Final answer:
Passive solar energy systems utilize architectural design to harness the sun's energy without electrical or mechanical devices by using natural materials and building orientation. Photovoltaic devices, in contrast, convert solar energy to electricity through the photoelectric effect using semiconductors.
Step-by-step explanation:
Passive solar energy systems harness the sun’s energy primarily through architectural design. Such systems are designed to collect and store thermal energy from the sun without the use of mechanical or electrical devices. This is often achieved through smart design elements, such as strategically placed windows, thermal mass, and specific building materials that absorb and release solar heat. An example includes a water wall that absorbs sunlight during the day and releases heat at night to warm the interior of a building.
In contrast, photovoltaic devices, which are related to option c, directly convert solar energy to electrical energy using the photoelectric effect. Semiconductors in these devices absorb photons and release electrons, creating an electric current.
Heliostats, which are large mirrors used to track the sun and focus its light, are commonly used in concentrating solar power (CSP) systems, which are a type of active solar energy system. These systems utilize concentrated sunlight to heat a fluid which is then used to generate steam and electricity.