Thermal Expansion and Thermal Stresses

Thermal expansion is another important temperature effect which must be taken into account when modules are designed.

Use of stress relief loops to accommodate expansion between cells with increases in temperature.

The spacing between cells tries to increase an amount δ given by:

where:
αG and αC are the expansion coefficients of the glass and the cell respectively;
D is the cell width; and
C is the cell centre to centre distance.

Typically, interconnections between cells are looped, as shown, to minimise cyclic stress. Double interconnects are used to protect against the probability of fatigue failure caused by such stress.

In addition to interconnect stresses, all module interfaces are subject to temperature-related cyclic stress which may eventually lead to delamination.