Solar-powered thermo-pneumatic actuators for passively controlled adaptive shading

The operational energy demand of buildings plays a significant role in global energy consumption. Especially, the energy required for cooling is predicted to rise due to climate change. Adaptive shading is a promising approach to save operational energy in buildings. State-of-the-art adaptive shading systems employ both active and passive actuation as well as control strategies, to lower energy consumption while maintaining the thermal and visual comfort of building occupants. However, both approaches still must overcome challenges that hinder widespread adoption. Active systems need motors and pumps, dedicated power supplies, and control electronics. These components make the systems heavy and complex to maintain and repair. Passive systems work without dedicated power supplies and control electronics but can face limitations based on the active materials used, e.g. material degradation, toxicity, narrow response windows, and unknown performance in varying conditions. This work presents a solar-powered, thermo-pneumatic actuator for use in adaptive shading applications that works without specialized active materials, electronic actuation and controls. The actuator incorporates elastic bellows to transform the thermal expansion of air into motion and adapts to changes in irradiance. The actuator is built as a functional prototype and its performance in different irradiance scenarios is evaluated. The actuator is capable of considerable motion, moving a rotational mechanism close to 90° powered by an irradiance of 1000 W m⁻². The actuator response is sensitive enough to react to hourly changes in irradiance as well as to a simulated solar cycle. The paper concludes with the presentation of a shading device concept incorporating the actuator to highlight its potential for use in adaptive shading applications to reduce operational energy in buildings.