1,720,990 research outputs found
Solar PV Stochastic Hosting Capacity Assessment Considering Epistemic (E) Probability Distribution Function (PDF)
No full textThis paper presents a stochastic approach to assessing the hosting capacity for solar PV. The method is part of the optimal techniques for the integration of renewables. There are two types of uncertainties, namely aleatory and epistemic uncertainties. The epistemic and aleatory uncertainties influence distribution networks’ hosting capacity differently. The combination of the two uncertainties influences the planning of distribution networks. The study introduces and considers the epistemic probability distribution function (PDF). DSO does take levels of risk for a parameter violation when planning. Epistemic PDF is a range of values of the planning risk margin for quantifying the hosting capacity. The planning risk acknowledges that overvoltages may occur at weaker conceivable locations in a distribution network. In the paper, it has been shown that the number of customers who will be able to connect solar PV in future is influenced by the DSO’s planning risk margin. The DSO can be stricter or less strict in planning risk margin. It has been concluded that fewer customers can connect solar PV to a distribution network when a DSO takes a stricter planning risk. Alternatively, more customers can connect solar PV units for a less strict planning risk. How stricter or less strict the DSO is with the planning risk margin determines the investment needed for mitigation measures. The mitigation measures in the future will lead to not exceeding the overvoltage limit when solar PV is connected to the weaker conceivable points of the distribution network.Validerad;2023;Nivå 1;2023-01-01 (joosat);Funder: Skellefteå Kraft Elnät AB; Umeå Energi ABLicens full text: CC BY license</p
Fuel Cell Technology: An Optional Back-Up Power Supply System for Zambia
No full textFuel cell technology is slowly growing in other countries and is being used for power production. In Zambia, the technology is yet to penetrate. The increase in power demand at a time of poor rainfall patterns entail diversification to other power sources. This paper presents knowledge on fuel cell technology, types, applications, sample simulation and its adaptation to Zambia as back-up power supply from literature, applied systems and simulation set-up in matlab-simulink. Massive investment in solar technology, rise in fuel prices for diesel generators and possibility of combining fuel cell with photovoltaics or as storage to store away variability has necessitated the review of this technology as an optional back-up power supply for Zambia. The sample simulation of a 6 kW fuel cell system in Matlab showed results of dc power. The same power type from PV array before power conditioning. Fuel cell technology exist in different types due electrolyte used. These are proton exchange membrane, phosphoric acid fuel cell, alkaline fuel cell, direct methanol fuel cell, solid oxide fuel cell and molten carbonate fuel cell. Systems of sizes up to 59 MW have been installed. The by-products of industrial, mining and metallurgical processes (oxygen and hydrogen) could make implementation much feasible. Large investments in photovoltaics, which could share power conditioning equipment with fuel cell technology, could aids this technology in Zambia. Fuel cell technology system is possible as an optional power source for Zambia. It can be used as a stand-by unit, part of a hybrid system, an independent power plant and storage for photovoltaic (PV) systems
Fuel Cell Technology: An Optional Back-Up Power Supply System for Zambia [Elektronisk resurs]
No full textFuel cell technology is slowly growing in other countries and is being used for power production. In Zambia, the technology is yet to penetrate. The increase in power demand at a time of poor rainfall patterns entail diversification to other power sources. This paper presents knowledge on fuel cell technology, types, applications, sample simulation and its adaptation to Zambia as back-up power supply from literature, applied systems and simulation set-up in matlab-simulink. Massive investment in solar technology, rise in fuel prices for diesel generators and possibility of combining fuel cell with photovoltaics or as storage to store away variability has necessitated the review of this technology as an optional back-up power supply for Zambia. The sample simulation of a 6 kW fuel cell system in Matlab showed results of dc power. The same power type from PV array before power conditioning. Fuel cell technology exist in different types due electrolyte used. These are proton exchange membrane, phosphoric acid fuel cell, alkaline fuel cell, direct methanol fuel cell, solid oxide fuel cell and molten carbonate fuel cell. Systems of sizes up to 59 MW have been installed. The by-products of industrial, mining and metallurgical processes (oxygen and hydrogen) could make implementation much feasible. Large investments in photovoltaics, which could share power conditioning equipment with fuel cell technology, could aids this technology in Zambia. Fuel cell technology system is possible as an optional power source for Zambia. It can be used as a stand-by unit, part of a hybrid system, an independent power plant and storage for photovoltaic (PV) systems.</p
Impacts of integrating solar PV power to an existing grid. Case Studies of Mölndal and Orust energy distribution (10/0.4 kV and 130/10 kV) grids.
