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  • 1.
    Bright, Jamie M
    et al.
    Fenner School of Environment and Society, Australian National University, Canberra, Australia .
    Gueymard, Christian A
    Solar Consulting Services, Colebrook, NH, USA.
    Killinger, Sven
    Fraunhofer Institute for Solar Energy Systems ISE, 79100 Freiburg, Germany .
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sun, Xixi
    Department of Mathematics and System Sciences, Beihang University, Beijing, China .
    Wang, Peng
    Department of Mathematics and System Sciences, Beihang University, Beijing, China;Beijing Advanced Innovation Center for Big Data, Beihang University, Beijing, China .
    Engerer, Nicholas A
    Fenner School of Environment and Society, Australian National University, Canberra, Australia .
    Climatic and Global Validation of Daily MODIS Precipitable Water Data at AERONET Sites for Clear-sky Irradiance Modelling2018In: Proceedings of the ISES EuroSun 2018 Conference: 12th International Conference on Solar Energy for Buildings and Industry, International Solar Energy Society, 2018, p. 1490-1501Conference paper (Refereed)
    Abstract [en]

    Precipitable water (PW) is an influential variable in regards to clear-sky radiation modelling and solar resource assessment. Thus, the accuracy of solar energy estimates depends on the accuracy of PW measurements. Gridded satellite information is commonly used for solar modelling because of its benefit of a broad geographical coverage, thus a global validation of commonly utilised PW products is imperative. Here, all Level-3 Moderate Resolution Imaging Spectroradiometer (MODIS) daily PW products from the Aqua and Terra satellites (at 1° × 1° spatial resolution) from 01/2000 to 02/2018 are compared and validated against all of NASA’s ground-sensing Aerosol Robotic NETwork (AERONET) V3 Level-2 PW daily averages from sites that have at least one year of observa- tions during 2000–2018 (452 sites representing 675,158 observations). Furthermore, sub-categorisation by Kö- ppen-Geiger climate regions enables climate specific validation to ascertain any distinct climatic influence. The results demonstrate significant climatological influences that impact the derived PW products. It is found that the Terra PW is more accurate than the Aqua PW, and that blending these two products yields a higher accuracy of daily PW estimates. The MODIS PW product also suffers from overestimation at larger magnitudes (>3 cm). The absolute errors do not reduce linearly with the PW magnitude, so that relative errors are far worse in areas of low PW, such as the polar climate. The equatorial climate, with the highest PW records, behaves best. Finally, a simple sensitivity test using the REST2 clear-sky radiation model shows that the global PW RMSE (0.511 cm) of the combined MODIS data would result in a 1.5-2.5% under- or overestimate on direct normal irradiance (DNI) de- pending on latitude relative to using the AERONET mean PW of 1.8971 cm. It is thus concluded that the daily MODIS PW product is not ideal for clear-sky radiation modelling, at least whenever accurate DNI predictions are necessary on a global scale.

  • 2.
    Bright, Jamie M.
    et al.
    Australian Natl Univ, Fenner Sch Environm & Soc, Canberra, ACT 2601, Australia.
    Killinger, Sven
    Australian Natl Univ, Fenner Sch Environm & Soc, Canberra, ACT 2601, Australia.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Australian Natl Univ, Fenner Sch Environm & Soc, Canberra, ACT 2601, Australia.
    Engerer, Nicholas A.
    Australian Natl Univ, Fenner Sch Environm & Soc, Canberra, ACT 2601, Australia.
    Improved satellite-derived PV power nowcasting using real-time power data from reference PV systems2018In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 168, p. 118-139Article in journal (Refereed)
    Abstract [en]

    Rapid growth in the global penetration of solar photovoltaic (PV) systems means electricity network operators and electricity generators alike are increasingly concerned with the short-term solar forecasting (nowcasting) of solar irradiance. This paper proposes a methodology that considers a varying number of available reference PV systems for supporting satellite-derived PV power real-time nowcasting. We evaluate conventional satellite-only and upscaling-only PV fleet estimate methodologies and compare them to two newly developed correction and hybrid cases. When using only a single reference PV system to estimate the aggregated power of 48 independent target PV systems for the location of Canberra, Australia; we show that the newly proposed correction or hybrid cases improve the performance of the satellite-derived PV power estimate medians in terms of MBE, rMBE, RMSE and rRMSE from 0.031 W/W-p, 7.46%, 0.079 W/W-p and 23.4%, down to 0.006 W/W-p,-0.711%, 0.068 W/W-p and 20.0%, representing relative improvements of 80.6%, 90.5%, 13.9% and 14.5%, respectively. Similarly, when using 30 reference PV systems, we report median improvements from 0.036 W/W-p, 8.25%, 0.083 W/W-p and 24.8%, down to 0.01 W/W-p, 1.41%, 0.049 W/W-p and 11.4%, representing relative improvements of 72.2%, 82.9%, 41.0% and 54.0%, respectively. We discuss the fundamental challenges facing the use of reference PV systems, satellite-derived power estimates, combining the two data sources, and the knowledge required to address these issues. We ultimately conclude that combining satellite-based PV power estimates with data from reference PV systems is always more beneficial than either on their own.

  • 3.
    Bright, Jamie M
    et al.
    Australian National University.
    Killinger, Sven
    Fraunhofer ISE, Freiburg (Germany).
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Engerer, Nicholas A
    Australian National University, Canberra (Australia).
    Integration of distributed solar forecasting with distribution network operations in Australia2017In: Proc. of the ISES Solar World Congress 2017, 2017Conference paper (Other academic)
    Abstract [en]

    Advances in solar integration technologies such as high-resolution solar forecasting and photovoltaic (PV) modelling are making it possible to remove some of the uncertainty facing electrical network operators and service providers with behind-the-meter (BtM) solar PV. However, a key challenge facing energy markets and networks is the integration ofthese technologies with their operations in a manner that is both useful and secure. The current lack of visibility of the aggregated power output from BtM solar PV within areas of the electrical distribution grid results in a dependency on reactive grid management; the future of effective management is to facilitate proactive strategies. Little published information is available on the usefulness ofsolar forecasting data at the distribution network level as well as best practice for the integration of such forecasts with their operations. This paper is intended to inform readers ofa large Australian Renewable Energy Agency (ARENA) fundedsolar forecasting research project at the Australian National University (ANU) in collaboration with new solar forecasting company Solcast. The overall aim is to offer distribution networks service providers (DNSPs) and other interested parties (e.g. researchers) with historic, real-time and forecasted BtM solar PV power outputs at multiple levels of the electricity grid infrastructure. To date, 11 of the 15 Australian DNSPs are partnered with the project and have started to use the solar forecasting information. Furthermore, at least one international inverter manufacturer has engaged in a partnership for real-time visibility of BtM solar PV systems. The first key take home message is that the project can deliver real-time solar estimates (currently at 30-min mean resolution) for anywhere around the world, along with a 7 day forecast; note that post-coded/substation specific information is only available where a DNSP has provided the relevant metadata. The second is that research collaborations are welcomed in order to work together to the overall goal of increasing the global penetration of solar PV in the world’s energy mix. The structure of this paper is as follows. The scene is set for BtM solar PV installations in Australia beforeintroducing the problems faced by DNSPs with regards to PV interaction with the electricity grid. A brief overview of the solar forecasting methodology is provided as well as the nature of the ARENA-funded ANU project collaboration with Solcast. The current status of the project is detailed before showing examples of the project in action. Lastly, the future outlook of the project is made stating the nature of contemporary and ambitious goals.

