The roof of the Paul VI auditorium will be redone next year, with its cement panels replaced with photovoltaic cells to convert sunlight into electricity, engineer Pier Carlo Cuscianna said in a telephone interview on Tuesday.
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, which has a 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.
Cuscianna said Benedict is aware of the plan, the feasibility study for which was recently published in the Vatican's newspaper L'Osservatore Romano.
The study, which found the conversion made economic sense, 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 noted.
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 (share) 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 to a design by architect Pier Luigi Nervi.
The auditorium "was born half-ecological," Cuscianna said, explaining that Nervi had the hall constructed with cement panels on its 54,000 square-foot flattened vaulted roof in part to help keep the pilgrims cool.
The new roof panels will have the same form and almost the same color as the cement panels they are replacing, minimizing the aesthetic impact, Cuscianna said.
He said weathering has deteriorated the condition of the cement panels, which needed replacement, so he thought it was the right time to make the move to solar in Mediterranean Italy, which is blessed by 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.