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  • 1901.
    Widén, Joakim
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Improved photovoltaic self-consumption with appliance scheduling in 200 single-family buildings2014Ingår i: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 126, s. 199-212Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Self-consumption of on-site photovoltaic (PV) electricity in buildings is gaining interest as a way to accommodate high PV penetrations in the power system. On markets where there is no substantial feed-in support for renewables, there is also an economic incentive for PV self-consumption, as selling prices for PV electricity are normally lower than retail electricity prices. One option for improved self-consumption is rescheduling of programmable appliances, typically washing machines, clothes dryers and dishwashers. This paper determines the potential to increase PV self-consumption through scheduling of these appliances in Swedish single-family buildings. Simulations of daily load scheduling were performed to match on-site PV power generation and recent (2008–2012) hourly electricity market prices, using a set of high-resolution (10-min) appliance load profiles from 200 monitored Swedish households. Since these data provide appliance ownership and daily appliance use patterns in a wide range of households, a realistic upper limit to the self-consumption potential is obtained. The conclusions are that load shifting can potentially increase PV self-consumption by around 200 kWh on average, corresponding to a few percent of the total PV power generation for the system sizes studied (3–9 kWp). The maximum economic benefit over the studied years was 20 EUR per year and household. For the larger PV system sizes that could inject critical peak powers to the distribution grid, the peak hourly PV surplus decreased less than a few percent. The main conclusion is that there is an overall low potential for improved self-consumption through optimal scheduling of the studied appliances, at least with the current Swedish market conditions.

  • 1902.
    Widén, Joakim
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Internationell forskning för omfattande utbyggnad av solel2011Rapport (Refereegranskat)
  • 1903.
    Widén, Joakim
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Modellering av elanvändning i hushållssektorn2007Ingår i: Att analysera system - reflektion och perspektiv, Linköping University , 2007Kapitel i bok, del av antologi (Refereegranskat)
  • 1904.
    Widén, Joakim
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Modellering av lastkurvor för hushållsel utifrån tidsanvändningsdata2008Rapport (Övrigt vetenskapligt)
  • 1905.
    Widén, Joakim
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Modelling and statistical analysis of the variability of large-scale solar power in high-latitude power systems2011Ingår i: Proceedings of the 1st International Workshop on Integration of Solar Power into Power Systems, Aarhus, Denmark, October 24, 2011, 2011Konferensbidrag (Refereegranskat)
  • 1906.
    Widén, Joakim
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    System Studies and Simulations of Distributed Photovoltaics in Sweden2010Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Grid-connected photovoltaic (PV) capacity is increasing worldwide, mainly due to extensive subsidy schemes for renewable electricity generation. A majority of newly installed systems are distributed small-scale systems located in distribution grids, often at residential customers. Recent developments suggest that such distributed PV generation (PV-DG) could gain more interest in Sweden in the near future. With prospects of decreasing system prices, an extensive integration does not seem impossible.

    In this PhD thesis the opportunities for utilisation of on-site PV generation and the consequences of a widespread introduction are studied. The specific aims are to improve modelling of residential electricity demand to provide a basis for simulations, to study load matching and grid interaction of on-site PV and to add to the understanding of power system impacts.

    Time-use data (TUD) provided a realistic basis for residential load modelling. Both a deterministic and a stochastic approach for generating different types of end-use profiles were developed. The models are capable of realistically reproducing important electric load properties such as diurnal and seasonal variations, short time-scale fluctuations and random load coincidence.

    The load matching capability of residential on-site PV was found to be low by default but possible to improve to some extent by different measures. Net metering reduces the economic effects of the mismatch and has a decisive impact on the production value and on the system sizes that are reasonable to install for a small-scale producer.

    Impacts of large-scale PV-DG on low-voltage (LV) grids and on the national power system were studied. Power flow studies showed that voltage rise in LV grids is not a limiting factor for integration of PV-DG. Variability and correlations with large-scale wind power were determined using a scenario for large-scale building-mounted PV. Profound impacts on the power system were found only for the most extreme scenarios.

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  • 1907.
    Widén, Joakim
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Using analytical expressions for the location-pair correlation to determine the output variability of a solar power plant2012Ingår i: Proceedings of the 2nd International Workshop on Integration of Solar Power into Power Systems, Lisbon, Portugal, November 12-13, 2012, 2012Konferensbidrag (Refereegranskat)
    Abstract [en]

    When increasing the integration of solar power in power systems, the short-term output variability of solar power plants will affect the requirements on balancing reserves. Methods to predict the degree of variability from arbitrary PV system configurations over different sub-hourly time scales, subject to the smoothing that takes place as a result of cloud movements, will be important for determining new requirements on reserve capacity. In particular, a better understanding of the smoothing of high-frequency irradiation variability over extended areas with a nearly continuous distribution of PV systems, such as dense PV fleets in urban areas or large PV power plants, is needed. This paper presents an analytical model for the autocorrelation of high-resolution irradiance data (in so-called virtual radiation networks) and uses this to obtain a model for the irradiance variability integrated over a geographical area. The proposed model explains and reproduces accurately the features of virtual radiation networks and is able to predict the total variability of a PV field for an arbitrary choice of time resolution, cloud speed and extension in the direction of cloud movement.

