Vatican City - The Vatican inaugurated Wednesday its new solar power energy system, which will heat the hall where Pope Benedict XVI holds his weekly general audience - in a move in keeping with the pontiff's concern for environmental issues.

Benedict, together with the visiting Armenian Apostolic Church Catholicos Aram I, joined hundreds of people gathered in the Paul VI Hall, inside Vatican City, for the ceremony.

Built in 1971, the structure, one of the Vatican's most modern, recently had its 5,000 square-metre roof covered by 2,400 photovoltaic panels.

These - which Vatican officials say are almost invisible from the ground and thus won't impinge on a skyline dominated by St Peter's Basilica - are set to harness enough "clean" energy to generate some 300 kilowatt-hours a year.

That amount is sufficient to provide all the hall's power needs and that of several surrounding buildings, according to SolarWorld, the German company that devised the system.

The system will allow the 108-acre city-state to cut its carbon dioxide emissions by about 225,000 kilograms and save the equivalent of 80 tons of oil each year.

The Vatican is aiming to install enough renewable energy sources to provide 20 per cent of its needs by 2020, broadly in line with a proposal by the European Union, the Holy See's newspaper said Tuesday.

Since his 2005 election, Benedict, in several homilies and in his encyclical writings has stressed the need to safeguard the environment leading some to dub him the "Green Pope".

The pontiff won praise from environmentalists last year when he urged the human race to listen to "the voice of the earth" or risk destroying the planet. (dpa)