The roof of the Paul VI auditorum will be redone next year, with its cement panels replaced with photovoltaic cells to convert sunlight into electricity, engineer Pier Carlo Cuscianna said.
The 6,300-seat auditorium is used for the pontiff's general audiences on Wednesdays in winter and in bad weather during the rest of the year. Concerts in honor of pontiffs are also occasionally staged in the hall, with its sweeping stage.
The cells will produce enough electricity to illuminate, heat or cool the hall, Cuscianna said.
"Since the auditorium isn't used every day, the (excess) energy will feed into the network providing (the Vatican) with power, so other Vatican offices can use the energy," he said.
A feasibility study for the planned conversion, published recently in the Vatican newspaper L'Osservatore Romano, found the conversion made economic sense. It quoted from Benedict's speeches defending the environment and noted that his predecessor, the late John Paul II, also championed the safeguarding of natural resources.
Cuscianna recalled a speech in which Benedict lamented "the unbalanced use of energy" in the world.
Last summer, Benedict called on Christians to unite to take "care of creation without squandering its resources and sharing them in a convivial manner." He said lifestyle choices were damaging the environment and making "the lives of poor people on Earth especially unbearable."
The modernistic hall, at the southern end of Vatican City, was built in 1969, designed by architect Pier Luigi Nervi.
The auditorium "was born half-ecological," Cuscianna said, noting that Nervi used cement panels on its 6,000-square-yard flattened vaulted roof in part to help keep pilgrims cool.
The new roof panels will have the same form and almost same color the the cement panels they are replacing, minimizing the esthetic impact, Cuscianna said.
Weathering has deteriorated the condition of the cement panels, which needed replacement, so Cuscianna thought it was the right time to make the move to solar in Mediterranean Italy, which enjoys many sunny days.
The Vatican is considering the installation of photovoltaic cells on roofs of other Holy See buildings, although centuries-old landmarks like St. Peter's Basilica won't be touched.