| 1. |
- Cabral, Diogo, et al.
(författare)
-
Electrical and thermal performance evaluation of a district heating system composed of asymmetric low concentration PVT solar collector prototypes
- 2018
-
Ingår i: PROCEEDINGS OF THE ISES EUROSUN 2018 CONFERENCE - 12TH INTERNATIONAL CONFERENCE ON SOLAR ENERGY FOR BUILDINGS AND INDUSTRY. - Freiburg, Germany : INTL SOLAR ENERGY SOC. ; , s. 755-763
-
Konferensbidrag (refereegranskat)abstract
- Photovoltaic-Thermal (PVT) solar collectors generate electricity and heat from the same gross area. The annual electrical and thermal yields of these systems are dependent on the PVT collector technology, as well as the climate and the type of solar thermal system implemented. This review presents an evaluation of a district heating system composed of 20 asymmetric hybrid low concentrator PVT (C-PVT) solar collector prototypes. The system is installed in a South wall facade in order to maximise the available space (with a tilt of 20 degrees and an orientation of 5 degrees W). The thermal system is connected to the district heating network, thus heating the University buildings. On the other hand, the electrical system is grid-connected, where it feeds the grid directly. Real measurement data has been collected and compared with a thermal (through ScenoCalc tool) and electrical performance models. The annual thermal and electrical yield achieved 86% and 89% of the simulated thermal and electrical yield, respectively.
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| 2. |
- Costeira, João, et al.
(författare)
-
Development of a compact and didactic solar energy kit using Arduino
- 2018
-
Ingår i: PROCEEDINGS OF THE ISES EUROSUN 2018 CONFERENCE - 12TH INTERNATIONAL CONFERENCE ON SOLAR ENERGY FOR BUILDINGS AND INDUSTRY. - Freiburg, Germany : INTL SOLAR ENERGY SOC. ; , s. 1663-1667
-
Konferensbidrag (refereegranskat)abstract
- When the sun rises, so does the key element that will shape the future of the world energy landscape. It is not an understatement to say that the solar energy industry is beginning to lead the path towards a sustainable future for all of us. However, the awareness of the potential of this amazing source of energy must begin from the most basic levels of education all the way to university. The scope of this paper is to display a new compact and didactic solar energy kit with the potential to replace current high cost and complex solar energy kits. These solutions are often too expensive and therefore unavailable for most of Europe’s public schools. As such, an equipment was developed using an open-source platform called Arduino that will enable students to conduct practical experiments in a fast, effective and simple manner and thus allow students to acquire the proper expertise in areas like energy, electronics, and programming.
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| 3. |
- Afzali Gorouh, Hossein, et al.
(författare)
-
Thermal modelling and experimental evaluation of a novel concentrating photovoltaic thermal collector (CPVT) with parabolic concentrator
- 2022
-
Ingår i: Renewable energy. - : Elsevier. - 0960-1481 .- 1879-0682. ; 181, s. 535-553
-
Tidskriftsartikel (refereegranskat)abstract
- In the present study, a zero-dimensional thermal model has been developed to analyze a novel low concentration photovoltaic-thermal (CPVT) collector. The model has been developed by driving heat transfer and energy balance equations for each part of the collector and then solving all the equations simultaneously. Moreover, a Monte-Carlo ray-tracing software has been used for optical stimulations of the parabolic trough solar collector. The novel CPVT collector has been experimentally tested at Gävle University (Sweden) and the model has been validated against the experimental results. The primary energy saving equivalent to the thermal-electrical power cogeneration of the CPVT collector has been determined. The effect of glass cover removal, heat transfer fluid (HTF) inlet temperature and mass flow rate on the collector performance has been investigated. The optimum HTF mass flow rates of the collector for maximum electrical yield and overall primary energy saving were determined under specified operating conditions by considering the pump consumption. The effect of mean fluid temperature on the thermal and electrical efficiencies has been studied and the characteristic equation of the thermal efficiency has been obtained. The thermal and electrical peak efficiencies of the collector have been found to be 69.6% and 6.1%, respectively.
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| 4. |
- Cabral, Diogo, PhD, 1990-, et al.
(författare)
-
Experimental Electrical Assessment Evaluation of a Vertical n-PERT Half-Size Bifacial Solar Cell String Receiver on a Parabolic Trough Solar Collector
- 2023
-
Ingår i: Energies. - : MDPI. - 1996-1073. ; 16:4
-
Tidskriftsartikel (refereegranskat)abstract
- A two-trough parabolic-shaped concentrating photovoltaic solar collector with a vertical half-size ‘phosphorus-passivated emitter rear totally diffused’ bifacial cell string receiver was designed and built for household applications, with the aim of smooth the electrical ‘duck curve’. The study consisted in testing the concentrating photovoltaic solar collector outdoors, under real weather conditions, for its daily electrical peak power and efficiency, as well as for its electrical transversal and longitudinal Incidence Angle Modifier direction. The outdoor testing measurements were conducted in a parabolic trough with low concentration coupled with a central vertical half-size ‘phosphorus-passivated emitter rear totally diffused’ bifacial cell string receiver. Furthermore, the electrical transversal Incidence Angle Modifier showed to be very delicate due to the position and outline of the receiver, which led to an electrical peak efficiency close to 10% at ±25° (i.e., for an electrical power output of around 49.3 W/m2). To validate the measured parameters, a ray-tracing software has been used, where the measured Incidence Angle Modifiers have a very good agreement with the simulated Incidence Angle Modifiers (e.g., deviation of <4%). Consequently, the concentrating solar collector met the objective of lowering the Photovoltaic cell stress and high radiation intensity, by shifting the electrical peak power at normal (e.g., at 0°) to higher incidence angles (e.g., ±25°); this aids the electrical demand peak shaving, by having the highest electrical power production displaced from the highest intensity solar radiation during the day.
