Fraunhofer Center for Silicon Photovoltaics CSP
Fraunhofer Center for Silicon Photovoltaics CSP

Finite Element Simulation

FES-image of the wind-speed distribution
© Fraunhofer CSP
FES-image of the wind-speed distribution around a solar module frontally exposed to wind. The arrows indicate the direction of the air currents.

As a part of our method portfolio, the finite-element method is applied to photovoltaics, especially in the field of structural mechanics in order to determine deformations and stresses in module components exposed to mechanical loads (wind, snow). Other fields of application are thermodynamics (calculation of temperature distribution and heat transport), the simulation of wind flow (pressure distribution, calculation of heat transition) as well as the electric simulation (currents and electric fields). The various physical tasks can also be studied in various combinations.

The results of finite-element simulation are applied to reliability and fatigue strength assessments of module components. Furthermore, they can be applied to optimize processing steps of production processes, such as soldering or lamination. The results ultimately produce a variety of interpretations, for example, for robustness evaluations or the definition of quality criteria.

Services

  • Material model building and characterizations (e.g. viscoelasticity, elastic-plastic)
  • Simulation of the structural mechanics of components and complete solar modules as well as the system technology
  • Temperature field simulation of manufacturing processes and operating conditions
  • Thermomechanical simulation of PV components, modules and systems
  • Flow simulation of solar modules and systems
  • Simulation of multi-physical tasks
  • Execution of optimizations, robustness and sensitivity studies
  • Reliability evaluation of
    • PV components (connectors, solar cell, glass, encapsulating material)
    • Modules and systems (holders, substructures)

Examples

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Simulationsmodell Infrarot-Lötprozess
© Fraunhofer CSP
Simulation model of the infrared soldering process (left) and resulting temperature distribution in the wafer during the soldering process (right).

Thermomechanical Simulation of PV Components and Modules

Thermomechanical stresses occur in PV modules whenever the temperature changes because the individual components have different coefficients of expansion. In the field of module production, in particuöar the soldering process and the lamination of the solar cells cause stresses for the solar cells. During operation, temperature changes occur due to day and night changes as well as seasons. The Thermocycle test is an over-imitation of these stresses.
In order to evaluate the stresses of the components right during the processes, we work with finite-element simulation models. The mechanical stresses arising as a result of different solder materials and material properties can be compared during the soldering of the cells and allow to derive the resulting optimization potentials.
The simulation of the cell shift in a module under temperature changes is an important tool for evaluating the fatigue strength of the cell connectors. On the basis of the results, the cycles can be estimated until failure. Among other things, we investigate the impact of the encapsulation material and the backsheet on these cycles until failure. The calculation of the stresses in the cells after soldering and laminating can be superimposed with mechanical simulation results in further steps in order to evaluate the breaking behavior of the cells more precisely.

Fluid Dynamics Simulation
© Fraunhofer CSP
Distribution of the first main voltage in the cells with frontal inflow and 30 ° (left), 60 ° (middle) and 90 ° (right) Module inclination (low voltage = blue ... high voltage = red).

Fluid Dynamics Simulation of Solar Modules

With the help of flow simulations (CFD) we are able to simulate the wind pressure distribution on a module and the associated stress distribution in the glass and the cells under real conditions. Furthermore, it is possible tp calculate the local heat transfer conditions and the resulting temperature distribution in the module.

Simulation for the plastic expansion
© Fraunhofer CSP
Simulation for the plastic expansion of mountings for PV modules.

Reliability Assessment

Using mechanical simulations, storage variants can be individually optimized, compared with each other, and the optimal variant can be determined. Alternatively, for quality control purposes, it is possible to determine the minimum requirements for the strength parameters for a defined storage.