Researchers analyse wind cooling effect for 5.9 MW rooftop PV array

From pv magazine Global

Researchers at Turkey’s Bursa Uludağ University investigated the cooling effect of wind on rooftop PV plants. They measured temperature changes at a 57-acre rooftop facility during the summer of 2023 and found that wind could provide a cooling effect of up to 7 C, depending on its direction and speed.

“A significant portion of the studies in the literature have been observed to focus on ground-mounted PV plants. In this study, however, rooftop PV plants, which are increasingly being used by many industrial facilities to reduce energy costs, have been examined,” the research team said. “The most significant difference distinguishing rooftop PV systems from ground-mounted applications is roof geometry. Panels arranged in sequence on congested rooftops are at a disadvantage compared to ground-mounted plants in terms of receiving cool winds.”

The solar site sits on top of a TOFAS car production facility in Bursa, Turkey. Bursa receives an average solar radiation intensity of 1,393 kWh/m² per year, and during the measurement period, winds predominantly blew from the northeast. The average wind speed from all directions was about 1 m/s, with the east experiencing the strongest winds at an average of 1.49 m/s.

The roof hosts 10,806 monocrystalline PERC half-cut PV panels, each with a capacity of 545 W, contributing to a total nominal capacity of approximately 5.9 MW. The panels are oriented 22° east of south, with a 17.8° inclination angle and a 15 cm gap between the panels and the roof.

“The measured facility is actively in use, and the owner of the facility collects measurements from a single point. The measurement instruments include ambient temperature, irradiance, and wind sensors. The PV temperature sensor is mounted beneath the panel,” the group said. “Wind measurement data is collected at one-minute intervals, while all other data is collected at 15-minute intervals.”

To account for wind speed effects, researchers paired and compared 50 events with similar irradiance, temperature, and wind direction but different wind speeds. They found that wind speeds below 0.5 meters per second (m/s) result in a limited cooling effect of 1 C to 3 C on solar panels, while speeds exceeding 0.5 m/s increase the cooling effect to 3 C to 7 C.

Using rear and side wind pairs, the research group was also able to analyze the effect of wind direction.

“Due to the roof slope and the minimal gap between the panels and the roof, winds from behind were less effective, as they could not penetrate the back of the PV panels,” said the group. “Side winds, on the other hand, faced no difficulty in flowing over the panel surfaces but lost their cooling effect as they passed along the long rows of panels.”

The researchers concluded that selecting locations with higher wind speeds is crucial during the design phase of a solar plant. They noted the importance of configuring the plant appropriately to ensure that wind can effectively reach all PV arrays. They added that optimising the design phase can enhance performance without incurring significant costs, especially because modifying an existing plant poses challenges and expenses.

They presented their results in “Investigation of the cooling effect of wind on rooftop PV power plants,” which was recently published in Case Studies in Thermal Engineering.

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