Optimal Control Methods for PV-integrated Shading Devices.

Abstract

The main reason for the under-utilization of natural light is glare caused by excessive admission of daylight into interior spaces. Absence of a dynamic and effective shading control system entails leaving shading devices at a closed position for glare prevention. For increasing building energy efficiency, it is imperative to develop shading control methods that provide both visual comfort and electric lighting energy savings.

A tracking PV system has higher light-to-electricity conversion efficiency than its fixed counterpart. Previous studies on louver controls indicate that louver slat surfaces blocking sunlight receive higher solar radiation than a vertical or tilted-up position. As such, a louver coated with photovoltaics cells, when appropriately controlled, has potentials to achieve high energy production efficiency and visual comfort simultaneously. This is the motivation of the development of a novel hybrid of PV system and shading device: a PV-integrated shading device (PVIS).

The performance of a PVIS, whose louvers are coated with photovoltaic cells, was evaluated in terms of electricity production, daylight admission, and occupant visual comfort. Three different shading control methods were developed and tested: 1) maximizing the louver PV output only, 2) maximizing the PV output while meeting an indoor daylight level requirement, and 3) maximizing the PV output while satisfying an indoor daylight level and daylight glare criteria. An artificial neural network was developed to predict the effect of solar radiation and slat tilt angle on PV output and visual comfort.

Through experimental testings, it was found that artificial neural network can effectively incorporated in the optimization of shading control. It was also found that the control method with the visual comfort criteria resulted in 9% reduction of PV output compared to that without them. The total building energy benefits of the control method with visual comfort criteria was at least 36% higher than that without due to the reduction of electric lighting energy consumption. Due to the PV-output criterion, the daylight glare remained within the comfortable range. For this reason, the glare criterion made no difference in louver tilt angle control.