Institute Of Energy Conversion Research Articles

Decentralized wastewater treatment in an urban setting: a pilot study of the circulating fluidized bed bioreactor treating septic tank effluent

ABSTRACT To meet the increasing wastewater treatment demand while minimizing the land footprint of the treatment systems and plants, more efficient and compact processes are needed. The circulating fluidized bed bioreactor (CFBBR) has been proven to achieve high levels of biological nutrient removal. Past studies at the lab and pilot scale achieved 94% COD removal and 80% nitrogen removal at HRT's of 2–4 h. A collaborative project between Western University and the Guangzhou Institute of Energy Conversion (GIEC), in Guangzhou, China, further explored the treatment of municipal wastewater with the CFBBR. A pilot CFBBR, with aerobic and anoxic columns for nitrification and denitrification, was constructed at the GIEC for in-situ treatment of septic tank effluent from a residential building. Due to high concentrations of ammonia (NH4-N), the wastewater had a COD/N ratio of 2–3. Thus, operating at a longer HRT and supplementing COD, in the form of glucose, was necessary to achieve a high nitrogen removal efficiency. The system was run both with and without supplemental COD at HRT's between 16 and 21 h, treating approximately 1000–1270 L/d. Overall, a COD removal efficiency of at least 92%, ammonia removal of 97%, and nitrogen removal of 82% was achieved. The CFBBR system achieved an effluent with BOD and NH4-N concentrations both below 5 mg/L, a NO3-N concentration below 15 mg/L, and a total nitrogen concentration below 25 mg/L. The compact design of this pilot-CFBBR, coupled with its high BNR performance make it an excellent option for decentralized treatment of urban wastewaters.

Direct Selective Hydrogenation of Phenol and Derivatives over Polyaniline-Functionalized Carbon-Nanotube-Supported Palladium

Invited for this month′s cover are the groups of Prof. Jinzhu Chen and Prof. Longlong Ma from the Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences. The image shows a bifunctional stabilizing mechanism of the composite support PANI/CNT on palladium nanoparticles in the catalyst Pd–PANI/CNT, and how the PANI/CNT can play a role in controlling the conversion and selectivity in the direct hydrogenation of phenol to cyclohexanone.

Scaleup of Cu(InGa)Se2 Thin-Film Coevaporative Physical Vapor Deposition Process, 2. Evaporation Source Design

We recently presented the development and experimental validation of two models that are essential for effective commercial-scale source design for Cu(InGa)Se2 thin film coevaporative physical vapor deposition processes: a three-dimensional thermal model of the evaporation source, and a Direct Simulation Monte Carlo (DSMC)-method-based effusion model. We showed that these models can be used to obtain reasonably accurate melt temperature dynamics and nozzle effusion flow properties. We now present how these simulation tools are used to develop a scale-up methodology for the effective commercialization of the pilot-scale physical vapor deposition (PVD) process at the University of Delaware’s Institute of Energy Conversion (IEC). We illustrate the methodology using two commercial-scale source design studies: a three-nozzle single source and a four-nozzle modular source. We also show that the proposed source designs are robust to modeling errors and the important process parameter of the source-to-substrate d...

Scaleup of Cu(InGa)Se2Thin Film Coevaporative Physical Vapor Deposition Process, 1. Evaporation Source Model Development

Even though rapid advances have been made in improving Cu(InGa)Se2 thin-film-based solar cell efficiencies, the breakthroughs have been limited to the laboratory scale. Most commercially viable thin-film technologies reside at the premanufacturing development stage and scaleup has proven to be much more difficult than expected. Elemental in-line evaporation on flexible substrates in a roll-to-roll configuration is a commercially attractive process for the manufacture of large-area CuInSe2-based photovoltaics. At the University of Delaware’s Institute of Energy Conversion (IEC), such a process is being investigated, at the pilot scale, for a polyimide web substrate. The process works well for 6-in.-wide substrates and for short deposition runtimes. However, a commercially viable process is required to produce large-area, high-quality films at a much-higher throughput. Specifically, the desired film thickness (∼2 μm) and composition uniformity must be achieved continuously and reproducibly on large-area (12...

