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Photovoltaic Shading Testbed for Module-Level Power Electronics

Description: This document describes a repeatable test procedure that attempts to simulate shading situations, as would be experienced by typical residential rooftop photovoltaic (PV) systems. This type of shading test is particularly useful to evaluate the impact of different power conversion setups, including microinverters, DC power optimizers and string inverters, on overall system performance. The performance results are weighted based on annual estimates of shade to predict annual performance improvement. A trial run of the test procedure was conducted with a side by side comparison of a string inverter with a microinverter, both operating on identical 8kW solar arrays. Considering three different shade weighting conditions, the microinverter was found to increase production by 3.7% under light shading, 7.8% under moderate shading, and 12.3% under heavy shading, relative to the reference string inverter case. Detail is provided in this document to allow duplication of the test method at different test installations and for different power electronics devices.
Date: May 1, 2012
Creator: Deline, C.; Meydbray, J.; Donovan, M. & Forrest, J.
Partner: UNT Libraries Government Documents Department

Estimating solar access of typical residential rooftops: A case study in San Jose, CA

Description: Shadows cast by trees and buildings can limit the solar access of rooftop solar-energy systems, including photovoltaic panels and thermal collectors. This study characterizes rooftop shading in a residential neighborhood of San Jose, CA, one of four regions analyzed in a wider study of the solar access of California homes.High-resolution orthophotos and LiDAR (Light Detection And Ranging) measurements of surface height were used to create a digital elevation model of all trees and buildings in a 4 km2 residential neighborhood. Hourly shading of roofing planes (the flat elements of roofs) was computed geometrically from the digital elevation model. Parcel boundaries were used to determine the extent to which roofing planes were shaded by trees and buildings in neighboring parcels.In the year in which surface heights were measured (2005), shadows from all sources ("total shading") reduced the insolation received by S-, SW-, and W-facing residential roofing planes in the study area by 13 - 16percent. Shadows cast by trees and buildings in neighboring parcels reduced insolation by no more than 2percent. After 30 years of simulated maximal tree growth, annual total shading increased to 19 - 22percent, and annual extraparcel shading increased to 3 - 4percent.
Date: March 3, 2008
Creator: Levinson, Ronnen M.; Gupta, Smita; Akbari, Hashem & Pomerantz, Melvin
Partner: UNT Libraries Government Documents Department

Partial Shade Evaluation of Distributed Power Electronics for Photovoltaic Systems: Preprint

Description: Site survey data for several residential installations are provided, showing the extent and frequency of shade throughout the year. This background information is used to design a representative shading test that is conducted on two side-by-side 8-kW photovoltaic (PV) installations. One system is equipped with a standard string inverter, while the other is equipped with microinverters on each solar panel. Partial shade is applied to both systems in a comprehensive range of shading conditions, simulating one of three shade extents. Under light shading conditions, the microinverter system produced the equivalent of 4% annual performance improvement, relative to the string inverter system. Under moderate shading conditions, the microinverter system outperformed the string inverter system by 8%, and under heavy shading the microinverter increased relative performance by 12%. In all three cases, the percentage of performance loss that is recovered by the use of distributed power electronics is 40%-50%. Additionally, it was found that certain shading conditions can lead to additional losses in string inverters due to peak-power tracking errors and voltage limitations.
Date: June 1, 2012
Creator: Deline, C.; Meydbrav, J. & Donovan, M.
Partner: UNT Libraries Government Documents Department

Performance and Economic Analysis of Distributed Power Electronics in Photovoltaic Systems

Description: Distributed electronics like micro-inverters and DC-DC converters can help recover mismatch and shading losses in photovoltaic (PV) systems. Under partially shaded conditions, the use of distributed electronics can recover between 15-40% of annual performance loss or more, depending on the system configuration and type of device used. Additional value-added features may also increase the benefit of using per-panel distributed electronics, including increased safety, reduced system design constraints and added monitoring and diagnostics. The economics of these devices will also become more favorable as production volume increases, and integration within the solar panel?s junction box reduces part count and installation time. Some potential liabilities of per-panel devices include increased PV system cost, additional points of failure, and an insertion loss that may or may not offset performance gains under particular mismatch conditions.
Date: January 1, 2011
Creator: Deline, C.; Marion, B.; Granata, J. & Gonzalez, S.
Partner: UNT Libraries Government Documents Department

Tucannon River Temperature Study, Prepared for : Watershed Resource Inventory Area (WRIA) 35.