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| 5. |
- Cabral, Diogo, et al.
(författare)
-
Experimental investigation of a CPVT collector coupled with a wedge PVT receiver
- 2021
-
Ingår i: Solar Energy. - : Elsevier. - 0038-092X .- 1471-1257. ; 215, s. 335-345
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents an experimental investigation of a photovoltaic-thermal solar collector (commonly known as PVT) that generates both electricity and heat from the same gross area. PVT solar collectors, in theory, achieve higher combined electrical and heat yields. Additionally, PVT enables a thermal coupling between PV cells and a heat transfer cooling medium. Electrical and thermal outdoor testing measurements have been performed on alow concentration PVT solar collector based on a parabolic reflector geometry with a wedge PVT receiver. Several outdoor experiments have been carried out and presented, such as daily instantaneous electrical and thermal performance efficiency diagrams, as well as optical efficiency charts. Moreover, an electrical IncidenceAngle Modifier (for both transversal and longitudinal directions) assessment has been performed and presented. Furthermore, an overall heat loss coefficient of 4.1 W/m2.◦C has been attained. A measured thermal optical and electrical efficiency of 59% and 8% have been achieved, respectively. Additionally, the placement of the wedge receiver shown to be very sensitive to high incidence angles, as the electrical transversal Incidence AngleModifier factor decreases significantly after reaching its electrical peak efficiency at 10◦.
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| 6. |
- Cabral, Diogo, et al.
(författare)
-
Performance Evaluation of Non-Uniform Illumination on a Transverse Bifacial PVT Receiver in Combination with a CPC Geometry
- 2019
-
Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 194, s. 696-708
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Cabral, Diogo, et al.
(författare)
-
Ray tracing simulations of a novel low concentrator PVT solar collector for low latitudes
- 2017
-
Ingår i: ISES Solar World Congress 2017 - IEA SHC International Conference on Solar Heating and Cooling for Buildings and Industry 2017, Proceedings. - Freiburg, Germany : International Solar Energy Society. - 9783981465976 ; , s. 1068-1079
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 8. |
- Cabral, Diogo, PhD, 1990-
(författare)
-
Reflector Optimization for Low Concentration Photovoltaic-Thermal Solar Collectors
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The alarming new global warming and increasing awareness related to climate change (mainly due to the high emissions of carbon dioxide) in recent decades linked all nations into a common cause, which requires ambitious efforts to combat climate change by adapting energy systems to its effects.The knowledge gain presented in this dissertation establishes the foundations for the development of a more efficient concentrating photovoltaic-thermal (PVT) solar collector. The presented work provides decision-makers with a broader, more detailed performance assessment of concentrating PVT solar collectors.A critical issue for concentrating PVT solar collectors lies in the respective reflector shape, which will determine, to some extent, the overall performance of the CPVT collector. Therefore, several symmetrical reflector design concepts were designed and optimized through Monte Carlo ray-tracing software. With the support of a MATLAB script, a simulation test methodology has been developed and optimized, allowing a more thorough analysis of the results regarding the viability of the different reflector shapes, which established the compound parabolic collector (CPC) to be the most appropriate reflector geometry for PVT solar collectors.Moreover, CPC-PVT solar collectors (based on the findings described above) were designed, built and outdoor tested (under steady-state method guidelines) for their thermal and electrical peak efficiencies, heat losses and incidence angle modifier (IAM) coefficients.The developments achieved in this dissertation significantly enhanced the annual performance of CPC-CPVT solar collectors, which closes the efficiency/performance gap between mature technologies such as PV modules or ST collectors.
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| 9. |
- Cabral dos Santos, Alex, 1990, et al.
(författare)
-
Large Porewater-Derived Carbon Outwelling Across Mangrove Seascapes Revealed by Radium Isotopes
- 2024
-
Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS. - 2169-9275 .- 2169-9291. ; 129:9
-
Tidskriftsartikel (refereegranskat)abstract
- Mangrove-dominated coastlines have high carbon sequestration capacity, but it remains unclear whether tidally outwelled carbon is transformed within the coastal ocean or exported offshore. Here, we used radium isotopes (Ra-224 and Ra-223) to investigate carbon outwelling in two mangrove seascapes in Brazil across multiple spatial scales. We sampled porewaters to define the source composition, mangrove creek waters to resolve tidal cycles, and cross-shelf transects to trace outwelling in coastal seascapes. Radium isotopes were positively correlated with dissolved inorganic (DIC), organic (DOC) and particulate organic (POC) carbon across the seascapes. DIC was the primary form of carbon (mean +/- SD), representing 85% of the total carbon pool as bicarbonate (75 +/- 11%), carbonate (6 +/- 5%), and CO2 (4 +/- 9%). DOC and POC accounted for 10 +/- 6% and 5 +/- 6% of total carbon, respectively. Although mangrove waters emitted CO2 to the atmosphere (38-143 mmol m(-2) d(-1)), both bays and continental shelves were a CO2 sink (-2.5 to -0.5 mmol m-2 d-1) associated to chlorophyll-a enrichments (r(2) = 0.86). Total carbon outwelled from mangroves were 3-4 times higher than soil carbon burial at both mangrove sites. Bicarbonate export (27-72 mmol m(-2) d(-1)) to the continental shelf was the major fate of carbon outwelling, more than doubling the perceived capacity of mangrove soil to sequester carbon. Hence, disregarding outwelling as a blue carbon sink mechanism would lead to underestimated assessments of how mangroves capture CO2 and help to mitigate climate change.
