Sun-tracking photovoltaics for stadiums

Researchers in Italy have developed a sun-tracking PV system design for stadium covers. The proposed approach is said to offer both strong structural response and high energy yield compared to systems based on fixed structures.

Researchers at the University of Salerno and the University of Naples Federico II in Italy have developed a new PV system design for small-to-medium-sized sports stadiums.

The system is based on the combination of metal roofing modules with lightweight, flexible PV panels and is claimed to have lightweight construction and “remarkable” stiffness properties. “The deployable structure used to activate the sun-tracking mechanism has been designed in such a way that it can be easily applied to existing stadiums,” the research's corresponding author, Fernando Fraternali, told pv magazine. “It can be applied to any stadium roof by suitably connecting the bus cable to a supporting structure superimposed onto the existing roof.”

In the paper “A tensegrity structure for a solar stadium roof with sun-tracking capability,” published in Thin-Walled Structures, the research team described the proposed design as a class-4 tensegrity system, where the integrity of the structure depends on the balance of the tension members.

It also explained that the roof structure presented in the study is the so-called V-expander, which refers to the use of a v-shaped rigid strut in a tensegrity structure. “The original V-Expander was introduced by René Motro in his well-known textbook as a V-shaped system composed of eight bars arranged in two distinct sets of four bars each, with equal lengths,” it further explained. “Our variant is a class-4 tensegrity structure composed of eight bars and seven cables.”

The proposed PV roof cover is based on triangular metal roofing modules with sun-tracking PV panels. The motion that drives the tilting mechanism is activated through a winch located in an appropriate position and by adjusting the rest length of the bus cable, enabling a movement with reportedly very low energy consumption.

“The sun-tracking strategy utilizes a tensegrity actuation technique, which is controlled by adjusting the rest length of a bus cable connected to struts,” the researchers stated. “This mechanism allows the lightweight roof plates, covered with PV strips, to tilt optimallyfor maximum solar energy absorption. The PV strips can be made from amorphous thin-film cells, organic PV cells, or flexible PV panels. Additionally, more standard PV panels could be used, provided that their weight is accurately accounted for in the structural analysis.”

The proposed approach is said to increase the annual electrical energy production capacityof the solar roof by up to 54% compared to a fixed-slope solar roof. “The locally variable sun-tracking strategy is particularly effective during the winter months, achieving power production increases of up to 80%,” the academics emphasized. “At rest, the lifting structure behaves as a lightweight tensegrity system.

The research group said the system could be further optimized by deploying its sub-units with different tilting angles or by using two-axis solar trackers. “Additional improvements to the solar stadium design strategy could include the adoption of high-efficiency silicon solar cells, which offer efficiencies of up to 27% – 28%, as well as the use of bifacial cells,” it concluded. “Furthermore, the tensegrity-stadium concept can be scaled up for large-scale stadiums.”