Prince Charles's household has become more environmentally friendly, according to his annual accounts.
In addition to achieving carbon neutral status, the household also reduced its carbon emissions by 9% last year, the report said.
This was put down to the prince taking fewer flights and the switch to "green electricity" at Highgrove.
But the report said the carbon neutral rating did not include official overseas trips prior to 1 January 2007.
The household's carbon footprint was calculated at 3,425 metric tons of carbon dioxide in 2006-2007. This is the first time such a statistic has been published.
Workload
Prince Charles has been offsetting his carbon emissions since 2005 through specialist agency Climate Care, which invests in environmental projects around the world.
Tony Juniper, Friends of the Earth director, said he was "delighted" with the prince's green credentials.
He said: "The fact he reduced his carbon emissions by 9% in the last year alone highlights the potential for making rapid cuts in the nation's contribution to climate change."
The report also showed the prince's income from the Duchy of Cornwall, which consists of around 54,764 hectares of land in 22 counties, grew from £14 million in 2005-2006 to £15.2 million last year.
"He does work very hard to try to make a difference"
The prince's official travel by air and rail, paid for by taxpayers, rose 29% from £1.1 million in 2005-2006 to £1.5 million.
His personal expenditure was also up from £2.2 million to £2.6 million.
Sir Michael Peat, the prince's principal private secretary, said the rise in travel costs and personal spend reflected the prince's increased workload.
"He is very busy and gets increasingly so," he said. "He does work very hard to try to make a difference."
The report revealed the prince has more than 130 employees, including farmer workers, press officers and valets, and that one butler is on duty at all times.
But according to Sir Michael, the household is "understaffed".
Staff costs for the prince's official duties came to £4.8 million, rising from £4.4 million the year before.
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