Greg P. Smestad

Greg P. Smestad
Sol Ideas Technology Development

PhD

About

110
Publications
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Introduction
Working on soiling issues connected to photovoltaics from the optics and materials perspective.

Publications

Publications (110)
Article
Full-text available
The accumulation of soiling on photovoltaic (PV) modules affects PV systems worldwide. Soiling consists of mineral dust, soot particles, aerosols, pollen, fungi and/or other contaminants that deposit on the surface of PV modules. Soiling absorbs, scatters, and reflects a fraction of the incoming sunlight, reducing the intensity that reaches the act...
Preprint
Full-text available
This paper presents the results of an investigation on the spectral losses of photovoltaic (PV) soiling. The transmittance of a glass coupon exposed to natural outdoor soiling in Ja\'en, southern Spain, has been measured weekly and used to estimate the soiling losses that various types of photovoltaic materials would experience if installed in the...
Article
Full-text available
The transduction and conversion of light into work via a quantum process is dependent on the luminescent properties of the materials involved. Materials that can exhibit emission of light upon illumination are likely candidates for solar cells, detectors and optoelectronic devices. This radiative recombination in a material is directly related to t...
Article
Several models have been presented in the recent years to estimate the magnitude of soiling from environmental parameters. However, these models are often based on data from a single site, or at most a few sites, and only limited data are, as of yet, available on their uncertainty. The present work aims to present a first comparative analysis of so...
Presentation
Full-text available
In the context of discussions surrounding a clean energy economy and strategies to address climate change, policymakers and leaders throughout the world often speak of their proposed programs in terms of millions of jobs being created, induced and saved. Just how would one go about qualifying that with some degree of certainty so that it can be con...
Article
Deposition of particulate matter (PM) onto solar photovoltaic (PV) panels - known as soiling - has been estimated to reduce energy production by 10–40% in many regions of the world. Despite this, many key properties including soiling rates, PM source contributions, physical and optical properties of the deposited particles, and the impact of rain a...
Article
Soiling impacts the photovoltaic (PV) module performance by reducing the amount of light reaching the photovoltaic cells and by changing their external spectral response. Currently, the soiling monitoring market is moving toward optical sensors that measure transmittance or reflectance, rather than directly measuring the impact of soiling on the pe...
Preprint
Full-text available
Soiling impacts the photovoltaic (PV) module performance by reducing the amount of light reaching the photovoltaic cells and by changing their external spectral response. Currently, the soiling monitoring market is moving toward optical sensors that measure transmittance or reflectance, rather than directly measuring the impact of soiling on the pe...
Article
This paper presents the results of an investigation on the spectral losses of photovoltaic (PV) soiling. The transmittance of a glass coupon exposed to natural soiling outdoors in Jaén, southern Spain, has been measured weekly and used to estimate the soiling losses that various types of photovoltaic materials would experience if installed in the s...
Article
Greg P. Smestad has served as an editor for Solar Energy Materials and Solar Cells since its inception in 1990 through August 2016. This farewell editorial outlines the story of the journal from Dr. Smestad's perspective and his role in its early development. It also shares his insights for the journal's future development and introduces new editor...
Article
Full-text available
This paper provides an analysis of the benefits of passive cooling for High Concentrator Photovoltaic (HCPV) systems in terms of costs and kWh annual energy yields. For the first time, the performance of the heat sinks has been related to the calculated energy yield of a standard triple-junction GaInP/GaAs/Ge HCPV cell in a system deployed at sever...
Article
This work connects the electrical performance and economics of High Concentrator Photovoltaic technology beyond the cell and module levels. It analyses the impact of fundamental variables on the calculated energy output and economics of a typical system for real-world solar power plants in five locations with diverse climatic conditions. It was fou...
Chapter
Multijunction (MJ) concentrator solar cells are primarily constructed of III-V semiconductor materials. The high solar-conversion efficiencies of these devices are dependent on precise control of growth conditions using one of several techniques such as molecular beam epitaxy, metal organic chemical vapour, or metal organic vapour-phase epitaxy dep...
