On track for solar grade silicon through a Siemens process-type laboratory reactor: operating conditions and energy savings

Polysilicon cost impacts significantly on the photovoltaics (PV) cost and on the energy payback time. Nowadays, the besetting production process is the so called Siemens process, polysilicon deposition by chemical vapor deposition (CVD) from Trichlorosilane. Polysilicon purification level for PV is to a certain extent less demanding that for microelectronics. At the Instituto de Energía Solar (IES) research on this subject is performed through a Siemens process-type laboratory reactor. Through the laboratory CVD prototype at the IES laboratories, valuable information about the phenomena involved in the polysilicon deposition process and the operating conditions is obtained. Polysilicon deposition by CVD is a complex process due to the big number of parameters involved. A study on the influence of temperature and inlet gas mixture composition on the polysilicon deposition growth rate, based on experimental experience, is shown. Moreover, CVD process accounts for the largest contribution to the energy consumption of the polysilicon production. In addition, radiation phenomenon is the major responsible for low energetic efficiency of the whole process. This work presents a model of radiation heat loss, and the theoretical calculations are confirmed experimentally through a prototype reactor at our disposal, yielding a valuable know-how for energy consumption reduction at industrial Siemens reactorsPostprint (published version

Progress on the development of a technology for silicon purification

The polysilicon market is experiencing tremendous changes due to the strong demand from Photovoltaics (PV), which has by far surpassed the demand from Microelectronics. The need of solar silicon has induced a large increase in capacity, which has now given a scenario of oversupply, reducing the polysilicon price to levels that put a strong pressure on the cost structure of the producers. The paper reports on the R&D efforts carried out in the field of solar silicon purification via the chlorosilane route by a private-public consortium that is building a pilot plant of 50-100 tonnes/year, that will synthesize trichlorosilane, purify it and deposit ultrapure silicon in an industrial-size Siemens type reactor. It has also capabilities for ingot growth and material characterization. A couple of examples of the progress so far are given, the first one related to the recycling scheme of chlorinated compounds, and the second to the minimization of radiation losses in the CVD deposition process, which account for a relevant part of the total energy consumption. In summary, the paper gives details on the technology being developed in our pilot plant, which offers a unique platform for field-testing of innovative approaches that can lead to a cost reduction of solar silicon produced via the chlorosilane route

Psychological elements explaining the consumer's adoption and use of a website recommendation system: A theoretical framework proposal

The purpose of this paper is to understand, with an emphasis on the psychological perspective of the research problem, the consumer's adoption and use of a certain web site recommendation system as well as the main psychological outcomes involved. The approach takes the form of theoretical modelling. Findings: A conceptual model is proposed and discussed. A total of 20 research propositions are theoretically analyzed and justified. Research limitations/implications: The theoretical discussion developed here is not empirically validated. This represents an opportunity for future research. Practical implications: The ideas extracted from the discussion of the conceptual model should be a help for recommendation systems designers and web site managers, so that they may be more aware, when working with such systems, of the psychological process consumers undergo when interacting with them. In this regard, numerous practical reflections and suggestions are presented

Efectos Económicos de la Constitución de los Comités de Auditoría

El propósito de este trabajo consiste en analizar la valoración del mercado bursátil español respecto a la constitución del comité de auditoría en las empresas cotizadas, teniendo en cuenta que esta reacción puede diferir de la observada en mercados del ámbito anglosajón debido a las peculiaridades que presenta la auditoría de cuentas en España. Para ello, aplicando la metodología del estudio de eventos, se analizan las rentabilidades anormales próximas a la creación del comité, considerando factores como su voluntariedad, las opiniones previas del auditor o el tamaño de la firma auditora. Los resultados confirman que el mercado reacciona negativamente ante el establecimiento voluntario del comité y cuando éste se implanta en sociedades que venían recibiendo informes de auditoría favorables. No obstante, dicho anuncio no parece tener efecto cuando la compañía es receptora de informes calificados ni parece diferir por el hecho de ser auditada por una gran firma frente a otros auditores.The aim of this paper is to analyze the Spanish market reactions arising from the formation of the audit committees in the listed companies. This reaction could reasonably differ from that observed in Anglo-Saxon markets given the peculiarities of the audit process in Spain. With this aim, using the event study methodology, we have measured the abnormal returns surrounding the constitution of the audit committee, taking into account factors such as its voluntary formation, the auditor’s previous opinion and the auditor’s firm size. Our results confirm the existence of negative market reactions in the case of a voluntary formation of the committee and when this formation corresponds to a firm that has received a favourable audit report. However, we have observed no significant market reactions when the firm has received a qualified opinion and these reactions did not differ when the company was audited by one of the big audit firms or by other auditor

