characteristics of textured surfaces utilized in this design are described.
Date: January 1, 1981
Creator: Sopori, B.
Partner: UNT Libraries Government Documents Department

Development of a Visual Inspection Checklist for Evaluation of Fielded PV Module Condition (Presentation)

Description: A visual inspection checklist for the evaluation of fielded photovoltaic (PV) modules has been developed to facilitate collection of data describing the field performance of PV modules. The proposed inspection checklist consists of 14 sections, each documenting the appearance or properties of a part of the module. This tool has been evaluated through the inspection of over 60 PV modules produced by more than 20 manufacturers and fielded at two different sites for varying periods of time. Aggregated data from a single data collection tool such as this checklist has the potential to enable longitudinal studies of module condition over time, technology evolution, and field location for the enhancement of module reliability models.
Date: March 1, 2012
Creator: Packard, C. E; Wohlgemuth, J. H. & Kurtz, S. R.
Partner: UNT Libraries Government Documents Department

Thermal Study of Inverter Components: Preprint

Description: Thermal histories of inverter components were collected from operating inverters from several manufacturers and three locations. The data were analyzed to determine thermal profiles, the dependence on local conditions, and to assess the effect on inverter reliability. Inverter temperatures were shown to increase with the power dissipation of the inverters, follow diurnal and annual cycles, and have a dependence on wind speed. An accumulated damage model was applied to the temperature profiles and an example of using these data to predict reliability was explored.
Date: June 1, 2012
Creator: Sorensen, N. R.; Thomas, E. V.; Quintana, M. A.; Barkaszi, S.; Rosenthal, A.; Zhang, Z. et al.
Partner: UNT Libraries Government Documents Department

Photovoltaic (PV) Pricing Trends: Historical, Recent, and Near-Term Projections

Description: This report helps to clarify the confusion surrounding different estimates of system pricing by distinguishing between past, current, and near-term projected estimates. It also discusses the different methodologies and factors that impact the estimated price of a PV system, such as system size, location, technology, and reporting methods.These factors, including timing, can have a significant impact on system pricing.
Date: November 1, 2012
Creator: Feldman, D.; Barbose, G.; Margolis, R.; Wiser, R.; Darghouth, N. & Goodrich, A.
Partner: UNT Libraries Government Documents Department

Module Technology: Current Practice and Issues (Presentation)

Description: PV modules must provide mechanical support for the cells, protect the world from the voltages inside, protect the cells, diodes and interconnects from the weather outside, couple as much light as possible into the PV cells and minimize the temperature increase of the cells. The package must continue to serve these functions for at least 25 years as that is the typical module warranty period today. Furthermore the package must do all this for as low a cost as possible since the key to large scale PV growth is a reduction in cost while retaining excellent module reliability and durability. This paper will review current module construction practices for both crystalline silicon and thin film PV with emphasis on explaining why the present designs and materials have been selected. Possible long term issues with today's designs and materials will be discussed. Several proposed solutions to these issues will be presented, highlighting the research efforts that will be necessary in order to verify that they can cost effectively solve the identified issues.
Date: October 5, 2010
Creator: Wohlgemuth, J.
Partner: UNT Libraries Government Documents Department

Rapid Thermal Annealing of HWCVD a-Si:H Films: The Effect of the Film Hydrogen Content on the Crystallization Kinetics, Surface Morphology, and Grain Growth

Description: We report the effect of the hydrogen (H) content (CH) on the crystallization kinetics, surface morphology and grain growth for Hot Wire CVD a-Si:H films containing 12.5 and 2.7 at.% H which are crystallized by rapid thermal anneal (RTA). For the high CH film we observe explosive H evolution, with a resultant destruction of the film for RTA temperatures >750 deg C. At RTA temperatures ~600 deg C, both films remain intact with similar morphologies. At this same lower RTA, the incubation and crystallization times decrease, and the grain size as measured by X-Ray Diffraction increases with decreasing film CH. SIMS measurements indicate that a similar film CH (<0.5 at.%) exists in both films when crystallization commences. The benefits of a two-step annealing process for the high CH film are documented.
Date: November 1, 2005
Creator: Mahan, A. H.; Reedy, R. C. Jr.; Ginley, D. S.; Roy, B. & Readey, D. W.
Partner: UNT Libraries Government Documents Department

