We have studied the influence of defects on silicon heterojunction solar cell efficiency by a method based on the comparison of electroluminescence (EL) image data with a finite element circuit model of solar cell efficiency. For this purpose, a general curve that relates the solar cell efficiency to a parameter representative of the defect strength, i.e., the loss of VOC, ∆VOC, from EL maps is obtained, and it is shown that the efficiency can be predicted with a good degree of confidence.