What system is closely associated with a flat solar collector mounted on a roof?

A flat solar collector mounted on a roof is primarily associated with an active solar system. These systems use mechanical or electrical devices to enhance the conversion of solar energy into helpful energy forms, typically involving pumps or fans. The flat collectors are designed to absorb sunlight and convert it into heat. In an active solar heating system, this heat is often transferred to a fluid, which can either be used directly for space heating or heated water for various domestic applications.

The system's active component, such as pumps, circulates the heated fluid from the solar collector to where it's needed, which allows for greater efficiency and the ability to control the distribution of the collected thermal energy. This contrasts with passive systems, which do not rely on electric or mechanical means but rather use building design elements to maximize solar heat gain without such active mechanical components.

Understanding the key characteristics of active and passive systems highlights why the active system is the correct association with a flat solar collector, as its operation directly depends on mechanical equipment for energy conversion and distribution.