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Simulation and Model Validation of a Multi-Concentration Points Concentrated Photovoltaic Thermal System
Abstract
In this study, the transient behavior of a concentrated photovoltaic thermal (CPV/T) system is assessed using one-dimensional mathematical model. The model is based on the heat balance of the concentrated photovoltaic (CPV) solar cells, receiver pipe, thermal fluid, insulation, and the storage tank attached to PV/T system via insulated pipes. The mathematical model was developed and solved using ordinary differential equation solvers in MATLAB ® computer program. The interdependence thermo-electric dynamic responses of the CPV/T system were modeled and analyzed by considering two cases such as with and without glass enclosure around the receiver. The electrical and thermal efficiencies are evaluated as the function of enclosure effect, beam solar radiation, and circulating fluid flow rate. For the purpose of model validation, experimental measurements of the CPV/T system were performed. Satisfactory agreements were found between the experimental data and the predicted results. The developed dynamic model is most suitable to predict and evaluate the performance of a point-focused CPV/T system.
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Background: Various solar energy collecting systems have been developed and analyzed for agricultural applications. They include solar thermal and electric devices such as solar crop dryers, solar water pumps, solar greenhouse heating, ventilation for livestock, solar aeration pumps, solar electricity, and many more. Purpose: This review provides the current status of research and development in the field as well as the solar energy systems that are currently in use in the agriculture sector across the globe. Review: Solar energy is the largest and cheapest energy resource on earth; one hour of solar radiation exceeds the complete global energy consumption in one year. The potential annual total solar radiation in South Korea is 3.58–5.4 kWh/m 2 /day. The available solar energy is sufficient for agricultural applications across the entire country. Conclusion: The scope of solar energy utilization in agricultural machinery engineering in South Korea and in other countries is promising.
Since the influence of temperature on the conversion efficiencies of photovoltaic (PV) cells and thermoelectric (TE) generators are totally different and opposite, the system operating temperature becomes a key parameter which significantly determines the utilization efficiency of the common PV-TE system on solar energy. In order to make the PV-TE system obtain higher energy utilization efficiency, phase change material (PCM) is incorporated to construct a novel PV-PCM-TE hybrid system to maintain the system operating at the ideal working temperature. The performance of such a novel hybrid system is experimentally studied corresponding to a number of practical working conditions. The temperature, efficiency, and output power of the hybrid system are compared with those of the pure PV system under the same circumstance. The effects of the optical concentrations ratio and cooling approaches on the conversion efficiency of the hybrid system are experimentally investigated. The whole conversion efficiencies of the hybrid system incorporated with TE generators with different values of dimensionless thermoelectric coefficient (ZT) are discussed. The present work reveals that such a hybrid system possesses a promising potential on the full-spectrum utilization of solar energy.
Hybrid photovoltaic/thermal (PV/T) solar collectors can theoretically be designed to operate at near 80% in combined efficiency and has therefore been received ever increasing attention. In the present study, a 3D concentrated PV/T model was built and its photovoltaic/thermal system performances were investigated by a coupled TRNSYS and CFD simulation method. The influences of different kinds of solar cells and various parameters on the system performance have been systematically evaluated. As the most imporatant economic index for the practical use of PV/T system, in terms of the overall exergy efficiency under 50 times concentrations and 0.08 m·s⁻¹ inlet velocity, the sequence was found to be InGaP/GaAs/InGaAs (37.53%) > GaAs (29.62%) > GaInP (21.62%). InGaP/GaAs/InGaAs solar cell under 50 times of concentration and inlet fluid velocity of 0.02 m·s⁻¹ was therefore employed for further one-step static TRNSYS-CFD coupled investigation. It was analyzed per hour, per month and per day based on the meteorological condition of Xi’an, a typical city in west China. In terms of energy efficiency, the energy economy is worse when the solar irradiance is relatively higher. However, the energy output is relatively larger under same condition. The trend for the exergy economy and the exergy output is inversed. Not only the thermal exergy efficiency is larger with the increased solar irradiance, the higher solar irradiance is also preferred in the view of thermal exergy output. Finally, noon time of 12:00 was chosen as the time variable in the coupled simulation per month and per day in July and August to get the largest total exergy outputs. It was found that the optimum working conditions vary according to different evaluation factors, the reasonable results should be determined according to specific needs. Our work should be valuable for the prediction and evaluation of performance of a designed PV/T system operating under various meteorological conditions.
Comparative performance assessment and model validation of the linear Fresnel concentrator (LFC) and the conical solar reflector (CSR) systems were performed under identical operating and climatic conditions. This paper analyzes the amount of heat loss by convective heat transfer (natural or forced) from the receiver to ambient air with and without a glass-reinforced plastic sheet enclosure around the collector assembly. The MATLAB ORDINARY DIFFERENTIAL EQUATION (ODE) solvers were used for simulation of the transient states. Mathematical models were generated from energy balance equations of the glass cover, absorber pipe, heat transfer fluid, and storage tank for each system. Thermal and optical analyses of the LFC (with and without an enclosure) and CSR systems were carried out by using the measured and calculated results. Satisfactory agreement was found between the experimental data and predicted results. The given models are suitable to simulate the dynamic energy flow across the different components of the LFC and CSR systems.