Summary of 4 1/2 years of research experience of the US amorphous silicon research teams

The four national amorphous silicon research teams held their 8th guidance team and technical team meetings in conjunction with the 25th Anniversary Symposium of the Institute of Energy Conversion at the University of Delaware. The teams were formed in 1992 and represent a success story of teamed photovoltaics research, integrating the efforts of industrial groups, universities and national laboratories (NIST and NREL). In this paper, we will make an attempt to summarize the accomplishments and the lessons learned during this period. © 1997 John Wiley & Sons, Ltd.

Introduction to the Thin Film Photovoltaic Symposium commemorating the 25th Anniversary of the Institute of Energy Conversion at the University of Delaware, USA

Introduction to the Thin Film Photovoltaic Symposium commemorating the 25th Anniversary of the Institute of Energy Conversion at the University of Delaware, USA

Built-In Potentials Via Electroabsorption Measurements in a-Si:H p-i-n Solar Cells: a Critical Assessment

ABSTRACTWe have measured electroabsorption (EA) in a-Si:H p-i-n solar cells in order to estimate their built-in potentials Vbi. This Method was pioneered by the Osaka University group; in simple cases Vbi is identified with a parameter V0 obtained by a simple linear fit to the dependence of EA on external bias voltage. Using signal averaging techniques we are able to Measure V0 with a reproducibility of better than 2%. In one sample from the Institute of Energy Conversion with an a-SiC:H p+ layer we estimate Vbj = 0.97 ± 0.06 V, which is in good agreement with previous JVT Measurement. The reason that the error estimate is larger than the reproducibility error is the presence of several small effects not accounted for by the original EA theory: in particular V0 depends slightly on the laser wavelength. We attribute these effects to the small portion of Vbi dropped in the a-SiC:Hp+ layer, which has a different electroabsorption than a-Si:H. We discuss models for the wavelength dependence.

Device-quality CuInSe2 produced by the hybrid process

Abstract Solar cells with conversion efficiencies exceeding 7% have been fabricated based on CuInSe2 produced by a hybrid process combining sputtering of copper and indium with evaporation of selenium. This process has been shown to be highly controllable, with linear relationships observed between the target ion currents and the metal-constituent content of the resulting films. Furthermore, below saturation at 50 at.% the selenium content in the films has also been shown to vary linearly with incident selenium flux. To demonstrate the quality of the resulting material, heterostructure solar cells have been fabricated by the authors, the Institute of Energy Conversion at the University of Delaware (IEC), and International Solar Energy Technology (ISET). As a first step, Cu/In alloy layers deposited by codeposition of the metals in the hybrid system were selenized and fabricated into devices at ISET. These had V oc values as high as 0.34 V, which demonstrated that acceptable control of the copper and indium fluxes could be achieved. Following calibration of the deposition rates and film compositions as a function of substrate temperature and constituent fluxes, single-layer films were produced which had chalcopyrite structure and resistivities in agreement with previous observations (0.797 μ cm for copper-rich films and 2.094 × 10 4 μ cm for indium-rich layers). Transmission electron microscope analysis of the film structures showed no detectable differences between the hybrid process material and device-quality CuInSe2 produced by three-source evaporation. All films had substantial numbers of defects, including stacking faults, microtwins, dislocations and intergranular pores. The density of each defect is a function of film composition. No second-phase material was observed in any near-stoichiometric ( ±2 at .% in any constituent) film — even for copper-rich material. Stable defect structures were observed, with recognizable features in the electron diffraction pattern, probably by forming vacancies on one or more of the structure sublattices. Based on these results, bilayers were produced which consisted of copper-rich regions, 3 μm thick, capped with indium-rich layers of varying thickness. For the initial series of films these layers had nominal atomic per cent compositions of 26% Cu, 22% In, and 52% Se for the copper-rich layers.and 19% Cu, 29% In, and 52% Se for the indium-rich layers. Point-contact CuInSe2/CdS:In devices based on this material had diode-like behavior which improved significantly with air annealing. Under illumination, these devices produced V oc values as high as 0.34 V. Glass/Mo/CuInSe2/(Cd0.93Zn0.07)S:In/ITO/Ni devices with an area of 0.08 cm2 produced and tested at IEC using similar films had a best performance after air annealing of 7.2% efficiency, V oc = 0.348 V , J sc = 0.32.9 mA , and 55% fill factor under simulated 87.5 mW cm−2 solar illumination. Although all of these parameters can be improved by further optimization of the CuInSe2 layer, they are excellent for the first devices tested. The results to date clearly demonstrate the potential of the hybrid process.

