See also Crookes Radiometer (Light Mill)

Headworks of a passive tracker tilted to meet the morning Sun.

Solar Energy
Solar Electricity Solar Thermal Solar Vehicles Solar Building Agriculture Solar Lighting Solar Chemical Solar Mechanical Solar Storage

Solar mechanical technologies use sunlight to produce a mechanical effect. There are many such technologies covered in the solar thermal category but the devices listed here are notable for having both passive solar and mechanical characteristics.

A light mill or Crookes radiometer consists of a glass bulb containing a set of vanes mounted on a spindle. Each vane has a dark side and a white side. When illuminated, the dark side becomes warm due to absorbing light but the white side reflects light and stays cool. The vanes rotate due to the motion of gases from the hot to the cool side of each vane.

Passive solar tracking devices use imbalances caused by the movement of a low boiling point fluid to respond to the movement of the Sun. Tracking PV systems can generally produce 25% more electricity than fixed tilt PV systems.^[88] Shading systems that respond to the movement of the Sun can also be used in buildings to maximize natural lighting during winter, lessen summer glare, and reduce cooling loads associated with unwanted solar gain.^[89]

Passive trackers use a low boiling point compressed gas fluid that is driven to one side or the other (by solar heat creating gas pressure) to cause the tracker to move in response to an imbalance. As this is a non-precision orientation it is unsuitable for certain types of concentrating photovoltaic collectors but works fine for common PV panel types. These will have viscous dampers to prevent excessive motion in response to wind gusts. Shader/reflectors are used to reflect early morning sunlight to "wake up" the panel and tilt it toward the sun, which can take nearly an hour. The time to do this can be greatly reduced by adding a self-releasing tiedown that positions the panel slightly past the zenith (so that the fluid does not have to overcome gravity) and using the tiedown in the evening. (A slack-pulling spring will prevent release in windy overnight conditions.)

See also Crookes Radiometer (Light Mill)

Notes