  • 4.
    Etherden, Nicholas
    et al.
    Vattenfall R&D Power Technology.
    Aboukrat, Maxime
    Vattenfall R&D Power Technology.
    Cebollada, Virginia
    Vattenfall R&D Power Technology.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Karlsson, Björn O
    University of Gävle.
    Shading losses for different types of residential PV systems and its city-wide impact on PV potential2019In: Proceedings of Solar Integration Workshop Dublin 2019 / [ed] Energynautics, 2019Conference paper (Other academic)
    Abstract [en]

    Power optimiser are becoming increasingly popular in residential photovoltaic installations. Besides monitoring and safety advantages the power optimise can increase production under partial shading conditions due to the individual maximum power point tracking performed independently for each panel. This study quantifies the production gains with power optimisers through both empirical and theoretical city-wide simulations. Empirical measurements on adjacent string and optimiser PV systems showed that shading losses from a tree decreased from 17% to 13 %. A study of 1100 single family houses in an urban suburb showed that 2/3 of the houses would have a gain with optimisers above 20 kWh/kWp and year.

  • 5.
    Etherden, Nicholas
    et al.
    Vattenfall R&D Power Technology, Stockholm, Sweden.
    Ahlberg, Johan
    Vattenfall R&D Power Technology, Stockholm, Sweden.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Kvamme, Kjetil
    Powel A/S, Tromsö, Norway.
    Calculating the hosting capacity of electrical network with high penetration of solar PV2018In: Proc. of the 8th International Workshop on the Integration of Solar Power into Power Systems / [ed] Energynautics GmbH, 2018, p. 1-6Conference paper (Refereed)
    Abstract [en]

    This paper describes a method to determine the Hosting Capacity (HC) for solar Photovoltaics (PV) in distribution networks. The method uses hourly load data and roof-top PV power production simulation data in a commercial Network Information System (NIS). The HC – defined as the maximum amount of new PV that can be connected without endangering the reliability or quality for other customers - is monitored for each node in the network with different proportions of the buildings having PV installations. The times- series of PV power generation are influenced by both local weather conditions and shading to ensure that only profitable installations are simulated. The method captures the variability of load and production and enables simultaneous evaluation of several of the most common mitigation actions in networks with high PV penetration. Presented is a case study of a network with 51 secondary substations and 534 customer networks in central Sweden. With PV applied to 10% of the best roof locations, some local voltage issues arise. With limited mitigation actions at critical locations the network can host as much of 30% of the best roof-top locations having PV.

  • 6.
    Gueymard, Christian A.
    et al.
    Solar Consulting Serv, Colebrook, NH USA.
    Bright, Jamie M.
    Australian Natl Univ, Fenner Sch Environm & Soc, Canberra, ACT, Australia.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Habte, Aron
    Natl Renewable Energy Lab, Golden, CO USA.
    Sengupta, Manajit
    Natl Renewable Energy Lab, Golden, CO USA.
    A posteriori clear-sky identification methods in solar irradiance time series: Review and preliminary validation using sky imagers2019In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 109, p. 412-427Article, review/survey (Refereed)
    Abstract [en]

    This study examines all known methods that have been proposed in the literature to identify clear-sky periods in historical solar irradiance time series. Two different types of clear-sky detection (CSD) methods are discussed: those (16 total) that attempt to isolate periods of 1-min or more cloudless conditions, and those (5 total) that only attempt to detect clear-sun periods. All methods are found to rely on a diversity of inputs and on a variety of tests that typically examine the smoothness of the temporal variation of global and/or direct irradiance. Using samples of a few days with variable cloudiness, it is shown that these methods all have obvious strengths and weaknesses. Although this justifies a detailed validation to determine which method(s) could be best suited in the practice of solar radiation modeling or other applications, the current lack of appropriate equipment at high-quality reference radiometric stations prevents such an endeavor. Only a preliminary study is conducted here at seven stations of the SURFRAD network in the U.S., where 1-min irradiance measurements are available, along with sky data from a Total Sky Imager (TSI). The many limitations of the latter prevent its data to be considered "ground truth" here. Nevertheless, the comparison of the results from all CSD methods and 1.2 million TSI observations from all SURFRAD sites provides important qualitative and quantitative information, using a variety of performance indicators. Overall, two CSD methods appear more robust and are recommended, pending better high-resolution and high-performance cloud observations from modern sky cameras to redo these tests.

  • 7.
    Killinger, Sven
    et al.
    Australian National University.
    Bright, Jamie M
    Australian National University.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Engerer, Nicholas A
    Australian National University.
    A tuning routine to correct systematic influences in reference PV systems' power outputs2017In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 157, p. 1082-1094Article in journal (Refereed)
    Abstract [en]

    Power output measurements from PV systems are subject to a wide variety of systematic external and internal influences, such as shading, soiling, degradation, module and inverter quality issues and other system-level losses. All of these influences upon PV power measurements make the use of PV power output datasets for higher-level analysis problematic, particularly in their use as reference PV systems for estimating the power of a regional portfolio. To address these issues, we present a three-step method. Firstly, a parameterisation and quality control of power measurements is performed, which also corrects for consistent inefficiencies by a loss factor LF. Secondly, the detection of systematic de-ratings affecting PV system power output differently for each time step of the day (predominantly due to shading) together with the implementation of a subsequent “re-rating” of the power output measurements in a process referred to as tuning. The pivotal element of this approach is a 30-day running 90th percentile of the clear-sky index for photovoltaics kpv and the computation of a daily de-rating profile. Lastly, high kpv related variance in the early morning and evening is detected and filtered. Whilst these three methods are independent of each other, we suggest applying them in combination following the same order as in our paper. Cross-validations of these methods demonstrate significant improvements to the PV power measurement profiles, particularly in their use as reference PV systems for upscaling approaches. The RMSE falls from 0.174 to 0.09 W/Wp, rRMSE from 46.5% to 21.9%, MAPE from 47.9% to 20.8% and the correlation r increases from 0.767 to 0.919. Hence, we report overall improvements to RMSE, rRMSE, MAPE and r by 48%, 53%, 57% and 20%, respectively

  • 8.
    Killinger, Sven
    et al.
    Australian National University.
    Bright, Jamie M
    Australian National University.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Engerer, Nicholas A
    Australian National University.
    Towards a Tuning Method of PV Power Measurements to Balance Systematic Influences2017In: Proceedings of the ISES Solar World Congress 2017, AbuDhabi, United Arab Emirates, October 29 - November 2, 2017Conference paper (Refereed)
    Abstract [en]

    With rapid deployment and penetration rates of residential photovoltaic (PV) systems in the distribution grid, there is growing need for accurate assessment of the real-time power generation for grid management and energy market operations. Many of these installed PV systems report their live power generation to online databases and can be used as references to estimate the power generation of neighbouring systems. Upscaling approaches have demonstrated their capability of using the data from these reference PV systems to estimate the power output of target PV systems that do not report their power generation data. However, there is an inherent issue with the representativeness of these reference PV systems power data, e.g. due to quality issues or system specific influences such as shading. Three methods were developed by the authors in earlier work: (1) a parametrisation of PV system metadata and quality control of the measured power, (2) a tuning routine that detects diurnal influences from shading and tunes the PV power in order to reach the expected generation without any shading. And (3) a method which eliminates high variances in kpv based upscaling. An extensive cross-validation with 308 systems in Canberra, Australia in this paper shows significant improvements as a direct result of the application of these three methods. Furthermore, we present the preliminary findings for developments in: the parametrisation of shaded/multi-azimuth reference PV systems, as well as a method to reduce inertia in the shade detection and tuning. Overall, we successfully improve the management of reference PV system power data for use in upscaling.