Deposition reactors for solar grade silicon: a comparative thermal analysis of a Siemens reactor and a fluidized bed reactor

Polysilicon production costs contribute approximately to 25–33% of the overall cost of the solar panels and a similar fraction of the total energy invested in their fabrication. Understanding the energy losses and the behaviour of process temperature is an essential requirement as one moves forward to design and build large scale polysilicon manufacturing plants. In this paper we present thermal models for two processes for poly production, viz., the Siemens process using trichlorosilane (TCS) as precursor and the fluid bed process using silane (monosilane, MS). We validate the models with some experimental measurements on prototype laboratory reactors relating the temperature profiles to product quality. A model sensitivity analysis is also performed, and the effects of some key parameters such as reactor wall emissivity and gas distributor temperature, on temperature distribution and product quality are examined. The information presented in this paper is useful for further understanding of the strengths and weaknesses of both deposition technologies, and will help in optimal temperature profiling of these systems aiming at lowering production costs without compromising the solar cell quality.Peer ReviewedPostprint (published version

On track for solar grade silicon through a siemens process-type laboratory reactor: operating conditions and energy savings

Polysilicon cost impacts significantly on the photovoltaics (PV) cost and on the energy payback time. Nowadays, the besetting production process is the so called Siemens process, polysilicon deposition by chemical vapor deposition (CVD) from Trichlorosilane. Polysilicon purification level for PV is to a certain extent less demanding that for microelectronics. At the Instituto de Energía Solar (IES) research on this subject is performed through a Siemens process-type laboratory reactor. Through the laboratory CVD prototype at the IES laboratories, valuable information about the phenomena involved in the polysilicon deposition process and the operating conditions is obtained. Polysilicon deposition by CVD is a complex process due to the big number of parameters involved. A study on the influence of temperature and inlet gas mixture composition on the polysilicon deposition growth rate, based on experimental experience, is shown. Moreover, CVD process accounts for the largest contribution to the energy consumption of the polysilicon production. In addition, radiation phenomenon is the major responsible for low energetic efficiency of the whole process. This work presents a model of radiation heat loss, and the theoretical calculations are confirmed experimentally through a prototype reactor at our disposal, yielding a valuable know-how for energy consumption reduction at industrial Siemens reactors

Deposition reactors for solar grade silicon: a comparative thermal analysis of a Siemens reactor and a fluidized bed reactor

Polysilicon production costs contribute approximately to 25-33% of the overall cost of the solar panels and a similar fraction of the total energy invested in their fabrication. Understanding the energy losses and the behaviour of process temperature is an essential requirement as one moves forward to design and build large scale polysilicon manufacturing plants. In this paper we present thermal models for two processes for poly production, viz., the Siemens process using trichlorosilane (TCS) as precursor and the fluid bed process using silane (monosilane, MS).We validate the models with some experimental measurements on prototype laboratory reactors relating the temperature profiles to product quality. A model sensitivity analysis is also performed, and the efects of some key parameters such as reactor wall emissivity, gas distributor temperature, etc., on temperature distribution and product quality are examined. The information presented in this paper is useful for further understanding of the strengths and weaknesses of both deposition technologies, and will help in optimal temperature profiling of these systems aiming at lowering production costs without compromising the solar cell quality

Heat losses in a CVD reactor for polysilicon: comprehensive model and experimental validation

This work addresses heat losses in a CVD reactor for polysilicon production. Contributions to the energy consumption of the so-called Siemens process are evaluated, and a comprehensive model for heat loss is presented. A previously-developed model for radiative heat loss is combined with conductive heat loss theory and a new model for convective heat loss. Theoretical calculations are developed and theoretical energy consumption of the polysilicon deposition process is obtained. The model is validated by comparison with experimental results obtained using a laboratory-scale CVD reactor. Finally, the model is used to calculate heat consumption in a 36-rod industrial reactor; the energy consumption due to convective heat loss per kilogram of polysilicon produced is calculated to be 22-30 kWh/kg along a deposition process

Intoxicación por Metahemoglobinizante, tipo Propanil

Intoxications by propanil herbicides are common in different agricultural areas, especially in rice fields. We present the case of a farmer patient, with no risk factors, who suffered moderate propanil intoxication. Despite the diagnostic limitations in each hospital center, the doubts, and the clinical data at the time of admission may be sufficient for the diagnosis and its respective management.  Las intoxicaciones por herbicidas propanil son frecuentes en las diferentes áreas agrícolas, sobre todo en los campos de cultivos de arroz. Se presenta el caso de un paciente agricultor, sin factores de riesgo, quien sufrió una intoxicación moderada por propanil. Pese a las limitaciones diagnósticas en cada centro hospitalario, la sospecha y los datos clínicos al ingreso pueden ser suficientes para la elaboración diagnóstica y su respectivo manejo