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System Studies and Simulations of Distributed Photovoltaics in Sweden
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2010. , p. 110
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 781
Keyword [en]
Photovoltaics, Solar energy, Distributed generation, Load modelling, Time-use data, Markov chain, Power flow, Power system
National Category
Other Engineering and Technologies
Research subject
Engineering Science
Identifiers
URN: urn:nbn:se:uu:diva-132907ISBN: 978-91-554-7931-2 (print)OAI: oai:DiVA.org:uu-132907DiVA, id: diva2:359601
Public defence
2010-12-10, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Note
Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 711Available from: 2010-11-18 Created: 2010-10-28 Last updated: 2011-03-21Bibliographically approved
List of papers
1. Constructing load profiles for household electricity and hot water from time-use data-Modelling approach and validation
Open this publication in new window or tab >>Constructing load profiles for household electricity and hot water from time-use data-Modelling approach and validation
Show others...
2009 (English)In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 41, no 7, p. 753-768Article in journal (Refereed) Published
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.

Keyword
Hot water, Household electricity, Load modelling, Load profiles, Time-use data
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-101288 (URN)10.1016/j.enbuild.2009.02.013 (DOI)000266769500007 ()
Available from: 2009-04-22 Created: 2009-04-22 Last updated: 2017-12-13
2. A combined Markov-chain and bottom-up approach to modelling of domestic lighting demand
Open this publication in new window or tab >>A combined Markov-chain and bottom-up approach to modelling of domestic lighting demand
2009 (English)In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 41, no 10, p. 1001-1012Article in journal (Refereed) Published
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.

Keyword
Domestic lighting, Markov chain, Bottom-up, Load model, Occupancy
National Category
Engineering and Technology
Research subject
Solid State Physics
Identifiers
urn:nbn:se:uu:diva-122405 (URN)10.1016/j.enbuild.2009.05.002 (DOI)000270076900001 ()
Available from: 2010-04-12 Created: 2010-04-12 Last updated: 2017-12-12Bibliographically approved
3. A high-resolution stochastic model of domestic activity patterns and electricity demand
Open this publication in new window or tab >>A high-resolution stochastic model of domestic activity patterns and electricity demand
2010 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 87, no 6, p. 1880-1892Article in journal (Refereed) Published
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.

Keyword
Bottom-up, Domestic electricity demand, Load model, Markov chain, Stochastic
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-132899 (URN)10.1016/j.apenergy.2009.11.006 (DOI)000278306300010 ()
Available from: 2010-10-28 Created: 2010-10-28 Last updated: 2017-12-12Bibliographically approved
4. Options for improving the load matching capability of distributed photovoltaics: Methodology and application to high-latitude data
Open this publication in new window or tab >>Options for improving the load matching capability of distributed photovoltaics: Methodology and application to high-latitude data
2009 (English)In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 83, no 11, p. 1953-1966Article in journal (Refereed) Published
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.

Keyword
Photovoltaics, Distributed generation, Load matching, Demand side management
National Category
Engineering and Technology
Research subject
Solid State Physics
Identifiers
urn:nbn:se:uu:diva-122403 (URN)10.1016/j.solener.2009.07.007 (DOI)000271158600003 ()
Note

Correction in:Solar Energy, 2011, vol. 85, issue.1, p. 215, doi:10.1016/j.solener.2010.11.016