Laboratory safety procedures for processing II-VI and related compounds for thin film photovoltaics

The Institute of Energy Conversion (IEC) at the University of Delaware has been fabricating and evaluating thin film solar cells from II-VI and related compounds for over a decade. Materials of interest have included CdS, (CdZn)S, CdTe, (CdHg)Te, CuInSe 2, ZnS, ZnSe and ZnO. In this paper, we describe specific safety-driven procedures which have evolved for material handling, operating and cleaning of equipment, as well as environmental and biological monitoring. The emphasis of the paper is based on our experience with small-scale batch and unit operations-scale depositions of CdS and (CdHg)Te by evaporation in an academic research and development laboratory. The toxicology and techniques for monitoring environmental levels of cadmium and mercury are described.

Depth dependence of trapped holes in thin-film CdS/Cu2S solar cells determined from photoinduced transient capacitance

Trapping of light-generated holes in copper-doped CdS is important to the operation of the thin-film CdS/Cu2S solar cell. Consequently, there is interest in determining the distribution of the hole traps both in energy and in x, the depth from the junction. Capacitance transients are a useful probe of the depth dependence of trapped hole density, pT (x), since capacitance can be related by electrostatic theory to depletion layer width and charge density. It is shown from variation of capacitance in 1-cm2 thin-film CdS/Cu2S solar cells, prepared at the Institute of Energy Conversion with temperature, heat-treatment time, infrared quenching, and illumination intensity, that the observed photocapacitance is characteristic of copper impurity centers in CdS. Measurements of photocapacitance decay in these cells following abrupt shutoff of intense blue light show a time dependence different from that predicted by the usual theoretical treatment of p–n junctions. This starts from the assumption of a uniform fixed-charge density and leads to a prediction that C2−C2∞ decays exponentially with time, where C∞ is the dark capacitance. The theoretical relations have been rederived using a pT varying as exp(−x/d), where d is a distance characteristic of the depth dependence. The resulting expressions predict that pT should vary as C−2∞ −C−2. It is shown that this relation is closely satisfied by the measured photocapacitance transient data for temperatures from 77.5 K to ∼190 K, for times up to several tens of seconds, and for shorter times at higher temperatures. It is pointed out that some other dependence which confines the trapped hole density near the junction could equally well be used to fit the data. Possibilities for the physical origin of this depth dependence are discussed. It is shown that the relation of electric field at the junction to the measured capacitance derived from this model gives better agreement with measurements of the variation of collection efficiency with illumination intensity.

Low Cost Thin-Film CdS-Based Solar Cells—Progress and Promise

The direct conversion of sunlight to electricity using thin film solar cells is potentially a low cost renewable source of energy. A major factor contributing to the low projected costs is the very small quantities of materials required as the active layers of the cells can be as little as 2 μm thick. The efficiency of solar cells will have to exceed ten percent to achieve economic power generation. Until 1976 no thin film solar cells with above seven percent efficiency in sunlight had been reported, but since then the Institute of Energy Conversion has successively reported 7.8, 8.55 and 9.15 percent. This paper will describe the loss minimization methodology utilized to achieve these increases in performance. Analysis shows that efficiencies as high as 14–16 percent for CdS-based solar cells are achievable. The research and development necessary to achieve these high efficiencies will be described. The feasibility of an extremely low cost manufacturing process capable of producing solar cells costing 250 dollars/kWatt will be discussed. Recent progress in development of low-cost thin-film devices shows great promise that direct conversion of sunlight to electricity can make a measurable contribution to the electrical energy supply both nationally and internationally.

The CdS/Cu2S Solar Cell I. Minority Carrier Generation and Transport in the Cu2S Emitter

physica status solidi (a)Volume 40, Issue 2 p. 355-384 Review Article The CdS/Cu2S Solar Cell I. Minority Carrier Generation and Transport in the Cu2S Emitter K. W. BÖER, K. W. BÖER Institute of Energy Conversion, University of Delaware and SES, Inc., Newark Search for more papers by this author K. W. BÖER, K. W. BÖER Institute of Energy Conversion, University of Delaware and SES, Inc., Newark Search for more papers by this author First published: 16 April 1977 https://doi.org/10.1002/pssa.2210400202Citations: 62 Newark Delaware 19711, USA. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume40, Issue216 April 1977Pages 355-384 RelatedInformation