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| 10. |
- Cabral dos Santos, Alex, 1990, et al.
(författare)
-
Tidally driven porewater exchange and diel cycles control CO2 fluxes in mangroves on local and global scales
- 2024
-
Ingår i: Geochimica et Cosmochimica Acta. - 0016-7037. ; 374, s. 121-135
-
Tidskriftsartikel (refereegranskat)abstract
- Mangrove soils are highly enriched in organic carbon. Tidal pumping drives seawater and oxygen into mangrove soils during flood tide and releases carbon-rich porewater during ebb tides. Here, we resolve semi-diurnal (flood/ebb tides), diel (day/night) and weekly (neap/spring tides) drivers of porewater-derived CO2 fluxes in two mangroves and update global estimates of CO2 emissions building on earlier observations from other sites. Tidal pumping controlled pCO2 variability within the two mangrove creeks. The highest values of pCO2 (2,585–6,856 µatm) and 222Rn (2,315–6,159 dpm m−3) and lowest values of pH (6.8–7.1) and dissolved oxygen (1.7–3.7 mg L−1) at low tides were due to enhanced porewater export. 222Rn and pCO2 in mangrove porewater were 4–15 and 38–41 times greater than surface waters, respectively. pCO2 increased by 50 ± 30 % from high to low tide, 9 ± 22 % from day to night and 57 ± 5 % from neap to spring tide with clear changes in hourly, diel, and weekly time scales. Combining our new estimates with literature data, global porewater-derived (16 sites) and water-atmosphere (52 sites) CO2 fluxes in mangroves would upscale to 45 ± 12 and 41 ± 10 Tg C y−1, respectively. These fluxes represent 25 % of net primary production and are twice as high as the sediment carbon burial rates in global mangroves. Overall, our local observations and global compilation suggest that porewater-derived CO2 exchange is a major but often unaccounted source of CO2 in mangroves. The porewater-derived CO2 can be emitted to the atmosphere or laterally exported to the ocean and should be included in carbon budgets to solve global imbalances.
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| 11. |
- Cabral, Joao P, et al.
(författare)
-
Rapidly Testing the Interaction Model of a Pronunciation Training System via Wizard-of-Oz.
- 2012
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Ingår i: Proceedings of the International Conference on Language Resources and Evaluation. ; , s. 4136-4142
-
Konferensbidrag (refereegranskat)abstract
- This paper describes a prototype of a computer-assisted pronunciation training system called MySpeech. The interface of the MySpeech system is web-based and it currently enables users to practice pronunciation by listening to speech spoken by native speakers and tuning their speech production to correct any mispronunciations detected by the system. This practice exercise is facilitated in different topics and difficulty levels. An experiment was conducted in this work that combines the MySpeech service with the WebWOZ Wizard-of-Oz platform (http://www.webwoz.com), in order to improve the human-computer interaction (HCI) of the service and the feedback that it provides to the user. The employed Wizard-of-Oz method enables a human (who acts as a wizard) to give feedback to the practising user, while the user is not aware that there is another person involved in the communication. This experiment permitted to quickly test an HCI model before its implementation on the MySpeech system. It also allowed to collect input data from the wizard that can be used to improve the proposed model. Another outcome of the experiment was the preliminary evalua- tion of the pronunciation learning service in terms of user satisfaction, which would be difficult to conduct before integrating the HCI part.
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| 12. |
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| 13. |
- Cahill, Peter, et al.
(författare)
-
Ucd blizzard challenge 2011 entry
- 2011
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Ingår i: Proceedings of the Blizzard Challenge Workshop.
-
Konferensbidrag (refereegranskat)abstract
- This paper gives an overview of the UCD Blizzard Challenge 2011 entry. The entry is a unit selection synthesiser that uses hidden Markov models for prosodic modelling. The evaluation consisted of synthesising 2213 sentences from a high quality 15 hour dataset provided by Lessac Technologies. Results are analysed within the context of other systems and the future work for the system is discussed.
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| 14. |
- Cardoso, Carlos, et al.
(författare)
-
eNeuron project - facilitating the energy transition in a military campus by optimizing a local energy community
- 2023
-
Ingår i: Proceedings 27th International Conference on Electricity Distribution (CIRED 2023). - : IET. - 9781839538551
-
Konferensbidrag (refereegranskat)abstract
- The eNeuron project is an ongoing Horizon 2020 EU-funded project with the main objective of setting out a practical framework for optimising the design and operation of local energy communities (LECs), acting as multi-carrier energy hubs (EH) and micro-energy hubs (mEH). LECs are key in the transition towards green, decarbonised power from local and renewable sources. The consortium is developing and applying pioneering software and hardware solutions, putting them to the test in real energy communities and introducing new governance models. There are four demonstration Pilots in the eNeuron Project: The Polish City of Bydgoszcz, the Skagerak Energilab in Norway, the Lisbon Naval Base (LNB) in Portugal, and the UNIVPM University Campus in Italy. This paper focuses on presenting the Portuguese demo pilot: the Lisbon Naval Base, namely the development of the demonstration activities so far, roughly half of the duration of the project, as well as a balance of all supporting activities, such as Use Case definition, technical activities (asset definition and installation) and social activities (stakeholder engagement). This paper presents a description and conclusion of these activities so far, at the time that the eNeuron preliminary toolbox concept is ready to be shared and implemented in the Pilots.
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| 15. |
- Chacin, Luís, et al.
