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  • 1. Bernardo, Ricardo
    et al.
    Davidsson, Henrik
    Gentile, Niko
    Gomes, João
    Solarus Sunpower AB.
    Gruffman, Christian
    Chea, Luis
    Chabu, Mumba
    Karlsson, Björn
    Mälardalens högskola.
    Measurements of the Electrical Incidence Angle Modifiers of an Asymmetrical Photovoltaic/Thermal Compound Parabolic Concentrating-Collector2013In: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 5, p. 37-43Article in journal (Refereed)
    Abstract [en]

    Reflector edges, sharp acceptance angles and by-pass diodes introduce large variations in the electrical performance of asymmetrical concentrating photovoltaic/thermal modules over a short incidence angle interval. It is therefore important to quantify these impacts precisely. The impact on the electrical performance of the optical properties of an asymmet-rical photovoltaic/thermal CPC-collector was measured in Maputo, Mozambique. The measurements were carried out with the focus on attaining a high resolution incidence angle modifier in both the longitudinal and transversal directions, since large variations were expected over small angle intervals. A detailed analysis of the contribution of the diffuse radiation to the total output was also carried out. The solar cells have an electrical efficiency of 18% while the maxi-mum measured electrical efficiency of the collector was 13.9 % per active glazed area and 20.9 % per active cell area, at 25 °C. Such data make it possible to quantify not only the electrical performance for different climatic and operating conditions but also to determine potential improvements to the collector design. The electrical output can be increased by a number of different measures, e.g. removing the outermost cells, turning the edge cells 90°, dividing each receiver side into three or four parts and directing the tracking, when used, along a north-south axis.

  • 2.
    Cabral, Diogo
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Gomes, João
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Solarus Sunpower Sweden AB, Gävle, Sweden.
    Dostie-Guindon, Paul-Antoine
    Ecole Polytechnique Montréal, Montréal, Canada.
    Karlsson, Björn O.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Ray tracing simulations of a novel low concentrator PVT solar collector for low latitudes2017In: ISES Solar World Congress 2017 - IEA SHC International Conference on Solar Heating and Cooling for Buildings and Industry 2017, Proceedings, International Solar Energy Society , 2017, p. 1068-1079Conference paper (Refereed)
    Abstract [en]

    One way to reduce solar collector's production costs is to use concentrators that increase the output per photovoltaic cell. Concentrating collectors re-direct solar radiation that passes through an aperture into an absorber. The current study evaluates electrical performance of symmetric C-PVT solar collectors with a vertical bifacial receiver, through a numerical ray tracing model software, Tonatiuh. Several designs have been analysed, such as the Pure Parabola (PP) and MaReCo CPC geometries, both symmetric. Parameters such as concentration factor, electrical performance, transversal and longitudinal IAM (Incidence Angle Modifier), the influence of optical elements and influence of the length of the reflector in the shadow effect have been studied for different geometries. The simulations were performed for Mogadishu, Somalia and showed good results for the Pure Parabola collector (PPc) annual received energy, 379 and 317 kWh/m2/year for a focal length of 15 e 30 mm, respectively. A symmetrical double MaReCo CPC collector has been simulated with the annual received energy of 315 kWh/m2/year. The addition of the optical elements will decrease the annual received energy of the PPc by around 11.5%, where the optical properties (7.1%) and glass (4.1%) have the biggest impact in the annual received energy. Overall, symmetric geometries proved to be the most suitable geometries for low latitudes applications, being the geometry f1 (focal length of 15 mm) the best one. 

