Solar cells represent the fundamental power conversion unit of a photovoltaic system. They are made from semiconductors, and have much in common with other solid-state electronic devices, such as diodes, transistors and integrated circuits. A particular class of high-efficiency solar cells from single crystal silicon are used in the rovers.

The solar cell operation is based on the ability of semiconductors to convert sunlight directly into electricity by exploiting the photovoltaic effect. In the conversion process, the incident energy of light creates mobile charged particles in the silicon which are then separated by the device structure and produce electrical current.

Fig 3 shows the diagram of a silicon cell, the typical solar cell in use. The electrical current generated in the semiconductor is extracted by contacts to the front and rear of the cell. The top contact structure which must allow light to pass though is made in the form of widely spaced thin metal strips that supply current to a large bus bar. The cell is covered with a thin layer of dielectric material to minimise light reflection from the top surface.

The Photovoltaic Generator

The heart of the solar power system is the photovoltaic generator. Fig 4. It consists of photovoltaic (PV) modules which are interconnected to form a DC power-producing unit. Then physical assembly of the modular with supports becomes array. Fig 5.

A schematic diagram of a PV generator consisting of several modules is shown in Fig 6. In addition to PV modules, the generator contains by-pass and blocking diodes; these diodes protect the modules and prevent the generator acting as a load in the dark.