(författare)
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Impact study of operating temperatures and cell layout under different concentration factors in a CPC-PV solar collector in combination with a vertical glass receiver composed by bifacial cells
- 2019
-
Ingår i: Proceedings of the ISES Solar World Conference 2019 and the IEA SHC Solar Heating and Cooling Conference for Buildings and Industry 2019. - Freiburg, Germany : International Solar Energy Society. - 9783982040813 ; , s. 836-847
-
Konferensbidrag (refereegranskat)abstract
- Solar Collectors with Compound Parabolic Concentrator (CPC) reflectors redirect solar irradiance into the receiver (placed in optimal position). The concept of such devices is to reduce the installation area and energy costs [1]. This research focuses on the behaviour and efficiency of a stationary CPC-PV solar collector. Each trough of this collector has different concentration factors (1.25 and 1.66) with vertically placed bi-facial cell receivers. An analysis of the electrical efficiency is performed in order to evaluate the viability of a CPC geometry with a vertical bifacial PV receiver. Furthermore, an investigation on bifacial cells performance due to concentration (and consequently increased cell temperature) is carried out. A numerical simulation of the yearly available radiation and the Incident Angle Modifiers (IAM) for each geometry is also conducted. Finally, a comparison between the simulations and the outdoor testing on the prototype collector is detailed. The tests took place in Gävle, Sweden (61º Latitude). The results showed that higher concentration factors led to larger operating temperatures (114ºC for a concentration factor of 1.66 and 96ºC for a concentration factor of 1.25). Although this may compromise the cell performance and shorten the device’s life cycle, it is shown that appropriate ventilation will allow manageable operating temperatures.
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| 16. |
- Clark, Leigh, et al.
(författare)
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The State of Speech in HCI : Trends, Themes and Challenges
- 2019
-
Ingår i: Interacting with computers. - : Oxford University Press. - 0953-5438 .- 1873-7951. ; 31:4, s. 349-371
-
Tidskriftsartikel (refereegranskat)abstract
- Speech interfaces are growing in popularity. Through a review of 99 research papers this work maps the trends, themes, findings and methods of empirical research on speech interfaces in the field of human-computer interaction (HCI). We find that studies are usability/theory-focused or explore wider system experiences, evaluating Wizard of Oz, prototypes or developed systems. Measuring task and interaction was common, as was using self-report questionnaires to measure concepts like usability and user attitudes. A thematic analysis of the research found that speech HCI work focuses on nine key topics: system speech production, design insight, modality comparison, experiences with interactive voice response systems, assistive technology and accessibility, user speech production, using speech technology for development, peoples' experiences with intelligent personal assistants and how user memory affects speech interface interaction. From these insights we identify gaps and challenges in speech research, notably taking into account technological advancements, the need to develop theories of speech interface interaction, grow critical mass in this domain, increase design work and expand research from single to multiple user interaction contexts so as to reflect current use contexts. We also highlight the need to improve measure reliability, validity and consistency, in the wild deployment and reduce barriers to building fully functional speech interfaces for research.
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| 17. |
- Furbo, Simon, et al.
(författare)
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Best Practices for PVT Technology
- 2021
-
Ingår i: SWC2021 Proceedings. - Freiburg, Germany : ISES.
-
Konferensbidrag (refereegranskat)abstract
- The PVT technology combines solar PV and solar thermal in the same PVT panel. In this way, both electricity and heat are produced by the PVT panel. Compared to the PV technology and the solar heating technology the PVT technology is in the early market stage with only few small and weak industries active. Best practices for the PVT technology, which is still under rapid development, are summarized. Marketed systems with different PVT panel types, different PVT system types with different components for different applications are considered. The potential advantages for PVT systems and the needs for key actors in order to establish a successful sustainable future PVT market are given. Finally, recommendations for a subsidy scheme for PVT systems are given, so that a PVT market can be developed in parallel with the successful PV market.
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| 18. |
- Gomes, João, 1979-, et al.
(författare)
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Defining an Annual Energy Output Ratio between Solar Thermal Collectors and Photovoltaic Modules
- 2022
-
Ingår i: Energies. - : MDPI. - 1996-1073. ; 15:15
-
Tidskriftsartikel (refereegranskat)abstract
- Photovoltaics (PV) and Solar Thermal (ST) collectors are sometimes competitors, as investment capacity, energy demand, and roof space are limited. Therefore, a ratio that quantifies the difference in annual energy output between ST and PV for different locations is useful. A market survey assessing the average price and performance both in 2013 and 2021 was conducted, showing a factor of 3 cell price decrease combined with a 20% efficiency increase, while ST showed negligible variation. Winsun simulations were conducted, and the results were plotted on the world map. Despite variations due to local climate, the ratio of energy production (ST/PV) increases at lower latitudes mainly due to (a) higher air temperature increasing ST output but decreasing the PV output; (b) solar radiation reducing ST efficiency to zero while having a minor impact on PV efficiency. The ratio was calculated for several ST operating temperatures. For latitudes lower than 66 degrees, the ratio of a flat plate at 50 degrees C to a PV module ranges from 1.85 to 4.46, while the ratio between a vacuum tube at 50 degrees C and a PV module ranges from 3.05 to 4.76. This ratio can support the decision between installing ST or PV while combining different factors such as energy value, system complexity, and installation cost.
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| 19. |
- Hosouli, Sahand, et al.
(författare)
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Performance Assessment of Concentrated Photovoltaic Thermal (CPVT) Solar Collector at Different Locations
- 2021
-
Ingår i: SWC2021 Proceedings. - Freiburg, Germany : ISES.
