A detailed mathematical models is developed for a fully wetted absorber photovoltaic thermal (PVT) collector with and without phase change material (PCM) under its absorber channel. Thermal and ...electrical investigations were carried out using PCM OM37 for typical winter and summer days in Lyon, France. The system is analyzed under energy and exergy performances. PCM incorporation in a water PVT absorber improves the performance of system in terms of electrical and thermal parameters. Enhanced electrical and thermal energy is attributed to dissipation of excess heat of PV module by latent heat absorption mechanism that reduces the PV module temperature and release heat at the night as well, provides better electrical and thermal stabilities to the system. Overall thermal energy and overall exergy of PVT system for a winter day as well as for a typical summer day, are found to be strongly in favor of adding PCM. The effects of mass of PCM on module temperature, outlet water temperature, and PV module electrical efficiency, have also been investigated. During sunshine hours, increment in the PCM mass up to its optimal value decreases temperature resulting in higher electrical efficiency and also allows providing higher water temperature at the nighttime.
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•Thermal model for a fully wetted absorber PVT collector with PCM was developed.•During night or off sunshine hours PCM acts as a heat source for the collector water.•A model was also developed for the same system without PCM to compare its performance with PCM.•PCM maximizes the electrical and thermal performance of PVT collector.•Characteristic curves, energy and exergy analysis have been carried out for these systems.
Reconciling the use of space and the production of low‐carbon electricity is a key challenge in the face of changing human needs. In this context, floating photovoltaics (FPV) is proving to be a key ...application to colocate energy production with several activities (hydroelectricity and aquaculture). A major benefit of FPV technologies is the reduced module temperature. However, the causes of this thermal observation are still unknown. The density of the distribution of the floaters and the thermal behavior of the waterbody are two postulated roots that show positive correlations with regard to the module temperature. Therefore, there is interest in identifying precise thermal features in the application because the yield surplus promised in FPV technology is based on this cooling effect. This research aims to understand the heat mechanisms that arise in this application in comparison with ground‐mounted photovoltaics (PV). A special framework based on 1‐D thermal modeling and statistical classification of the results by dimensionless related features is proposed. This strategy offers a possibility to differentiate the influence of the thermal modes separately over the module temperature. First, a gain of 20% to 50% in the convective transfers is demonstrated for FPV compared with ground‐mounted applications. Data exploitation associates these gains with the forced convective effects of the wind blowing on the front of the modules. Gains in free convective transfers are associated to the airflow around the module rear face, reducing the phenomenon of thermal buffering. The framework also demonstrates that the emissivity‐based correlations for the radiative boundaries are in good agreement with the radiative phenomena involved in FPV. When convection preferentially cools down the module, the participating media nearby acts as a heat source, warming the installation. Thus, understanding these mechanisms in the FPV application would provide opportunities for improved temperature management through floats or array‐scale optimizations.
Convective and radiative heat rates are derived for floating photovoltaic applications by combining monitoring and local environmental data. An increase in the convection rate is observed on the order of 20 to 50% for both sides of the modules. A new sky temperature is built to better describe the radiative action of the humidity field above waterbodies.
The temperature of photovoltaic (PV) cells is a critical factor in evaluating energy yield and predicting system degradation. Although thermo-electrical models allows predicting the evolution of the ...system over time, precise understanding of the thermal exchanges between the system and its environment is needed as they are implemented in the yield assessment using thermal correlations. These empirical correlations are based on heat transfer magnitudes undergone by similar PV set-ups.
The aim of this study is to introduce a non-intrusive experimental methodology for precisely determining the convective heat transfer coefficient (CHTC) at the front of photovoltaic modules using two setups. The method integrates a heat flux sensor glued to the PV surface coupled with environmental data (e.g., irradiance, ambient temperature). This experimental method is applied to PV modules on a roof in an urban area and to a floating photovoltaic (FPV) system. It is demonstrated that the method significantly improves the accuracy of prediction of PV module temperatures in operating conditions compared to the conventional method based on the energy balance of a PV module.