  • 1908.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Carpman, Nicole
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Castellucci, Valeria
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Lingfors, David
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Olauson, Jon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Remouit, Flore
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Bergkvist, Mikael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Grabbe, Mårten
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Waters, Rafael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Variability Assessment and Forecasting of Renewables: A Review for Solar, Wind, Wave and Tidal Resources2015Ingår i: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 44, s. 356-375Artikel i tidskrift (Refereegranskat)
  • 1909.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Elfving, Gustav
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Jansson, Emil
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Munkhammar, Joakim
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Lingfors, David
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Characterization of extensive city-scale solar power generation: Findings from the UppScaleSolar project2017Rapport (Refereegranskat)
  • 1910.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Ellegård, Kajsa
    Wäckelgård, Ewa
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Markov-chain modelling of high-resolution activity patterns and household electricity demand2009Ingår i: Proceedings of the Scientific Conference on Energy Systems and IT, Älvsjö, Sweden, March 11-12, 2009, 2009Konferensbidrag (Refereegranskat)
  • 1911.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Karlsson, Björn
    Mälardalen University.
    End-user value of on-site domestic photovoltaic generation with different metering options in Sweden2010Ingår i: Proceedings of EuroSun 2010, Graz, Austria, September 28 - October 1, 2010, 2010Konferensbidrag (Refereegranskat)
  • 1912.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Karlsson, Kristina
    Linköping University.
    The influence of Swedish households' everyday activities and electricity-use patterns on the utilization of small-scale photovoltaic systems2009Ingår i: Proceedings of the eceee 2009 Summer Study, La Colle-sur-Loup, France, June 1-6, 2009, 2009Konferensbidrag (Refereegranskat)
  • 1913.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Lundh, Magdalena
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Vassileva, Iana
    School of Sustainable Development of Society and Technology, Mälardalen University.
    Dahlquist, Erik
    School of Sustainable Development of Society and Technology, Mälardalen University.
    Ellegård, Kajsa
    Technology and Social Change, Linköping University.
    Wäckelgård, Ewa
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Constructing load profiles for household electricity and hot water from time-use data-Modelling approach and validation2009Ingår i: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 41, nr 7, s. 753-768Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Time-use data, describing in detail the everyday life of household members as high-resolved activity sequences, have a largely unrealized potential of contributing to domestic energy demand modelling. A model for computation of daily electricity and hot-water demand profiles from time-use data was developed, using simple conversion schemes, mean appliance and water-tap data and general daylight availability distributions. Validation against detailed, end-use specific electricity measurements in a small sample of households reveals that the model for household electricity reproduces hourly load patterns with preservation of important qualitative features. The output from the model, when applied to a large data set of time use in Sweden, also shows correspondence to aggregate profiles for both household electricity and hot water from recent Swedish measurement surveys. Deviations on individual household level are predominantly due to occasionally ill-reported time-use data and on aggregate population level due to slightly non-representative samples. Future uses and developments are identified and it is suggested that modelling energy use from time-use data could be an alternative, or a complement, to energy demand measurements in households.

  • 1914.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Molin, Andreas
    Division of Energy Systems, Dept of Management and Engineering, Linköping Universitet.
    Ellegård, Kajsa
    Technology and Social Change, Linköping Universitet.
    Models of domestic occupancy, activities and energy use based on time-use data: deterministic and stochastic approaches with application to various building-related simulations2012Ingår i: Journal of Building Performance Simulation, Taylor & Francis, ISSN 1940-1493, E-ISSN 1940-1507, Vol. 5, nr 1, s. 27-44Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Time-use data (TUD) have a large potential for improving occupancy and load modelling and for introducing realistic behavioural patterns into various simulations. In this article, previously developed models of occupancy, activities and energy use based on TUD are extended and described in a general framework. Two extensions are studied: deterministic conversion of empirical TUD is extended into a complete thermal load model encompassing both occupancy and various end-uses and a Markov-chain approach for generating synthetic TUD sequences is extended to include a model for load management. Three examples of building-related applications are presented: simulation of indoor climate in a low-energy building, household electricity load management in response to time-differentiated electricity tariffs and simulations of load matching in a net zero energy building. The main conclusion is that the extended model framework can generate detailed and realistic behavioural patterns that allow diversity and correlations between end-uses to be taken into account.

  • 1915.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Munkhammar, Joakim
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Evaluating the benefits of a solar home energy management system: impacts on photovoltaic power production value and grid interaction2013Ingår i: Proceedings of the eceee 2013 Summer Study, Presqu'île de Giens, France, June 3-8, 2013, 2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    On mature photovoltaic (PV) markets where feed-in support has declined, as well as on immature markets where there is yet no feed-in support, home energy management systems could be interesting for increasing the value of on-site PV power generation. These systems typically provide scheduling of programmable appliances and may also include battery storage for shifting surplus PV power from day to night. In this paper we investigate how these systems perform in Swedish detached single-family buildings equipped with PV systems. How much can the households’ self-consumption of the on-site PV be increased with load shifting and battery storage? How is the value of the on-site PV generation affected by these options? Is there any benefit for the distribution grid with a widespread adoption of such systems? Simulation models for energy management systems with optimized load shifting and small battery storage capabilities were developed and applied to appliance-specific and highly resolved monitoring data from 20 Swedish detached single-family buildings. These detailed data provide information on individual appliance duty cycles and allow a realistic assessment of the load shifting potential. The main conclusion is that these systems have a potential for improving the PV self-consumption and production value by a few percent, but unless extensive battery storage is introduced, they are unlikely to have any marked impact on distribution system management.

  • 1916.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Munkhammar, Joakim
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Widespread integration of distributed photovoltaics at high latitudes: Opportunities and challenges2011Ingår i: Proceedings of the 26th European Photovoltaic Solar Energy Conference (EU-PVSEC), Hamburg, Germany, September 5-9, 2011, 2011Konferensbidrag (Refereegranskat)
  • 1917.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Nilsson, Annica
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Wäckelgård, Ewa
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    A combined Markov-chain and bottom-up approach to modelling of domestic lighting demand2009Ingår i: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 41, nr 10, s. 1001-1012Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Detailed simulations of distributed generation in residential areas   have prompted the need for improved models of domestic electricity   demand that are able to reproduce important features of real household   loads. The high share and temporal variability of the lighting demand   make it of special interest, in particular when the models are to be   used in simulations of distributed photovoltaics (PV), which to a high   degree is negatively correlated with the lighting demand. In this   paper, a stochastic bottom-up model based on domestic occupancy   patterns and data on daylight availability is presented. A threestate   non-homogeneous Markov chain is used for generation of occupancy   patterns and a conversion model transforms occupancy patterns to   lighting demand, with respect to the daylight level. Markovchain   transition probabilities are determined from a detailed set of time-use   (TU) data in Swedish households and the parameters in the   occupancy-to-lighting conversion model are adjusted to make the   resulting load curves fit recent measurements on aggregate population   level. The performance of the model is analysed by comparison of   simulated demand to measured lighting demand. It is concluded that for   both individual households and aggregate demand, all relevant features   of measured demand are realistically reproduced.

