| A solar array is made up of many individual solar cells that generate a low current. Each individual cell is made up of two layers of different semiconductor materials: a p-type layer (containing free holes) overlain by an n-type layer (containing free electrons). Where the two layers are joined the free electrons in the n-type layer will move over to fill the holes in the p-type layer. As a result, the p-type layer (which had no net charge before) now has a negative charge due to the acquisition of electrons and the n-type layer (which also had no net charge before) has a positive charge due to the loss of electrons. |
When sunlight hits the cell, electrons are knocked free of the crystal lattice. The free electrons move toward the positively-charged n-type layer, creating a current. The current closes through a circuit and returning electrons fill previously evacuated holes.
High speed ions that slam into the solar array also liberate electrons thus degrading the semiconductor material and limiting the on-orbit lifetime of the solar array. Solar panels cannot be shielded from the damaging radiation as is usually done with other sensitive electronics. Any shielding would prevent the sunlight from entering the solar cells and cut off the spacecraft power source.