No full textAbundance existence of solar energy from the sun on the globe has brought potential for rapid growth of solar photovoltaic (PV) rooftops/power plants connection to existing grids at transmission and distribution levels. The connections are likely to bring impact challenges of integration and operations of the grids by utility companies. The steady state integration impacts of solar PV power to existing grids were studied with focus on the distribution grids of Mölndal energy (10/0.4 kV) residential distribution grid and Orust energy (130/10 kV) distribution grid. The steady state impacts on voltage level, voltage profile, voltage drop, losses, line loading and voltage stability on the distribution grids were studied. The study approached the integration impacts by comparison method of the distribution grids without solar PV power integrated, with solar PV power integrated and with different penetration levels (0%, 30%, 60% and 90%) of integrated solar PV power with aid of simulation software NEPLAN, Paladin Designbase and PVSyst for solar PV power production for the grid areas. The impacts study revealed that integration of solar PV power for the distribution grids studied in general caused an increase in voltage profile, voltage level, decrease in voltage drop and losses, and improvement in steady state voltage stability of the studied grids. In addition, integration of rooftop PV systems caused a decrease in line loading of feeder cables while integration of large ground utility PV systems caused an increase in line loading of the feeder cable/line to the coupling substation to the grid. The increase in PV power penetrations caused similar latter results in voltage level, voltage drop and voltage stability. However, the grid losses decreased for 40% penetrations level and below for Orust energy distribution grid. The losses started to increase at penetrations higher than 40%. From these results, there is a limit to how much maximum PV power (hosting capacity) a grid could allow. For the grids under study, the hosting capacities were determined. Hosting capacities of 30%, 40% and 25% penetration levels were found for Mölndal area 1, Mölndal area 2 and Orust area distribution grids
Impacts of integrating solar PV power to an existing grid. Case Studies of Mölndal and Orust energy distribution (10/0.4 kV and 130/10 kV) grids.
No full textAbundance existence of solar energy from the sun on the globe has brought potential for rapid growth of solar photovoltaic (PV) rooftops/power plants connection to existing grids at transmission and distribution levels. The connections are likely to bring impact challenges of integration and operations of the grids by utility companies. The steady state integration impacts of solar PV power to existing grids were studied with focus on the distribution grids of Mölndal energy (10/0.4 kV) residential distribution grid and Orust energy (130/10 kV) distribution grid. The steady state impacts on voltage level, voltage profile, voltage drop, losses, line loading and voltage stability on the distribution grids were studied. The study approached the integration impacts by comparison method of the distribution grids without solar PV power integrated, with solar PV power integrated and with different penetration levels (0%, 30%, 60% and 90%) of integrated solar PV power with aid of simulation software NEPLAN, Paladin Designbase and PVSyst for solar PV power production for the grid areas. The impacts study revealed that integration of solar PV power for the distribution grids studied in general caused an increase in voltage profile, voltage level, decrease in voltage drop and losses, and improvement in steady state voltage stability of the studied grids. In addition, integration of rooftop PV systems caused a decrease in line loading of feeder cables while integration of large ground utility PV systems caused an increase in line loading of the feeder cable/line to the coupling substation to the grid. The increase in PV power penetrations caused similar latter results in voltage level, voltage drop and voltage stability. However, the grid losses decreased for 40% penetrations level and below for Orust energy distribution grid. The losses started to increase at penetrations higher than 40%. From these results, there is a limit to how much maximum PV power (hosting capacity) a grid could allow. For the grids under study, the hosting capacities were determined. Hosting capacities of 30%, 40% and 25% penetration levels were found for Mölndal area 1, Mölndal area 2 and Orust area distribution grids
On the hosting capacity of distribution networks for solar power