  • 1918.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Shepero, Mahmoud
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Munkhammar, Joakim
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    On the properties of aggregate clear-sky index distributions and an improved model for spatially correlated instantaneous solar irradiance2017Ingår i: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 157, s. 566-580Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An important factor in grid integration of solar power is the so-called dispersion-smoothing effect, i.e., that differences in cloudiness over dispersed systems make the aggregate output less variable. This effect has been studied for irradiance step-changes on different time horizons, but not so much for instantaneous irradiance. In this paper, an improved probabilistic model is proposed for how instantaneous solar irradiance is correlated and aggregated over a network with arbitrary number of sites and dispersion. The model is fitted to irradiance data with a 1-s resolution from a network with 17 pyranometers in Hawai’i. A previously proposed three-state model of the instantaneous clear-sky index is partly confirmed by showing that clear and cloudy states can be separated and modeled by independent distribution models. It is also shown that the station-pair correlations for the instantaneous clear-sky index, as well as the shape of the distribution for the cloudy states, depend characteristically on the average degree of cloudiness, represented by the daily clear-sky index. For dispersed sites within the studied network, separated by distances up to 1km, and for daily clear-sky indices above approximately 0.5, the model performs better in reproducing the aggregate clear-sky index than non-spatial data. The proposed model could assist distribution system operators (DSOs) in grid planning and operation, as shown in a case study.

  • 1919.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Shepero, Mahmoud
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Munkhammar, Joakim
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Probabilistic Load Flow for Power Grids With High PV Penetrations Using Copula-Based Modeling of Spatially Correlated Solar Irradiance2017Ingår i: IEEE Journal of Photovoltaics, ISSN 2156-3381, E-ISSN 2156-3403, Vol. 7, nr 6, s. 1740-1745Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents and applies an improved model for the instantaneous power generation from distributed photovoltaic (PV) systems intended for probabilistic load flow (PLF) simulations. The model combines a probability distribution model for the instantaneous solar irradiance at individual sites with an improved spatial correlation model and uses a Gaussian copula to allow correlated sampling from the distributions for an arbitrary set of distributed PV systems. We show that the model realistically reproduces the spatially distributed clear-sky index over a set of sites, based on comparisons with irradiance sensor network data. We also demonstrate that the probability distributions for system parameters such as customer voltage, substation loading, and power losses, obtained from PLF simulations with the model, differ substantially from those of a nonspatial approach. The results show that spatial irradiance modeling needs to be incorporated in PLF simulations in order not to overestimate the grid impacts of PV systems.

  • 1920.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Weiss, Philipp
    Solenergi i Dalarnas bebyggelse: Potential till år 2020 och 20502012Rapport (Övrigt vetenskapligt)
  • 1921.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Wäckelgård, Ewa
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    A high-resolution stochastic model of domestic activity patterns and electricity demand2010Ingår i: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 87, nr 6, s. 1880-1892Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Realistic time-resolved data on occupant behaviour, presence and energy use are important inputs to various types of simulations, including performance of small-scale energy systems and buildings' indoor climate, use of lighting and energy demand. This paper presents a modelling framework for stochastic generation of high-resolution series of such data. The model generates both synthetic activity sequences of individual household members, including occupancy states, and domestic electricity demand based on these patterns. The activity-generating model, based on non-homogeneous Markov chains that are tuned to an extensive empirical time-use data set, creates a realistic spread of activities over time, down to a 1-min resolution. A detailed validation against measurements shows that modelled power demand data for individual households as well as aggregate demand for an arbitrary number of households are highly realistic in terms of end-use composition, annual and diurnal variations, diversity between households, short time-scale fluctuations and load coincidence. An important aim with the model development has been to maintain a sound balance between complexity and output quality. Although the model yields a high-quality output, the proposed model structure is uncomplicated in comparison to other available domestic load models.

  • 1922.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Wäckelgård, Ewa
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Net zero energy solar buildings at high latitudes: The mismatch issue2010Konferensbidrag (Refereegranskat)
  • 1923.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Wäckelgård, Ewa
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Ellegård, Kajsa
    Modeling household electricity load from time-use data2008Ingår i: Proceedings of the Scientific Conference on Energy Saving and Green Energy, Älvsjö, Sweden, March 11-12, 2008, 2008Konferensbidrag (Refereegranskat)
  • 1924.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Wäckelgård, Ewa
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Lund, Peter
    HUT, Helsinki.
    Options for improving the load matching capability of distributed photovoltaics: Methodology and application to high-latitude data2009Ingår i: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 83, nr 11, s. 1953-1966Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    At high latitudes, domestic electricity demand and insolation are   negatively correlated on both an annual and a diurnal basis. With   increasing integration of distributed photovoltaics (PV) in low-voltage   distribution grids of residential areas, limits to the penetration   level are set by voltage rise due to unmatched production and load. In   this paper a methodology for determining the impacts of three options   for increased load matching is presented and applied to high-latitude   data. The studied options are PV array orientation, demand side   management (DSM) and electricity storage. Detailed models for domestic   electricity demand and PV output are used. An optimisation approach is   applied to find an optimal distribution of PV systems on different   array orientations and a best-case evaluation of DSM and a storage   model are implemented. At high penetration levels, storage is the most   efficient option for maximising the solar fraction, but at lower   overproduction levels, the impact of DSM is equal or slightly better.   An east-west orientation of PV arrays is suggested for high penetration   levels, but the effect of the optimised orientation is small. Without   an optimised storage operation, the overproduced power is more   efficiently reduced by DSM than storage, although this is highly   dependent on the applied DSM algorithm. Further research should be   focused on the DSM potential and optimal operation of storage.

