Finite Element and Volume Simulation
Fraunhofer Center for Silicon Photovoltaics CSP
The utilization of the Finite Element Method is a well-established tool in many industries. Fraunhofer CSP uses this method in Photovoltaic especially in field of structure mechanics for determination of deformations and stresses in the module components. Other fields are thermodynamics (simulation of temperature distribution and heat transport), fluid dynamics simulation (pressure distribution, heat transfer) as well as electrical simulation (current and electric fields).
The results of Finite Element Simulations are used to evaluate the reliability and fatigue strength of module components, the optimization of process steps as well as definition of quality criteria.
Thermo-mechanical Simulation of PV Components and Modules
Thermomechanical loads always occur in PV modules when the temperature changes, since the particular components have different coefficients of thermal expansions. In module manufacturing the soldering and lamination process induce stresses on solar cells. During operation temperature cycling arises from day-/night-shifts and seasons. An exaggerated simulation of these loads is the thermo-cycle test.
For Evaluation of the stresses on the components during these processes Finite Element simulation models are developed at Fraunhofer CSP. With these models mechanical stresses due to soldering of solar cells for different solder materials and interconnector properties can be compared. Resultant optimization potentials can be identified.
The Simulation of cell shift inside a module during temperature cycling is important to evaluate the fatigue strength of solar cell interconnectors. On the basis of these results cycles to failure can be estimated. Among other things the influence of encapsulant materials and back sheets on the cycle to failure can be investigated. The simulation of stresses in the cells after soldering and lamination can be superposed in further steps with results of mechanical simulations to evaluate the fracture behaviour of solar cells more accurate.
Fluid Dynamic Simulation of Solar Modules
With computational fluid dynamics simulation (CFD) wind pressure distribution on a module and related stress distribution in glass and solar cells under real life condition can be simulated. Further the local heat transfer conditions and the resulting temperature distribution inside the module can be simulated.
With mechanical simulations mountings can be optimized, compared and cost efficient possibilities can be identified. Alternatively for a defined mounting minimum requirement of strength parameters can be determined for quality control.