-
Konferensbidrag (refereegranskat)abstract
- The double MaReCo (symmetric reflector geometry) solar collector (DM-CPVT) has been designed and developed by MG Sustainable Engineering AB (MG) and the University of Gävle (HiG). Performance and overall electrical and thermal parameters of the collector have been studied and presented. The outdoor tests have been performed in both Sweden during the summer months of 2020 and Greece in September of 2020. The goal of the studied designs is to optimize the incoming solar radiation that can be collected without the need for tracking. This is possible due to the use of a symmetric reflector geometry with low concentration factor and lower collector depth. The use of a symmetric reflector geometry allows higher annual outputs worldwide. Furthermore, a low concentration factor is necessary to avoid tracking and a lower collector depth to reduce the shading, which is particularly important for the electrical production of these DM-CPVT design concepts. The testing facilities in both locations are also described in this paper. The information on the thermal performance of a collector is important for the prediction of the energy output of any solar system. The thermal properties assessment of the DM-CPVT collector followed the procedures of the ISO 9806:2017 standard and reported. The outdoor testing results have been validated with a deviation of 2.8% and 2.4% for both thermal and electrical peak efficiencies between the testing facilities, respectively. Regarding the Incidence Angle Modifier testing results, the deviation is negligible for all angles of incidence, which shows that outdoor testing procedures can be fairly accurate when tracking systems are not available.
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| 20. |
- Lança, Miguel, et al.
(författare)
-
Thermal performance of three concentrating collectors with bifacial photovoltaic cells part I – Experimental and computational fluid dynamics study
- 2024
-
Ingår i: Proceedings of the Institution of mechanical engineers. Part A, journal of power and energy. - : Sage. - 0957-6509 .- 2041-2967. ; 238:1, s. 140-156
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Tidskriftsartikel (refereegranskat)abstract
- Bifacial photovoltaic cells can produce electricity from incoming solar radiation on both sides. These cells have a strong potential to reduce electricity generation costs and may play an important role in the energy system of the future. However, today, these cells are mostly deployed with one side receiving only ground reflection, which leads to a profound sub-optimal utilization of one of the sides of the bifacial cells. Concentration allows a better usage of the potential of bifacial cells, which can lead to a lower cost per kWh. However, concentration also adds complexity due to the higher temperatures reached which add the requirement of cooling in order to achieve higher outputs. This way, this paper focuses on the effectiveness of forced air circulation methods by comparing the thermal performance of three specific concentrating bi-facial collector designs. This paper developed a computational model, using ANSYS Fluent intending to assess the thermal performance of a covered concentrating collector with bifacial Photovoltaic (PV) cells. These results have then been validated by outdoor measurements. Results show that even a simple natural ventilation mechanism such as removing the side gable can effectively reduce the receiver temperature, thus resulting in favourable cell operation conditions when compared to the case of an airtight collector. Therefore, compared with a standard model, a decrease of 13.5% on the cell operating temperature was reported when the side gables are removed. However, when forced ventilation is apllied a 22.8% reduction on temperature is found compared to the standard air-tight model. The validated CFD model has proven to be a useful and robust tool for the thermal analysis of solar concentrating systems.
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| 21. |
- Lança, Miguel, et al.
(författare)
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Thermal performance of three concentrating collectors with bifacial PV cells. Part II – parametrical study
- 2024
-
Ingår i: Proceedings of the Institution of mechanical engineers. Part A, journal of power and energy. - : SAGE. - 0957-6509 .- 2041-2967.
-
Tidskriftsartikel (refereegranskat)abstract
- One of the problems in using PV cells to extract energy from sunlight is the temperature effect on PV cells. As the solar panel is heated, the conversion efficiency of light to electrical energy is diminished. Moreover, successive temperature elevations can cause dilatations in the array of cells which may also contribute to the degradation of the receiver. Some of the operating temperature mitigation approaches may include air-flow ventilation. In this study, data obtained by experimental and numerical simulations of a collector with bifacial PV cells is compared to the expressions found in the literature for the estimation of the heat transfer coefficient. Forced ventilation was applied to the studied collector as it accounts for much better heat dissipation. A new correlation for the estimation of the heat transfer coefficient is developed for such a geometry, for inlet velocities ranging between 3 and 8 m/s. Values of heat transfer coefficient estimated in the present work have been compared with studies of other researchers.
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| 22. |
- Nasseriyan, Pouriya, et al.
(författare)
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Numerical and Experimental Study of an Asymmetric CPC-PVT Solar Collector
- 2020
-
Ingår i: Energies. - : MDPI. - 1996-1073. ; 13:7
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Tidskriftsartikel (refereegranskat)abstract
- Photovoltaic (PV) panels and thermal collectors are commonly known as mature technologies to capture solar energy. The efficiency of PV cells decreases as operating cell temperature increases. Photovoltaic Thermal Collectors (PVT) offer a way to mitigate this performance reduction by coupling solar cells with a thermal absorber that can actively remove the excess heat from the solar cells to the Heat Transfer Fluid (HTF). In order for PVT collectors to effectively counter the negative effects of increased operating cell temperature, it is fundamental to have an adequate heat transfer from the cells to the HTF. This paper analyzes the operating temperature of the cells in a low concentrating PVT solar collector, by means of both experimental and Computational Fluid Dynamics (CFD) simulation results on the Solarus asymmetric Compound Parabolic Concentrator (CPC) PowerCollector (PC). The PC solar collector features a Compound Parabolic Concentrator (CPC) reflector geometry called the Maximum Reflector Concentration (MaReCo) geometry. This collector is suited for applications such as Domestic Hot Water (DHW). An experimental setup was installed in the outdoor testing laboratory at Gävle University (Sweden) with the ability to measure ambient, cell and HTF temperature, flow rate and solar radiation. The experimental results were validated by means of an in-house developed CFD model. Based on the validated model, the effect of collector tilt angle, HTF, insulation (on the back side of the reflector), receiver material and front glass on the collector performance were considered. The impact of tilt angle is more pronounced on the thermal production than the electrical one. Furthermore, the HTF recirculation with an average temperature of 35.1C and 2.2 L/min flow rate showed that the electrical yield can increase by 25%. On the other hand, by using insulation, the thermal yield increases up to 3% when working at a temperature of 23 C above ambient.
