Prince Charles' income grew last year, while his carbon footprint shrank.
The eco-friendly prince even has an Aston Martin that runs on wine.
An annual review of Charles' accounts released Monday said the prince made more than $32 million from property and investments between April 1, 2007 and March 31 this year, 7 percent more than in 2006-7. Charles paid $6.8 million in tax, $10,000 less than the year before.
The prince's office said greater use of green energy and fewer plane and car journeys helped Charles cut the amount of carbon dioxide he produced by 18 percent to 3,081 tons.
Charles has promised to reduce his emissions of greenhouse gases by 25 percent between 2007 and 2012.
The report said Charles and his wife Camilla, Duchess of Cornwall, traveled 37,000 miles on official duties and overseas travel accounted for the largest chunk of the prince's carbon footprint.
For domestic travel, the prince's Jaguars, Audi and Range Rover now run entirely on biodiesel made from used cooking oil, and his 38-year-old Aston Martin is fueled by bioethanol from surplus wine.
The prince has also installed wood-chip stoves at his country homes — the Highgrove estate, where he farms organically, and Birkhall in Scotland — and energy-efficient boilers at his Clarence House residence in London.
"I hope it shows a good picture," said royal aide Sir Michael Peat. "I really do believe that the contribution their royal highnesses make to national life continues to develop and broaden."
The 59-year-old heir to the throne receives private income from properties of The Duchy of Cornwall, the 136,000-acre estate established in 1337 by King Edward II to provide income for his heir.
Charles' official spending, including money spent on charitable work and official duties, was $20.8 million. His personal spending, which includes the salaries of 30 full-time staff, was $4.4 million, down from 2.6 million pounds.
However, Charles' thrifty gene appears to have skipped his oldest son. A British newspaper reported Monday that five helicopter flights taken by Prince William during training with the Royal Air Force cost taxpayers more than $100,000.
The most contentious was a flight to attend a stag party on the Isle of Wight off southern England, which cost just over $17,400, The Guardian reported.
The newspaper said it obtained the figures from the Ministry of Defense under a freedom of information request.
William also flew military aircraft to his girlfriend Kate Middleton's home, his father's country house and the royal residence at Sandringham.
The Ministry of Defense said "all flights undertaken by Flying Officer Wales were a legitimate part of his RAF training." But the ministry acknowledged there had been "a degree of naivety in the planning of the training sorties."