By using quantile regression, an empirical forced convection correlation is found based on the average wind speed. Compared to the traditional approach which relies on global transmittance, the CHTC is mainly dependent on the wind, whereas the global transmittance includes the radiative heat transfer which depends on the module temperature. The correlation for CHTC tailored for the floating photovoltaic system shows sensitivity to wind speed that is slightly higher compared to the inland setup in the literature.
•Convective Heat Transfer Coefficient (CHTC) is determined using heat flux sensor.•Measured CHCTs for photovoltaics (PV) are robust to varying environmental conditions.•Quantile regressions are used to identify CHTC sensitivity to wind speed.•Regressions of global transmittance against wind speed is influenced by irradiations.•Measured CHTC is less impacted by irradiations, improving the analysis of convection.•Predictions of PV temperatures are enhanced using measured CHTCs.•A new empirical correlation for convective transfers in Floating PV is provided.
•Experimental measurements are made at various external temperature stratifications.•The mass flow rate is strongly impacted by the external temperature stratification.•A steady one-dimensional ...theory is developed to predict its impact.•The model is in excellent agreement with available experimental data.
Many works have been performed on heated vertical rectangular open-ended channels. Whilst in most cases, thermal fields are quite well predicted or reproducible, there were often large unexplained variations in the experimental flow rate for apparently the same conditions. An experimental and theoretical investigation has therefore been carried out to identify the effect of external thermal stratifications on the flow rate. Four values of steady and uniform heat flux, equivalent to Rayleigh numbers between 2.9×104 and 1.6×108 were imposed experimentally either on one or both sides of a vertical rectangular channel, with various ambient thermal gradients external to the channel. It was observed that the mass flow rate was significantly reduced as the positive upward, external thermal gradient increased. A theoretical model of the phenomenon was also developed. There is an excellent agreement between the theoretically predicted and experimentally measured mass flow rates. This clearly highlights that external temperature distributions are key driving factors and their influence is accurately quantified in this work.
This paper addresses the numerical simulation of a partially transparent, ventilated PV façade designed for cooling in summer (by natural convection) and for heat recovery in winter (with the aid of ...mechanical ventilation). For both configurations, air in the cavity between the two building skins (photovoltaic façade and the primary building wall) is heated by transmission through transparent glazed sections, and by convective and radiative exchange. First we describe the model for the naturally ventilated envelope. Validation of the model and the subsequent simulation of a building-coupled system are then presented, which were undertaken using experimental data from the RESSOURCES project (ANR-PREBAT 2007). The dataset comprise measurements from a full scale prototype system installed on a real office building in Toulouse, France. Finally the heating and cooling needs of a simulated building were calculated and the impact of climatic variations on the system performance was investigated. The PV double-skin was found to result in a slight increase in cooling needs for all the French climates considered, whereas the impact of the façade on heating needs was found to be not predominant from point of view energetic.
The achievement of the targets for reducing greenhouse gas emissions set by the Paris Agreements and the Swiss federal law on the reduction of greenhouse gas emissions (CO2 law) requires massive use ...of renewable energies, which cannot be achieved without their adoption by the general public. The solar cadaster developed as part of the INTERREG G2 Solar project is intended to assess the solar potential of buildings at the scale of Greater Geneva—for both industrial buildings and for individual residential buildings—at a resolution of 1 m. The new version of the solar cadaster is intended to assess the solar potential of roofs, as well as that of vertical facades. The study presented here aims to validate this new version through a comparison with results obtained with two other simulation tools that are widely used and validated by the scientific community. The good accordance with the results obtained with ENVI-met and DIVA-for-Rhino demonstrates the capability of the radiative model developed for the solar cadaster of Greater Geneva to accurately predict the radiation levels of building facades in configurations with randomly distributed buildings (horizontally or vertically).