Description: This report presents the results of a temperature analysis of the Tucannon River completed for the WRIA 35 Planning Unit. The Tucannon River is located in southeastern Washington and flows approximately 100 kilometers (km) (62 miles) from the Blue Mountains to the Snake River. High water temperature in the Tucannon River has been identified as a limiting factor for salmonid fish habitat (Columbia Conservation District, 2004). Several segments of the Tucannon River are included on Washington State Department of Ecology (Ecology) 303(d) list of impaired waterbodies due to temperature. Ecology is currently conducting scoping for a temperature Total Maximum Daily Load (TMDL) study of the Tucannon River. The WRIA 35 Planning Unit retained HDR Engineering to evaluate water temperature in the Tucannon River. The project objectives are: (1) Review recent and historic data and studies to characterize temperature conditions in the river; (2) Perform field studies and analyses to identify and quantify heating and cooling processes in the river; (3) Develop and calibrate a computer temperature model to determine the sources of heat to the Tucannon River and to predict the temperature of the river that would occur with increased natural riparian shading assuming the current river morphology; (4) Evaluate differences in river temperatures between current and improved riparian shading during the 'critical' period - low river flows and high temperatures; and (5) Determine the potential benefits of riparian shading as a mechanism to decrease river temperature.
Date: June 30, 2006
Creator: Engineering., HDR
Partner: UNT Libraries Government Documents Department

Solar Energy Development Assistance for Fort Hunter Liggett

Description: Pacific Northwest National Laboratory provided assistance to Fort Hunter Liggett to determine the opportunities for solar energy development on the site. Increasing use of renewable energy is mandated by several executive orders and legislation. Fort Hunter Liggett has many attributes that enhance its suitability for renewable energy development. First, the site is located south of San Francisco in a remote portion of the costal foothills. Brush and forest fires are frequent and often result in power outages, which subsequently impacts the site’s training mission. In addition, the site’s blended electric rate during fiscal year (FY) 2010 was high at 12 ¢/kWh. Lastly, the solar resource is moderately high; the site receives nearly 5.7 kWh/m2/day on a south facing, latitude-tilted surface. In light of these factors, the site is a clear candidate for a solar photovoltaic array. Prior to Pacific Northwest National Laboratory’s (PNNL) involvement, the site secured funding for a 1 megawatt (MW) photovoltaic (PV) array that will also provide shading for site vehicles. To best implement this project, PNNL conducted a site visit and was tasked with providing the site technical guidance and support regarding module selection, array siting, and other ancillary issues.
Date: March 30, 2011
Creator: Russo, Bryan J.; Hoffman, Michael G. & Chvala, William D.
Partner: UNT Libraries Government Documents Department

Measured performance of selective glazings

Description: Measurements of the net heat flow through four selective glazings in comparison with clear double glazing under late summer outdoor conditions are presented. The SHGC for each glazing is extracted from the data and shown to be angle-dependent. The method of extracting the angle-dependent SHGC from the data is checked by comparing the measured SHGC for the clear double glazing to the calculation of OW 4. 1, which is assumed to be correct. Good agreement between the two is found. The measured angle-dependent SHGC`s of the selective glazings are then used to test the OW 4.1 selective glazing calculation and good agreement is again found.
Date: July 1, 1995
Creator: Klems, J.H.; Yazdanian, M. & Kelley, G.O.
Partner: UNT Libraries Government Documents Department

Observation of the moon shadow in deep underground muon flux.