Module Packaging Research and Reliability: Activities and Capabilities

Description: Our team activities are directed at improving PV module reliability by incorporating new, more effective, and less expensive packaging materials and techniques. New and existing materials or designs are evaluated before and during accelerated environmental exposure for the following properties: (1) Adhesion and cohesion: peel strength and lap shear. (2) Electrical conductivity: surface, bulk, interface and transients. (3) Water vapor transmission: solubility and diffusivity. (4) Accelerated weathering: ultraviolet, temperature, and damp heat tests. (5) Module and cell failure diagnostics: infrared imaging, individual cell shunt characterization, coring. (6) Fabrication improvements: SiOxNy barrier coatings and enhanced wet adhesion. (7) Numerical modeling: Moisture ingress/egress, module and cell performance, and cell-to-frame leakage current. (8) Rheological properties of polymer encapsulant and sheeting materials. Specific examples are described.
Date: November 1, 2005
Creator: McMahon, T. J.; delCueto, J.; Glick, S.; Jorgensen, G.; Kempe, M.; Pern, J. et al.
Partner: UNT Libraries Government Documents Department

Exploratory Reliability and Performance R&D

Description: This paper presents a brief overview of the status and accomplishments during fiscal year (FY) 2005 of the Photovoltaic (PV) Exploratory Reliability and Performance R&D Subtask, which is part of the PV Module Reliability R&D Project (a joint NREL-Sandia project).
Date: November 1, 2005
Creator: Osterwald, C. R.
Partner: UNT Libraries Government Documents Department

Cold-Climate Solar Domestic Hot Water Systems Analysis

Description: The Solar Heating and Lighting Sub-program has set the key goal to reduce the cost of saved energy [Csav, defined as (total cost, $)/(total discounted savings, kWh_thermal)] for solar domestic water heaters (SDWH) by at least 50%. To determine if this goal is attainable and prioritize R&D for cold-climate SDWH, life-cycle analyses were done with hypothetical lower-cost components in glycol, drainback, and thermosiphon systems. Balance-of-system (BOS, everything but the collector) measures included replacing metal components with polymeric versions and system simplification. With all BOS measures in place, Csav could be reduced more than 50% with a low-cost, selectively-coated, glazed polymeric collector, and slightly less than 50% with either a conventional selective metal-glass or a non-selective glazed polymer collector. The largest percent reduction in Csav comes from replacing conventional pressurized solar storage tanks and metal heat exchangers with un-pressurized polymer tanks with immersed polymer heat exchangers, which could be developed with relatively low-risk R&D.
Date: November 1, 2005
Creator: Burch, J.; Salasovich, J. & Hillman, T.
Partner: UNT Libraries Government Documents Department

Integrating Deposition, Processing, and Characterization Equipment within the National Center for Photovoltaics

Description: The purpose of the process integration project of the National Center for Photovoltaics (NCPV) is to develop an infrastructure that will allow researchers to gain new knowledge that is difficult--if not impossible--to obtain with existing equipment. This difficulty is due, in part, to the state of our existing tool set, which lacks sufficient in-situ or real-time measurement capabilities, or lacks access to analytical tools where the sample remains in a controlled environment between deposition and processing or measurement. This new infrastructure will provide flexible and robust integration of deposition, processing (etching, annealing, etc.), and characterization tools via a standardized transfer interface such that samples move between tools in a controlled ambient. Ultimately, this synergistic effort between NREL staff, universities, and the photovoltaic (PV) industry--around an integrated tool base--will add to the PV knowledge base and help move many PV technologies forward.
Date: November 1, 2005
Creator: Nelson, B.; Robbins, S. & Sheldon, P.
Partner: UNT Libraries Government Documents Department

Calculations of Optimal Source Geometry and Controlled Combinatorial Gradients in Fixed- and Rotating-Substrate PVD Systems