The main objective of this study is to develop a novel photovoltaic thermal collector (PVT) to improve the electrical and thermal efficiencies of the solar collector. The goal is to maximize the ...electrical power and minimize the thermal losses of the solar panel. A novel photovoltaic thermal collector is designed and tested. The new PVT collector includes: (1) An optical anti-reflective and low-emissivity coating to reduce the radiation losses; (2) A thermal resistance to reduce the conduction losses between the photovoltaic and absorber plate; and (3) A channel heat exchanger to decrease the thermal losses between the solar cells and the cooling fluid. A transient two-dimension multi-physics model for the PVT sheet-tube and the advanced PVT collector is developed. The state variable variations are predicted by the finite volume method. A comparison between the two considered hybrid collectors in terms of thermal and electrical efficiencies and temperature distribution is performed. Moreover, the impact of arrangement (anti-reflective and low-emissivity coating, thermal resistance between the absorber plate and the cooling fluid, enhanced exchange surface area between the flat plat exchanger and the cooling fluid) on the new PVT collector is studied and analyzed. The simulation results showed clearly the advantages of using this evolution of the PVT collector compared to the basic one. Indeed, this new PVT configuration represents a series of improvements that lead to a lower PV module and higher fluid operating temperatures. Higher electrical and thermal efficiencies for the proposed PVT (15.4%, 73%) are obtained compared to the basic PVT collector (13.7%, 58%), respectively under no loss and standard test conditions.
•Design choices for a high performance solar PV/Thermal collector.•A detailed finite-volume model to predict the thermal and electrical performance.•Analysis of optical properties, with anti-reflective or low-emissivity coatings.•Analysis of heat transfer, thermal resistance, and exchanger geometry.•Theoretical electrical and thermal efficiency gain: (13.7%, 58%) to (15.4%, 73%).
This paper addresses the simulation of a partially transparency, ventilated PV facade integrated into the envelope of an energy efficient building. Such an arrangement exploits the heat transfer ...between cavity air, the PV façade and the primary wall of the building for the purpose of PV cooling in summer (with natural convection) and heat recovery in winter (mechanical ventilation). A simplified physical model of the system is proposed for the summer operating configuration, which is more challenging from a numerical perspective. The model describes the active envelop in terms of a simplified geometry, and includes parameters such as density of PV cells, relative coverage of degree of transparency/opaque surfaces, and the ratio of height/width of the double-skin. For a given set of meteorological conditions, the surface and air temperatures, mass flow rate and PV power output are obtained by solving a system of thermal and aerodynamic balance equations. Validation of the model was undertaken using experimental data from a full scale prototype system installed in Toulouse, France as part of the RESSOURCES project (ANR-PREBAT2007). Coupling of the system to a simulated building was achieved with the aid of TRNSYS, and this combined system was evaluated in terms of heating and cooling needs for a range of French climates. It was found that the cooling needs are marginally higher for all locations considered, whereas the impact of the façade on the heating needs is weak as these needs are already low for these all locations.
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•Numerical model of a semi-transparent ventilated PV double-skin façade with zonal approach.•Validation of numerical model with experimental results monitored during summer and winter.•Identification of daily and seasonal behavior.•Coupling of the PV double-skin façade to an office building model with different control strategies for different seasons.•Impact of the degree of transparency on the heating and cooling needs of the building.
•Building integrated earth-to-air heat exchanger for global footprint reduction.•Offering similar energy gains than traditional earth-to-air heat exchanger.•Two time-dependent 3-dimensional finite ...volume models are developed and coupled.•Coupled heat and moisture transfers and complex boundary conditions are considered.•Successful validation against in-situ temperature and water content measurements.
This paper investigates an innovative earth-to-air heat exchanger (EAHE), namely the geothermal foundation Fondatherm®. This system solves numerous technical problems inherent to a traditional EAHE. However, an accurate understanding of its thermal behavior is crucial to ensure the best energy gain and its economic viability. This current paper focuses on a numerical study of the ventilated foundation. A time-dependent three-dimensional finite volume numerical model is developed. This model considers coupled heat and moisture transfers as well as complex boundary conditions such as the weather, the building and the water table simultaneous influences. A matric-head based system of equations is used to represent the heat, vapor and liquid transfers within the soil. It is combined to a capillary pressure-based formulation of the heat and vapor balance equation for the concrete foundation. Furthermore, a numerical method built on a switching from a potential- to a flux-based system of equations is proposed. It is added to a variable time-step method of resolution and allow to handle the greatest hygric loads variations at the ground surface. The numerical code is successfully validated against analytical solutions for simple cases, and against experimental and in situ measurements.
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