  • 1925.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Wäckelgård, Ewa
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Lund, Peter
    Options for improving the match between household electricity demand and photovoltaic generation at high latitudes2008Ingår i: Proceedings of EuroSun 2008, Lisbon, Portugal, October 7-10, 2008, 2008Konferensbidrag (Refereegranskat)
  • 1926.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Wäckelgård, Ewa
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Lund, Peter D.
    Corrigendum to "Options for improving the load matching capability of distributed photovoltaics: Methodology and application to high-latitude data"2009Ingår i: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 83, s. 1953-1966Artikel i tidskrift (Refereegranskat)
  • 1927.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Wäckelgård, Ewa
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Paatero, Jukka
    Lund, Peter
    Corrigendum to "Impacts of different data averaging times on statistical analysis of distributed domestic photovoltaic systems"2010Ingår i: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 84, s. 492-500Artikel i tidskrift (Refereegranskat)
  • 1928.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Wäckelgård, Ewa
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Paatero, Jukka
    Helsinki University of Technology.
    Lund, Peter
    Helsinki University of Technology.
    Impacts of different data averaging times on statistical analysis of distributed domestic photovoltaic systems2010Ingår i: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 84, nr 3, s. 492-500Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The trend of increasing application of distributed generation with solar photovoltaics (PV-DG) suggests that a widespread integration in existing low-voltage (LV) grids is possible in the future. With massive integration in LV grids, a major concern is the possible negative impacts of excess power injection from on-site generation. For power-flow simulations of such grid impacts, an important consideration is the time resolution of demand and generation data. This paper investigates the impact of time averaging on high-resolution data series of domestic electricity demand and PV-DG output and on voltages in a simulated LV grid. Effects of 10-minutely and hourly averaging on descriptive statistics and duration curves were determined. Although time averaging has a considerable impact on statistical properties of the demand in individual households, the impact is smaller on aggregate demand, already smoothed from random coincidence, and on PV-DG output. Consequently, the statistical distribution of simulated grid voltages was also robust against time averaging. The overall judgement is that statistical investigation of voltage variations in the presence of PV-DG does not require higher resolution than hourly.

  • 1929.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Wäckelgård, Ewa
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Paatero, Jukka
    Helsinki University of Technology.
    Lund, Peter
    Helsinki University of Technology.
    Impacts of distributed photovoltaics on network voltages: Stochastic simulations of three Swedish low-voltage distribution grids2010Ingår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 80, nr 12, s. 1562-1571Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The continuously increasing application of distributed photovoltaics (PV-DG) in residential areas around the world calls for detailed assessment of distribution grid impacts. Both photovoltaic generation and domestic electricity demand exhibit characteristic variations on short and long time scales and are to a large extent negatively correlated, especially at high latitudes. This paper presents a stochastic methodology for simulation of PV-DG impacts on low-voltage (LV) distribution grids, using detailed generation and demand models. The methodology is applied to case studies of power flow in three existing Swedish LV grids to determine load matching, voltage levels and network losses at different PV-DG penetration levels. All studied LV grids can handle significant amounts of PV-DG, up to the highest studied level of 5 kWp PV per household. However, the benefits of PV-DG in terms of relative improvement of on-site reduction of demand, mitigated voltage drops and reduced losses were most significant at a penetration level of 1 kWp PV per household.

  • 1930.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Åberg, Magnus
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Henning, Dag
    Optensys Energianalys AB.
    Impacts of large-scale solar and wind power production on the balance of the Swedish power system2011Ingår i: Proceedings of the World Renewable Energy Congress, Linköping, May 8-13, 2011, 2011Konferensbidrag (Refereegranskat)
  • 1931.
    Wikberg, J. M.
    et al.
    Radboud Univ Nijmegen, Inst Mol & Mat, NL-6525 AJ Nijmegen, Netherlands..
    Razdolski, I.
    Radboud Univ Nijmegen, Inst Mol & Mat, NL-6525 AJ Nijmegen, Netherlands..
    Kirilyuk, A.
    Radboud Univ Nijmegen, Inst Mol & Mat, NL-6525 AJ Nijmegen, Netherlands..
    Rasing, Th.
    Radboud Univ Nijmegen, Inst Mol & Mat, NL-6525 AJ Nijmegen, Netherlands..
    Sadowski, J.
    Lund Univ, MAX Lab, SE-22100 Lund, Sweden..
    Ottosson, Mikael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Oorganisk kemi.
    Wei, Y.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Svedlindh, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Evolving magnetization dynamics in Mn3-xGa2015Ingår i: Ultrafast Magnetism I / [ed] Bigot, JY; Hubner, W; Rasing, T; Chantrell, R, 2015, s. 23-25Konferensbidrag (Refereegranskat)
  • 1932.
    Wikberg, J. Magnus
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Dahbi, M.
    ECME, LP2E2M, FST Marrakech, University Cadi Ayyad.
    Saadoune, I.
    ECME, LP2E2M, FST Marrakech, University Cadi Ayyad.
    Gustafsson, Torbjörn
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Strukturkemi.
    Edström, Kristina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Svedlindh, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Dimensionality crossover and frustrated spin dynamics on a triangular lattice2010Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, nr 22, s. 224411-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Investigations of the magnetic behavior of the layered oxide, LiNi0.65Co0.25Mn0.10O2, through ac and time-dependent susceptibility, dc linear and nonlinear susceptibility as well as neutron-diffraction measurements are presented. A ferrimagneticlike spin ordering appears at 119 K with a spontaneous magnetization coexisting with spin frustration in two dimensions (2D). At lower temperature, a cluster-glass transition is found at 17.4 K indicating a transformation to a completely frustrated state in three dimensions (3D). A dimensionality crossover with temperature, from 2D to 3D, in a magnetically frustrated system has been demonstrated. The observed magnetic behavior is believed to originate from a percolating system of spin clusters defined by disordered and frustrated exchange interactions and the findings conform well with predictions of the percolation cluster model.

  • 1933.
    Wikberg, J. Magnus
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Dahbi, Mohammed
    ECME, LP2E2M, FST Marrakech, University Cadi Ayyad.
    Saadoune, Ismael
    ECME, LP2E2M, FST Marrakech, University Cadi Ayyad.
    Gustafsson, Torbjörn
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Strukturkemi.
    Edström, Kristina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Svedlindh, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Magnetic order, aging, and spin frustration in a percolating spin system, LiNi0.8Co0.1Mn0.1O22010Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, nr 8, s. 083909-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Structural and magnetic properties of the Li layered oxide, LiNi0.8Co0.1Mn0.1O2, have been studied by means of x-ray diffraction, dc magnetization, ac linear, and nonlinear susceptibility as well as by magnetic aging and temperature cycling experiments. A percolating spin system interacting via antiferromagnetic and ferromagnetic superexchange interactions of different strength induce a ferrimagnetic quasilong-range order with a transition temperature Tc ≈ 70 K, a Weiss temperature of −25 K and an effective magnetic moment of 2.07 μB. On cooling below Tc the two-dimensional (2D) triangular lattice built up of edge-sharing metal oxide octahedras first exhibits a 2D spin glass like behavior followed by complete spin frustration in three dimensions below 30 K. The findings correlate well with expectations for a ferrimagnetic reentrant cluster glass system as well as with predictions of the percolating cluster model.