  • 9.
    Killinger, Sven
    et al.
    Fraunhofer ISE, Freiburg (Germany).
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Saint-Drenan, Yves-Marie
    MINES ParisTech, PSL Research University, Sophia Antipolis (France).
    Moraitis, Panagiotis
    Copernicus Institute of Sustainable Development, Utrecht University, Utrecht (The Netherlands).
    van Sark, Wilfried
    Copernicus Institute of Sustainable Development, Utrecht University, Utrecht (The Netherlands).
    Taylor, Jamie
    Sheffield Solar, University of Sheffield, Sheffield (UK).
    Engerer, Nicholas A
    Australian National University, Canberra (Australia).
    Bright, Jamie M
    Australian National University.
    On the search for representative characteristics of PV systems: Data collection and analysis of PV system azimuth, tilt, capacity, yield and shading2018In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 173, p. 1087-1106Article in journal (Refereed)
    Abstract [en]

    Knowledge of PV system characteristics is needed in different regional PV modelling approaches. It is the aim of this paper to provide that knowledge by a twofold method that focuses on (1) metadata (tilt and azimuth of modules, installed capacity and specific annual yield) as well as (2) the impact of shading. Metadata from 2,802,797 PV systems located in Europe, USA, Japan and Australia, representing a total ca-pacity of 59 GWp (14.8% of installed capacity worldwide), is analysed. Visually striking interdependencies of the installed capacity and the geographic location to the other parameters tilt, azimuth and specific annual yield motivated a clustering on a country level and between systems sizes. For an eased future utilisation of the analysed metadata, each parameter in a cluster was approximated by a distribution function. Results show strong characteristics unique to each cluster, however, there are some commonalities across all clusters. Mean tilt values were reported in a range between 16.1° (Australia) and 35.6° (Belgium), average specific annual yield values occur between 786 kWh/kWp (Denmark) and 1426 kWh/kWp (USA South). The region with smallest median capacity was the UK (2.94 kWp) and the largest was Germany (8.96 kWp). Almost all countries had a mean azimuth angle facing the equator. PV system shading was considered by deriving viewsheds for ≈48,000 buildings in Uppsala, Sweden (allranges of solar angles were explored). From these viewsheds, two empirical equations were derived related to irradiance losses on roofs due to shading. The first expresses the loss of beam irradiance as a function of the solar elevation angle. The second determines the view factor as a function of the roof tilt including the impact from shading and can be used to estimate the losses of diffuse and reflected irradiance.

  • 10.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Solar Variability Assessment and Grid Integration: Methodology Development and Case Studies2015Licentiate 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.

    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, p. 356-375Article 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: 2018-08-01
    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: 2018-02-20
    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: 2018-02-20
    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, p. 559-566Article 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.

    Keywords
    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: 2018-02-20Bibliographically 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, p. 991-1002Conference 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: 2018-02-20
    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: 2018-02-20
  • 11.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Solar Variability Assessment in the Built Environment: Model Development and Application to Grid Integration2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    During the 21st century there has been a rapid increase in grid-connected photovoltaic (PV) capacity globally, due to falling system component prices and introduction of various economic incentives. To a large extent, PV systems are installed on buildings, which means they are widely distributed and located close to the power consumer, in contrast to conventional power plants. The intermittency of solar irradiance poses challenges to the integration of PV, which may be mitigated if properly assessing the solar resource. In this thesis, methods have been developed for solar variability and resource assessment in the built environment on both national and local level, and have been applied to grid integration studies. On national level, a method based on building statistics was developed that reproduces the hourly PV power generation in Sweden with high accuracy; correlation between simulated and real power generation for 2012 and 2013 were 0.97 and 0.99, respectively. The model was applied in scenarios of high penetration of intermittent renewable energy (IRE) in the Nordic synchronous power system, in combination with similar models for wind, wave and tidal power. A mix of the IRE resources was sought to minimise the variability in net load (i.e., load minus IRE, nuclear and thermal power). The study showed that a fully renewable Nordic power system is possible if hydropower operation is properly planned for. However, the contribution from PV power would only be 2-3% of the total power demand, due to strong diurnal and seasonal variability. On local level, a model-driven solar resource assessment method was developed based on low-resolution LiDAR (Light Detection and Ranging) data. It was shown to improve the representation of buildings, i.e., roof shape, tilt and azimuth, over raster-based methods, i.e., digital surface models (DSM), which use the same LiDAR data. Furthermore, the new method can provide time-resolved data in contrast to traditional solar maps, and can thus be used as a powerful tool when studying the integration of high penetrations of PV in the distribution grid. In conclusion, the developed methods fill important gaps in our ability to plan for a fully renewable power system.

    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, p. 356-375Article 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: 2018-08-01
    2. 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, p. 559-566Article 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.

    Keywords
    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: 2018-02-20Bibliographically approved
    3. Net load variability in Nordic countries with a highly or fully renewable power system
    Open this publication in new window or tab >>Net load variability in Nordic countries with a highly or fully renewable power system
    Show others...
    2016 (English)In: Nature Energy, ISSN 2058-7546, Vol. 1, p. 1-8, article id 16175Article in journal (Refereed) Published
    Abstract [en]

    Increasing the share of intermittent renewable energy (IRE) resources such as solar, wind, wave and tidal energy in a power system poses a challenge in terms of increased net load variability. Fully renewable power systems have previously been analysed, but more systematic analyses are needed that explore the effect of different IRE mixes on system-wide variability across different timescales and the optimal combinations of IRE for reducing variability on a given timescale. Here we investigate these questions for the Nordic power system. We show that the optimal mix of IRE is dependent on the frequency band considered. Long-term (>4 months) and short-term (<2 days) fluctuations can be similar to today’s, even for a fully renewable system. However, fluctuations with periods in between will inevitably increase significantly. This study indicates that, from a variability point of view, a fossil- and nuclear-free Nordic power system is feasible if properly balanced by hydropower.

    National Category
    Materials Engineering
    Identifiers
    urn:nbn:se:uu:diva-302836 (URN)10.1038/NENERGY.2016.175 (DOI)000394793000001 ()
    Funder
    StandUpStandUp for Wind
    Available from: 2016-09-11 Created: 2016-09-11 Last updated: 2019-04-05
    4. Comparing the capability of low- and high-resolution LiDAR data with application to solar resource assessment, roof type classification and shading analysis
    Open this publication in new window or tab >>Comparing the capability of low- and high-resolution LiDAR data with application to solar resource assessment, roof type classification and shading analysis
    Show others...
    2017 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 205, p. 1216-1230Article in journal (Refereed) Published
    Abstract [en]

    LiDAR (Light Detection and Ranging) data have recently gained popularity for use in solar resource assessment and solar photovoltaics (PV) suitability studies in the built environment due to robustness at identifying building orientation, roof tilt and shading. There is a disparity in the geographic coverage of low- and high-resolution LiDAR data (LL and LH, respectively) between rural and urban locations, as the cost of the latter is often not justified for rural areas where high PV penetrations often pose the greatest impact on the electricity distribution network. There is a need for a comparison of the different resolutions to assess capability of LL. In this study, we evaluated and improved upon a previously reported methodology that derives roof types from a LiDAR-derived, low-resolution Digital Surface Model (DSM) with a co-classing routine. Key improvements to the methodology include: co-classing routine adapted for raw LiDAR data, applicability to differing building type distribution in study area, building height and symmetry considerations, a vector-based shading analysis of building surfaces and the addition of solar resource assessment capability.

    Based on the performance of different LiDAR resolutions within the developed model, a comparison between LL (0.5-1 pts/m(2)) and LH (6-8 pts/m(2)) LiDAR data was applied; LH can confidently be used to evaluate the applicability of LL, due to its significantly higher point density and therefore accuracy. We find that the co-classing methodology works satisfactory for LL for all types of building distributions. Roof-type identification errors from incorrect co-classing were rare (< 1%) with LL. Co-classing buildings using LL improves accuracy of roof-type identification in areas with homogeneous distribution of buildings, here from 78% to 86% in accuracy. Contrastingly, co-classing accuracy using LH is marginally reduced for all building distributions from 94.8% to 94.4%. We adapt the Hay and Davies solar transposition model to include shading. The shading analysis demonstrates similarity of results between LL and LH. We find that the proposed methodology can confidently be used for solar resource assessments on buildings when only LiDAR data of low-resolution (< 1 pts/m(2)) is available.