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| 23. |
- Panchal, Rajan, et al.
(författare)
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Evaluation of Symmetric C-PVT Solar Collector Designs with Vertical Bifacial Receivers
- 2019
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Ingår i: Proceedings of the ISES Solar World Congress 2019 and IEA SHC International Conference on Solar Heating and Cooling for Buildings and Industry 2019. - Freiburg, Germany : International Solar Energy Society. - 9783982040813 ; , s. 165-176
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Konferensbidrag (refereegranskat)abstract
- Photovoltaic thermal (PVT) solar collectors can be an effective solution for system output improvement. Photovoltaic thermal collectors naturally have a more expensive receiver than simpler photovoltaic or thermal only collectors, therefore making concentration a more appealing solution to achieve cost reduction. However, concentrating systems need careful analysis on the design phase in order to optimize the annual output. In addition, for stationary (non-tracking) collectors, it is critical to determine the incidence angle modifier (IAM).For this reason, a reflector study was carried out to determine suitable reflector designs for a stationary concentrating PVT collector. The reflectors were simulated using a Monte Carlo raytracing software called Tonatiuh. The two selected reflectors designs were named “pure parabola” (PP) and “compound parabolic concentrator” (CPC). The concentration ratio of 1.2 and 1.6 were selected for each reflector designs, which means a total of 4 collector troughs. The next step involved the construction of the two selected C-PVT collector designs, which were built and subsequently tested by the authors. The IAM was assessed and discussed by simulation and outdoor testing in detail.The IAM results show similar decreases in longitudinal IAM for both the PP and the CPC CPVT collector for the 1.2 concentration factor. For the transversal IAM with 1.2 of concentration factor, the CPC over performs. For the 1.6 concentration prototype collectors, the results are fairly similar. Lastly, the annual output was also simulated and presented.
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| 24. |
- Stevens-Sostre, Whitney A., et al.
(författare)
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An intracellular hydrophobic nexus critical for hERG1 channel slow deactivation
- 2024
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Ingår i: Biophysical Journal. - : Elsevier BV. - 0006-3495 .- 1542-0086. ; 123:14, s. 2024-2037
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Tidskriftsartikel (refereegranskat)abstract
- Slow deactivation is a critical property of voltage-gated K + channels encoded by the human Ether-a`-go-goRelated Gene 1 ( hERG ). hERG1 channel deactivation is modulated by interactions between intracellular N-terminal PerArnt-Sim (PAS) and C-terminal cyclic nucleotide-binding homology (CNBh) domains. The PAS domain is multipartite, comprising a globular domain (gPAS; residues 26-135) and an N-terminal PAS-cap that is further subdivided into an initial unstructured "tip"(residues 1-12) and an amphipathic a-helical region (residues 13-25). Although the PAS-cap tip has long been considered the effector of slow deactivation, how its position near the gating machinery is controlled has not been elucidated. Here, we show that a triad of hydrophobic interactions among the gPAS, PAS-cap a helix, and the CNBh domains is required to support slow deactivation in hERG1. The primary sequence of this "hydrophobic nexus"is highly conserved among mammalian ERG channels but shows key differences to fast-deactivating Ether-a`-go-go 1 (EAG1) channels. Combining sequence analysis, structure-directed mutagenesis, electrophysiology, and molecular dynamics simulations, we demonstrate that polar serine substitutions uncover an intermediate deactivation mode that is also mimicked by deletion of the PAS-cap a helix. Molecular dynamics simulation analyses of the serine-substituted channels show an increase in distance among the residues of the hydrophobic nexus, a rotation of the intracellular gating ring, and a retraction of the PAS-cap tip from its receptor site near the voltage sensor domain and channel gate. These findings provide compelling evidence that the hydrophobic nexus coordinates the respective components of the intracellular gating ring and positions the PAS-cap tip to control hERG1 deactivation gating.
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| 25. |
- Székely, Éva, et al.
(författare)
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Clustering Expressive Speech Styles in Audiobooks Using Glottal Source Parameters.
- 2011
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Ingår i: 12th Annual Conference of the International-Speech-Communication-Association 2011 (INTERSPEECH 2011). - : ISCA-INT SPEECH COMMUNICATION ASSOC. - 9781618392701 ; , s. 2409-2412
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Konferensbidrag (refereegranskat)abstract
- A great challenge for text-to-speech synthesis is to produce ex- pressive speech. The main problem is that it is difficult to syn- thesise high-quality speech using expressive corpora. With the increasing interest in audiobook corpora for speech synthesis, there is a demand to synthesise speech which is rich in prosody, emotions and voice styles. In this work, Self-Organising Fea- ture Maps (SOFM) are used for clustering the speech data using voice quality parameters of the glottal source, in order to map out the variety of voice styles in the corpus. Subjective evalu- ation showed that this clustering method successfully separated the speech data into groups of utterances associated with dif- ferent voice characteristics. This work can be applied in unit- selection synthesis by selecting appropriate data sets to synthe- sise utterances with specific voice styles. It can also be used in parametric speech synthesis to model different voice styles separately.
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| 26. |
- Székely, Éva, et al.