Data
Full-text available
This document provides supplemental information and explains the content found in the files (OSA_SOLAR12_12113_final.pdf and Solyndra_Data.pdf) that you can download. The reference for the former is R. John Koshel, Greg P. Smestad, Daniel Shull, Peter Stephens, and Tim Healy, "Cylindrical and Flat Solar Collector Geometries: Theory and Experiment -...
Conference Paper
Full-text available
We present a bottom-up model of III-V multi-junction cells, as well as a high concentration PV (HCPV) module. We calculate $0.59/W(DC) manufacturing costs for our model HCPV module design with today’s capabilities, and find that reducing cell costs and increasing module efficiency offer the most promising paths for future cost reductions. Cell cost...
Conference Paper
Full-text available
This paper describes a new program that gives engineering students from the freshman year through graduate school the opportunity to learn interdisciplinary engineering in the sector of sustainable energy through practical projects. Many of today's students enter the University prepared and eager to learn through practical engineering projects, fac...
Conference Paper
Full-text available
Comparisons between theory, ray-tracing, and experiments for flat and cylindrical PV-panels are made. Results show agreement, with cylindrical geometries working better in the morning and afternoon, while flat panels work better around noon.
Article
Full-text available
Metal oxides are reviewed as catalysts to convert H2O and CO2 to fuels using solar energy. For photochemical conversion, TiO2 has been found to be the most stable and useful oxide material, but it is currently limited by its large bandgap and a mismatch between its conduction band and the redox couples for water splitting and CO2 reduction. A theor...
Article
The fabrication and testing of screen printed dye-sensitized large solar cell (15 cm × 15 cm) based on nanocrystalline TiO2 is described. It is the largest photo-electrochemical (PEC) cell that is based on the dye sensitization of thin (8-18 μm) films of TiO2 nanoparticles in contact with a non-aqueous liquid electrolyte. The cell has the potential...
Article
Full-text available
The editorial section of Solar Energy Materials & Solar Cells informs about solar cells. The journal has a wide scope and breadth and considers works on all solar energy materials, energy efficient films, and devices made from these materials. It encourages all innovative approaches in materials science and engineering as it applies to the field of...
Article
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Key advances in solar concentrator and non-concentrator photovoltaic module optics will be reviewed. Likewise, we present how the optics within the solar cell itself can maximize its solar conversion efficiency while reducing the cost.
Article
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A Systems Analysis for the solar energy industry and solar R&D is presented to identify key positive reinforcements that can accelerate the adoption of solar technologies through a process of solar value creation. Such an analysis can also identify constraints that can decelerate solar technology adoption, as well as points of leverage where invest...
Article
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With widespread deployment of PV power imminent, it is useful for researchers to have a basic knowledge of the economic principles that govern PV modules and systems. Several simplified and illustrative equations are presented.
Article
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In order to improve the accuracy, validity, reliability and reproducibility of reported power conversion efficiencies for solar cells, the journal, Solar Energy Materials and Solar Cells (SOLMAT), wishes to define how power conversion efficiencies should be reported. This expands upon what is specified in our Guide for Authors. This editorial also...
Article
The current interest in solar energy should be self-sustaining due to economies of scale, new materials and processes, and an understanding of the requirements for economical, efficient solar converters. A brief history will be presented. Article not available.
Article
Full-text available
The Solar Power 2006 conference in San José was the largest solar conference event in United States history. This meeting marks a new awakening of the United States to Solar Power, since the peak in interest in it during the 1970s. This editorial reviews the highlights of the meeting, with an emphasis on the companies that participated, and the are...
Chapter
Versuche zur Photochemie und Photophysik Versuchvorschriften Themenbereich: Photooxidationen, PhotoreduktionenThemenbereich: Reaktionen an und mit Halbleitern Versuchvorschriften Themenbereich: Photooxidationen, PhotoreduktionenThemenbereich: Reaktionen an und mit Halbleitern Themenbereich: Photooxidationen, PhotoreduktionenThemenbereich: Reaktione...