  • 3.
    Cabral, Diogo
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Energy Systems and Building Technology.
    Gomes, João
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Energy Systems and Building Technology.
    Karlsson, Björn O.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Energy Systems and Building Technology.
    Performance Evaluation of Non-Uniform Illumination on a Transverse Bifacial PVT Receiver in Combination with a CPC Geometry2019In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 194, p. 696-708Article in journal (Refereed)
    Abstract [en]

    PVT collectors co-generate electricity and heat from the same gross area, thus achieving higher combined heat and electric yields. A comprehensive evaluation has been carried out on non-uniform solar irradiation profile distributions on four symmetric low concentration CPC PVT (LCPVT) solar collector design concepts. Additionally, an electrical and thermal performance evaluation of symmetric truncated LCPVT solar collectors based on a CPC reflector geometry with a central transverse bifacial PVT receiver has been carried out, through a numerical ray-tracing model software and a multi-paradigm numerical computing environment software. A simplified thermal (quasi-dynamic testing method for liquid heating collectors described in the international standard for solar thermal collectors ISO 9806:2017) and electrical performance models were employed to evaluate the LCPVT design concepts. The evaluation was carried out for heating Domestic Hot Water (DHW) for a Single Family House (SFH) in Fayoum (Egypt), where energy yields between 351 and 391 kWh/m2/year have been achieved. The non-uniform solar irradiation assessment showed that the PV cells are exposed to high levels of radiation due to the specific reflector geometry. Furthermore, the study showed that the CPC geometries are very sensitive to the shading effect, as partial shadowing is substantial for high incidence angles.

  • 4.
    Cabral, Diogo
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Karlsson, Björn O.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Electrical and thermal performance evaluation of symmetric truncated C-PVT trough solar collectors with vertical bifacial receivers2018In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 174, p. 683-690Article in journal (Refereed)
    Abstract [en]

    One way to reduce solar collectors’ production costs is to use concentrators that increase the output per photovoltaic cell. Concentrating collectors re-direct solar radiation that passes through an aperture into an absorber/receiver. Symmetrical truncated non-tracking C-PVT trough collectors based on a parabola and compound parabolic concentrator (CPC) geometries have been developed. The collector type has a central vertical bifacial (fin) receiver and it was optimized for lower latitudes. In this paper, the electrical and thermal performance of symmetric truncated non-tracking low concentrator PVT solar collectors with vertical bifacial receivers is analysed, through a numerical ray-tracing model software and a multi-paradigm numerical computing environment. A thermal (quasi-dynamic testing method for liquid heating collectors described in the international standard for solar thermal collectors ISO 9806:2013) and electrical performance models were implemented to evaluate the design concepts. The evaluation was made for heating Domestic Hot Water for a Single Family House in Fayoum (Egypt), where CPC geometries with a concentration factor of 1.6 achieved 8 to 13%rel higher energy yields (in kWh/m2/year) than the Pure Parabola geometries.

  • 5.
    Contero, Francisco
    et al.
    University of Zaragoza.
    Gomes, João
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Gustafsson, Mattias
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Karlsson, Björn O.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    The impact of shading in the performance of threee different solar PV systems2016Conference paper (Refereed)
  • 6. Davidsson, Henrik
    et al.
    Bernardo, Ricardo
    Gomes, João
    Solarus AB.
    Gentile, Niko
    Gruffman, Christian
    Chea, Luis
    Karlsson, Björn
    Mälardalens högskola.
    Construction of laboratories for solar energy research in developing countries2014In: Energy Procedia, ISSN 1876-6102, E-ISSN 1876-6102, Vol. 57, p. 982-988Article in journal (Refereed)
    Abstract [en]

    A large number of PV-systems have been installed in developing countries around the world duringnumerous projects. The aim is often to improve the quality of life in rural areas, often lacking electricity.Many of these installations provide important services such as lighting and charging of different devices.However, when the projects are finished, there is a large risk that maintenance is not carried out properlyand that malfunctions are never repaired. This situation can leave an otherwise well functioning systemunusable. A key problem is that there are not enough trained technicians that can maintain and repair thesystem locally. One reason to this is the lack of practical education in many developing countries.Furthermore, the availability of spare parts is essential for the long term effectiveness.During 2011 a group of researchers from Lund University in Sweden built a small scale laboratory inMaputo, Mozambique, together with local researchers. The project was successful and today thelaboratory functions both as a teaching facility and as a measurement station for solar energy research forlicentiates, masters and PhD students.The main goal is now to widen the project in order to incorporate more universities in developingcountries. We are now looking for new interested partners in developing countries that believe that such alaboratory could strengthen their possibility to teach practical work and to perform research at the localuniversity. Partners for planning and executing the project are also needed.

