Which of the following is the smallest installable part of a photovoltaic (PV) system?

The solar module is considered the smallest installable part of a photovoltaic (PV) system because it refers specifically to the individual unit that converts sunlight into electricity. A solar module typically comprises multiple solar cells, usually arranged in a rectangular grid, electrically connected and encapsulated to protect the cells from environmental conditions.

While the terms "solar panel" and "solar array" are often used contextually to describe aspects of a PV system, they refer to broader concepts. A solar panel is often used interchangeably with a solar module but can also denote a collection of modules that form part of an installation. A solar array consists of multiple modules connected together to increase the overall power output of the PV system, making it a larger assembly and not the smallest installable part.

The PV source circuit describes the electrical connections and other components that comprise the wiring and arrangement supplying power from the modules to the inverter and eventually to the grid or battery storage, which also positions it above the module in terms of size and complexity.

Overall, the solar module is the smallest distinct functional unit in a PV system, making it the correct answer.