Analysis of Heat Transfer in a Solar Pv Module Using Finite Elements Analysis

doi:10.21203/rs.3.rs-2503869/v1

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Analysis of Heat Transfer in a Solar Pv Module Using Finite Elements Analysis

https://doi.org/10.21203/rs.3.rs-2503869/v1

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Solar cells' photovoltaic (PV) efficiency declines as their operating temperature increases. The PV module may experience thermal stresses as a result of inefficient heating. It is crucial to understand the ideal temperature range for solar cells to operate. This article describes how to do a finite element thermal analysis to determine how the temperature is distributed among the various PV module layers. The components of this technology comprise bus bars, solar cells, ethylvinylacetate (EVA), glass on top, and tedlar on the back. We also designed the structural strength for the PV module to provide a more comprehensive perspective. The reflectivity, transmission, and adsorption capacities of the layers can be used to compute the real heat loss in solar-exposed areas. Convectional and radiative heat loss are also taken into account in this simulation. There is a clear temperature differential across strata, with the coolest areas concentrated at the margins, as may be seen in temperature contour plots. The cells nearest to the frame experience a temperature difference of about 5 °C, but the middle cells of the module are fairly cool. When compared to the temperatures of its various layers, the thickness of the PV module does not vary by more than 1 °C. The potential impact of operation on the coefficient of convection heat loss at the surface of the module is also calculated. This study illustrates how the coefficient of convection heat loss at the module surfaces affects solar cell temperature and system efficiency.

Thermal

photovoltaic

finite elements

simulations

analysis

The effectiveness by which a solar panel transforms light into electricity influences how much power it can produce (PV). Transferring to solar electricity from filthy energy sources like coal and natural gas is a no-brainer due to PV's higher efficiency. Researchers have optimised the electrical characteristics of solar cells and looked into optical techniques like non-reflective coatings to facilitate light transmission in an effort to increase PV efficiency. One such method would be to use the energy produced by solar panels to run an air conditioner. Both “Zondag et al.” and “Huang “demonstrated lowering the temperature of the PV modules improved the system's performance. The substance fluid is carried out below the panel to collect the heat produced by the module during solar exposure, making photovoltaic-thermal (PVT) modules a viable option. The collected heat may then be put to good use, such as heating a building's water supply or the interior space of a home.”Tripana-gnostopoulos” investigated the efficacy of PVT while Prakash completed the theoretical research for an air/water PVT module. Both analyses took into consideration the reduction in PV efficiency that occurs as a result of a solar cell's temperature increasing.

The anticipated operating temperatures of the solar cells are one of the most crucial pieces of information for forecasting PV performance. In this study, we employ finite element analysis to draw a temperature distribution map of the PV laminate's many layers. Since PV efficiency changes with temperature, preliminary estimates of PV efficiency may need iterations to get at the proper temperatures. In order to provide a realistic environment, we simulate both the aluminum frame and the silicone sealant required to keep the PV lamination in place, since they often come into contact with each other and generate heat.In simulations, the parameters for reflectivity, transmissivity, and absorption of each material are taken from experimental findings. The simulation model may be tuned to specifics by adjusting a number of different factors. This study highlights the use of finite element modelling to the challenge of reconstructing the PV laminate's thermal history. Using these models, we can have a better idea of what circumstances work best for running the PV lamination, how to best cool the solar cells by choosing the right materials, and how to best construct the framework that will hold everything up. It is possible to investigate PV performance after cooling the solar cells.

The model's PV laminate had dimensions of 1580 mm 790 mm and had 12 cells by 6 cells. Multi-crystalline silicon wafers measuring 125 mm on each side are used to construct solar cells. Each solar cell is separated from the next by 2 mm. The cells' width is 21 mm, and their length from the frame is 6 mm. We have omitted the copper ribbons that serially connect the cells out of simplicity. The laminate's bus-bar has a specific shape. In reality, it combines the top and bottom cell rows. A transparent front sheet, solar cells and busbar, EVA, and a Tedlar backsheet comprise the parts of the PV laminate. After being laminated, the EVA is then fitted with the solar cells and busbar. The PV module construction implemented here was bifurcated all along centerline, as seen in Fig. 1.described about the principle and their operation.