  • 1934.
    Wikberg, J Magnus
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Knut, Ronny
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Audren, A
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Ottosson, Mikael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Oorganisk kemi.
    Linnarsson, M K
    Royal Institute of Technology, KTH-ICT, Electrum, Stockholm.
    Karis, Olof
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Hallén, A
    Royal Institute of Technology, KTH-ICT, Electrum, Stockholm.
    Svedlindh, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Annealing effects on structural and magnetic properties of Co implanted ZnO single crystals2011Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 109, nr 8, s. 083918-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Single crystals of ZnO were implanted with 100 keV-Co ions at room temperature with a fluence of 4.8 x 10(16) cm(-2) and subsequently annealed at different temperatures up to 800 degrees C. The samples were analyzed by Rutherford backscattering spectrometry, secondary ion mass spectrometry, X-ray diffraction, X-ray photoemission spectroscopy and magnetometry. The as-implanted Co:ZnO crystal shows a homogeneous distribution of Co in the near surface region of the crystal. Upon annealing, clear evidence of secondary phases is found. At the highest annealing temperature (800 degrees C) a ferromagnetic behavior is observed at room temperature with a coercive field of 120 Oe assigned mainly to metallic fcc Co nano-crystallites. We find that for the annealed samples, the temperature dependent magnetization cannot be explained within a model containing only a paramagnetic contribution due to well dispersed Co ions and a ferromagnetic contribution due to Co nano-crystallites, at least one more ferromagnetic contribution is needed for a consistent explanation of the experimental results.

  • 1935.
    Wikberg, J Magnus
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Knut, Ronny
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Yt- och gränsskiktsvetenskap.
    Bhandary, Sumanta
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Di Marco, Igor
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ottosson, Mikael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Oorganisk kemi.
    Sadowski, Janusz
    MAX-lab, Lund University.
    Sanyal, Biplab
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Palmgren, Pål
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Yt- och gränsskiktsvetenskap.
    Tai, Cheuk W
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University.
    Eriksson, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Karis, Olof
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Yt- och gränsskiktsvetenskap.
    Svedlindh, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Magnetocrystalline anisotropy and uniaxiality of MnAs/GaAs(100) films2011Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, nr 2, s. 024417-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present an investigation of the magnetic behavior of epitaxial MnAs films grown on GaAs(100). We address the dependence of the magnetic moment, ferromagnetic transition temperature (Tc), and magnetocrystalline anisotropy constants on epitaxial conditions. From thorough structural and magnetic investigations, our findings indicate a more complex relationship between strain and magnetic properties in MnAs films than a simple stretch/compression of the unit cell axes. While a small increase is seen in the anisotropy constants, the enhancement of the magnetic moment at saturation is significant. Results of x-ray magnetic circular dichroism show a behavior of the spin and orbital moment that is consistent with a structural transition at Tc. In particular, we find that the ratio of the orbital to the spin moment shows a marked increase in the coexistence region of the ferromagnetic α- and paramagnetic β-phases a result that is well in accord with the observed increase in the c/a ratio in the same temperature region. The ab initio density functional calculations reveal that the magnetic properties are more sensitive towards change in the ab-plane compared to change in the c-axis which is explained by the analysis of band structures. The effects of electron correlation in MnAs using ab initio dynamical mean field theory are also presented.

  • 1936.
    Wikberg, J. Magnus
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Mansson, Martin
    Dahbi, Mohammed
    Kamazawa, Kazuya
    Sugiyama, Jun
    Magnetic order and frustrated dynamics in Li(Ni0.8Co0.1Mn0.1)O-2: a study by mu+SR and SQUID magnetometry2012Ingår i: 12TH INTERNATIONAL CONFERENCE ON MUON SPIN ROTATION, RELAXATION AND RESONANCE (MUSR2011), 2012, s. 202-205Konferensbidrag (Refereegranskat)
    Abstract [en]

    Recently, the mixed transition metal oxides of the form Li(Ni1-y-zCoyMnz)O-2, have become the center of attention as promising candidates for novel battery material. These materials have also revealed very interesting magnetic properties due to the alternate stacking of planes of metal oxides on a 2D triangular lattice and the Li-layers. The title compound, Li(Ni0.8Co0.1Mn0.1)O-2, has been investigated by both magnetometry and measurements and mu+SR. We find the evolution of localized magnetic moments with decreasing temperature below 70 K. The magnetic ground state (T = 2 K) is, however, shown to be a frustrated system in 3D, followed by a transition into a possible 2D spin-glass above 22 K. With further increasing temperature the compound show the presence of remaining correlations with increasing effective dimensionality all the way up to the ferrimagnetic transition at T-C = 70 K.

  • 1937.
    Wiksell, Marit
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Underlag för solcellsproducerad el i Stockholm: Potential och klimatpåverkan2015Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The City of Stockholm has decided to invest in renewable energy and especially in photovoltaics. The objective of this thesis is to investigate the photovoltaic potential on roof areas that the city possesses and to further investigate some buildings of the Property Management Department. The thesis also compares some existing photovoltaic plants with the solar irradiance map which shows available roof area on each building in Stockholm. The report ends with a literature study about the climate impact and greenhouse gas emissions of photovoltaic.

    The total available roof area suitable for photovoltaic plants is estimated to 700 000 m2, with a potential electricity production of 110 GWh per year. This corresponds to 17 % of the City of Stockholm’s yearly electricity consumption. A selection of sport facilities and fire stations owned by the Property Management Department has been investigated and 13 of the 33 buildings have roof areas which are well suited for photovoltaics. The potential electricity production from these buildings is estimated to 1 050 MWh per year. The 5 existing plants investigated occupies on average 49 % of the roof area which is available according to the solar irradiance map. In a life cycle perspective, photovoltaics purchased on the global market are expected to cause greenhouse gas emissions of 45 g CO2-eq/kWh.

