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Solar Variability Assessment and Grid Integration: Methodology Development and Case Studies
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. (Built Environment Energy Systems Group)ORCID iD: 1-6586-4932
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

During the 21st century there has been a tremendous increase in grid-connected photovoltaic (PV) capacity globally, due to falling prices and introduction of economic incentives. PV systems are in most cases small-scale, installed on residential dwellings, which means that the power production is widely distributed and close to the end-user of electricity. In this licentiate thesis the distributed PV in the built environment is studied. A methodology for assessing short-term (sub-minute) solar variability was developed, which in the continuation of this PhD project could be used to study the aggregated impact on the local distribution grid from dispersed PV systems. In order to identify potential locations for PV systems in a future scenario, methodology was developed to assess the rooftop topography on both local level using LiDAR data and nationally through building statistics. Impacts on the distribution grid were investigated through a case study on a rural municipality in Sweden. It was found that the hosting capacity, i.e. the amount of PV power generation that can be integrated in the grid without exceeding certain power quality measures, is high, at least 30%. However, the hosting capacity on transmission level needs further investigation. As a first step a methodology was developed in order to model scenarios for hourly solar power generation, aggregated over wide areas, here applied to the whole Swedish power system. The model showed high correlation compared to PV power production reported to the Swedish transmission system operator (TSO). Furthermore, it was used to model scenarios of high PV penetration in Sweden, which give some indications on the impact on the power system, in terms of higher frequency of extreme ramps.

Place, publisher, year, edition, pages
Uppsala: Uppsala University, Department of Engineering Sciences , 2015. , 55 p.
Keyword [en]
Solar variability, Photovoltaics, Grid integration, GIS, Distributed generation
National Category
Energy Systems
Research subject
Engineering Science
Identifiers
URN: urn:nbn:se:uu:diva-265451OAI: oai:DiVA.org:uu-265451DiVA: diva2:866415
Presentation
2015-11-25, ITC 1111, Lägerhyddsvägen 1, Uppsala, 14:00 (English)
Opponent
Supervisors
Funder
StandUp
Available from: 2016-01-12 Created: 2015-10-29 Last updated: 2016-01-12Bibliographically approved
List of papers
1. Variability Assessment and Forecasting of Renewables: A Review for Solar, Wind, Wave and Tidal Resources
Open this publication in new window or tab >>Variability Assessment and Forecasting of Renewables: A Review for Solar, Wind, Wave and Tidal Resources
Show others...
2015 (English)In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 44, 356-375 p.Article in journal (Refereed) Published
National Category
Energy Engineering Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity; Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-225870 (URN)10.1016/j.rser.2014.12.019 (DOI)000351324300025 ()
Available from: 2014-06-09 Created: 2014-06-09 Last updated: 2017-12-05
2. Characteristics of a low-cost solar irradiance logger
Open this publication in new window or tab >>Characteristics of a low-cost solar irradiance logger
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Since photovoltaic (PV) power is highly intermittent the impact on the power system has been studied more thoroughly the last few years. However, there is a lack of high resolution data needed for solar variability studies, which demand dense solar irradiance monitoring networks. Here we present a silicon cell based data logger gathering global irradiance data with sampling intervals down to one second. In all it costs around \euro 40, making it significantly cheaper than commercial products, but also cheaper compared to similar dataloggers. It has a root-mean-square error (RMSE) of 16 W/m$^2$ compared to a commercial thermopile pyranometer. Since the solar logger is intended to be used in solar variability studies,the RMSE of the clear sky index step change was studied and was shown to be 0.014 averaged over 5 minutes, and 0.029 averaged over 10 seconds. The low cost yet high accuracy of the logger, combined with its high mobility and and low power consumption makes it a viable choice when designing a monitoring network for solar variability studies or in other solar energy related projects, e.g. in developing countries, where low-cost is important.

National Category
Energy Systems
Identifiers
urn:nbn:se:uu:diva-265448 (URN)
Available from: 2015-10-29 Created: 2015-10-29 Last updated: 2016-01-12
3. Determining Intra-hour Solar Irradiance Variability with a Low-cost Solar Logger Network
Open this publication in new window or tab >>Determining Intra-hour Solar Irradiance Variability with a Low-cost Solar Logger Network
2014 (English)In: Proceedings of 4th International Workshop on Integration of Solar Power into Power Systems, Berlin, Germany, 10-11 November, 2014, 2014Conference paper, Published paper (Other academic)
Abstract [en]

The study of solar irradiance is of vital importance in order to quantify the fluctuation that the transmission system needs to handle in case of large scale solar power integration. In this paper, early results from a low-cost solar irradiance logger network are presented. The main advantages of the solar logger are its low cost (~$50) and mobility. Our results confirm previous models of the station pair correlation of clear sky index step changes, with the modification that the isotropic correlation appears to decrease exponentially as a function of Δt-1/2 rather than Δt-1 as has been proposed earlier.