The photovoltaic panels and main switch above it will conceal the back sheet from full light. Therefore, even when the sun isn't blazing, it may still be able to store energy. The model was segmented to constrain the heat flux to the regions of the back sheet model that came into contact with the radiation source. The outside corners of the glass and back-sheet will receive even more shade from the mounting frame for the PV lamination. Walls should be employed to separate them as a result..

The PV module's thermal performance is analyzed using finite elements. Some assumptions are made: It is believed that all material properties are constant regardless of orientation or temperature. The reflectance of the several substances under study is crucial to the process. When the sun's rays are not reflected by an opaque surface, they are able to heat the layer below. In this case, we will assume that the EVA has a transmisivity of 1.

The fact that the glass, bus bar, and solar cells all contribute to total internal reflections is not a concern.
Under standard circumstances, at a temperature of 27 degrees Celsius, the PV efficiency of the solar cells is only 14%.
The cell partially reflects sunshine and, if any is left over after photosynthesis, transforms that reflection into heat.
It's a common misconception that solar cells generate a lot of ohmic heat.
Towards solar noon, with the PV module pointed directly at the sun, the expected solar irradiation is 1000 W m2.
The average surface temperature is the same on all exposed surfaces.
When considering heat transmission, only the back of the PV lamination and the base of the frame are below ground. A common misconception is that the temperature of the ground is the same as that of the atmosphere. This is a common assumption made in solar collector investigations.
The front frame and PV lamination both serve to block out the sky. Clouds are common in a city like Singapore, UAE, Saudi Arabia which is situated in the tropics. If there are clouds, Schott's temperature should be depended upon.

Tsky = Tambient (1)

It is assumed that the wind speed in front of the PV module is v = 1 m s-1. According to the equation, which is based on the work of Watmuff et al., as given in References, the convective coefficient (in units of W m-2 K-1) is produced..

h = 2.8 + 3.0v (2)

Since convective heat transmission at the rear of the PV module is considered to be only 50% of that at the front, the back is assumed to not cool as well as the front.
The status quo is taken for granted.

The symmetry of laminated materials is a major factor in their selection. Since x and y symmetry are only applied to the necessary locations, a 1/4 scale model is created.The PV module's subassemblies are listed in 1, along with their individual properties. 2 displays the underlying assumptions that were utilized to calculate these numbers. These calculations are based on the first-stage heat flow on the cells and an assumed PV efficiency of 15%.The simulation results showing a decrease in PV efficiency with increasing temperature led to the adoption of an iterative solution strategy. Iteration may help locate the best solution for the temperature distribution.

5.1. DIFFERENTIAL TEMPERATURE SCOPE

The efficiency of a PV module changes in a straight line with temperature [1, 9]:

pv = reference[1-(Temperature of cell-Temperature of reflectivity)] (3)

An item's value is determined by the materials from which it is crafted. Valued at 0.0045°C-1 for crystalline silicon. At the reference temperature Tref, the photovoltaic (PV) efficiency of a solar cell is denoted by the symbol ref. The value of ref is 15% when temperature is 26 degrees Celsius.

In the first, the PV efficiency is maintained at a constant reference value while the cells are fed with a constant heat flow. It can be seen from the data that the module's cells are 64.9 degrees Fahrenheit hotter in the middle than at the edges. When a PV cell is heated, its efficiency drops as shown in Eq. (3). Because of the series connection between the cells, the overall efficiency of the module is always going to be the same as the efficiency of the cell in the module's centre. At 64.9 °C, the PV efficiency of a cell may be calculated using equation (3) to provide a result of 12.3 percent. The actions performed to identify cases with comparable characteristics are summarized in 3. To make up for the decrease in PV efficiency, the heat loss from the PV cells was reduced to 760.2 W m-2 in the second iteration. This procedure is continued until the desired maximum temperature is attained in the cells and PV efficiency is achieved. Within 1% of the theoretical maximum, the cell's maximum temperature reached 66.0 °C by the third repetition, and the PV efficiency reached 12.2%.

