New design for vacuum integrated photovoltaic curtain walls

A group of researchers in China has developed a new design for vacuum integrated photovoltaic (VPV) curtain walls, which they claim can efficiently combine PV power generation and thermal insulation for the building.

“For the first time, a multi-function partitioned design method for PV curtain walls was proposed, which aims at reconciling the competing demand of different functions of PV curtain walls such as daylight, view, and power generation,” the research's lead author, Jinqing Peng, told pv magazine. “Now, we are optimizing the height and PV coverage rate of each section, and after this study, we will cooperate with enterprises to produce the partitioned PV curtain wall.”

The researchers explained that VPV curtain walls with high PV coverage may be beneficial to a building, as they may prevent large amounts of solar radiation from entering the building, thus preventing overheating issues. By contrast. VPV curtain walls with low PV coverage may have overheating issues, but may help the building require less energy for lighting and heating.

“Thus, the single-objective optimal design of the VPV curtain walls is unable to balance its restrictive and even contradictory functions,” they stated. “The primary objective of this study is to balance the trade-offs between the different functions of the VPV curtain wall and improve its energy-saving potential while ensuring the comfort of the occupants.”

The system consists of a PV laminate glass based on cadmium telluride (CdTe) solar cells, an air cavity, and a sheet of vacuum glazing. The scientists etched the solar cells into strips by laser.

The system is also divided into daylight, view, and spandrel sections based on the different functions, and the PV coverage of each section must be determined separately. The daylight and view sections are designed to provide daylight and a visual connection to the exterior, while the spandrel section is mainly intended for power generation. This allows the modulation of the transmittances of each section by adjusting the density of the PV cell strips.

The Chinese group simulated the performance of the VPV curtain via the Radiance and EnergPlus software and the technique for order of preference by similarity to ideal solution (TOPSIS). They assumed the system is deployed in a south-facing private office building.

“It is assumed to be the middle floor of a high-rise glass curtain wall building with dimensions of 2.7 m in height, 4.0 m in depth, and 3.0 m in width,” the researchers stated. “The VPV curtain wall was equipped on the southern façade with a large window-to-wall ratio of 86%.”

The simulation showed that the PV coverage variation of the daylight section has a big impact on useful daylight illuminance (UDI) and the discomfort glare index (DGP). Discomfort glare is a psychological sensation caused by high brightness, and UDI refers to the amount of daylight that is useful to a space's occupants. 

Furthermore, the academics found that the optimal system configuration would require 20% PV coverage in the daylight section, 40% PV coverage in the view section, and 90% coverage in the spandrel section. “The optimal VPV curtain wall, with 50%, 40%, and 90% PV coverages for daylight, view, and spandrel sections, achieved a 34.5% reduction in glare index, 4.9% increment on the UDI, 5.2%
increment on the ratio of net-zero energy hours (RNEH), and 112.59 kWh augment of surplus electricity,” they also explained.

The system was described in the study “Multi-function partitioned design method for photovoltaic curtain wall integrated with vacuum glazing towards zero-energy buildings,” published in Renewable Energy. The research group comprises scientists from the Shanghai Jiao Tong University and the Hunan University in China.

“As for the cost of this system, the partitioned PV curtain wall only differs from the traditional PV curtain wall solely in the arrangement of solar cell strips,” Peng concluded. “Consequently, there is no significant cost difference between the two designs, but the proposed partitioned PV curtain wall can reduce building energy consumption and yield more surplus power generation electricity.”