(författare)
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Evaluating expressive speech synthesis from audiobooks in conversational phrases
- 2012
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Konferensbidrag (refereegranskat)abstract
- Audiobooks are a rich resource of large quantities of natural sounding, highly expressive speech. In our previous research we have shown that it is possible to detect different expressive voice styles represented in a particular audiobook, using unsupervised clustering to group the speech corpus of the audiobook into smaller subsets representing the detected voice styles. These subsets of corpora of different voice styles reflect the various ways a speaker uses their voice to express involvement and affect, or imitate characters. This study is an evaluation of the detection of voice styles in an audiobook in the application of expressive speech synthesis. A further aim of this study is to investigate the usability of audiobooks as a language resource for expressive speech synthesis of utterances of conversational speech. Two evaluations have been carried out to assess the effect of the genre transfer: transmitting expressive speech from read aloud literature to conversational phrases with the application of speech synthesis. The first evaluation revealed that listeners have different voice style preferences for a particular conversational phrase. The second evaluation showed that it is possible for users of speech synthesis systems to learn the characteristics of a certain voice style well enough to make reliable predictions about what a certain utterance will sound like when synthesised using that voice style.
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| 27. |
- Székely, Éva, et al.
(författare)
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Predicting synthetic voice style from facial expressions. An application for augmented conversations
- 2014
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Ingår i: Speech Communication. - : Elsevier BV. - 0167-6393 .- 1872-7182. ; 57, s. 63-75
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Tidskriftsartikel (refereegranskat)abstract
- The ability to efficiently facilitate social interaction and emotional expression is an important, yet unmet requirement for speech generating devices aimed at individuals with speech impairment. Using gestures such as facial expressions to control aspects of expressive synthetic speech could contribute to an improved communication experience for both the user of the device and the conversation partner. For this purpose, a mapping model between facial expressions and speech is needed, that is high level (utterance-based), versatile and personalisable. In the mapping developed in this work, visual and auditory modalities are connected based on the intended emotional salience of a message: the intensity of facial expressions of the user to the emotional intensity of the synthetic speech. The mapping model has been implemented in a system called WinkTalk that uses estimated facial expression categories and their intensity values to automat- ically select between three expressive synthetic voices reflecting three degrees of emotional intensity. An evaluation is conducted through an interactive experiment using simulated augmented conversations. The results have shown that automatic control of synthetic speech through facial expressions is fast, non-intrusive, sufficiently accurate and supports the user to feel more involved in the conversation. It can be concluded that the system has the potential to facilitate a more efficient communication process between user and listener.
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| 28. |
- Székely, Éva, et al.
(författare)
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WinkTalk : a demonstration of a multimodal speech synthesis platform linking facial expressions to expressive synthetic voices
- 2012
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Ingår i: Proceedings of the Third Workshop on Speech and Language Processing for Assistive Technologies. - : Association for Computational Linguistics. ; , s. 5-8
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Konferensbidrag (refereegranskat)abstract
- This paper describes a demonstration of the WinkTalk system, which is a speech synthe- sis platform using expressive synthetic voices. With the help of a webcamera and facial ex- pression analysis, the system allows the user to control the expressive features of the syn- thetic speech for a particular utterance with their facial expressions. Based on a person- alised mapping between three expressive syn- thetic voices and the users facial expressions, the system selects a voice that matches their face at the moment of sending a message. The WinkTalk system is an early research pro- totype that aims to demonstrate that facial expressions can be used as a more intuitive control over expressive speech synthesis than manual selection of voice types, thereby con- tributing to an improved communication expe- rience for users of speech generating devices.
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| 29. |
- Székely, Éva, et al.
(författare)
-
WinkTalk: a multimodal speech synthesis interface linking facial expressions to expressive synthetic voices
- 2012
-
Ingår i: Proceedings of the Third Workshop on Speech and Language Processing for Assistive Technologies.
-
Konferensbidrag (refereegranskat)abstract
- This paper describes a demonstration of the WinkTalk system, which is a speech synthe- sis platform using expressive synthetic voices. With the help of a webcamera and facial ex- pression analysis, the system allows the user to control the expressive features of the syn- thetic speech for a particular utterance with their facial expressions. Based on a person- alised mapping between three expressive syn- thetic voices and the users facial expressions, the system selects a voice that matches their face at the moment of sending a message. The WinkTalk system is an early research pro- totype that aims to demonstrate that facial expressions can be used as a more intuitive control over expressive speech synthesis than manual selection of voice types, thereby con- tributing to an improved communication expe- rience for users of speech generating devices.
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| 30. |
- Tyagi, Gunjan, et al.
(författare)
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Light Responsiveness and Assembly of Arylazopyrazole-Based Surfactants in Neat and Mixed CTAB Micelles
- 2022
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863. ; 2:12, s. 2670-2677
-
Tidskriftsartikel (refereegranskat)abstract
- The self-assembly of an arylazopyrazole-based photosurfactant (PS), based on cetyltrimethylammonium bromide (CTAB), and its mixed micelle formation with CTAB in aqueous solution was investigated by small angle neutron and X-ray scattering (SANS/SAXS) and UV-vis absorption spectroscopy. Upon UV light exposure, PS photoisomerizes from E-PS (trans) to Z-PS (cis), which transforms oblate ellipsoidal micelles into smaller, spherical micelles with larger shell thickness. Doping PS with CTAB resulted in mixed micelle formation at all stoichiometries and conditions investigated; employing selectively deuterated PS, a monotonic variation in scattering length density and dimensions of the micellar core and shell is observed for all contrasts. The concentration- and irradiance-dependence of the E to Z configurational transition was established in both neat and mixed micelles. A liposome dye release assay establishes the enhanced efficacy of photosurfactants at membrane disruption, with E-PS exhibiting a 4-fold and Z-PS a 10-fold increase in fluorescence signal with respect to pure CTAB. Our findings pave the way for external triggering and modulation of the wide range of CTAB-based biomedical and material applications.