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  • 1938.
    Wilhelmsson, Ola
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Oorganisk kemi.
    Bijelovic, Stojanka
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Lindquist, Mattias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    André, Benny
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Wiklund, Urban
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Svedlindh, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Jansson, Ulf
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Oorganisk kemi.
    Deposition and characterization of magnetic Ti–Fe–C nanocomposite thin films2010Ingår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 518, nr 10, s. 2607-2616Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nanocomposite (Ti1−xFex)Cy films with different compositions have been deposited by dc magnetron sputtering at 450 °C. The sputtered films could dissolve as much as 20–30 at.% of Fe on the Ti sites which is far above the maximum solid solubility at equilibrium. The solubility was dependent on the carbon content and more carbon-rich films could dissolve more Fe without the formation of Fe-precipitates. The addition of Fe also reduced the grain size of the carbide particles. Upon annealing, α-Fe starts to precipitate and the amount and size of these precipitates can be controlled by the annealing procedure and from the total composition of the as-deposited films. Mechanical and tribological studies show that some compositions of the (Ti1−xFex)Cy films have very good wear-resistant properties. These results together with magnetization measurements suggest that Ti–Fe–C films can be used as a wear-resistant magnetic thin film material.

  • 1939.
    Wilkinson, Kai
    et al.
    Dept of Chemistry, SLU BioCenter, Uppsala.
    Ekstrand-Hammarström, Barbro
    FOI, Umeå.
    Ahlinder, Linnea
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Guldevall, Karolin
    Science for Life Laboratory, Cell Physics, Dept of Applied Physics, Albanova University center, KTH, Stockholm.
    Pazik, Robert
    Dept of Chemistry, SLU BioCenter, Uppsala.
    Kępiński, Leszek
    Inst Low Temp Struct Res, Polish Academy of Sciences, Wroclaw, Polen.
    Kvashnina, Kristina O.
    European Synchrotron Radiation Facility, Grenoble, Frankrike.
    Butorin, Segei M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Brismar, Hjalmar
    Science for Life Laboratory, Cell Physics, Dept of Applied Physics, Albanova University center, KTH, Stockholm.
    Önfelt, Björn
    Science for Life Laboratory, Cell Physics, Dept of Applied Physics, Albanova University center, KTH, Stockholm.
    Österlund, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Seisenbaeva, Gulaim A.
    Dept of Chemistry, SLU BioCenter, Uppsala.
    Kessler, Vadim G.
    Dept of Chemistry, SLU BioCenter, Uppsala.
    Visualization of custom-tailored iron oxide nanoparticles chemistry, uptake, and toxicity2012Ingår i: Nanoscale, ISSN 2040-3364, Vol. 4, nr 23, s. 7383-7393Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nanoparticles of iron oxide generated by wearing of vehicles have been modelled with a tailored solution of size-uniform engineered magnetite particles produced by the Bradley reaction, a solvothermal metal–organic approach rendering hydrophilic particles. The latter does not bear any pronounced surface charge in analogy with that originating from anthropogenic sources in the environment. Physicochemical properties of the nanoparticles were thoroughly characterized by a wide range of methods, including XPD, TEM, SEM, DLS and spectroscopic techniques. The magnetite nanoparticles were found to be sensitive for transformation into maghemite under ambient conditions. This process was clearly revealed by Raman spectroscopy for high surface energy magnetite particles containing minor impurities of the hydromaghemite phase and was followed by quantitative measurements with EXAFS spectroscopy. In order to assess the toxicological effects of the produced nanoparticles in humans, with and without surface modification with ATP (a model of bio-corona formed in alveolar liquid), a pathway of potential uptake and clearance was modelled with a sequence of in vitro studies using A549 lung epithelial cells, lymphocyte 221-B cells, and 293T embryonal kidney cells, respectively. Raman microscopy unambiguously showed that magnetite nanoparticles are internalized within the A549 cells after 24 h co-incubation, and that the ATP ligand is retained on the nanoparticles throughout the uptake process. The toxicity of the nanoparticles was estimated using confocal fluorescence microscopy and indicated no principal difference for unmodified and modified particles, but revealed considerably different biochemical responses. The IL-8 cytokine response was found to be significantly lower for the magnetite nanoparticles compared to TiO2, while an enhancement of ROS was observed, which was further increased for the ATP-modified nanoparticles, implicating involvement of the ATP signalling pathway in the epithelium.

  • 1940.
    Willén, Oscar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Acceptansgränsen för solceller i lågspänningsnät: Kan den ökas?2015Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Microproduction, also called distributed generation, is something that has become more and more popular in the electric grid. Microproduction can however lead to unacceptable performance if several units are installed in the same low voltage network. It is therefore good to know a limit where the performance of the low voltage network becomes unacceptable based on given parameters. This limit is usually called hosting capacity.

    In this report the hosting capacity with respect to voltage and current have been studied in three low voltage networks which are located in Falu Elnäts concession area. This has been done by simulations in a GIS-program where critical times of the grid have been simulated. When the hosting capacity had been decided attempts have been made to increase the hosting capacity with four different measures. The measures examined are line gain, tap changer, reactive compensation and voltage regulation in the form of MPV.

    For the investigated network the hosting capacity varied virtuously. For all three grids were too high voltage during low load with maximum power production however the reason that the performance of the grid became unacceptable. The reasons that the voltage became unacceptable at different amounts of microproduction depends mainly on four things. These were the voltage in the substation, the amount of customers in the grid, the quality of the lines and the line length between the customer and substation.

    The best measure to increase the hosting capacity in a net is line gain in the most of the cases. Tap changer and the voltage regulator MPV are however two other measures that are recommended, but mainly as temporary solutions. Reactive compensation on the other hand is something that isn’t recommended based on this report.