  • 7.
    Francisco Contero, Jose
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Zaragoza.
    Gomes, João
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Gustafsson, Mattias
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Karlsson, Björn O.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    The impact of shading in the performance of three different solar PV systems2017In: PROCEEDINGS OF THE 11TH ISES EUROSUN 2016 CONFERENCE, INTL SOLAR ENERGY SOC , 2017, p. 1168-1179Conference paper (Refereed)
    Abstract [en]

    Partial shading decreases the performance of PV modules due to the series connection between the solar cells. In the recent years, several new technologies have emerged within the photovoltaics field to mitigate the effect of shading in the performance of the PV modules. For an accurate assessment of the performance of these devices, it is required to evaluate them comparatively in different circumstances. Three systems with six series-connected PV modules (each containing 60 cells) have been installed at the University of Gavle. System One comprises a string inverter system with 6 PV modules; System Two features a DC-DC optimizer per panel and a string inverter; System Three incorporates three micro inverters for six modules. A major conclusion of this study was that under partial shading of one (or more) modules both System Two (DC-DC optimizers) and System Three (micro inverters) perform considerably better than System One (string inverter), as long as the Impp of the shadowed module is lower than the Impp of the unshaded string It is also important that the Vmpp in the shaded module is higher than the lowest allowed voltage of the DC-DC optimizer or module inverter. The economic implications of the usage of these devices were also analyzed.

  • 8.
    Gallardo-Saavedra, Sara
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Universidad de Valladolid (UVa), School of Forestry, Agronomic and Bioenergy Industry Engineering (EIFAB), Department of Agricultural and Forestry Engineering, Campus Duques de Soria, Soria, Spain.
    Karlsson, Björn O.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Simulation, validation and analysis of shading effects on a PV system2018In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 170, p. 828-839Article in journal (Refereed)
    Abstract [en]

    A simulation program for calculating the IV-curve for series connected PV-modules during partial shadowing has been developed and experimentally validated. The software used for modelling the modules is LTspice IV. The validation has been done by means of a comparative analysis using the experimental results obtained in a set of tests performed on the mono-crystalline modules of the Gävle University's laboratory in Sweden. Experimental measurements were carried out in two groups. The first group is a string of six modules with bypass diodes while the second one corresponds to a single PV module. The simulation results of both groups demonstrated a remarkable agreement with the experimental data, which means that the designed model can be used for simulating the influence of shading on the power of a string. The model has been used for analysing the performance of strings of PV modules with shadows and the benefits of installing DC-DC optimizers or module inverters, that minimise the impact of shading, have been investigated.

  • 9. Giovinazzo, Carine
    et al.
    Bonfiglio, Luc
    Gomes, João
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Karlsson, Björn
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Ray Tracing Modelling of an Asymmetric Concentrating PVT2014In: EuroSun 2014 Proceedings, 2014Conference paper (Refereed)
    Abstract [en]