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| 31. |
- Vilela, Wembley R., et al.
(författare)
-
Metabolic dysfunction induced by HFD + L-NAME preferentially affects hippocampal mitochondria, impacting spatial memory in rats
-
Ingår i: Journal of Bioenergetics and Biomembranes. - 0145-479X.
-
Tidskriftsartikel (refereegranskat)abstract
- High-fat diet-induced metabolic changes are not restricted to the onset of cardiovascular diseases, but also include effects on brain functions related to learning and memory. This study aimed to evaluate mitochondrial markers and function, as well as cognitive function, in a rat model of metabolic dysfunction. Eight-week-old male Wistar rats were subjected to either a control diet or a two-hit protocol combining a high fat diet (HFD) with the nitric oxide synthase inhibitor L-NAME in the drinking water. HFD plus L-NAME induced obesity, hypertension, and increased serum cholesterol. These rats exhibited bioenergetic dysfunction in the hippocampus, characterized by decreased oxygen (O2) consumption related to ATP production, with no changes in H2O2 production. Furthermore, OPA1 protein expression was upregulated in the hippocampus of HFD + L-NAME rats, with no alterations in other morphology-related proteins. Consistently, HFD + L-NAME rats showed disruption of performance in the Morris Water Maze Reference Memory test. The neocortex did not exhibit either bioenergetic changes or alterations in H2O2 production. Calcium uptake rate and retention capacity in the neocortex of HFD + L-NAME rats were not altered. Our results indicate that hippocampal mitochondrial bioenergetic function is disturbed in rats exposed to a HFD plus L-NAME, thus disrupting spatial learning, whereas neocortical function remains unaffected.
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| 32. |
- Vilela, Wembley R., et al.
(författare)
-
Metabolic dysfunction induced by HFD plus L-NAME preferentially affects hippocampal mitochondria, impacting spatial memory in rats
- 2024
-
Ingår i: Journal of Bioenergetics and Biomembranes. - : SPRINGER/PLENUM PUBLISHERS. - 0145-479X .- 1573-6881.
-
Tidskriftsartikel (refereegranskat)abstract
- High-fat diet-induced metabolic changes are not restricted to the onset of cardiovascular diseases, but also include effects on brain functions related to learning and memory. This study aimed to evaluate mitochondrial markers and function, as well as cognitive function, in a rat model of metabolic dysfunction. Eight-week-old male Wistar rats were subjected to either a control diet or a two-hit protocol combining a high fat diet (HFD) with the nitric oxide synthase inhibitor L-NAME in the drinking water. HFD plus L-NAME induced obesity, hypertension, and increased serum cholesterol. These rats exhibited bioenergetic dysfunction in the hippocampus, characterized by decreased oxygen (O2) consumption related to ATP production, with no changes in H2O2 production. Furthermore, OPA1 protein expression was upregulated in the hippocampus of HFD + L-NAME rats, with no alterations in other morphology-related proteins. Consistently, HFD + L-NAME rats showed disruption of performance in the Morris Water Maze Reference Memory test. The neocortex did not exhibit either bioenergetic changes or alterations in H2O2 production. Calcium uptake rate and retention capacity in the neocortex of HFD + L-NAME rats were not altered. Our results indicate that hippocampal mitochondrial bioenergetic function is disturbed in rats exposed to a HFD plus L-NAME, thus disrupting spatial learning, whereas neocortical function remains unaffected. A two-hit protocol using HFD + L-NAME induces metabolic dysfunction in rats.Spatial memory is impacted in HFD + L-NAME rats.Hippocampal but not neocortex bioenergetics is affected in HFD + L-NAME rats.OPA-1 expression is upregulated in the hippocampus of HFD + L-NAME rats.Cortical calcium dynamics was not affected by HFD + L-NAME.
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| 33. |
- Yau, Yvonne Yu Yan, et al.
(författare)
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Efficient oxidation attenuates porewater-derived methane fluxes in mangrove waters
- 2024
-
Ingår i: LIMNOLOGY AND OCEANOGRAPHY. - 0024-3590 .- 1939-5590.
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Tidskriftsartikel (refereegranskat)abstract
- Mangroves store significant amounts of carbon in both sediment and water. Methane (CH4) is often produced in anoxic, organic-rich sediments during carbon degradation and released to overlying waters via porewater exchange. Yet, a portion of CH4 can be oxidized to CO2 before emission. Here, we investigate whether CH4 oxidation impacts its emissions using high-temporal resolution CH4 concentration and stable isotope (delta C-13-CH4) observations collected over 14 tidal cycles in 2 Brazilian mangrove creeks with no river inputs. We found higher CH4 concentrations (similar to 150 nM) more depleted in C-13 (-75 parts per thousand) during low tide than high tide at both creeks. Similar delta C-13-CH4 values between low tide surface waters and porewaters further suggest tidally driven porewater exchange as the main source of CH4. More C-13-enriched CH4 in surface waters and surface sediments than deep sediments indicate partial CH4 oxidation prior to exchange with the atmosphere. A stable isotope mass balance revealed that 17-58% of CH4 was oxidized at rates of 3-25 mu mol m(-2) d(-1) in the water column of tidal creeks. A larger portion of deep porewater CH4 (45-61%) was oxidized in sediments prior to porewater exchange with surface creek waters. The two mangrove creeks had average water-air CH4 fluxes of 51-109 mu mol m(-2) d(-1) over spring-neap tidal cycles. These aquatic CH4 emissions offset only < 3% of the mangroves' soil carbon sequestration. Overall, CH4 oxidation in both surface water and sediment attenuated CH4 emissions to the atmosphere.
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