National Category
Energy Systems
Research subject
Engineering Science
Identifiers
urn:nbn:se:uu:diva-239146 (URN)9783981654905 (ISBN)
Conference
4th International Workshop on Integration of Solar Power into Power Systems, Berlin, Germany, 10-11 November, 2014
Available from: 2014-12-18 Created: 2014-12-18 Last updated: 2017-09-15
4. Development and validation of a wide-area model of hourly aggregate solar power generation
Open this publication in new window or tab >>Development and validation of a wide-area model of hourly aggregate solar power generation
2016 (English)In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 102, 559-566 p.Article in journal (Refereed) Published
Abstract [en]

The impact of photovoltaics (PV) on the power system becomes increasingly important to study as the penetration of PV has increased rapidly over the last decade. A physical model for aggregated PV generation has been developed for the Swedish spot market areas. Information about PV systems within the Swedish electricity certificate system and irradiance data from the meteorological model STRÅNG were used as inputs. The model was trained and validated against production data reported to the Swedish transmission system operator. Our model shows high correlation (0.95-0.99) to reported historical production data. However, it overestimates extreme 1h ramp rates, which are -20% and 22% for down- and up-ramps respectively, compared to -13% and 14% for the reported data. Furthermore a weighting function was developed, which takes demography, available solar irradiance and today's PV deployment into account, to model likely deployment in a Swedish high penetration scenario, where PV covers 6% of the total annual power demand. The difference in extreme 1 and 4 hour step changes before and after introducing PV is small. The model could thus be used with confidence to model the impact on the power system for future scenarios of high PV penetration.

Keyword
PV power; Step changes; Solar variability; Physical model
National Category
Energy Systems
Identifiers
urn:nbn:se:uu:diva-265450 (URN)10.1016/j.energy.2016.02.085 (DOI)000375889400050 ()
Funder
StandUp
Available from: 2015-10-29 Created: 2015-10-29 Last updated: 2017-12-01Bibliographically approved
5. Self-consumption enhancement of residential photovoltaics with battery storage and electric vehicles in communities
Open this publication in new window or tab >>Self-consumption enhancement of residential photovoltaics with battery storage and electric vehicles in communities
2015 (English)In: Proceedings of the eceee 2015 Summer Study on energy efficiency, 1–6 June 2015, Presqu’île de Giens, Toulon/Hyères, France, 2015, 991-1002 p.Conference paper, Published paper (Refereed)
Abstract [en]

Grid-connected photovoltaic (PV) systems have been dependent on supporting schemes to be competitive with conventional electricity generation. Selling prices of PV power production are now lower than buying prices in several countries, making it profitable to match generation with household consumption. Self-consumption, calculated as in situ instantaneous consumption of PV power production relative to total power production, can be used to improve the profitability with higher buying than selling prices of electricity. Another measure, self-sufficiency, similar to self-consumption but calculated relative to the yearly consumption, can also be used. Battery storage and electric vehicle (EV) home-charging are interesting alternatives to increase the self-consumption, since the PV power production can be stored for later use. This study uses high-resolution consumption data for 21 single-family houses in Sweden and irradiance data for the year 2008 to examine the potential for battery storage and EV home-charging for communities of single-family houses with PV systems. The aim is to compare how self-consumption and self-sufficiency are affected by individual power grid connections for all households versus one shared grid connection for the whole community. These scenarios are combined with battery storage and EV charging (individual versus centralized). It is found that total consumption profiles level out when several houses are connected together, the self-consumption increases from 52 to 71 % and the self-sufficiency from 12 to 17 %. The size of a centralized storage can be reduced compared to the aggregated size of storages in every house to reach the same level of self-consumption. The potential for EV charging is limited due to mismatch between irradiance and charging patterns. The extra revenue from increased self-consumption with battery storage is too low for all the cases to justify an investment in batteries since the prices are still too high. With dedicated support schemes, higher buying prices of electricity and cheaper battery, PV-battery systems can still be an interesting solution in countries with high solar irradiance throughout the year.

National Category
Energy Engineering
Identifiers
urn:nbn:se:uu:diva-254455 (URN)978-91-980482-6-1 (ISBN)
Conference
eceee 2015 Summer Study on energy efficiency, 1–6 June 2015, Presqu’île de Giens, Toulon/Hyères, France
Projects
Småskalig solel i byggnader - kraft för förändring i energisystem och vardagslivet
Funder
Swedish Energy Agency
Available from: 2015-06-08 Created: 2015-06-08 Last updated: 2016-01-12
6. Maximizing PV hosting capacity by smart allocation of PV: A case study on a Swedish distribution grid
Open this publication in new window or tab >>Maximizing PV hosting capacity by smart allocation of PV: A case study on a Swedish distribution grid
2015 (English)In: Proceedings of ASES Solar 2015, Pennsylvania State University, Pennsylvania, USA, July 28-30, 2015, 2015Conference paper, Published paper (Other academic)
Abstract [en]

Detailed simulations of large amounts of PV production in Swedish rural power grids show that as module and system prices keep declining and thus increasing the profitability and demand for solar power, current grid performance will limit the potential. Simulations have been made on a case distribution grid (10 kV) with actual hourly load data for 2014 and calculated hourly production with respect to building roof area, tilt and azimuth together with irradiation data. At high production, especially voltage rises along cables in the outer part of the grid is problematic, but also currents in cables close to transformer buses increases substantially at these conditions. Resulting hosting capacity for the case grid is 32%, as of annual production compared to annual demand. What is limiting the hosting capacity is the tolerated voltage rise, which is set to 5% of nominal grid voltage. Through smart allocation of PV systems to the strongest nodes in the grid the hosting capacity of the same grid can be increased to 74%.

National Category
Energy Systems
Research subject
Engineering Science
Identifiers
urn:nbn:se:uu:diva-265444 (URN)
Conference
ASES Solar 2015, Pennsylvania State University, Pennsylvania, USA, July 28-30, 2015
Available from: 2015-10-29 Created: 2015-10-29 Last updated: 2017-10-25

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