    Place, publisher, year, edition, pages
    Elsevier, 2017
    Keywords
    LiDAR, Solar resource assessment, Shading, Building classification, Low-resolution, High-resolution
    National Category
    Energy Systems
    Research subject
    Engineering Science
    Identifiers
    urn:nbn:se:uu:diva-332226 (URN)10.1016/j.apenergy.2017.08.045 (DOI)000414817100098 ()
    Available from: 2017-10-25 Created: 2017-10-25 Last updated: 2018-02-20Bibliographically approved
    5. Identification of PV system shading using a LiDAR-based solar resource assessment model: an evaluation and cross-validation
    Open this publication in new window or tab >>Identification of PV system shading using a LiDAR-based solar resource assessment model: an evaluation and cross-validation
    Show others...
    2018 (English)In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 159, p. 157-172Article in journal (Refereed) Published
    Abstract [en]

    Photovoltaic (PV) systems are subject to several different systematic de-rating factors, such as soiling, degradation, inverter mismatch and shading. With increasing penetration of PV in the local grid, Distribution Network Service Providers (DNSPs) are inclined to assess such losses, in order to accurately estimate the total regional power output of distributed PV. The most influential de-rating factor is shading, which can cause ramps on the generated power output, similar to clouds. In this study we evaluate and compare two fundamentally different methods for module orientation parametrisation and shading analysis of PV systems that have been developed in previous work. In the first method, LiDAR (Light Detection and Ranging) data are used to derive the PV module orientation and shading, referred to herein as LiDAR model. The second method, referred to as the QCPV-Tuning model, is based on reported PV power generation, which is firstly quality controlled and parametrised in order to derive module orientation and a loss factor, LF, representing systematic de-rating factors. Secondly, variations in de-ratings throughout the day, mainly due to shading, are explored in a process referred to as Tuning. For both methods, binary time series are derived expressing the presence of shading, which are used to evaluate how the methods corroborate. We evaluate four cases; case 1) evaluates the original versions of the LiDAR and QCPV-Tuning models, while in case 2-4 improvements to the models are introduced. A new filter for extracting representative LiDAR data points for the shading analysis was introduced for the LiDAR model (case 2). For the QCPV-Tuning model significant inaccuracies in the parametrisation of the module orientation were identified due to strong shading in either morning or evening and were thus corrected to observed parameters (case 3). For case 4) improvements on both models were introduced. The Pearson correlation coefficients of shading events for the methods were 0.28, 0.36, 0.42 and 0.50 for case 1-4, respectively. A mismatch in the timing of shading events motivated the comparison of the mean hourly shading, with correlation coefficients of 0.34, 0.43, 0.49 and 0.57 for case 1-4, respectively. The results of this study show that both methods can confidently be used for solar resource assessment, given the suggested improvements.

    Place, publisher, year, edition, pages
    Elsevier, 2018
    Keywords
    Solar resource assessment, Shading, PV Tuning, LiDAR
    National Category
    Energy Systems
    Research subject
    Engineering Science
    Identifiers
    urn:nbn:se:uu:diva-332235 (URN)10.1016/j.solener.2017.10.061 (DOI)000423007300016 ()
    Available from: 2017-10-25 Created: 2017-10-25 Last updated: 2018-03-12Bibliographically approved
    6. Self-consumption enhancement and peak shaving of residential photovoltaics using storage and curtailment
    Open this publication in new window or tab >>Self-consumption enhancement and peak shaving of residential photovoltaics using storage and curtailment
    2016 (English)In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 112, p. 221-231Article in journal (Refereed) Published
    Abstract [en]

    Increasing the self-consumption of photovoltaic (PV) power is an important aspect to integrate more PV power in the power system. The profit for the PV system owner can increase and the stress on the power grid can be reduced. Previous research in the field has focused on either self-consumption of PV power in individual buildings or PV power curtailment for voltage control. In this paper self-consumption of residential PV power in a community of several single-family houses was investigated using high-resolution irradiance and power consumption data. Cases with individual or shared battery energy storages for the houses were examined. PV power curtailment was investigated as a method to reduce feed-in power to the grid, i.e. peak shaving. Results indicated that the self-consumption ratio increased when using shared instead of individual storage. Reducing the feed-in power from the community by almost 50% only led to maximum 7% yearly production losses due to curtailment and storage losses. The economics for shared storage are slightly better than for individual ones. These results suggest that residential PV-battery systems should use (i) shared energy storage options if local regulations allow it and (ii) PV power curtailment if there are incentives to lower the feed-in power.

    Place, publisher, year, edition, pages
    Elsevier, 2016
    Keywords
    Photovoltaics, Solar energy, Self-consumption, Energy storage, Battery, Curtailment
    National Category
    Energy Engineering
    Research subject
    Engineering Science with specialization in Solid State Physics
    Identifiers
    urn:nbn:se:uu:diva-283612 (URN)10.1016/j.energy.2016.06.039 (DOI)000385318700021 ()
    Projects
    Småskalig solel i byggnader – kraft för förändring i energisystem och vardaglivet
    Funder
    Swedish Energy Agency, P37511-1
    Available from: 2016-04-13 Created: 2016-04-13 Last updated: 2018-10-10Bibliographically approved
    7. Large-scale integration of photovoltaic power in a distribution grid using power curtailment and energy storage
    Open this publication in new window or tab >>Large-scale integration of photovoltaic power in a distribution grid using power curtailment and energy storage
    2017 (English)In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 155, p. 1319-1325Article in journal (Refereed) Published
    Keywords
    Photovoltaics, Power distribution system, Energy storage, Power and voltage control, Overvoltage
    National Category
    Energy Engineering
    Research subject
    Engineering Science
    Identifiers
    urn:nbn:se:uu:diva-328066 (URN)10.1016/j.solener.2017.07.083 (DOI)000414819900057 ()
    Projects
    Småskalig solel i byggnader – kraft för förändring i energisystem och vardaglivetUtvärdering av tekniska lösningar för att hantera omfattande anslutning av solcellssystem i eldistributionsnät
    Funder
    Swedish Energy Agency, P37511-1
    Note

    Photovoltaic (PV) power generation is an important component for the future energy system. High penetrationof PV power in a power distribution system might however lead to problems with overvoltage and overload. In this study, a method for PV power curtailment and placement of decentralized energy storage is developed to control voltage, feeder currents and distribution substation overloading. The method determines an individual feed-in power limit for each PV system owner based on a voltage-power relationship. Measured data from a 10 kV/400 V three-phase distribution grid in the Swedish municipality of Herrljunga with more than 5000 end-users and simulated PV electricity production data are used for a case study to verify the model. The method is evaluated for yearly PV electricity productionof up to 100% of the yearly electricity consumption. The results show that the method is able to prevent overvoltage for all penetration levels in the studied distribution grid, reduce the number of feeders affected by overcurrent and lower the maximum load on the two substations.