No full textThe future will bring changes in energy production and consumption that will affect the performance of electricity distribution networks. Electric vehicle charging will increase consumption; the installation of solar photovoltaic (PV) units will increase production. Both will change the energy flow and affect the power quality. The installation of solar PV units or electric vehicle (EV) charging has a limit above, which they unacceptably deteriorate the distribution networks' performance. This limit is referred to as the hosting capacity of the distribution network. This work is about developing, applying and studying methods for estimating the hosting capacity, especially solar PV. Three fundamentally different methods to estimate solar PV hosting capacity for single-phase and three-phase units have been identified by a detailed review of the literature: deterministic, stochastic and time-series. The methods were shown to differ in the required input data, accuracy, computation time, consideration of uncertainties, and time-correlation between different phenomena. The methods have also been compared in relation to their application for the assessment of connection requests (screening) or detailed analysis. Solar power production, energy consumption and distribution networks’ all have uncertainties associated with them. It is helpful to distinguish between two types of uncertainties when estimating the hosting capacity: aleatory (“certain”) and epistemic (“uncertain”) uncertainties. A stochastic approach, ‘mixed aleatory-epistemic’, was applied to about 1500 low-voltage distribution networks. A similar stochastic approach and models were applied to estimate low-voltage networks' hosting capacity for electric vehicle charging. A deterministic method was applied to determine the hosting capacity considering the thermal overload phenomenon for both PV and EV charging. A planning risk has been introduced to quantify the risk of the distribution network not being able to cope with a future penetration of solar PV or EV charging. The planning level entails that a distribution network operator accepts a certain risk of exceeding the overvoltage limit. The concept has been applied as part of the stochastic approach. The hosting capacity for a distribution network is quantified considering a performance index and a limit to what is an acceptable deterioration of that index. The 90th percentile of the annual peak demand (overvoltage or overload) has been used as a performance index in most of the hosting capacity studies in this work. The time-of-day (ToD) and time-of-year (ToY) concepts were introduced to model the aleatory uncertainties. The time-of-day exemplifies the relevant part of the day, and the time-of-year shows the parts of the year applicable for hosting capacity studies when high solar power production can be expected. The time-of-day of 10 am to 2 pm has been applied. The period from 21st March to 21st September was the applied time-of-year. The latter two, ToD and ToY, need to be defined for the application of the concept to other areas than those covered in this work. It was shown that the hosting capacity would be underestimated by about 10% if an incorrect ToD were used. Voltage magnitude and solar power production measurements, over one year with a 10-minute resolution, were obtained for thirty-three 10/0.4 kV distribution transformers in Northern Sweden. A method of obtaining the ‘background voltage’ from the measurements was formulated. The background voltage (including its uncertainties) was one of the factors with the greatest influence on the hosting capacity. Stochastic models for distribution networks were built, and the hosting capacity for low voltage distribution networks has been studied. The outcome shows that three-phase solar PV units have a higher hosting capacity than single-phase units. The model and method developed can be used as a planning tool by distribution network operators (DSOs). The inclusion of the uncertainties and correct handling of planning risks is paramount for decision making by DSOs. The results show that background voltage variations should be considered from measurements, and appropriate ToD/ToY should be used. The quantification of the hosting capacity requires both consumption and voltage measurements in the distribution networks. The work has also shown that the time of the day and year (ToD and ToY) need to be considered for the many hosting capacity methods. The impact is expected to be highest in the ToD and ToY. Also, the two types of uncertainties have been clarified in this work. They need to be considered as the decisions DSOs make will depend on them. This work has generally found that hosting capacity estimation methods are many and different. They are all applicable and useful tools for identifying the factors in distribution networks that can hold up solar PV and EV charging penetration. It has also been found that there is a strong link between distribution network planning and hosting capacity estimation methods. The hosting capacity methods in this work can undertake the risks connected to solar PV and EV charging.
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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