    Photovoltaic thermal (PVT) collectors are able to produce both heat and electricity from the same area. The studied PVT collector is an asymmetric Compound Parabolic Collector (CPC) which is composed two parts: a quarter of a circle and a parabola. This reflector design belongs to the MaReCo (Maximum Reflector Collector) family. The main advantages of this collector design are the reduction of material cost due to concentration and the increase cell efficiency by reducing its working temperature through active cooling.Tonatiuh is a Monte Carlo ray tracing software that is able to simulate the interaction between the sunlight and a concentrating collector. A script was written to repeat the process and simulate the course of the year. The data was processed using Matlab and the annual received radiation on both receiver sides was obtained.A collector model was drawn in Tonatiuh and its material properties were described. Incremental changes were used both to validate the models results and to assess the impact of each change. The first model had only the reflector geometry and the receiver with perfect properties while the final model had a very accurate description of the studied collector and its properties. The final model performed 21% worse than the initial with ideal properties. Additionally, the homogeneity of the solar radiation on the receiver was analyzed and the 3D effective solar radiation graph was plotted. Finally, it was found that over the year, the receiver under concentration produces 13% more energy than the flat side of the receiver, at the best tilt, for both 0º and 60º of latitudes.

  • 10.
    Gomes, João
    et al.
    Solarus Sunpower AB.
    Davidsson, Henrik
    Gruffman, Christian
    Maston, Stefan
    Karlsson, Björn
    Mälardalens högskola.
    Testing bifacial PV cells in symmetric and asymmetric concentrating CPC collectors2013In: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 5, p. 185-190Article in journal (Refereed)
    Abstract [en]

    Bifacial PV cells have the capacity to produce solar electricity from both sides and, thus, amongst other advantages, allow a significantly increase both in peak and annual power output while utilizing the same amount of silicone. Ac-cording to the manufacturer, the bifacial cells are around 1.3 times more expensive than the single-sided cells. This way, bifacial PV cells can effectively reduce the cost of solar power for certain applications.Today, the most common application for these cells is in stationary vertical collectors which are exposed to sunlight from both sides, as the relative position of the sun changes throughout the day. Another possible application is to utilize these cells in concentrating collectors. Three test prototypes utilizing bifacial PV cells were built. The initial two proto-types were built for indoor testing and differed only in geometry of the reflector, one being asymmetric and the other symmetric. Both prototypes were evaluated in an indoor solar simulator. Both reflector designs yielded positive electri-cal performance results and similar efficiencies from both sides of the cell were achieved. However, lower fill factor than expected was achieved for both designs when compared to the single cell tests. The results are discussed and sug-gestions for further testing are presented. A third prototype was built in order to perform outdoor evaluations. This pro-totype utilized a bifacial PV cells string laminated in silicone enclosed between 2 standard glass panes and a collector box with an asymmetric CPC concentrator. The prototype peak electrical efficiency and temperature dependence were evaluated. A comparison between the performance of the bottom and top sides of the asymmetric collector is also pre-sented. Additionally, the incidence modifier angle (IAM) is also briefly discussed.

  • 11.
    Gomes, João
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Diwan, Linkesh
    Instituto Superior Tecnico, Av. Rovisco Pais, Lisboa, Portugal .
    Bernardo, Ricardo
    Energy and Building Design, Lund University, Lund, Sweden .
    Karlsson, Björn
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Minimizing the impact of shading at oblique solar angles in a fully enclosed asymmetric concentrating PVT collector2014In: Energy Procedia, ISSN 1876-6102, E-ISSN 1876-6102, Vol. 57, p. 2176-2185Article in journal (Refereed)
    Abstract [en]

    PVT collectors produce both electricity and heat from the same area. PVT collectors with low concentration factor allow both stationary and tracking configurations. For stationary or single axis tracking, the daily variation in the solar incidence angle can cause significant shading in concentrating collectors. Shading has a larger impact on PV than on thermal collectors and thus the evaluations was more focused on the electrical part. Several prototype versions of a novel design for a concentrating asymmetric PVT collector have been tested and compared. One tested improvement was replacing the reflective end gables with transparent end gables. Another improvement was to use different cell sizes. These actions were expected to minimize the impact of the shading at oblique solar incidence angles. The second action was found to be more beneficial than the first. Measurements were also performed in the solar simulator to fully understand the impact of shading in cell strings with 1/6 the size of standard cells. The latest version of the PVT was found to have, at 25 °C and 1000w/m2, a collector efficiency of 13,7%, a cell area efficiency of 20,3% and an electrical power output of 237W. Lower side of the receiver was producing 58% of the total power.