    Available from: 2017-08-16 Created: 2017-08-16 Last updated: 2018-10-10Bibliographically approved
  • 12.
    Lingfors, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Bright, Jamie M
    Australian National University.
    Engerer, Nicholas A
    Australian National University.
    Ahlberg, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Killinger, Sven
    Australian National University.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Comparing the capability of low- and high-resolution LiDAR data with application to solar resource assessment, roof type classification and shading analysis2017In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 205, p. 1216-1230Article in journal (Refereed)
    Abstract [en]

    LiDAR (Light Detection and Ranging) data have recently gained popularity for use in solar resource assessment and solar photovoltaics (PV) suitability studies in the built environment due to robustness at identifying building orientation, roof tilt and shading. There is a disparity in the geographic coverage of low- and high-resolution LiDAR data (LL and LH, respectively) between rural and urban locations, as the cost of the latter is often not justified for rural areas where high PV penetrations often pose the greatest impact on the electricity distribution network. There is a need for a comparison of the different resolutions to assess capability of LL. In this study, we evaluated and improved upon a previously reported methodology that derives roof types from a LiDAR-derived, low-resolution Digital Surface Model (DSM) with a co-classing routine. Key improvements to the methodology include: co-classing routine adapted for raw LiDAR data, applicability to differing building type distribution in study area, building height and symmetry considerations, a vector-based shading analysis of building surfaces and the addition of solar resource assessment capability.

    Based on the performance of different LiDAR resolutions within the developed model, a comparison between LL (0.5-1 pts/m(2)) and LH (6-8 pts/m(2)) LiDAR data was applied; LH can confidently be used to evaluate the applicability of LL, due to its significantly higher point density and therefore accuracy. We find that the co-classing methodology works satisfactory for LL for all types of building distributions. Roof-type identification errors from incorrect co-classing were rare (< 1%) with LL. Co-classing buildings using LL improves accuracy of roof-type identification in areas with homogeneous distribution of buildings, here from 78% to 86% in accuracy. Contrastingly, co-classing accuracy using LH is marginally reduced for all building distributions from 94.8% to 94.4%. We adapt the Hay and Davies solar transposition model to include shading. The shading analysis demonstrates similarity of results between LL and LH. We find that the proposed methodology can confidently be used for solar resource assessments on buildings when only LiDAR data of low-resolution (< 1 pts/m(2)) is available.

  • 13.
    Lingfors, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Donarelli, Anna
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Arts, Department of Art History, Conservation.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Solenergi på kulturhistoriska byggnader2018In: Bygg & Teknik, ISSN 0281-658X, Vol. 5Article in journal (Refereed)
    Abstract [sv]

    År 2040 ska 5-10 procent av den svenska elmixen komma från sol- energi. En stor del av dagens sol- cellsinstallationer är uppförda på byggnader och det är troligt att den trenden kommer att hålla i sig. Samtidigt omfattas en stor del av byggnadsbeståndet av olika lag- skydd på grund av kulturhistoriska värden vilket kräver särskild varsamhet när man installerar sol- celler på dessa byggnader. I ett nystartat forskningsprojekt kom- mer verktyg och riktlinjer tas fram som tar hänsyn till både de tekniska och arkitektoniska aspekterna av solcellsinstallationer på kulturhistoriskt värdefulla byggnader.

  • 14.
    Lingfors, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Hallqvist, Rebecca
    Volotinen, Tarja
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lighting Performance and Energy Saving of a Novel Fibre Optic Lighting System2013In: Proceedings of CISBAT 2013 - International Conference - Cleantech for Sustainable Buildings, 2013, p. 317-322Conference paper (Other academic)
    Abstract [en]

    The abundant luminous ux of 3000 - 4600 lm at 100 000 - 130 000 lx direct sun illuminanceat a 10 m ber distance was obtained from Parans ber optic solar lighting system SP3.The illuminance of 2400 lm at 100 000 lx, after a 20 m distance, was higher than specied.The illumination performance and energy savings of a solar ber optic lighting system havebeen veried in a study hall - corridor interior within the EU FP7 NMP project Clear-upat Uppsala University in Sweden. The system provides the intensive full spectrum whitelight with the color temperature (that describes the light color perceived) being 5800 300 K, i.e. close to the direct sunlight outside. The color rendering index (85) (thatdescribes how well colors are rendered under the light source) is higher for the solar lightsthan for the supplementary uorescent lights (77). Thus this high quality solar lightingimproves the visibility of all kinds of objects compared to the uorescent lights. Annuallighting energy savings of 19 % in Uppsala, Sweden and 46 % in southern Europe wereestimated for a study hall interior, as well as 27 % and 55 % respectively for an interiorilluminated 16 h per day all days of a year. The ecacy (the total output ux divided bythe consumed electric energy) of 300 lm/W was obtained at sun illuminance over 100 000lx is signicantly higher than for any articial light sources available. Furthermore, thespatial light distribution was noticed to be wider than the expected, and a new .ldt-le wasdeveloped from the data for lighting simulation tools. The illuminance distributions werestudied in the study hall under various sunlight conditions and the experimental data wasfound to correspond to the simulated light scenes. This solar lighting technology wouldhave the greatest impact in oces and other commercial environments where humanbeings would work under these lights.

  • 15.
    Lingfors, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics, Byggteknik.
    Johansson, Tim
    Gitter AB.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics, Byggteknik.
    Broström, Tor
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Arts, Department of Art History, Conservation.
    Target-based visibility assessment on building envelopes: Applications to PV and cultural-heritage values2019In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 204, article id 109483Article in journal (Refereed)
    Abstract [en]

    Solar energy applications have, in recent years, become a common element in the urban landscape, especially on roofs and facades. However, it is important that the integration of solar energy in the built environment do not distort the fabric or expression of the existing building envelope, not at least in areas of high cultural-heritage values. The aesthetics depend, to a large extent, on how visible the new technology, such as photovoltaic (PV) panels, is. This paper describes a method for visibility assessment of building envelopes. It is referred to as target-based as it, in contrast to previously reported methods, bases the assessment from the perspective of the building envelope itself, rather than possible vantage points on the ground. The method was evaluated for two Swedish cities; Stockholm and Visby. In Stockholm, each building was evaluated based on its cultural-heritage values, solar irradiation and visibility. Deploying PV only on the roofs with the lowest cultural-heritage values, with insolation > 900 kWh/m2, and with no visibility from ground, results in a total PV yield of up to 2% of the total electricity demand. In Visby, various definitions of the vantage area were evaluated, from which the building envelope can be seen. It was found that the choice of vantage area greatly impacts the solar energy potential. If the vantage area is defined by the public domain, i.e., streets and other public open spaces, the non-visible roof area doubles compared to if all ground/terrain defines it. Compared to previous studies, the use of a vantage area, instead of discrete vantage points, seems to result in higher visibility of the roofs.

  • 16.
    Lingfors, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Killinger, Sven
    Australian National University.
    Engerer, Nicholas A
    Australian National University.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Bright, Jamie M
    Australian National University.
    Identification of PV system shading using a LiDAR-based solar resource assessment model: an evaluation and cross-validation2018In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 159, p. 157-172Article in journal (Refereed)
    Abstract [en]

    Photovoltaic (PV) systems are subject to several different systematic de-rating factors, such as soiling, degradation, inverter mismatch and shading. With increasing penetration of PV in the local grid, Distribution Network Service Providers (DNSPs) are inclined to assess such losses, in order to accurately estimate the total regional power output of distributed PV. The most influential de-rating factor is shading, which can cause ramps on the generated power output, similar to clouds. In this study we evaluate and compare two fundamentally different methods for module orientation parametrisation and shading analysis of PV systems that have been developed in previous work. In the first method, LiDAR (Light Detection and Ranging) data are used to derive the PV module orientation and shading, referred to herein as LiDAR model. The second method, referred to as the QCPV-Tuning model, is based on reported PV power generation, which is firstly quality controlled and parametrised in order to derive module orientation and a loss factor, LF, representing systematic de-rating factors. Secondly, variations in de-ratings throughout the day, mainly due to shading, are explored in a process referred to as Tuning. For both methods, binary time series are derived expressing the presence of shading, which are used to evaluate how the methods corroborate. We evaluate four cases; case 1) evaluates the original versions of the LiDAR and QCPV-Tuning models, while in case 2-4 improvements to the models are introduced. A new filter for extracting representative LiDAR data points for the shading analysis was introduced for the LiDAR model (case 2). For the QCPV-Tuning model significant inaccuracies in the parametrisation of the module orientation were identified due to strong shading in either morning or evening and were thus corrected to observed parameters (case 3). For case 4) improvements on both models were introduced. The Pearson correlation coefficients of shading events for the methods were 0.28, 0.36, 0.42 and 0.50 for case 1-4, respectively. A mismatch in the timing of shading events motivated the comparison of the mean hourly shading, with correlation coefficients of 0.34, 0.43, 0.49 and 0.57 for case 1-4, respectively. The results of this study show that both methods can confidently be used for solar resource assessment, given the suggested improvements.

