Which type of solar heating system does not have any moving parts?

A passive solar heating system is characterized by the absence of moving parts, relying instead on natural processes to collect, store, and distribute solar energy. This system operates by using building materials and architectural designs that capture sunlight, such as large windows and thermal mass, to absorb heat during the day and release it slowly at night. This method utilizes the sun's energy without mechanical assistance, making it inherently energy-efficient.

In contrast, active solar heating systems involve mechanical components like pumps and fans to circulate fluids that absorb and transfer heat. Conventional gas heating systems operate using combustion processes and are reliant on gas fuel, which is separate from solar energy techniques. Instantaneous heating systems deliver hot water on demand and typically rely on mechanical operations as well. Thus, passive solar heating stands out as the only option that functions without any moving parts, utilizing design and materials to harness solar energy effectively.