Description: Normalized forms of conventional flux-distribution formulas are applied to physical-vapor deposition from open-boat type sources onto static and rotating substrates. For the rotating-substrate case, the deposition geometry that yields optimal film-thickness uniformity for different source-substrate separations is derived empirically. In addition, flux-distribution formulas are used to develop a novel method for combinatorial physical-vapor deposition. With this method, a single deposition system may be used, without modification, to deposit either highly uniform or graded-composition thin-film materials.
Date: November 1, 2005
Creator: Teeter, G.
Partner: UNT Libraries Government Documents Department

Plasma Surface Modification of Polymer Backsheets: Origins of Future Interfacial Barrier/Backsheet Failure

Description: Flexible polymer substrates coated with inorganic oxide moisture barriers are a potential replacement for glass backsheets in thin film PV modules. Silicon oxynitride (SiOxNy) deposited by PECVD on polyethylene terephthalate (PET) represents one potential new backsheet candidate. Barrier deposition runs at NREL have typically included a nitrogen-rich plasma pretreatment prior to actual barrier deposition with the intention of cleaning the PET surface as well as enhancing adhesion of the SiOxNy barrier film to PET; however, test coupons of PET/barrier/EVA/TPE failed after damp heat exposure. PET substrates exposed to plasma conditions similar to those used in pre-treatment were examined by X-ray photoelectron spectroscopy (XPS) to reveal new low molecular weight PET fragments are created which are volatile upon heating and water soluble. Failure analysis of the coupons determined that the moisture barrier is, in fact, transferred to the encapsulant side.
Date: November 1, 2005
Creator: Pankow, J. W. & Glick, S. H.
Partner: UNT Libraries Government Documents Department

Methods for Analysis of Outdoor Performance Data (Presentation)

Description: The ability to accurately predict power delivery over the course of time is of vital importance to the growth of the photovoltaic (PV) industry. Two key cost drivers are the efficiency with which sunlight is converted to power and secondly how this relationship develops over time. The accurate knowledge of power decline over time, also known as degradation rates, is essential and important to all stakeholders--utility companies, integrators, investors, and scientists alike. Different methods to determine degradation rates and discrete versus continuous data are presented, and some general best practice methods are outlined. In addition, historical degradation rates and some preliminary analysis with respect to climate are given.
Date: February 1, 2011
Creator: Jordan, D.
Partner: UNT Libraries Government Documents Department

PVWatts Version 1 Technical Reference

Description: The NREL PVWatts(TM) calculator is a web application developed by the National Renewable Energy Laboratory (NREL) that estimates the electricity production of a grid-connected photovoltaic system based on a few simple inputs. PVWatts combines a number of sub-models to predict overall system performance, and makes several hidden assumptions about performance parameters. This technical reference details the individual sub-models, documents assumptions and hidden parameters, and explains the sequence of calculations that yield the final system performance estimation.
Date: October 1, 2013
Creator: Dobos, A. P.
Partner: UNT Libraries Government Documents Department

Results from the Second International Module Intercomparison

Description: The peak-watt rating is a primary indicator of PV performance. The peak power rating is the maximum electrical power that is produced when the PV device is continuously illuminated at 1000 Wm/sup-2/ total irradiance under International Electrotechnical Commission Standard 60904-2 reference spectrum, and 25 deg C cell temperature. Most manufacturers trace their peak-watt rating through calibrations performed at recognized terrestrial calibration facilities. Manufacturers typically perform intercomparisons among a set of their modules internally with other plants and among. Sometimes they have the same module measured at different calibration facilities to determine the differences in calibration. This intercomparison was to mimic this procedure and supply new thin film samples along with samples that could pose other problems. These intercomparisons sample the laboratories' everyday procedures better than a formal intercomparison where the laboratories' best procedures and data scrutiny are used.
Date: November 1, 2005
Creator: Rummel, S.; Anderberg, A. & Emery, K.
Partner: UNT Libraries Government Documents Department