Description: A shadow of the moon, with a statistical significance of 5{sigma}, has been observed in the underground muon flux at a depth of 2090 mwe using the Soudan 2 detector. The angular resolution of the detector is well described by a Gaussian with {sigma} {le}0.3{degree}. The position of the shadow confirms the alignment of the detector to better than 0.15{degree}. This alignment has remained stable during 10 years of data taking from 1989 through 1998.
Date: June 22, 1999
Creator: Allison, W. W. M.; Alner, G. J.; Ayres, D. S.; Cobb, J. H.; Fields, T. H.; Goodman, M. C. et al.
Partner: UNT Libraries Government Documents Department

Calorimetric measurements of inward-flowing fraction for complex glazing and shading systems

Description: This paper presents a calorimetric measurement of layer-specific inward-flowing fractions of absorbed solar energy for a number of geometric configurations common in fenestrations with shading. The inward-flowing fractions are found to be relatively insensitive to exterior conditions. Results for an interior venetian blind over double glazing agree with thermal model calculations in literature, and are the first layer-specific verification of these calculations. It is argued that a data base of these inward-flowing fractions for a suitably broad class of geometries will make possible the determination of solar heat gain coefficient from noncalorimetric measurements of solar-optical properties of complex fenestration components, a procedure termed solar-thermal separation.
Date: May 1, 1995
Creator: Klems, J.H. & Kelley, G.O.
Partner: UNT Libraries Government Documents Department

Solar heat gain through fenestration systems containing shading: Summary of procedures for estimating performance from minimal data

Description: The computational methods for calculating the properties of glazing systems containing shading from the properties of their components have been developed, but the measurement standards and property data bases necessary to apply them have not. It is shown that with a drastic simplifying assumption these methods can be used to calculate system solar-optical properties and solar heat gain coefficients for arbitrary glazing systems, while requiring limited data about the shading. Detailed formulas are presented, and performance multipliers are defined for the approximate treatment of simple glazings with shading. As higher accuracy is demanded, the formulas become very complicated.
Date: March 1, 2001
Creator: Klems, Joseph H.
Partner: UNT Libraries Government Documents Department

Solar Heat Gain Through Fenestration Systems Containing Shading: Procedures for Estimating Performance from Minimal Data

Description: The computational methods for calculating the properties of glazing systems containing shading from the properties of their components have been developed, but the measurement standards and property data bases necessary to apply them have not. It is shown that with a drastic simplifying assumption these methods can be used to calculate system solar-optical properties and solar heat gain coefficients for arbitrary glazing systems, while requiring limited data about the shading. Detailed formulas are presented, and performance multipliers are defined for the approximate treatment of simple glazings with shading. As higher accuracy is demanded, the formulas become very complicated.
Date: August 1, 2000
Creator: Klems, J.H.
Partner: UNT Libraries Government Documents Department

Designing PV Incentive Programs to Promote System Performance: AReview of Current Practice

Description: Some stakeholders continue to voice concerns about the performance of customer-sited photovoltaic (PV) systems, particularly because these systems typically receive financial support through ratepayer- or publicly-funded programs. Although much remains to be understood about the extent and specific causes of poor PV system performance, several studies of the larger programs and markets have shed some light on the issue. An evaluation of the California Energy Commission (CEC)'s Emerging Renewables Program, for example, found that 7% of systems, in a sample of 95, had lower-than-expected power output due to shading or soiling (KEMA 2005). About 3% of a larger sample of 140 systems were not operating at all or were operating well below expected output, due to failed equipment, faulty installation workmanship, and/or a lack of basic maintenance. In a recent evaluation of the other statewide PV incentive program in California, the Self-Generation Incentive Program, 9 of 52 projects sampled were found to have annual capacity factors less than 14.5%, although reasons for these low capacity factors generally were not identified (Itron 2005). Studies of PV systems in Germany and Japan, the two largest PV markets worldwide, have also revealed some performance problems associated with issues such as shading, equipment and installation defects, inverter failure, and deviations from module manufacturers' specifications (Otani et al. 2004, Jahn & Nasse 2004). Although owners of PV systems have an inherent incentive to ensure that their systems perform well, many homeowners and building operators may lack the necessary information and expertise to carry out this task effectively. Given this barrier, and the responsibility of PV incentive programs to ensure that public funds are prudently spent, these programs should (and often do) play a critical role in promoting PV system performance. Performance-based incentives (PBIs), which are based on actual energy production rather than the rated capacity ...
Date: November 12, 2006
Creator: Barbose, Galen; Wiser, Ryan & Bolinger, Mark
Partner: UNT Libraries Government Documents Department

