Vatican, view from the roof of St. Peter. Paul VI Audience Hall, covered with 2,400 photovoltaic panels, Monte del Gallo and south-western Rome behind.

The Paul VI Audience Hall (Italian: Aula Paolo VI) is a building in Rome named for Pope Paul VI with a seating capacity of 6,300, designed in reinforced concrete by the Italian architect Pier Luigi Nervi and completed in 1971. It lies partially in the Vatican City but mostly in Italy: the Italian part of the building is treated as an extraterritorial area of the Holy See and is used by the Pope as an alternative to Saint Peter's Square when conducting his Wednesday morning General Audience. It is dominated by an 800-quintal (8 metric ton) bronze/copper-alloy sculpture by Pericle Fazzini entitled La Resurrezione (Italian for "The Resurrection"). A smaller meeting hall, known as Synod Hall (Italian: Aula del Sinodo), is located in the building as well. This hall sits at the east end on a second floor.

On 25 May 2007, it was revealed that the roof of the building was to be covered with 2,400 photovoltaic panels, generating sufficient electricity to supply all the heating, cooling and lighting needs of the building throughout the year. The system was donated by SolarWorld, a German manufacturer, and valued at $1.5 million. It was officially placed into service on 26 November 2008, and was awarded the 2008 European Solar Prize in the category for "Solar architecture and urban development".

more on https://en.wikipedia.org/wiki/Paul_VI_Audience_Hall