Thermo-Mechanical Simulations

Using the Finite Element Method (FEM), we couple structural mechanics with other physical fields, such as heat transfer for thermomechanical simulations. We are capable of solving very complex and thus computationally intensive problems through the interfacing with a CAD program and the use of a High Performance Computing Cluster (HPC cluster).

FEM simulation of a commercial solar module.
© Fraunhofer ISE

FEM simulation of a commercial solar module with 60 cells in mechanical load test from 2400 Pa pull to 5400 push load. Shown is the tensile stress in the solar cells.

R&D Services for Thermo-Mechanical Simulations

In the Reserach Topic Module Technology we offer the following services in the field of thermo-mechanical FEM simulation:

  • FEM modelling of any component and calculation on a High Performance Computing Cluster (HPC cluster)
  • Virtual product development and material qualification
  • Virtual product optimization
  • Material characterization to determine the material properties, e.g. as input for FEM simulations
  • Experimental validation in the test laboratories of Fraunhofer ISE 

Application Examples

Thermomechanical Optimization of PV Modules

In a PV module, stresses occur during production and operation due to temperature changes and mechanical loads. These stresses can lead to cracks in the solar cells, joints or fatigue of the cell interconnectors. Simulations help us to understand these stresses and develop strategies for stress reduction. In the manufacturing process, thermomechanical stresses occur mainly during the interconnection of the solar cells and module lamination. If the modules are installed in a PV power plant, mechanical and thermal loads act on the modules due to weather conditions.

In simulations, we reproduce the manufacturing processes and the load scenarios. For example, we simulate the mechanical load test and the thermal cycling test according to the requirements of the IEC 61215 test standard or use measured climate data to determine the thermal stresses that occur in real operation. From the FEM simulations we can derive how damage to the module can be avoided.

FEM simulation of load conditions of a commercial solar module with 60 cells
© Fraunhofer ISE
FEM simulation of load conditions of a commercial solar module with 60 cells.

Short Description:

  • Objective
    • Analysis of the influence of different solar cell and module sizes on the mechanical stability
    • Analysis of the influence of different materials and their thickness
  • Procedure
    • Creation of a 3D FEM model of the entire PV module, including frame
    • Simulation of the manufacturing process
    • Simulation of the mechanical load test at different temperatures
    • Evaluation based on the deflection of the PV module and the solar cell fracture probability
  • Result

    Module optimization through the following measures to reduce the probability of solar cell breakage:
    • more suitable material selection, e.g. softer encapsulation
    • Adaptation of the module design, e.g. glass-glass module
    • matched encapsulation properties and material thicknesses
    • more suitable module mounting

ECA Joining of Shingle Modules

In the shingle interconnection, solar cell strips are connected in a way comparable to roof shingles. The absence of cell interconnectors results in a particularly aesthetic and homogeneous appearance of PV modules. They are also more resistant to shading. Due to their mechanical properties, electrically conductive adhesives (ECA) are particularly well suited for shingle connections. 

In the Reserach Topic Module Technology, we use thermomechanical FEM simulations to investigate the mechanical behavior of such an ECA shingle joint. Special attention is paid to the viscoelastic material behavior of the ECAs.

FEM-Simulation of a  ECA shingle joint at thermal cycling
© Fraunhofer ISE
FEM-Simulation of a ECA shingle joint at thermal cycling.

Short Description:

  • Objective
    • Analysis of the mechanical behavior of ECA-based shingle joints
    • Optimization of the ECA shingle joint for low ECA use and increased reliability under thermal cycling
  • Procedure
    • Creation of 2D and 3D FEM models of shingle joints
    • Determination of viscoelastic properties of ECAs
    • Simulation of the manufacturing process
    • Simulation of thermal cycling and mechanical load
  • Result
    • Identification of the important parameters influencing the stress in the joints
    • Optimized joint and module design for increased reliability

Optimization of the Thermal Resistance of a Junction Box

Bypass diodes are located in the junction box of a PV module. If a bypass condition occurs, the high currents can cause the bypass diodes to generate a lot of heat. If the heat is not dissipated well, this leads to overheating of the junction boxes and thus to module failure.

FEM Simulation of the thermal resistance of a junction box
© Fraunhofer ISE
FEM Simulation of the thermal resistance of a junction box.

Short Description:

  • Objective
    • Optimized heat dissipation from the bypass diodes in a PV module junction box
  • Procedure
    • 3D FEM model of the junction box based on a CAD model
    • Simulation of the bypass condition
    • Validation by temperature measurement with an IR camera
    • Simulation of different fillers
  • Result
    • Reduction of the junction box temperature
    • Identification of suitable filler materials

Simulation of PV noise barriers

In the ongoing project PVwins, noise barriers with integrated PV modules are being developed for use on motorways and railroad tracks. With FEM we simulate the acousto-mechanical behaviour of a noise protection element.

Noise barrier with PV modules
© R. Kohlhauer GmbH
Noise barrier with partly transparent design and standard PV modules.

Short Description:

  • Objective
    • • Development and optimization of PV noise protection elements
    • • Identification of suitable material classes
  • Procedure
    • 3D FEM model of a noise protection element with integrated PV module
    • Simulation of sound absorption
    • Simulation of dynamic mechanical loads, e.g. pressure wave of a passing train
    • Coupling of both simulations for the acousto-mechanical design of the noise protection element