  • 17.
    Lingfors, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Marklund, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Maximizing PV hosting capacity by smart allocation of PV: A case study on a Swedish distribution grid2015In: Proceedings of ASES Solar 2015, Pennsylvania State University, Pennsylvania, USA, July 28-30, 2015, 2015Conference 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%.

  • 18.
    Lingfors, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Shepero, Mahmoud
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Good, Clara
    The Arctic University of Norway.
    Bright, Jamie M
    Australian National University.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Boström, Tobias
    The Arctic University of Norway.
    Munkhammar, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Modelling City Scale Spatio-temporal Solar Energy Generation and Electric Vehicle Charging Load2018In: Proc. of the 8th International Workshop on the Integration of Solar Power into Power Systems / [ed] Energynautics GmbH, 2018Conference paper (Refereed)
    Abstract [en]

    This study presents a model for estimatingbuilding-applied photovoltaic (PV) energy yield and electric ve- hicle (EV) charging temporally over time and spatially on a city scale. The model enables transient assessment of the synergy between EV and PV, thus is called the EV-PV Synergy Model. Spatio-temporal data on solar irradiance is used in combination with Light Detection and Ranging (LiDAR) data to generate realistic spatio-temporal solar power generation profiles. The spatio-temporal EV charging profiles are produced with a stochastic Markov chain model trained on a large Swedish data set of travel patterns combined with OpenStreetMap (OSM) for deterministically identifying parking spaces in cities. The modelled estimates of solar power generation andEV charging are combined to determine the magnitude and correlation between PV power generation and EV charging over time on city scale for Uppsala, Sweden. Two months (January and July) were simulated to represent Sweden’s climate extremes. The EV penetration level was assumed to be 100% and all the roofs with yearly irradiation higher than 1000 kWh/m2 were assumed to have PV panels. The results showed that, even in January with the lowestsolar power generation and maximum EV load, there can be a positive net-generation (defined as the integration of PV generation minus EV charging load over time) in some locations within the city. Central locations exhibited a positive temporal correlation between EV charging load and PV generation. Negative temporal correlations were observed in the outskirts of the city, where typically night time home-charging was prevalent. In the highest PV power generation month (July) the solar generation was 16 times higher than the EV charging load. Spatially, the net-generation was positive in almost the entire city. However, the time-series correlation between the EV charging load and the PV generation reached more extreme positive and negative values in comparison with January. This was a result of the higher variability in irradiance during July in comparison with January. In summary, we find that there is a favorable synergy of EV-PV technology within the city center with assumptions of workplace charging behaviors for both winter and summer months. An unfavorable synergy with suburban areas where typically nighttime charging behaviors negatively correlate to PV generation. This suggests that distributed PV should be targeted around city center/workplace EV charging stations.

  • 19.
    Lingfors, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Volotinen, Tarja
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Illumination performance and energy saving of a solar fiber optic lighting system2013In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 21, no 13, p. A642-A655Article in journal (Refereed)
    Abstract [en]

    The illumination performance and energy savings of a solar fiber optic lighting system have been verified in a study hall - corridor interior. The system provides intensive white light with a high luminous flux of 4500 lm under 130000 lx direct sun radiation at a 10 m fiber distance from the sun-tracking light collector. The color temperature that describes the light color perceived is 5800 +/- 300 K, i.e. close to the direct sunlight outside, and the color rendering index (86), that describes how well colors are rendered under the light source, is higher for the solar lights than for the supplementary fluorescent lights (77). Thus this high quality solar lighting improves the visibility of all kinds of objects compared to the fluorescent lights. Annual lighting energy savings of 19% in Uppsala, Sweden and 46% in southern Europe were estimated for a study hall interior, as well as 27% and 55% respectively in an interior illuminated 16 h per day all days of a year. 

  • 20.
    Lingfors, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Development and validation of a wide-area model of hourly aggregate solar power generation2016In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 102, p. 559-566Article in journal (Refereed)
    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.

  • 21.
    Lingfors, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Solenergipotentialen för Blekinges bebyggelse enligt två framtidsscenarier2014Report (Other academic)
  • 22.
    Lingfors, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Solenergipotentialen för Skånes bebyggelse enligt två framtidsscenarier2018Report (Other academic)
    Abstract [sv]

    Under de senaste åren har det skett en mycket snabb utbyggnad av solenergi i bebyggelsen i många länder, initialt i europeiska länder som Tyskland, Italien och Spanien men idag sker en snabb utveckling i de flesta länder i världen. I Sverige har användningen av solenergi tagit fart lite senare än i de södra grannländerna, mycket på grund av låga elkostnader från vatten- och kärnkraft. I samband med att investeringsstöd för solceller introducerades 2009 har dock solcellsmarknaden tagit fart om än från en låg nivå (se Figur 1). Från att solenergi framförallt nyttjats för uppvärmning eller för elgenerering vid fritidshuset eller båten sker nu installeringar av solcellsystem på framförallt villatak och lokaler i Sverige.För att möta både internationella såväl som lokala målsättningar att minskaklimatpåverkan är det viktigt att få en bild av potentialen för olika typer av förnybar energitillförsel. Den här studien är genomförd på uppdrag av Länsstyrelsen i Skåne med syfte att bedöma potentialen för solenergi på takytor inom hela länet, men även uppdelat på kommunnivå, både i närtid och med en längre tidshorisont. Utifrån trenden med sjunkande priser på solceller har potentialen för solvärme bedömts mycket liten, men kan delvis vara intressant för småhus.Potentialberäkningarna utgår från byggnadsbeståndet i fastighetskartan, uppdelat på olika byggnadstyper, där kvalificerade antaganden gjorts för vilken grad takytor för olika byggnadstyper kan utnyttjas för solenergi.Resultaten visar att det finns ungefär 105 km2 tillgänglig takyta för solenergi. Den realiserbara potentialen bedöms vara 3.1 TWh i scenario A samt 7.5 TWh i scenario B. Detta kan jämföras med elkonsumtionen i Skåne län som uppgick till 12.1 TWh 2014.

  • 23.
    Lingfors, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Marklund, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Boork, Magdalena
    SP Technical Research Institute of Sweden.
    Larsson, David
    School of Business Society and Engineering, Mälardalen University.
    Photovoltaics in Swedish agriculture: Technical potential, grid integration and profitability2015In: Proceedings of the ISES Solar World Congress 2015, Daegu, Korea, November 8-12, 2015, 2015Conference paper (Other academic)
    Abstract [en]

    This paper investigates the realizable potential for photovoltaic (PV) systems in Swedish agriculture. Marginal lands and available building areas for PV systems are quantified, and factors limiting the potential are analyzed. It is shown that the potential for PV in Swedish agriculture is high, but what is fully realizable is limited by the capacity of the rural power grid. A case study in the rural municipality of Herrljunga was conducted and scaled to national level. The study shows that the risk of surges in the medium voltage grid (10 kV) in rural areas are small in case where all roof surfaces with an annual solar irradiance of over 950 kWh/m2 are used for solar power. The total electricity production from the Swedish agriculture, if all roof areas with this irradiance level were used, is estimated to 4 TWh annually. With solar power on all roof surfaces with an annual irradiance of at least 900 kWh per m2 problems with voltage rise and overloads in the electricity grid might occur. The electrical grid capacities thus substantially limit how much solar power can be installed. Our results also show that the profitability limits the potential to 0.2 TWh on a national level, but that it could increase if more optimistic economic conditions are assumed.