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  • 1941. Wilson, Helen Rose
    et al.
    Nilsson, Annica M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Bretschneider, Joachim
    Hoffmann, Thomas
    Hutchins, Michael G.
    Jonsson, Jacob
    Kremel, Christine
    Marenne, Ingrid
    Roos, Arne
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    van Nijnatten, Peter A.
    Transmittance of patterned solar glass panes results of a measurement roud-robin by ICG TC10.11th ESG Conference2012Konferensbidrag (Refereegranskat)
  • 1942.
    Wolf, Tobias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Model-based Assessment of Heat Pump Flexibility2016Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Today's energy production is changing from scheduled to intermittent generation due to the increasing energy injection from renewable sources. This alteration requires flexibility in energy generation and demand. Electric heat pumps and thermal storages were found to have a large potential to provide demand flexibility which is analysed in this work. A three-fold method is set up to generate thermal load profiles, to simulate heat pump pools and to assess heat pump flexibility. The thermal profile generation based on a combination of physical and behavioural models is successfully validated against measurement data. A randomised system sizing procedure was implemented for the simulation of heat pump pools. The parameter randomisation yields correct seasonal performance factors, full load hours and average operation cycles per day compared to 87 monitored systems. The flexibility assessment analysis the electric load deviation of representative heat pump pool in response to 5 different on / off signals. The flexibility is induced by the capacity of thermal storages and analysed by four parameters. Generally, on signals are more powerful than off signals. A generic assessment by the ambient temperature yield that the flexibility is highest for heating days and the activated additional space heating storage: Superheating of the storage to the maximal temperature provides a flexible energy of more than 400 kWh per 100 heat pumps in a temperature range between -10 and +13 °C.

    Ladda ner fulltext (pdf)
    MSc_Report_Tobias_Wolf
  • 1943.
    Wu, Hua
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström. ilin Univ, State Key Lab Integrated Optoelect, Changchun 130012, Jilin, Peoples R China;Jilin Univ, Coll Elect Sci & Engn, Changchun 130012, Jilin, Peoples R China.
    Zhu, Huimin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi.
    Erbing, Axel
    Stockholm Univ, Alballova Univ Ctr, Dept Phys, S-10691 Stockholm, Sweden.
    Johansson, Malin B
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi.
    Mukherjee, Soham
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Man, Gabriel
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Rensmo, Håkan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Odelius, Michael
    Stockholm Univ, Alballova Univ Ctr, Dept Phys, S-10691 Stockholm, Sweden.
    Johansson, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi.
    Bandgap Tuning of Silver Bismuth Iodide via Controllable Bromide Substitution for Improved Photovoltaic Performance2019Ingår i: ACS APPLIED ENERGY MATERIALS, ISSN 2574-0962, Vol. 2, nr 8, s. 5356-5362Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work, silver-bismuth-halide thin films, exhibiting low toxicity and good stability, were explored systemically by gradually substituting iodide, I, with bromide, Br, in the AgBi2I7 system. It was found that the optical bandgap can be tuned by varying the I/Br ratio. Moreover, the film quality was improved when introducing a small amount of Br. The solar cell was demonstrated to be more stable at ambient conditions and most efficient when incorporating 10% Br, as a result of decreased recombination originating from the increased grain size. Thus, replacing a small amount of I with Br was beneficial for photovoltaic performance.

  • 1944. Wu, Y
    et al.
    Tamaki, T
    Volotinen, Tarja
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Lova, L B
    Rao, K V
    Enhanced Photoresponse of Inkjet-Printed ZnO Thin Films Capped with CdS Nanoparticles2010Ingår i: JOURNAL OF PHYSICAL CHEMISTRY LETTERS, ISSN 1948-7185, Vol. 1, nr 1, s. 89-92Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Composite semiconductors provide routes for realizing high-performance electronic devices, but for many applications of such devices, low-cost manufacturing techniques are desirable. We have engineered a 3 orders of magnitude enhancement of the ultraviolet photoresponse of ZnO thin films, fabricated "in situ" by drop-on-demand inkjet printing, and then capped with CdS nanoparticles by dip. coating. As a consequence, the decay time of the photoresponse is. reduced to about 4 ms. Thus, capping with CdS not only suppresses the detrimental passivation layer of ZnO thin films, but also generates an interfacial carrier transport layer to reduce the probability of carrier recombination.

  • 1945. Wu, Yan
    et al.
    Tamaki, T.
    Volotinen, Tarja
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Riazanova, A.
    Belova, L.
    Rao, K. V.
    Enhanced photoresponse of inkjet printed ZnO thin films induced by chemically capped CdS nanoparticles by dip coating2009Ingår i: Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X, E-ISSN 1996-756X, Vol. 7402, s. 740207-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Monodispersed CdS nanoparticles (NP) are dip coated on porous ZnO thin film deposited by inkjet printing. Optical absorption characteristics of the composite films show that the composite exhibits two main peaks centered at 355 nm due to the absorption at UV region from ZnO, and 433 nm arising from CdS NP. On UV radiations the electrical conductivity of CdS/ZnO composite thin film with 5 dip cycles is found to be enhanced more than three orders magnitude compared with that of the ZnO which we attribute to be the effect of interfacial charge transfer. Also, the UV photoresponse of ZnO shows pronounced enhancement after CdS capping.

  • 1946.
    Wu, Yongxin
    et al.
    Beihang Univ, Ctr Condensed Matter & Mat Phys, Beijing 100191, Peoples R China..
    Wang, Cong
    Beihang Univ, Ctr Condensed Matter & Mat Phys, Beijing 100191, Peoples R China..
    Sun, Ying
    Beihang Univ, Ctr Condensed Matter & Mat Phys, Beijing 100191, Peoples R China..
    Ning, Yuping
    Beihang Univ, Ctr Condensed Matter & Mat Phys, Beijing 100191, Peoples R China..
    Liu, Yingfang
    Beihang Univ, Ctr Condensed Matter & Mat Phys, Beijing 100191, Peoples R China..
    Xue, Yafei
    Beihang Univ, Ctr Condensed Matter & Mat Phys, Beijing 100191, Peoples R China..
    Wang, Wenwen
    Beihang Univ, Ctr Condensed Matter & Mat Phys, Beijing 100191, Peoples R China..
    Zhao, Shuxi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Tomasella, Eric
    Univ Clermont Ferrand, Clermont Univ, ICCF, CNRS UMR 6296, F-63171 Aubiere, France..
    Bousquet, Angelique
    Univ Clermont Ferrand, Clermont Univ, ICCF, CNRS UMR 6296, F-63171 Aubiere, France..
    Study on the thermal stability of Al/NbTiSiN/NbTiSiON/SiO2 solar selective absorbing coating2015Ingår i: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 119, s. 18-28Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work, the NbTiSiN and NbTiSiON layers are used instead of NbTiN and NbTiON layers to further improve the thermal stability of Al/NbTiN/NbTiON/SiO2 multilayer solar selective absorbing coating. The thermal stability of Si-doped individual layers and multilayer coatings are investigated. The X-ray diffraction (XRD) results show that Si incorporation into NbTiN (NbTiSiN) layer does not change its preferred orientation, and the Si-doped NbTiON (NbTiSiON) layer remains in amorphous phase. On the other hand, by introducing Si into NbTiN and NbTiON layers induce significant improvement of the oxidation resistance at 500 degrees C in air. After ageing in air at 500 degrees C for 2 h, the absorptance and emittance (at 400 degrees C) of Al/NbTiN/NbTiON/SiO2 and Al/NbTiSiN/NbTiSiON/SiO2 multilayer coatings change from 0.934/0.13 and 0.931/0.12 to 0.538/0.14 and 0.922/0.13, respectively. Meanwhile the surface roughness increases from 18.3 and 7.9 to 41.5 and 14.7 respectively, as atomic force microscopy (AFM) shows. The Al/NbTiSiN/NbTiSiON/SiO2 coating still has a high absorptance (0.910) and low emittance (0.13, at 400 degrees C) after ageing at 550 degrees C in vacuum for 100 h. It displays that Si-doping play an important role in the improvement of the thermal stability.

