TY - JOUR

T1 - Use of digital image correlation technique to determine thermomechanical deformations in photovoltaic laminates

T2 - Measurements and accuracy

AU - Eitner, Ulrich

AU - Köntges, Marc

AU - Brendel, Rolf

PY - 2010/8

Y1 - 2010/8

N2 - An experimental technique to measure the deformation of solar cells in transparent PV modules is presented. This method uses the digital image correlation technique with a stereo camera system. Deformations resulting from thermal loading, where rather small deformations occur compared to tensile or bending experiments, are measured by viewing through the window of a climate chamber. We apply this method to measure the thermomechanical deformation of the gap between two crystalline silicon solar cells by viewing through the transparent back sheet of the laminate. Two PV laminates are prepared, each with three crystalline silicon solar cells that are embedded in transparent polymer sheets on a glass substrate. The first laminate (A) contains non-interconnected cells while the second laminate consists of a standard-interconnected cell string (B). We find the gap between two solar cells to deform 66.3±2 μm between 79.6 and -17.3 °C (laminate A) and 66.4±2 μm (laminate B) between 84.4 and -39.1 °C. We determine an accuracy of 1 μm in displacement for the gap experiment by measuring free expansion of a copper strip and averaging displacement values over regions with homogeneous deformation. Furthermore, the relative error contribution in strain due to the optical influence of the layers on top of the object surface is less than 1×10-6 for one camera. This is proven by a geometrical consideration.

AB - An experimental technique to measure the deformation of solar cells in transparent PV modules is presented. This method uses the digital image correlation technique with a stereo camera system. Deformations resulting from thermal loading, where rather small deformations occur compared to tensile or bending experiments, are measured by viewing through the window of a climate chamber. We apply this method to measure the thermomechanical deformation of the gap between two crystalline silicon solar cells by viewing through the transparent back sheet of the laminate. Two PV laminates are prepared, each with three crystalline silicon solar cells that are embedded in transparent polymer sheets on a glass substrate. The first laminate (A) contains non-interconnected cells while the second laminate consists of a standard-interconnected cell string (B). We find the gap between two solar cells to deform 66.3±2 μm between 79.6 and -17.3 °C (laminate A) and 66.4±2 μm (laminate B) between 84.4 and -39.1 °C. We determine an accuracy of 1 μm in displacement for the gap experiment by measuring free expansion of a copper strip and averaging displacement values over regions with homogeneous deformation. Furthermore, the relative error contribution in strain due to the optical influence of the layers on top of the object surface is less than 1×10-6 for one camera. This is proven by a geometrical consideration.

KW - Deformation

KW - Digital image correlation

KW - Experimental technique

KW - PV module

KW - Thermomechanics

UR - http://www.scopus.com/inward/record.url?scp=77953137817&partnerID=8YFLogxK

U2 - 10.1016/j.solmat.2010.03.028

DO - 10.1016/j.solmat.2010.03.028

M3 - Article

AN - SCOPUS:77953137817

VL - 94

SP - 1346

EP - 1351

JO - Solar Energy Materials and Solar Cells

JF - Solar Energy Materials and Solar Cells

SN - 0927-0248

IS - 8

ER -