The prince has reduced his carbon footprint
The Prince of Wales's private income rose by 7% to more than £16m last year, Clarence House accounts show.
Money generated by the Duchy of Cornwall increased by just over £1m to £16.2m in the last financial year.
But the amount of carbon dioxide (CO2) generated by the prince's activities fell by 18%.
Clarence House said the reduction was due to a switch to "green" electricity supplies and a further reduction in travel-related emissions.
Figures showed the amount of carbon dioxide (CO2) generated by the prince's travel and domestic energy use fell by 630 tonnes to 2,795 tonnes during 2007-08.
The cost of the prince's official travel by air and rail fell 22% from £1.4m to £1.1m. Journeys by plane and train are paid for by the taxpayer.
The prince's personal costs, referred to in the accounts as "non-official expenditure", fell from £2.6m to £2.2m.
The amount of tax the heir to the throne paid to HM Revenue and Customs dropped by £5,000 to £3.4m.
Sir Michael Peat, the prince's top aide, said he hoped the figures showed "a good picture".
He said: "I don't want to sound complacent but I really do believe that the contribution their royal highnesses make to national life continues to develop and broaden and strengthen.
"The Prince of Wales has a special knack of putting his finger on issues of underlying and long-term importance and for seeing beyond fashion and political correctness - and there are some good examples in the annual review."
Meanwhile, following a Freedom of Information request by the Guardian newspaper, it was revealed that five helicopter flights made by Prince William while training with the RAF cost more than £50,000.
The flights - which included journeys to a stag party and a trip to the family home of his girlfriend, Kate Middleton - have been criticised as an alleged abuse of military training.