The system prototype

Researchers from Japan’s Nagoya University have proposed a novel building-integrated photovoltaic (BIPV) system that integrates an airflow-type PV-integrated shading device (PVSD) with ventilated louvers.

The system enables passive cooling and heat recovery without extra energy input. “An airflow-type PVSD is a façade system designed with openings at the top and bottom of the louvers, allowing air to pass through.” the team explained. “During the cooling period, outside air was introduced at the bottom of the louvers to facilitate the passive cooling of the solar panels. As the outside air rose through the louvers, it passively cooled the solar panels and subsequently exited at the top of the louvers. During the heating period, indoor air was introduced at the bottom of the louvers and warmed via heat exchange with the solar panels. Warmed air was supplied to the room from the top of the louvers.”

The prototype of the system consists of a 200 mm × 1,500 mm solar PV panel installed in front of seven aluminum solar-shading louvers. The solar panel, which uses monocrystalline cells, has a rated output of 39 W and an efficiency of 13%. Opening holes allows air passage to the system. A second prototype included all of the above characterizations but had no air flow opening holes.

The performance of the system was measured on a January day in 2022 in Shizuoka City.

“At 11:40, when the solar irradiation was at its peak, the non-airflow-type PVSD generated 242.21 W, whereas the airflow-type PVSD produced 247.25 W. This indicates that electricity generation by the airflow-type PVSD did not significantly change. The slight improvement in electricity generation can be attributed to low outdoor temperatures, which did not affect the increase in the surface temperature of the PV panels,” the team said. “However, it is expected that, in actual buildings where multiple units are installed, the difference in energy output between airflow- and non-airflow-type PVSDs will be more pronounced.”

Following the actual measurements, the team conducted numerical modeling via the EnergyPlus software. Using the single-room model, seven PVSDs were installed at two window locations. Three study cases were tested, namely, a system with no PVSD, a system with PVSD without airflow, and a system with PVSD with airflow. The software simulated a year of operation and found the measured solar panel temperatures and the outlet air temperatures to be within around 20%.

In the no PVSD case, the annual cooling consumption was 386 kWh, the heating power consumption was 58 kWh, and the lighting demanded 295 kWh, for a total consumption of 739 kWh. In the case of the PVSD without airflow, the cooling, heating, and lighting were 364 kWh, 65 kWh, and 391 kWh, respectively, while the PV generated 496 kWh for a total net consumption of 324 kWh. The PVSD with airflow had the lowest net consumption of 303 kWh; that is, it produced 503 kWh and consumed 364 kWh of cooling, 50 kWh of heating, and 391 kWh of lighting.

“Compared to the non-airflow-type PVSD, the installation of the airflow-type PVSD increased PV generation by approximately 1.4% and decreased heating demand by approximately 29%,” the researchers highlighted. “The results of the annual calculations indicated an enhancement in the electricity generation efficiency and indoor heating effects with the airflow-type PVSD.”

After proving that the airflow-type PVSD yields the best results, the team focused on optimizing it for installation angles, heights, and opening areas. Opening areas were either set to 0.0017 m², 0.0051 m², 0.0068 m², 0.0085 m², or 0.0102 m², which are 0.5, 1.5, 2.0, 2.5, and 3.0 times the original 0.0034 m2 opening in the prototype, respectively. Height was set to 0.8 m, 10 m, 20 m, 30 m, 40 m, 50 m, or 60 m above ground level, and installation angel were set to 70?, 75?, 80?, 85?, or 90?, relative to the ground.

“Multiplying the openings by 3.0 times resulted in the highest PV production, showing an increase of 1.2 kWh/y compared to values in the prototype model,” they said. “Heating demand exhibited a logarithmic decrease with the enlargement of the opening area. Multiplying it by 3.0 times resulted in the lowest heating demand, showing a decrease of 4.6 kWh/y compared to the values in the prototype model.”

As for the different heights, PV production reached its maximum at 60 m, with an increase of 14 kWh/y compared to its installation at 0.8 m above ground level. At this latter height, heating demand was at its lowest, decreasing by 7.7 kWh/y compared to its installation at 60 m above ground level. The difference in PV production between the airflow-type PVSD and non-airflow-type PVSD increased as the inclination angle decreased, reaching a maximum difference of 10.5 kWh/y at 70?.