The first of a planned 2,400 solar panels have been installed on top of the papal audience hall at Vatican City.
Workers on Monday began putting photovoltaic cells on the roof of Paul VI Hall to convert sunlight into electricity.
Pope Benedict XVI has made conserving the Earth's resources an important concern of his papacy.
Rome gets lots of sunshine, and engineers say the cells will produce enough electricity to illuminate, heat or cool the hall.
"With this plant, if it is working in about two weeks we avoid 210 tons of carbon dioxide and this is the equivalent to 70 tons of oil," said Andre Koekenhoff, from Thermovolt, the company installing the panels.
The solar panels were donated by SolarWorld, based in Bonn, Germany. The company's CEO gave the panels a Bonn-based company called SolarWorld. The company's CEO decided to give the solar project as a gift to the German-born pope.
According to Catholic New Service, the solar panels and inverters are worth nearly $1.5 million and should work without much maintenance for 25 years.
The 6,300-seat audience hall is used for the pontiff's general audiences on Wednesdays in winter and in bad weather during the rest of the year.
The auditorium had cement panels on its vast, flattened roof that needed replacement. The frames for the solar panels are the same shape and almost the same color as the cement panels they are replacing, reducing the aesthetic impact.