Renal agenesis. Renal agenesis is a medical condition in which one (unilateral) or both (bilateral) fetal kidneys fail to develop.
Polycrystalline cells are composed of multiple silicon crystals, which is a cheaper way to manufacture solar modules. Put simply, these cells are easier for a factory to produce, so they are less expensive. Polycrystalline cells are made by several methods, but most commonly with a cast of molten silicon.
PA (Polyamide) is a semi-crystalline polymer. There are two types: those made of one basic material (e.g. PA 6) and those made of two basic materials (e.g. PA 66). They can occur both naturally (e.g. wool and silk) and synthetically (e.g. nylon).