Available from: 2010-04-12 Created: 2010-04-12 Last updated: 2017-12-12Bibliographically approved
5. The influence of Swedish households' everyday activities and electricity-use patterns on the utilization of small-scale photovoltaic systems
Open this publication in new window or tab >>The influence of Swedish households' everyday activities and electricity-use patterns on the utilization of small-scale photovoltaic systems
2009 (English)In: Proceedings of the eceee 2009 Summer Study, La Colle-sur-Loup, France, June 1-6, 2009, 2009Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Research subject
Solid State Physics
Identifiers
urn:nbn:se:uu:diva-122287 (URN)
Conference
eceee 2009 Summer Study, La Colle-sur-Loup, France, June 1-6, 2009
Available from: 2010-04-07 Created: 2010-04-07 Last updated: 2013-09-25Bibliographically approved
6. End-user value of on-site domestic photovoltaic generation with different metering options in Sweden
Open this publication in new window or tab >>End-user value of on-site domestic photovoltaic generation with different metering options in Sweden
2010 (English)In: Proceedings of EuroSun 2010, Graz, Austria, September 28 - October 1, 2010, 2010Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-132900 (URN)
Conference
EuroSun 20102010, Graz, Austria, September 28 - October 1, 2010
Available from: 2010-10-28 Created: 2010-10-28 Last updated: 2013-09-25Bibliographically approved
7. Impacts of different data averaging times on statistical analysis of distributed domestic photovoltaic systems
Open this publication in new window or tab >>Impacts of different data averaging times on statistical analysis of distributed domestic photovoltaic systems
2010 (English)In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 84, no 3, p. 492-500Article in journal (Refereed) Published
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.

Keyword
Time averaging, Photovoltaics, Domestic electricity demand, Distribution grid, Low voltage, Power flow
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-132903 (URN)10.1016/j.solener.2010.01.011 (DOI)000276119000018 ()
Note

Correction in: Solar Energy, 2011, vol. 85, issue. 1, p. 214, doi:10.1016/j.solener.2010.11.015

Available from: 2010-10-28 Created: 2010-10-28 Last updated: 2017-12-12Bibliographically approved
8. Impacts of distributed photovoltaics on network voltages: Stochastic simulations of three Swedish low-voltage distribution grids
Open this publication in new window or tab >>Impacts of distributed photovoltaics on network voltages: Stochastic simulations of three Swedish low-voltage distribution grids
2010 (English)In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 80, no 12, p. 1562-1571Article in journal (Refereed) Published
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.

Keyword
Distributed generation, Photovoltaics, Low voltage, Distribution grids, Power flow
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-132904 (URN)10.1016/j.epsr.2010.07.007 (DOI)000282404500022 ()
Available from: 2010-10-28 Created: 2010-10-28 Last updated: 2017-12-12Bibliographically approved
9. Correlations between large-scale solar and wind power in a future scenario for Sweden
Open this publication in new window or tab >>Correlations between large-scale solar and wind power in a future scenario for Sweden
2011 (English)In: IEEE Transactions on Sustainable Energy, ISSN 1949-3029, E-ISSN 1949-3037, Vol. 2, no 2, p. 177-184Article in journal (Refereed) Published
Abstract [en]

Future power systems are likely to include large amounts of variable power generation such as solar and wind power. As a variable output has to be balanced by the power system's reserves, it is important to study the time variability, coincidence, and correlations between power sources. The effect of output smoothing from dispersion of wind power plants is well established, but there is a need to study more renewables in combination. This study analyses large-scale solar and wind power in a future scenario for Sweden, using climatic data covering eight years with an hourly resolution. It is shown that solar and wind power are negatively correlated on all time scales, from hourly to annual, but that the correlation is strongest for monthly totals. Combining solar and wind power reduces total variations in terms of standard deviation, but hour-to-hour variability is always higher with a larger share of solar power.

National Category
Engineering and Technology
Research subject
Engineering Science
Identifiers
urn:nbn:se:uu:diva-132905 (URN)10.1109/TSTE.2010.2101620 (DOI)000208788200008 ()
Available from: 2010-10-28 Created: 2010-10-28 Last updated: 2017-12-12Bibliographically approved
10. Impacts of large-scale solar and wind power production on the balance of the Swedish power system
Open this publication in new window or tab >>Impacts of large-scale solar and wind power production on the balance of the Swedish power system
2011 (English)In: Proceedings of the World Renewable Energy Congress, Linköping, May 8-13, 2011, 2011Conference paper, Published paper (Refereed)
National Category
Energy Systems
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-132906 (URN)
Conference
World Renewable Energy Congress 2011
Available from: 2010-10-28 Created: 2010-10-28 Last updated: 2016-04-20

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