The energy-savings potential of electrochromic windows in the UScommercial buildings sector

Description: Switchable electrochromic (EC) windows have been projected to significantly reduce the energy use of buildings nationwide. This study quantifies the potential impact of electrochromic windows on US primary energy use in the commercial building sector and also provides a broader database of energy use and peak demand savings for perimeter zones than that given in previous LBNL simulation studies. The DOE-2.1E building simulation program was used to predict the annual energy use of a three-story prototypical commercial office building located in five US climates and 16 California climate zones. The energy performance of an electrochromic window controlled to maintain daylight illuminance at a prescribed setpoint level is compared to conventional and the best available commercial windows as well as windows defined by the ASHRAE 90.1-1999 and California Title 24-2005 Prescriptive Standards. Perimeter zone energy use and peak demand savings data by orientation, window size, and climate are given for windows with interior shading, attached shading, and horizon obstructions (to simulate an urban environment). Perimeter zone primary energy use is reduced by 10-20% in east, south, and west zones in most climates if the commercial building has a large window-to-wall area ratio of 0.60 compared to a spectrally selective low-e window with daylighting controls and no interior or exterior shading. Peak demand for the same condition is reduced by 20-30%. The emerging electrochromic window with daylighting controls is projected to save approximately 91.5-97.3 10{sup 12} Btu in the year 2030 compared to a spectrally selective low-E window with manually-controlled interior shades and no daylighting controls if it reaches a 40% market penetration level in that year.
Date: April 30, 2004
Creator: Lee, Eleanor; Yazdanian, Mehry & Selkowitz, Stephen
Partner: UNT Libraries Government Documents Department

Energy and visual comfort performance of electrochromic windowswith overhangs

Description: DOE-2 building energy simulations were conducted to determine if there were practical architectural and control strategy solutions that would enable electrochromic (EC) windows to significantly improve visual comfort without eroding energy-efficiency benefits. EC windows were combined with overhangs since opaque overhangs provide protection from direct sun which EC windows are unable to do alone. The window wall was divided into an upper and lower aperture so that various combinations of overhang position and control strategies could be considered. The overhang was positioned either at the top of the upper window aperture or between the upper and lower apertures. Overhang depth was varied. EC control strategies were fully bleached at all times, modulated based on incident vertical solar radiation limits, or modulated to meet the design work plane illuminance with daylight. The EC performance was compared to a state-of-the-art spectrally selective low-e window with the same divided window wall, window size, and overhang as the EC configuration. The reference window was also combined with an interior shade which was manually deployed to control glare and direct sun. Both systems had the same daylighting control system to dim the electric lighting. Results were given for south-facing private offices in a typical commercial building. In hot and cold climates such as Houston and Chicago, EC windows with overhangs can significantly reduce the average annual daylight glare index (DGI) and deliver significant annual energy use savings if the window area is large. Total primary annual energy use was increased by 2-5% for moderate-area windows in either climate but decreased by 10% in Chicago and 5% in Houston for large-area windows. Peak electric demand can be reduced by 7-8% for moderate-area windows and by 14-16% for large-area windows in either climate. Energy and peak demand reductions can be significantly greater if the reference case does ...
Date: November 3, 2005
Creator: Lee, E.S. & Tavil, A.
Partner: UNT Libraries Government Documents Department