Article
Flat solid-state polymer photovoltaic (PV) cells were constructed using undoped poly(3-undecyl-2,2′-bithiophene) (P3UBT) and flat titanium dioxide (TiO2) films prepared using a sol–gel technique. Layers and interfaces were studied using AFM, SEM, EDX, XPS, and optical microscopy to determine the impact of the interfacial boundary morphology on the...
Article
Full-text available
The photoelectric and thermionic effects are combined in an illustrative experiment to demonstrate that solar light and heat can be converted into electrical energy simultaneously. When an electron is ejected from the cathode and is collected by the anode, a difference in chemical potential develops between the anode and cathode Fermi levels. Work...
Article
Full-text available
Deregulation and re-regulation of California's electricity market not only failed in terms of anticipated cost reductions, improved customer service and higher competition, it also led to the introduction of various additional energy subsidies. This paper analyzes California's electricity market deregulation process from a subsidy viewpoint. Under...
Article
Full-text available
A poly(3-undecyl-2,2′-bithiophene) in thin film TiO2 photovoltaic has been characterized electrochemically and optically. An oxidation potential and onset of oxidation of the polythiophene were determined by cyclic voltammetry to be 1.0 and 0.8 V (versus Ag|AgCl|sat KCl), respectively. From the onset oxidation, the HOMO has been estimated to be at...
Article
In this communication, we report on a technique to fabricate solid-state polythiophene-based dye sensitized solar cells (DSSCs) that can be directly compared to analogous liquid junction devices. The device configuration is based on non-porous TiO2 thin films and one of the three undoped polythiophene hole conductors: poly[3-(11 diethylphosphorylun...
Article
Full-text available
We report on the use of poly(3-undecyl-2,2′-bithiophene) and three different types of TiO2 film layers to determine the dependence of photovoltaic performance on the morphology of the TiO2 films. It was observed that the TiO2 film morphology plays an important role in the performance of photovoltaic solar cells with polythiophene used as both sensi...
Article
Application of a spin-coated poly(4-undecyl-2,2 ' -bithiophene) laver on dye sensitized TiO2 showed that it can act as an efficient charge mediator. Typical J-V values for flat TiO2 film devices are J(sc) = 60 muA/cm(2), and V-oc = 0.65 V, which is comparable to values obtained with liquid electrolytes in the same geometrical configuration. The pol...
Article
Titanium dioxide (TiO2) films have been deposited on SnO2 coated glass substrates by screen-printing. Film morphology and structure have been characterized by scanning electron microscopy, x-ray diffraction and BET analysis. Dye-sensitized TiO2 photoelectrochemical cells have been assembled and characterized. Cells sensitized with anthocyanin and a...
Article
Full-text available
Beets do not contain anthocyanin. Keywords (Audience): High School / Introductory Chemistry
Article
Full-text available
A simplified solar cell fabrication procedure is presented that uses natural anthocyanin or chlorophyll dyes extracted from plants. This procedure illustrates how interdisciplinary science can be taught at lower division university and upper division high school levels for an understanding of renewable energy as well as basic science concepts. Elec...
Article
A simplified solar cell fabrication procedure is presented that uses natural anthocyanin or chlorophyll dyes extracted from plants. This procedure illustrates how interdisciplinary science can be taught at lower division university and upper division high school levels for an understanding of renewable energy as well as basic science concepts. Elec...
Article
Full-text available
A unique solar cell fabrication procedure has been developed using natural anthocyanin dyes extracted from berries. It can be reproduced with a minimum amount of resources in order to provide an interdisciplinary approach for lower-division undergraduate students learning the basic principles of biological extraction, physical chemistry, and spectr...
Article
colloidal TiO2 powder, is shown to convert sunlight to electrical power at an efficiency of 0.56% under full sun. Fluorescence quenching is observed for the excited state of the TiO2-adsorbed anthocyanin dye, cyanin, and the photocurrent spectrum correlates well with the optical absorption of the cyanin-sensitized TiO 2 nanocrystalline film. The in...
