Thermomechanical design rules for photovoltaic modules

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In contrast to homogeneous mechanical load according to IEC 61215, photovoltaic modules in the field are mainly exposed to inhomogeneous loads like snow or wind. This paper deals with such inhomogeneous loads using computational fluid dynamics and finite element method simulations. Temperatures different to room temperature and the choice of encapsulates have significant influences on the thermomechanics of a photovoltaic module in case of snow load. Polyolefin is the encapsulant with the lowest storage modulus and has the lowest overall stress in solar cells and glass down to −30°C. Furthermore, with colder temperatures, the first principal stress decreases in solar cells but increases in the glass. For wind loads, the impact of module orientation, wind direction, module inclination angle, and wind speed is analyzed. A crosswind scenario is found to be most critical. Additionally, as a rule of thumb, higher module inclination angles result in higher stresses. Finally, general thermomechanical rules are extracted allowing for a deeper understanding of the underlying effects and therefore help to build more robust modules in the future.

“…It is to mention that the derived thermomechanical rules are in a good agreement by those derived by Beinert. 24…”

Section: Influence Of Cell Orientationmentioning

confidence: 99%

“…Many papers 5–11 investigate homogeneous mechanical loads according to the IEC 61215‐2:2021 or earlier versions. A few others investigate nonuniform loads caused by snow 12–14 or wind 15–20 .…”

Section: Introductionmentioning

confidence: 99%

Effect of inhomogeneous loads on the mechanics of PV modules

Romer,

Pethani,

Beinert

2023

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“…The Numerous works regarding this issue can be found in the literature. [23][24][25][26] Membrane stresses scale in proportion to ðLκÞ 2 . As a consequence, decreasing cell sizes is an efficient way to reduce this contribution.…”

Section: Relevance and Practical Consequencesmentioning

confidence: 99%

“…The first one (residual stresses) goes beyond the scope of the present paper. Numerous works regarding this issue can be found in the literature 23–26 …”

Section: Relevance and Practical Consequencesmentioning

confidence: 99%

“…Otherwise, the cell thickness

W

is. In the later case, other contributions may be affected by cell thickness (for instance residual stresses 24 ). Please note that the parameters used in the present work:

L = 78

mm

and

W = 0.2

mm

provide a low membrane to flexure ratio since it scales in proportion to

L^{2} κ false/ W

and cells sizes are and tend to be larger and thinner 27,28 …”

Section: Relevance and Practical Consequencesmentioning

confidence: 99%

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Photovoltaic integration in curved parts: Mechanical limits and key parameters from a theoretical point of view

Charpentier

Duigou

Chambion

et al. 2023

Photovoltaic cells are produced as thin flat layers. They behave as a brittle and elastic material that fails at a given level of stress. Conforming cells into curved geometries will a priori induce both flexure and membrane stresses. In the present work, an analytical model is derived to predict both stress distributions and intensities in a mono‐crystalline pseudo‐square cell. Furthermore, a second model is derived to find the main stresses within fractions of cells. For conventional cell dimensions, solutions predict a transition from flexure to membrane dominated stresses for most conformations as curvature increases. As a consequence, near failure stresses are mainly determined by cells size and aspect ratio. In contrast, flexion is the main contribution in a small subset of the curvature space or for small curvatures. In the corresponding cases, stresses scale in proportion to cells thickness. As a consequence, cell size and/or shape is the main parameter to reduce internal stresses in most cases. In particular, the use of fractions of cells can substantially decrease membrane stresses and thus increase the maximum curvature. For instance, in a case study with M0 cells and curvature radii of a few meters, the highest predicted tensile stress is 45 . In such a case, the larger M12 format gives a prediction of . In contrast, thirds of cells give predictions of 25 and , respectively.

Thermomechanical design rules for photovoltaic modules

Beinert

Romer

Heinrich

et al. 2022

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We present a set of thermomechanical design rules to support and accelerate future (PV) module developments. The design rules are derived from a comprehensive parameter sensitivity study of different PV module layers and material properties by finite element method simulations. We develop a three dimensional finite element method (FEM) model, which models the PV module geometry in detail from busbar and ribbons up to the frame including the adhesive. The FEM simulation covers soldering, lamination, and mechanical load at various temperatures. The FEM model is validated by mechanical load tests on three 60‐cell PV modules. Here, for the first time, stress within a solar cell is measured directly using stress sensors integrated in solar cells (SenSoCells®). The results show good accordance with the simulations. The parameter sensitivity study reveals that there are two critical interactions within a PV module: (1) between ribbon and solar cell and (2) between front/back cover and interconnected solar cells. Here, the encapsulant plays a crucial role in how the single layers interact with each other. Therefore, its mechanical properties are essential, and four design rules are derived regarding the encapsulant. Also four design rules concern front and back sides, and three address the solar cells. Finally, two design rules each deal with module size and frame, respectively. Altogether we derive a set of 15 thermomechanical design rules. As a rule of thumb of how well a bill of material will work from a thermomechanical point of view, we introduce the concept of specific thermal expansion stiffness as the product of Young's modulus , coefficient of thermal expansion , joint area , and materials height . The difference between two materials is a measure of how much thermal strain one material can induce in another. A strong difference means that the material with the larger value will induce thermal strain in the other.