A photovoltaic (PV) or solar cell is the basic building block of a PV (or solar electric) system. An individual PV cell is usually quite small, typically producing about 1 or 2 watts of power. To boost the power output of PV cells, we connect them together to form larger units called modules. Modules, in turn, can be connected to form even larger units called arrays, which can be interconnected to produce more power, and so on. In this way, we can build PV systems able to meet almost any electric power need, whether small or large.

The most common PV system for off-grid homes are the flat-plate systems.  By themselves, modules or arrays do not represent an entire PV system. We also need structures to put them on that point them toward the sun, and components that take the direct-current electricity produced by modules and "condition" that electricity, usually by converting it to alternate-current electricity. We might also want to store some electricity, usually in batteries, for later use. All these items are referred to as the "balance of system" (BOS) components.

Combining modules with the Balance of System components creates an entire PV system. This system is usually everything we need to meet a particular energy demand, such as powering a water pump, or the appliances and lights in a home, or, if the PV system is large enough, all the electrical requirements of a whole community.