Article
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Article
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A PC-based measuring system is presented for outdoor testing of solar cells and modules under real operating conditions. It consists of a sun-tracked sample holder, different electronic loads (including control), digital multimeters, a PC and a laser printer. Insolation is measured and recorded with pyranometers, pyrheliometers and a reference cell...
Article
Full-text available
Experimental photoluminescence spectra obtained for silicon are compared to predictions made using transmission and reflection data, as well as those using the action (or induced photo-product) spectrum. Although the absorptivity obtained from the optical measurements can be used to predict much of the photoluminescence curve, the predicted values...
Article
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Article
A number of devices have been constructed which directly convert light into electrical work or into a flow of chemical products with a free energy higher than the starting materials. Solar Concentrators have been developed which increase the irradiance on the converter material to levels above that used without the device even if the incident light...
Article
Full-text available
Detailed balance calculations have been applied to dye sensitized TiO2 solar cells in order to obtain an upper limit for the solar conversion efficiency of the finished cell given the particular optical absorption and the luminescence efficiency, or fluorescence yield, of the dye. While these models do not predict the actual efficiency of the devic...
Article
Full-text available
Recently, a paper was published by the Lausanne Group headed by Dr. M. Graetzel which reported a simple low cost 7% efficient photo electrochemical solar cell made from a trinuclear Ru dye complex adsorbed on the very rough surface of a colloidal TiO2 film. In the current paper, a verification of this result is presented using procedures described...
Article
Recently, a paper was published by the Lausanne Group headed by Dr. M. Gratzel which claimed to obtain a low cost 7% efficient photoelectrochemical solar cell from a Ru carboxylated bipyridyl charge transfer dye adsorbed on the very rough surface of a colloidal TiO2 film. In the current paper, a verification of this result is presented as well as t...
Article
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Article
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Erratum to Luminescence and current-voltage characteristics of solar cells and optoelectric [sic] devices: G. Smestad and H. Ries, Solar energy materials and solar cells 25 (1992) 51–71.
Article
Full-text available
Erratum to The thermodynamic limits of light concentrators: G. Smestad, H. Ries, R. Winston and E. Yablonovitch, Solar Energy Materials 21 (1990) 99–111.
Article
A connection is made between the luminescence or radiative recombination in an absorber material and the current voltage characteristics of a quantum converter of light. A relationship between luminescence and voltage is derived, using detailed balance and the chemical potential of the excitation, which is similar to that obtained using the techniq...
Article
Several recent patents have described Hewlett Packard Optoelectronics Division light emitting diode, or LED, lamp designs. These designs have led to several innovative, mass produced products that are now on the market. These designs can be directly traced to the known principles of non-imaging optics, and can thus serve as a guide to solar optics...
Article
Full-text available
Using the electrochemical procedure for the production of porous Si, material is produced which shows a solid state photovoltaic response. Under simulated sunlight, the open circuit voltage is near 0.36 V and the photocurrent is near 2 μA. The current-voltage characteristics exhibit a high series resistance which is on the order of 1 MΩ. The spectr...
Article
Full-text available
The transduction and conversion of radiant energy into work in a quantum process are dependant on the luminescent properties of the materials involved. Materials with photoluminescent efficiencies greater than 0.1% are likely candidates for solar cells and solar converters. The luminescent optical properties of a material are directly related to th...
Article
Full-text available
Concentrators based on geometrical optics increase the irradiance by increasing the projected solid angle, but conserve the radiance of radiation. The general principle for increasing the radiance, and thereby concentrating even diffuse radiation, resembles a light trap. Light, which enters the trap through a selective filter, is shifted in photon...
Conference Paper
Pyrite seems to be an interesting material for solar cell applications because of its band gap of 0.95 eV and its very high absorption coefficient. The preparation of pyrite thin films by four different methods is reported. The differences concerning the stoichiometry and the crystalline phases are discussed.