Smart switchable technologies for glazing and photovoltaic applications

One presents in this paper an idea to use switchable technologies to independently control the solar heat flow and the visible light transmission through windows, and potentially collect infrared radiant power on a photovoltaic cell. The system uses chiral liquid crystal and suspended particle device switchable technologies that are electronically tuned to optically control the quantity of infrared light rejected, the visible light transmission and the optical path to internally reflect the light and collect it on the photovoltaic cell. A characterized suspended particle device showed an average 48.5% to 1.3% transmission respectively in the transparent and opaque states of the window. A second characterization of a chiral liquid crystal mirror manufactured to reflect the visible range showed an average transmission modulation between 84% and 3% over 250nm reflection range respectively in the transparent and reflective states at small light incidence angles. Transmission is however significantly increasing in the reflective state while increasing light incidence angle and considered in ray-tracing simulation of the system. A ray tracing software has been developed to simulate the performance of a window 50cm height by 50cm long and 5.5cm wide consisting of two chiral liquid crystal mirrors and using the characterization results. Adaptation of the mirrors configuration was considered to collect light on the cell at various zenith and azimuth solar angles. Simulation results showed no significant benefit of internally reflecting the light to concentrate it on the photovoltaic cell located in the windows frame. However, an infrared chiral mirror with a reflection bandwidth wider than the wavelength range to modulate in transmission could potentially control solar heat radiation through the window between ~ 80% and 5% independently of the light incidence angle. The window system would technically benefit of a combined suspended particle device solely absorbing the visible range to realize the desired hybrid system.