Today, solar cells are very familiar to the broad public, and everyone has noticed their particular geometry resembling a square with rounded-off corners. However, the rationale behind this geometry is little known. This paper presents a precise study of the geometry of silicon solar cells and its evolution since their appearance in the early 1960s. Through a parametric approach taking into account different types of constraints, it is shown that the cell geometry is the result of an optimization process depending on both technical and economic aspects. The correlation between the parametric study and historical data shows that the photovoltaic panels that we see today on our roofs have been mainly shaped by the evolution of cost constraints over the past decades.