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.
As you may imagine, the most effective solar panels have the highest cost. The most effective and most expensive type of solar panel is Monocrystalline, which is constructed from one continuous sheet of silicone. Slightly less expensive, and less effective, is Polycrystalline.