The temperature profiles of the glass, cell, and back sheet layers are shown in Figures 3-5. PV laminates have a temperature gradient of less than 1 °C throughout their width because of the low thermal resistance between their layers. Despite the fact that convection only cools the rear of the laminate half in addition to the front, the temperature difference between the glass and the Tedlar back-sheet is just 0.12 °C.

When the border cells are enclosed in a frame, their temperature drops more quickly. According to the contour plots, the blue areas are where the metal frame completely protected the glass and back sheet from the sun. Those pieces are dispersed along the PV lamination's outside edges. By examining the temperature profile of the cells as they spread across the surface of the module, you can gain understanding of the frame cooling procedure. The cells along the building's length are separated from the framework by 6 mm, while across the width, they're set back 21 mm. Figure 4 demonstrates that the proportion of cells located in the lower temperature range is greater throughout the length of the graph than it is along its width. It has been theorized that bringing the frame closer to the cells would increase their cooling efficiency.

Tina and Abet et al. [11] measured the average temperature of a framed PV module by taking measurements from three different points on the module's back sheet using PT100 temperature sensors. Module surface temperature was measured, and it was found to be highest in the center and lowest on the edges. Regardless of the kind of light utilized for the measurement, a difference of around 5 °C was found. The finite element analysis results reported here also show that temperatures fluctuate throughout the system. They do their calculations and comparisons depending on where on their module the temperature sensors were placed (the centre of the corner cell and the centre of the cell in the middle of the module). A difference of 5.5 °C was computed using finite elements, which is quite similar to the value found in the experiment.

5.2. CONVECTIVE LOSS COEFFICIENTS AND THEIR EFFECT ON TEMPERATURE AND PV CELL OUTPUT

It is generally accepted that convection is the most unreliable means of heat dissipation in operating machinery. In order to evaluate how the convective coefficient changes with module length when subjected to forced convection, we employ the finding from Mitchell . It may also be expressed as

h = (8.6 v 0.6) / L 0.4 (4)

The front convective coefficient for a 2 m PV module at 1 m s-1 wind speed is determined to be 6.52 W m-2 K-1. The front convective coefficient for two parallel PV modules of the same length and wind speed is 4.94 W m-2 K-1. We assume that the convective loss coefficient at the back of the module is around 50% less than it is at the front under the identical circumstances. The results are summarized in 4. The effective convective loss coefficient is controlled by the length of the array, which in turn affects the temperature and, by extension, the efficiency of a PV system. In terms of PV efficiency, the difference is 0.22%.

A finite element thermal analysis takes optical and thermal losses of a functioning PV module into account. Based on these results, the cells can reach a maximum temperature of 66.0 °C when exposed to 1000 W m2 of sunlight. The PV efficiency is 15% at 25 degrees Celsius, which is the typical operating temperature in the solar energy sector. At this temperature, solar photovoltaic systems function with an efficiency of 12.2%. The fact that there is little to no temperature difference between the glass and the back sheet thanks to the thinness of the layers is another advantage. After being installed in the Al frame, the PV lamination edges may be cooled. Finally, the length of the array has an impact on the effective convective loss coefficient, which in turn affects the temperature of the solar cells and, consequently, the effectiveness of the PV system.

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Competing interest reported. thermal engineering

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Analysis of Heat Transfer in a Solar Pv Module Using Finite Elements Analysis

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Abstract

Figures

INTRODUCTION

MODEL WITH DISCRETE PARTS

THERMAL ANALYSIS OBJECTIVE PRESUMPTIONS

THE CONDITIONS AT THE EDGES AND THE USED PARAMETERS

RESULTS AND DISCUSSION

CONCLUSIONS

REFERENCES

Additional Declarations

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