  • 1947. Wu, Yongxin
    et al.
    Wang, Cong
    Sun, Ying
    Xue, Yafei
    Ning, Yuping
    Wang, Wenwen
    Zhao, Shuxi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Tomasella, Eric
    Bousquet, Angelique
    Optical simulation and experimental optimization of Al/NbMoN/NbMoON/SiO2 solar selective absorbing coatings2015Ingår i: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 134, s. 373-380Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For the applications in solar thermal power, the preparation and optimization of an Al/NbMoN/NbMoON/SiO2 multilayer solar selective absorbing coating are carried out by combining experiments with optical simulation. A series of NbMoN and NbMoON single layers are deposited by magnetron reactive sputtering method with different N-2/O-2 gas flowing rates. And then their optical constants are obtained by fitting their reflection (R) and transmission (T) spectra in the wavelength range of 300-2500 nm using SCOUT software. These optical constants are used to design the Al/NbMoN/NbMoON/SiO2 solar selective absorbing coating so as to get the ideal spectral selectivity, i.e. high alpha/epsilon ratio. According to the optical design of the coating structure, we prepared the all-layer coating, and the thickness of each layer was optimized until the best spectral selective properties are obtained. The experimental reflectance spectrum fits very well with the simulated result. The optimized solar absorbing coating deposited on stainless steel substrate exhibited high absorptance (alpha=0.948) and low emittance (epsilon=0.050) at 80 degrees C. It offers a good method to quickly reach the ideal spectral selectivity through optical simulation. The thermal stability of the coating is evaluated, and it exhibits a good thermal stability in vacuum at 400 degrees C.

  • 1948.
    Wäckelgård, Ewa
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Bartali, Ruben
    Fondazione Bruno Kessler.
    Gerosa, Riccardo
    Laidani, Nadhira
    Mattsson, Andreas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Micheli, Victor
    Rivolta, Barbara
    New Cermet Coatings for Mid-temperature Applications for Solar Concentrated Combine Heat and Power System2014Ingår i: Energy Procedia, ISSN 1876-6102, E-ISSN 1876-6102, Vol. 48, s. 242-249Artikel i tidskrift (Refereegranskat)
  • 1949.
    Wäckelgård, Ewa
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Boström, T.
    Mattsson, Andreas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Zhao, Shuxi
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Crema, L.
    Bartali, R.
    Rivolta, B.
    New development of spectrally selective solar-absorbing coating for low andintermediate temperature applications2010Ingår i: World Renewable Energu Congress XI (WREC), Abu Dhabi, Sept 25-30, 2010, 2010Konferensbidrag (Refereegranskat)
  • 1950.
    Wäckelgård, Ewa
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Mattsson, Andreas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Bartali, Ruben
    Center for Materials and Microsystems, Fondazione Bruno Kessler, Trento, Italy.
    Gerosa, Riccardo
    Dipartimento di Meccanica, Politecnico di Milano, Milan, Italy.
    Gloria, Gottardi
    Center for Materials and Microsystems, Fondazione Bruno Kessler, Trento, Italy.
    Gustavsson, Fredrik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Laidani, Nadhira
    Center for Materials and Microsystems, Fondazione Bruno Kessler, Trento, Italy.
    Micheli, Victor
    Center for Materials and Microsystems, Fondazione Bruno Kessler, Trento, Italy.
    Primetzhofer, Daniel
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Rivolta, Barbara
    Dipartimento di Meccanica, Politecnico di Milano, Milan, Italy.
    Development of W–SiO2 and Nb–TiO2 solar absorber coatings for combined heat and power systems at intermediate operation temperatures2015Ingår i: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 133, s. 180-193Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two new absorber coatings for mid-temperature operation (300–350 1C) in collectors for solar thermal electricity plants are presented in this study. The absorbers consist of two cermet layers of either W–SiO2 or Nb–TiO2, deposited on a molybdenum infrared reflector and coated with an antireflection layer of silicon oxide. The optimization of the optical performance was made in two steps. First, the layer structure was optimized in model calculations. The optical constants used in this modelling were derived directly from sputtered films of the cermet constituents using reflectance and transmittance measure- ments. The absorber coatings were then sputter-deposited using parameters from the modelling. The results show good agreement between modelled and sputtered optical performance evaluated as solar absorptance and thermal emittance at 350 1C. The optimal values reached for W–SiO2 was 0.91 in combination with 0.08 and 0.93 in combination with 0.09 for Nb–TiO2. The materials characterization from XRD, AES and TEM shows that the composite coatings contain nano-metal inclusions, meaning that they are cermet coatings. Scratch tests show that the coatings adhere well to the substrate of stainless steel. Temperature testing at 350 1C in vacuum for up to 1500 h shows that both coatings are stable under such conditions. Only a slight change occurs during the first 72 h that decreases the emittance but does not change the solar absorptance. ERDA confirms that there is no detectable level of ion migration between layers, only a small decrease in hydrogen content was observed, which indicates outgassing.

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36373839404142 1901 - 1950 av 2063
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