  • 12.
    Gomes, João
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Solarus Sunpower Sweden AB.
    Junge, Jana
    Karlsson, Björn
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Defining an annual energy output ratio between PV and solar thermal2014In: EuroSun 2014 Proceedings, 2014Conference paper (Refereed)
    Abstract [en]

    Photovoltaics (PV) and solar thermal (ST) collectors are often competing between themselves not only because the investment capacity is limited but also because the energy demand and roof space is limited and both types of panel provide energy which can be converted to a different type of energy under a certain efficiency. Therefore, it makes sense to develop a ratio that quantifies the difference in annual energy output between standard ST and PV for different locations. This ratio is useful, for example, to support the decision between installing ST or PV, when combined with other local specific information such as the value of heat and electricity for a specific location and application, the system complexity and efficiency, and others.A market survey was conducted for assessing the average performance specifications of the panels. Simulations were conducted and several ratios were plotted in the world map. Despite the large variations occurring due to local climate, the ratio increases at lower latitudes due to two factors: a) the efficiency of a PV panel is reduced with the increase of air temperature while, in solar thermal, the effect is the opposite; b) Under low intensity solar irradiance, the efficiency of a PV panel is maintained while a solar thermal collector can have its efficiency reduced to zero. For latitudes lower than 66º, the ratio flat plate at 50ºC to PV is ranging from 1,85 to 4,46 while in the ration between vacuum tube at 50ºC and PV from 3,05 to 4,76.

  • 13.
    Gustafsson, Mattias
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Gävle Energi AB, Gävle, Sweden.
    Karlsson, Björn
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Rönnelid, Mats
    Högskolan Dalarna.
    How the electric meter configuration affect the monitored amount of self-consumed and produced excess electricity from PV systems: case study in Sweden2017In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 138, p. 60-68Article in journal (Refereed)
    Abstract [en]

    This study evaluates how the principal function of bi-directional electric meters affects the monitored amount of self-consumed and produced excess electricity for dwelling buildings connected to the grid by three phases. The electric meters momentarily record the sum of the phases or the phases individually and then summarize the recorded values to a suitable time period and is then collected by the grid owner. In Sweden, both electric meter configurations fulfill laws and regulations.

    The meter configuration affects the monitored distribution of self-consumed and produced excess electricity significantly for the investigated single-family house but is negligible for the investigated multi-dwelling buildings. The monitored self-consumed electricity produced by the PV installation for the single-family house varies between 24% and 55% depending on the configuration and how the inverter is installed for the investigated year. The difference in economic value for the produced electricity varies between 79.3 to 142 Euros.

    Due to the electric meter configuration, the profitability of PV systems will be different for identical single-family houses with identical conditions. This should be corrected for a well-functioning market. It is also important to decide how the configuration should be designed to ensure that different incentives and enablers results in desired effects.

  • 14.
    Gustafsson, Mattias
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Gävle Energi AB, Gävle, Sweden .
    Rönnelid, Mats
    Energy Technology, Högskolan Dalarna, Falun, Sweden.
    Trygg, Louise
    Linköpings universitet.
    Karlsson, Björn
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    CO2 emission evaluation of energy conserving measures in buildings connected to a district heating system: case study of a multi-dwelling building in Sweden2016In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 111, p. 341-350Article in journal (Refereed)
    Abstract [en]

    When taking action to fulfill the directives from the European Union, energy conserving measures will be implemented in the building sector. If buildings are connected to district heating systems, a reduced heat demand will influence the electricity production if the reduced heat demand is covered by combined heat and power plants.

    This study analyze five different energy conserving measures in a multi-dwelling building regarding how they affect the marginal production units in the district heating system in Gävle, Sweden. For CO2 emission evaluations, two different combinations of heat and electricity conserving measures are compared to an installation of an exhaust air heat pump.