  • 24.
    Lingfors, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Seipel, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Visual Information and Interaction. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis and Human-Computer Interaction.
    Interactive visual simulation for photovoltaic design and planning in the built environment2013Conference paper (Other academic)
  • 25.
    Lingfors, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Zimmermann, Uwe
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Characteristics of a low-cost solar irradiance loggerManuscript (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.

  • 26.
    Lingfors, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Zimmermann, Uwe
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Determining Intra-hour Solar Irradiance Variability with a Low-cost Solar Logger Network2014In: Proceedings of 4th International Workshop on Integration of Solar Power into Power Systems, Berlin, Germany, 10-11 November, 2014, 2014Conference 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.

  • 27.
    Luthander, Rasmus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Munkhammar, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Self-consumption enhancement of residential photovoltaics with battery storage and electric vehicles in communities2015In: Proceedings of the eceee 2015 Summer Study on energy efficiency, 1–6 June 2015, Presqu’île de Giens, Toulon/Hyères, France, 2015, p. 991-1002Conference 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.

  • 28.
    Luthander, Rasmus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Large-scale integration of photovoltaic power in a distribution grid using power curtailment and energy storage2017In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 155, p. 1319-1325Article in journal (Refereed)
  • 29.
    Luthander, Rasmus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Munkhammar, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Preventing overvoltage in a distribution grid with large penetration of photovoltaic power2016In: Proceedings of the 6th International Workshop on Integration of Solar into Power Systems / [ed] Uta Betancourt / Thomas Ackermann, Darmstadt, Germany: Energynautics GmbH, 2016, p. 113-118Conference paper (Other academic)
    Abstract [en]

    Photovoltaic (PV) power generation is an important component in the future energy system. High penetration of PV power in a distribution power grid might however lead to overvoltage, i.e. +10% of rated voltage, for end-users. This study compares PV power curtailment and decentralized energy storage for overvoltage prevention in a 400V/10 kV distribution grid with large penetration of PV. LiDAR analysis is used to identify rooftops suitable for PV in a Swedish distribution grid with more than 5000 end-users. Results show that power curtailment allows 22% PV electricity (19 GWh) relative to total consumption on a yearly basis without overvoltage. PV production is reduced with 0.35 GWh due to curtailment. Decentralized energy storage of in total 86 MWh capacity achieves the same result.

  • 30.
    Luthander, Rasmus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Munkhammar, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Self-consumption enhancement and peak shaving of residential photovoltaics using storage and curtailment2016In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 112, p. 221-231Article in journal (Refereed)
    Abstract [en]

    Increasing the self-consumption of photovoltaic (PV) power is an important aspect to integrate more PV power in the power system. The profit for the PV system owner can increase and the stress on the power grid can be reduced. Previous research in the field has focused on either self-consumption of PV power in individual buildings or PV power curtailment for voltage control. In this paper self-consumption of residential PV power in a community of several single-family houses was investigated using high-resolution irradiance and power consumption data. Cases with individual or shared battery energy storages for the houses were examined. PV power curtailment was investigated as a method to reduce feed-in power to the grid, i.e. peak shaving. Results indicated that the self-consumption ratio increased when using shared instead of individual storage. Reducing the feed-in power from the community by almost 50% only led to maximum 7% yearly production losses due to curtailment and storage losses. The economics for shared storage are slightly better than for individual ones. These results suggest that residential PV-battery systems should use (i) shared energy storage options if local regulations allow it and (ii) PV power curtailment if there are incentives to lower the feed-in power.

  • 31.
    Monie, Svante
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Nilsson, Annica
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Åberg, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Thermal Energy Storages in Residential Areas: – a potential to increase renewable power generation?2018In: 2018 ACEEE Summer Study on Energy Efficiency in Buildings: Making Efficiency Easy and Enticing / [ed] Fred Grossberg, Washington D.C., 2018, Vol. 20, p. 11-1-11-12, article id 0194_0286_000156Conference paper (Refereed)
    Abstract [en]

    With an increased ambition of implementing renewable electricity production in our energy systems follows the need of handling the inherent variability from some of these production sources (e.g. wind and solar). This could be via curtailments, infrastructural reinforcements of the power grid, and/or increased utilization of power system reserves. The aim of this study was to investigate if power surplus and deficit due to mismatch between intermittent power generation and power demand could be reduced with electric heat pumps (used for power-to-heat purposes), combined heat and power (CHP) production (for power balancing), and seasonal thermal energy storage (STES) (as buffering capacity). A residential area consisting of buildings refurbished for improved energy performance, roof top solar photovoltaic (PV) systems, a local heat distribution system, a small-scale CHP plant, central heat pumps, and a STES, was simulated. The heat pumps were given priority to use surplus power from roof top PV generation or surplus from the grid (e.g. wind power). The CHP plant produced power during power deficits. Surplus heat from the CHP plant as well as from the heat pumps was stored in the STES. The results showed a reduction of the surplus power from the local PV systems towards the upstream power grid. Also, the possibility to offer regulative service towards upstream power grid by using CHP was demonstrated. The conclusion is that power-to-heat and CHP can significantly reduce the mismatch between variable power generation and power demand.

  • 32.
    Munkhammar, Joakim
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Simulating dispersed photovoltaic power generation using a bimodal mixture model of the clear-sky index2015Conference paper (Refereed)
    Abstract [en]

    Improved probability distribution models for power generation are useful e.g. forprobabilistic power flow simulations. This paper presents a distribution modelfor photovoltaic (PV) power generation based on the clear-sky index.With the use of minute-resolution data on globalhorizontal irradiation (GHI) we fit unimodal normal,bimodal normal and trimodal normal mixture distributionfamilies to the clear-sky index. Based on Kolmogorov-Smirnov (K-S) teststhe best fit distribution family consisting of a bimodal normal distribution isthen used for estimating an aggregate clear-sky index for multipledispersed locations that are assumed to be uncorrelated in terms of sky clearness.For five or more locations the aggregate clear-sky indexfollows a normal distribution due to the central limit theorem.Models for solar radiation on tilted planes and PV power generation areapplied to the clear-sky index to generate probability distributions for anarbitrary PV system.

  • 33. Norberg, Ida
    et al.
    Pettersson, Ola
    Gustavsson, Alf
    Kovacs, Peter
    Boork, Magdalena
    Ollas, Patrik
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Marklund, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Larsson, David
    Ingman, Daniel
    Jältorp, Hans
    Solel i lantbruket: Realiserbar potential och nya affärsmodeller2015Report (Other academic)
  • 34.
    Olauson, Jon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ayob, Mohd Nasir
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Malaysia Perlis, Sch Mechatron Engn, Arau 02600, Perlis, Malaysia.
    Bergkvist, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Carpman, Nicole
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Castellucci, Valeria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Net load variability in Nordic countries with a highly or fully renewable power system2016In: Nature Energy, ISSN 2058-7546, Vol. 1, p. 1-8, article id 16175Article in journal (Refereed)
    Abstract [en]

    Increasing the share of intermittent renewable energy (IRE) resources such as solar, wind, wave and tidal energy in a power system poses a challenge in terms of increased net load variability. Fully renewable power systems have previously been analysed, but more systematic analyses are needed that explore the effect of different IRE mixes on system-wide variability across different timescales and the optimal combinations of IRE for reducing variability on a given timescale. Here we investigate these questions for the Nordic power system. We show that the optimal mix of IRE is dependent on the frequency band considered. Long-term (>4 months) and short-term (<2 days) fluctuations can be similar to today’s, even for a fully renewable system. However, fluctuations with periods in between will inevitably increase significantly. This study indicates that, from a variability point of view, a fossil- and nuclear-free Nordic power system is feasible if properly balanced by hydropower.