Investigation of GPS/IMU Positioning System for Mining Equipment

Description: The objective of this project is to investigate the applicability of a combined Global Positioning System and Inertial Measurement Unit (GPS/IMU) for information based displays on earthmoving machines and for automated earthmoving machines in the future. This technology has the potential of allowing an information-based product like Caterpillar's Computer Aided Earthmoving System (CAES) to operate in areas with satellite shading. Satellite shading is an issue in open pit mining because machines are routinely required to operate close to high walls, which reduces significantly the amount of the visible sky to the GPS antenna mounted on the machine. An inertial measurement unit is a product, which provides data for the calculation of position based on sensing accelerations and rotation rates of the machine's rigid body. When this information is coupled with GPS it results in a positioning system that can maintain positioning capability during time periods of shading.
Date: September 13, 2006
Creator: Stratton, Ken L.
Partner: UNT Libraries Government Documents Department

High-Performance Home Technologies: Solar Thermal & Photovoltaic Systems

Description: This document is the sixth volume of the Building America Best Practices Series. It presents information that is useful throughout the United States for enhancing the energy efficiency practices in the specific climate zones that are presented in the first five Best Practices volumes. It provides an introduction to current photovoltaic and solar thermal building practices. Information about window selection and shading is included.
Date: June 1, 2007
Creator: Baechler, M.; Gilbride, T.; Ruiz, K.; Steward, H. & Love, P.
Partner: UNT Libraries Government Documents Department

Opportunities and Challenges for Power Electronics in PV Modules (Presentation)

Description: The presentation describes the value of adding DC converters and other power electronics to modules to improve their output even when shading or bad cells would otherwise decrease the module output. The presentation was part of a workshop sponsored by ARPA-E exploring the opportunities for power electronics to support PV applications.
Date: February 1, 2011
Creator: Kurtz, S.; Deline, C.; Wohlgemuth, J.; Marion, B. & Granata, J.
Partner: UNT Libraries Government Documents Department

Solar access of residential rooftops in four California cities

Description: Shadows cast by trees and buildings can limit the solar access of rooftop solar-energy systems, including photovoltaic panels and thermal collectors. This study characterizes residential rooftop shading in Sacramento, San Jose, Los Angeles and San Diego, CA. Our analysis can be used to better estimate power production and/or thermal collection by rooftop solar-energy equipment. It can also be considered when designing programs to plant shade trees. High-resolution orthophotos and LiDAR (Light Detection And Ranging) measurements of surface height were used to create a digital elevation model of all trees and buildings in a well-treed 2.5-4 km{sup 2} residential neighborhood. On-hour shading of roofing planes (the flat elements of roofs) was computed geometrically from the digital elevation model. Values in future years were determined by repeating these calculations after simulating tree growth. Parcel boundaries were used to determine the extent to which roofing planes were shaded by trees and buildings in neighboring parcels. For the subset of S+SW+W-facing planes on which solar equipment is commonly installed for maximum solar access, absolute light loss in spring, summer and fall peaked about two to four hours after sunrise and about two to four hours before sunset. The fraction of annual insolation lost to shading increased from 0.07-0.08 in the year of surface-height measurement to 0.11-0.14 after 30 years of tree growth. Only about 10% of this loss results from shading by trees and buildings in neighboring parcels.
Date: May 14, 2010
Creator: Levinson, Ronnen; Akbari, Hashem & Pomerantz, Melvin
Partner: UNT Libraries Government Documents Department

U.S. Aims for Zero-Energy: Support for PV on New Homes

Description: As a market segment for solar photovoltaic (PV) adoption, new homes have a number of attractive attributes. Homebuyers can easily roll the cost of the PV system into their mortgage and, with rebates or other financial incentives, potentially realize an immediate net positive cash flow from the investment. PV system performance can be optimized by taking roof orientation, shading, and other structural factors into account in the design of new homes. Building-integrated photovoltaics (BIPV), which are subject to fewer aesthetic concerns than traditional, rack-mounted systems, are well-suited to new construction applications. In large new residential developments, costs can be reduced through bulk purchases and scale economies in system design and installation. Finally, the ability to install PV as a standard feature in new developments - like common household appliances - creates an opportunity to circumvent the high transaction costs and other barriers typically confronted when each individual homeowner must make a distinct PV purchase decision.
Date: May 11, 2006
Creator: Barbose, Galen; Wiser, Ryan & Bolinger, Mark
Partner: UNT Libraries Government Documents Department