The experimental and theoretical analysis of a concentrating photovoltaic and thermal system (CPV/T) presented in this paper allows to evaluate the electrical parameters of the system, the concentration factor, the cell temperature in different working conditions and the fluid temperature. In particular, the experimental values of the cell temperature represent the input of a model developed in ANSYS-CFX. This model evaluates the theoretical temperature values of the fluid that flows into the cooling circuit of the CPV/T system, designed with the CATIA software. Hence, both electrical and thermal parameters have been analyzed in order to evaluate the potential energy production of a concentrating photovoltaic and thermal system. Different configurations of the CPV/T system have been analyzed and the value of the concentration factor has been determined by means of an experimental procedure. The experimental and theoretical electric powers are compared in different climatic conditions considering a solar radiation included between 500 and 900 W/m². The electric efficiency is also evaluated as function of solar irradiance and cloudiness. Moreover, the fluid temperature as function of the experimental cell temperature is determined in different working conditions by means of the ANSYS model. The fluid temperature is also theoretically determined varying the operating conditions along the circuit. Finally, a study of the electrical and thermal performances represents a key-factor to develop a more complex prototype of a CPV/T system.
Characteristics of a high concentration photovoltaic/thermal (HCPV/T) module equipped with point-focus Fresnel lens have been investigated in this paper. Both electrical and thermal models of the module are developed by numerical methods. The electrical model is based on the Shockley diode equation, and the thermal model is grounded on a two-dimensional steady-state heat transfer model. Influences of environmental parameters and coolant water are considered in the models. The inputs of the models consist of irradiance, ambient temperature, wind speed, water temperature and mass flow rate. The outputs mainly include electrical efficiency and thermal efficiency. The simulated results are compared with experimental results and a great agreement is obtained. By the virtue of the validated models, influences of different parameters on module performance are analyzed in detail. The results show that an electrical efficiency of 28% and a thermal efficiency of 60% can be obtained by the HCPV/T module. The electrical efficiency is mainly influenced by solar irradiation rather than cell temperature. The thermal efficiency increases with the increment of irradiance, ambient temperature and water mass flow rate. On the contrary, increasing water temperature and wind speed will lower the thermal efficiency. Also, the HCPV/T module can produce hot water as high as 70 °C without decreasing the electrical efficiency seriously.
Some of the main bottlenecks for the development and commercialization of photovoltaic/thermal hybrids are the lack of an internationally recognized standard testing procedure as well as a method to compare different hybrids with each other and with conventional alternatives. A complete methodology to characterize, simulate and evaluate concentrating photovoltaic/thermal hybrids has been proposed and exemplified in a particular case study. By using the suggested testing method, the hybrid parameters were experimentally determined. These were used in a validated simulation model that estimates the hybrid outputs in different geographic locations. Furthermore, the method includes a comparison of the hybrid performance with conventional collectors and photovoltaic modules working side-by-side. The measurements show that the hybrid electrical efficiency is 6.4% while the optical efficiency is 0.45 and the U-value 1.9W/m2°C. These values are poor when compared with the parameters of standard PV modules and flat plate collectors. Also, the beam irradiation incident on a north–south axis tracking surface is 20–40% lower than the global irradiation incident on a fixed surface at optimal tilt. There is margin of improvement for the studied hybrid but this combination makes it difficult for concentrating hybrids to compete with conventional PV modules and flat plate collectors.
Although the performance of hybrid photovoltaic-thermal (PV/T) collector had been studied both experimentally and numerically for some years, the thermal models developed in previous studies were mostly steady-state models for predicting the annual yields. The operation of a PV/T collector is inherently dynamic. A steady-state model is not suitable for predicting working temperatures of the PV module and the heat-removal fluid during periods of fluctuating irradiance or intermittent fluid flow. Based on the control-volume finite-difference approach, an explicit dynamic model was developed for a single-glazed flat-plate water-heating PV/T collector. A transport delay fluid flow model was incorporated. The proposed model is suitable for dynamic system simulation applications. It allows detailed analysis of the transient energy flow across various collector components and captures the instantaneous energy outputs.
This study explores the causal relationship between carbon dioxide (CO2) emissions, renewable and nuclear energy consumption and real GDP for the US for the period 1960–2007. Using a modified version of the Granger causality test, we found a unidirectional causality running from nuclear energy consumption to CO2 emissions without feedback but no causality running from renewable energy to CO2 emissions. The econometric evidence seems to suggest that nuclear energy consumption can help to mitigate CO2 emissions, but so far, renewable energy consumption has not reached a level where it can make a significant contribution to emissions reduction.
Version 8.1. 0.604 (R2013a)
- R Matlab
R. Matlab, Version 8.1. 0.604 (R2013a), The MathWorks Inc.,
Natrick, Massachusetts (2013).