  • 35.
    Olauson, Jon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ayob, Nasir
    Bergkvist, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Carpman, Nicole
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Castellucci, Valeria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    A highly/fully renewable Nordic power system: Which type of variability would hydropower need to deal with?2015Other (Other academic)
  • 36.
    Olauson, Jon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Bergkvist, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Quantifying variability: A Review of Metrics and a Case Study of Net Load Variability2014In: Proceedings of the 13th International Workshop on Large-Scale Integration of Wind Power into Power Systems, Berlin, Germany, November 11-13, 2014 / [ed] Ute Betancourt, Thomas Ackermann, 2014Conference paper (Other academic)
  • 37.
    Rångtell, Frida H.
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Functional Pharmacology.
    Ekstrand, Emelie
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Functional Pharmacology.
    Rapp, Linnea
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Functional Pharmacology.
    Lagermalm, Anna
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Functional Pharmacology.
    Liethof, Lisanne
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Functional Pharmacology.
    Bucaro, Marcela Olaya
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Functional Pharmacology.
    Lingfors, David H. S.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Jan-Erik, Broman
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Psychiatry, University Hospital.
    Schiöth, Helgi B.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Functional Pharmacology.
    Benedict, Christian
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Functional Pharmacology.
    Two hours of evening reading on a self-luminous tablet vs. reading a physical book does not alter sleep after daytime bright light exposure2016In: Sleep Medicine, ISSN 1389-9457, E-ISSN 1878-5506, Vol. 23, p. 111-118Article in journal (Refereed)
    Abstract [en]

    Background: The use of electronic devices emitting blue light during evening hours has been associated with sleep disturbances in humans, possibly due to the blue light-mediated suppression of the sleep promoting hormone melatonin. However, experimental results have been mixed. The present study therefore sought to investigate if reading on a self-luminous tablet during evening hours would alter sleepiness, melatonin secretion, nocturnal sleep, as well as electroencephalographic power spectral density during early slow-wave sleep. Methods: Following a constant bright light exposure over 6.5 hours (similar to 569 lux), 14 participants (six females) read a novel either on a tablet or as physical book for two hours (21:00-23:00). Evening concentrations of saliva melatonin were repeatedly measured. Sleep (23:15-07:15) was recorded by polysomnography. Sleepiness was assessed before and after nocturnal sleep. About one week later, experiments were repeated; participants who had read the novel on a tablet in the first experimental session continued reading the same novel in the physical book, and vice versa. Results: There were no differences in sleep parameters and pre-sleep saliva melatonin levels between the tablet reading and physical book reading conditions. Conclusions: Bright light exposure during daytime has previously been shown to abolish the inhibitory effects of evening light stimulus on melatonin secretion. Our results could therefore suggest that exposure to bright light during the day - as in the present study - may help combat sleep disturbances associated with the evening use of electronic devices emitting blue light. However, this needs to be validated by future studies with larger sample populations.

  • 38.
    Seipel, Stefan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Visual Information and Interaction. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis and Human-Computer Interaction.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Dual-domain visual exploration of urban solar potential2013In: Proc. Eurographics Workshop on Urban Data Modelling and Visualisation, 2013Conference paper (Other academic)
  • 39.
    Volotinen, Tarja T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lingfors, David H. S.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Benefits of glass fibers in solar fiber optic lighting systems2013In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 52, no 27, p. 6685-6695Article in journal (Refereed)
    Abstract [en]

    The transmission properties and coupling of solar light have been studied for glass core multimode fibers in order to verify their benefits for a solar fiber optic lighting system. The light transportation distance can be extended from 20 m with plastic fibers to over 100 m with the kind of glass fibers studied here. A high luminous flux, full visible spectrum, as well as an outstanding color rendering index (98) and correlated color temperature similar to the direct sun light outside have been obtained. Thus the outstanding quality of solar light transmitted through these fibers would improve the visibility of all kinds of objects compared to fluorescent and other artificial lighting. Annual relative lighting energy savings of 36% in Uppsala, Sweden, and 76% in Dubai were estimated in an office environment. The absolute savings can be doubled by using glass optical fibers, and are estimated to be in the order of 550 kWh/year in Sweden and 1160 kWh/year in Dubai for one system of only 0.159 m(2) total light collecting area. The savings are dependent on the fiber length, the daily usage time of the interior, the type of artificial lighting substituted, the system light output flux, and the available time of sunny weather at the geographic location. 

  • 40.
    Widén, Joakim
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Carpman, Nicole
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Castellucci, Valeria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Olauson, Jon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Remouit, Flore
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bergkvist, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Grabbe, Mårten
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Variability Assessment and Forecasting of Renewables: A Review for Solar, Wind, Wave and Tidal Resources2015In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 44, p. 356-375Article in journal (Refereed)
  • 41.
    Widén, Joakim
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Elfving, Gustav
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Jansson, Emil
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Munkhammar, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Characterization of extensive city-scale solar power generation: Findings from the UppScaleSolar project2017Report (Refereed)
  • 42.
    Åberg, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Fälting, Lars
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Economic History.
    Carlsson, Jonas
    ekoPerspektiv.
    Johansson, Lars
    EC-Power.
    Forssell, Anders
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Business Studies.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Nilsson, Annica
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Munkhammar, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Nya lösningar för fjärrvärme i miljonprogramsområden2017Report (Other academic)
  • 43.
    Åberg, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Olauson, Jon
    KTH, Dept Elect & Comp Engn, Stockholm, Sweden.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Can electricity market prices control power-to-heat production for peak shaving of renewable power generation?: The case of Sweden2019In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 176, p. 1-14Article in journal (Refereed)
    Abstract [en]

    100% renewable energy systems require high penetration of variable renewable electricity (VRE) generation. This causes the net load in the system to be more variable and could cause operational problems in local power grids. Demand side management (DSM), such as fuel or energy carrier switching in response to a price signal, can provide flexibility to meet the increased variability. This study investigates the impact of VRE production on electricity prices and their potential to act as an incentive to control district heating power-to-heat (P2H) production in order to shave VRE production peaks. Also, the potential to increase P2H production flexibility with additional heat storages is studied. Electricity prices are simulated by modification of historical electricity market supply curves. A heat storage component is implemented in an existing model for district heat production. The results show that P2H production is significantly increased (up to 98%) when electricity prices are influenced by VRE production. Thermal storages further increase the P2H production by up to 46%. The increased P2H production, however, does not necessarily coincide with the peaks of VRE. Thus, in conclusion, the pricing mechanism on the Nord pool electricity market is insufficient to control P2H production for shaving VRE production peaks. (C) 2019 Elsevier Ltd. All rights reserved.

  • 44.
    Åberg, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Nilsson, Annica
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Munkhammar, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Luthander, Rasmus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electricity self-sufficiency and primary energy use in a Swedish residential community, after building renovation and implementation of photovoltaics, small-scale CHP, and electric vehicles2016In: Proceedings of the 2016 ACEEE Summer Study on Energy Efficiency in Buildings, Pacific Grove, CA, USA, August 21-26, 2016, 2016Conference paper (Refereed)
1 - 44 of 44
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