    The different energy conserving measures affect the district heating system in different ways. The results show that installing an exhaust air heat pump affects the use/production of electricity in the district heating system most and electricity conserving measures result in reduced use of electricity in the building, reduced use of electricity for production of heat in the district heating system and an increase of electricity production.

    The conclusion is that electricity use in the building is the most important factor to consider when energy conserving measures are introduced in buildings within the district heating system in Gävle.

  • 15.
    Gustafsson, Mattias
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Thygesen, Richard
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Karlsson, Björn
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Ödlund, Louise
    Division of Energy Systems, Department of Management and Engineering, Linköping University, Linköping, Sweden.
    Rev-Changes in Primary Energy Use and CO2 Emissions: An Impact Assessment for a Building with Focus on the Swedish Proposal for Nearly Zero Energy Buildings2017In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 10, no 7, article id 978Article in journal (Refereed)
    Abstract [en]

    In the European Union's Energy Performance of Buildings Directive, the energy efficiency goal for buildings is set in terms of primary energy use. In the proposal from the National Board of Housing, Building, and Planning, for nearly zero energy buildings in Sweden, the use of primary energy is expressed as a primary energy number calculated with given primary energy factors. In this article, a multi-dwelling building is simulated and the difference in the primary energy number is investigated when the building uses heat from district heating systems or from heat pumps, alone or combined with solar thermal or solar photovoltaic systems. It is also investigated how the global CO2 emissions are influenced by the different energy system combinations and with different fuels used. It is concluded that the calculated primary energy number is lower for heat pump systems, but the global CO2 emissions are lowest when district heating uses mostly biofuels and is combined with solar PV systems. The difference is up to 140 tonnes/year. If the aim with the Swedish building code is to decrease the global CO2 emissions then the ratio between the primary energy factors for electricity and heat should be larger than three and considerably higher than today.

  • 16.
    Mantei, Franz
    et al.
    Technische Universität, Berlin, Germany.
    Henriques, Mafalda
    University of Castelo Branco, Portugal.
    Gomes, João
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Olsson, Olle
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Solarus Sunpower Sweden AB, Gävle, Sweden.
    Karlsson, Björn
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    The night cooling effect on a C-PVT solar collector2015In: ISES Solar World Congress 2015, Conference Proceedings, International Solar Energy Society, 2015, p. 1167-1175Conference paper (Refereed)
    Abstract [en]

    Night cooling consists in running a fluid through a solar panel during the night in order to reduce the fluid temperature which can be used for cooling applications. Radiative heat losses can allow the fluid to reach temperatures below ambient while conduction and convection works to equalize the collector with the ambient temperature. This paper analyzes the possibility of using an asymmetric concentrating photovoltaic thermal solar collector (C-PVT) for cooling applications during the night by losing heat through convection, conduction and irradiation. The cooling performance of the C-PVT collector has been measured during the night at different inlet temperatures in the interval of 13 to 38°C which corresponded to a AT (between the collector average and the ambient) from 6 to 28°C. The performance of the tested C-PVT collector has been measured at different inlet temperatures in an interval of 13 to 38°C. During all performed measurements, the radiation losses did not drive the collector temperature below ambient temperature. With high AT (between the inlet and the ambient) of 30°C, a 1,85°C temperature decrease in the fluid was obtained. For AT of 14°C, the temperature decrease was only 0,88°C. The measurements showed a night U-value for the Solarus C-PVT of 4,2 W/m2K This correlates well with previous papers showing measurements taken during the day. Heat losses seem to be dominated by convection and conduction due to the existence of the glass in the collector. Despite this, a measurable relation between heat losses and cloudiness factor exists. This shows that the irradiance losses are not negligible. Only very specific applications can be suited for night cooling with this collector design, since it is not so common to have applications that require low grade cooling during the night time or justify storing this energy. However, if the C-PVT design was made without a glass cover, the results could potentially be very different for locations with many clear nights.

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