Dynamic photovoltaic blinds for glaze-façade buildings

Researchers from China have developed a new dynamic and vertical photovoltaic integrated building envelope (dvPVBE) system for high-rise glaze-façade buildings.

The novelty of the system lies in its flexibility with weather-responsive slat angles and blind positions. “Recently, highly dynamic and weather-responsive PVBEs have been studied to further improve building energy efficiency,” the academics said. “However, relatively complex structures are not suitable for high-rise buildings because of their weak windproofing characteristics, which prevent their large-scale application in cities. Consequently, the development of simple, flexible, and intelligent PV shading devices continues to present significant challenges.”

To solve those issues, the scientists designed the proposed system as a tight external layer of windows. In a prototype they made, the frame structure and blind slats were made of aluminum alloy, with the solar cells being integrated into the slats. The slats were controlled by a motor, hidden in a top-frame structure.

“Unlike traditional static external blinds, the slats of the dvPVBE can stop at any height of the frame and rotate between 0 degrees and 90 degrees via the precise stroke control of the motor,” they explained. “The blinds can be deployed partially or fully.”

The dvPVBE can be controlled either manually by the building's occupants or automatically by three automatic control strategies, which the group called power generation priority (PGP), natural daylight priority (NDP), and energy-saving priority (ESP). In each, the slat angle and blind position are controlled by a set of inputs – such as incident solar radiation, room occupation, indoor illumination, and real-time electrical power consumption and generation. Blind position refers to the distance from the top frame to the bottom slat.

The PGP and ESP control strategies were further investigated in a computer simulation. A 24-story office building in Beijing, China, was designed for the tasks, with no additional high-rise buildings surrounding it. A representative room of 5 m × 5 m × 3 m located on the south-facing façade was simulated in that building, with a window-to-wall ratio of 70%. The heating, ventilation, and air conditioning (HVAC) temperatures were set to below 26 C in summer and above 18 C in winter.

Including a start-up period, during the working days, the system was in operation from 7:00 to 18:00. The PV on the slats was simulated as having 26 monocrystalline silicon cells per slat on 24 slats per window. The cells were assumed to be provided by Chinese manufacturer JinkoSolar, with an efficiency of 21.32%. The slat angels were able to change by increments of 5 degrees. Four typical days around the vernal equinox, summer solstice, autumnal equinox, and winter solstice were selected for the analysis.

“For the control strategies of the dvPVBE, the PGP strategy was used during non-working hours, and the ESP strategy was used during working hours,” the researcher said. “To further demonstrate the viability of the dvPVBE in enhancing building energy efficiency and conduct a fair comparison with static PV blinds, the simulation primarily focused on evaluating the influence of adjustable slat angles on energy performance.”

The simulation showed that the dvPVBE system exhibited superior energy performance compared with the static PVBEs throughout the year. The dvPVBE covered 131% of the office room's annual energy demand. Compared to the static system, the net energy output increased by at least 226%.

“For most of the daytime throughout the year in Beijing, 45° – 60° slat angles are recommended to balance the utilization of natural light and solar energy,” the academic group emphasized. “In the early morning, large slat angles are recommended to allow sufficient daylight penetration to lower the lighting load, particularly in the winter.”

The academics introduced the novel concept in the study “A New Dynamic and Vertical Photovoltaic Integrated Building Envelope for High-Rise Glaze-Facade Buildings,” published in Engineering. The group was formed by scientists coming from China's Shenzhen University, Tsinghua University, Songshan Lake Materials Laboratory, the Chinese Academy of Sciences, Hunan University, State Key Laboratory of Intelligent Geotechnics and Tunnelling, and the Ministry of Education.