PHOTOVOLTAIC (PV) CELLS

Some types of silicon diodes can generate dc all by themselves if sufficient IR, visible-light, or UV energy strikes their p-n junctions. This is known as the photovoltaic effect, and it is the principle by which solar cells work. Photovoltaic (PV) cells have large p-n junction surface area (Fig. 1).
This maximizes the amount of energy that strikes the junction after passing through the thin layer of p-type material. A single silicon PV cell produces approximately 0.6 V dc in direct sunlight under no-load conditions (that is, when there is nothing connected to it that will draw current from it). The maximum amount of current that a PV cell can deliver depends on the surface area of the p-n junction.
Silicon PV cells are connected in series-parallel combinations to provide solar power for solid-state electronic devices such as portable radios. A large assembly of such cells constitutes a solar panel. The dc voltages of the cells add when they are connected in series. A typical solar battery supplies 6, 9, or 12 V dc. When two or more identical sets of series-connected PV cells are connected in parallel, the output voltage is not increased, but the solar battery becomes capable of delivering more current. The currentdelivering capacity increases in direct proportion to the number of sets of series-connected cells that are connected in parallel.

Fig. 1. Simplified cross-sectional drawing of a photovoltaic (PV) cell.