Rheological and Mechanical Considerations for Photovoltaic Encapsulants

Description: Photovoltaic (pv) devices are encapsulated in polymeric materials not only for corrosion protection, but also for mechanical support. Even though ethylene-vinyl acetate (EVA) suffers from having both glass and melting phase transitions at temperatures experienced under environmental exposure, its low cost and good optical transmission made EVA the most commonly used material for PV modules. These transitions, however, cause EVA to embrittle at low temperatures (~ -15 deg C) and to be very soft at high temperatures (>40 deg C). From mechanical considerations, one would prefer a material that was relatively unchanged under a wide temperature range. This would produce a more predictable and reliable package. These concerns are likely to become more important as silicon based cells are made thinner.
Date: November 1, 2005
Creator: Kempe, M. D.
Partner: UNT Libraries Government Documents Department

Surfactant-Assisted Growth of CdS Thin Films for Photovoltaic Applications

Description: A common non-ionic surfactant, Triton X-100, was used to modify the chemical bath deposition (CBD) of CdS "buffer" layers on Cu(In,Ga)Se2 (CIGS) thin films. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) data demonstrate that films produced with the surfactant have about the same levels of impurities as films grown without it. For thin, ~130 ..ANG.. CdS layers and relative to devices made without the surfactant, average absolute cell efficiencies were increased from 10.5% to 14.8%, or by a relative 41%. Visual inspection of the CdS depositions reveals one possible mechanism of the surfactant's effects: bubbles that form and adhere to the CIGS surface during the CBD reaction are almost completely eliminated with the addition of the TX-100. Thus, pinholes and thin areas in the CdS layers caused by poor wetting of the substrate surface are sharply reduced, leading to large increases in the open circuit voltage in devices produced with the surfactant.
Date: November 1, 2005
Creator: Perkins, C. L. & Hasoon, F. S.
Partner: UNT Libraries Government Documents Department

Oxynitride Thin Film Barriers for PV Packaging

Description: Dielectric thin-film barrier and adhesion-promoting layers consisting of silicon oxynitride materials (SiOxNy, with various stoichiometry) were investigated. For process development, films were applied to glass (TCO, conductive SnO2:F; or soda-lime), polymer (PET, polyethylene terephthalate), aluminized soda-lime glass, or PV cell (a-Si, CIGS) substrates. Design strategy employed de-minimus hazard criteria to facilitate industrial adoption and reduce implementation costs for PV manufacturers or suppliers. A restricted process window was explored using dilute compressed gases (3% silane, 14% nitrous oxide, 23% oxygen) in nitrogen (or former mixtures, and 11.45% oxygen mix in helium and/or 99.999% helium dilution) with a worst-case flammable and non-corrosive hazard classification. Method employed low radio frequency (RF) power, less than or equal to 3 milliwatts per cm2, and low substrate temperatures, less than or equal to 100 deg C, over deposition areas less than or equal to 1000 cm2. Select material properties for barrier film thickness (profilometer), composition (XPS/FTIR), optical (refractive index, %T and %R), mechanical peel strength and WVTR barrier performance are presented.
Date: November 1, 2005
Creator: Glick, S. H.; delCueto, J. A.; Terwilliger, K. M.; Jorgensen, G. J.; Pankow, J. W.; Keyes, B. M. et al.
Partner: UNT Libraries Government Documents Department

Performance Evaluation of a 1.5-kWdc a-Si PV Array Using the PVUSA Power Rating Method at NREL's Outdoor Test Facility

Description: As part of the work conducted in the PV Systems Reliability and Performance R&D Task, a 1.5-kWdc photovoltaic (PV) array consisting of 36 Solarex MST-43MV dual-junction a-Si modules was installed and its performance monitored for almost six years (September 1999 through May 2005) at the National Renewable Energy Laboratory (NREL) Outdoor Test Facility (OTF). This paper describes the system and its performance based on the PV for Utility-Scale Applications (PVUSA) power rating method.
Date: November 1, 2005
Creator: McNutt, P.; Adelstein, J. & Sekulic, W.
Partner: UNT Libraries Government Documents Department